Internet Engineering Task Force (IETF)                  E. Grossman, Ed.Request for Comments: 9055                                         DOLBYCategory: Informational                                       T. MizrahiISSN: 2070-1721                                                   HUAWEI                                                               A. Hacker                                                                 THOUGHT                                                               June 2021       Deterministic Networking (DetNet) Security ConsiderationsAbstract   A DetNet (deterministic network) provides specific performance   guarantees to its data flows, such as extremely low data loss rates   and bounded latency (including bounded latency variation, i.e.,   "jitter").  As a result, securing a DetNet requires that in addition   to the best practice security measures taken for any mission-critical   network, additional security measures may be needed to secure the   intended operation of these novel service properties.   This document addresses DetNet-specific security considerations from   the perspectives of both the DetNet system-level designer and   component designer.  System considerations include a taxonomy of   relevant threats and attacks, and associations of threats versus use   cases and service properties.  Component-level considerations include   ingress filtering and packet arrival-time violation detection.   This document also addresses security considerations specific to the   IP and MPLS data plane technologies, thereby complementing the   Security Considerations sections of those documents.Status of This Memo   This document is not an Internet Standards Track specification; it is   published for informational purposes.   This document is a product of the Internet Engineering Task Force   (IETF).  It represents the consensus of the IETF community.  It has   received public review and has been approved for publication by the   Internet Engineering Steering Group (IESG).  Not all documents   approved by the IESG are candidates for any level of Internet   Standard; see Section 2 of RFC 7841.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained at   https://www.rfc-editor.org/info/rfc9055.Copyright Notice   Copyright (c) 2021 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject to BCP 78 and the IETF Trust's Legal   Provisions Relating to IETF Documents   (https://trustee.ietf.org/license-info) in effect on the date of   publication of this document.  Please review these documents   carefully, as they describe your rights and restrictions with respect   to this document.  Code Components extracted from this document must   include Simplified BSD License text as described in Section 4.e of   the Trust Legal Provisions and are provided without warranty as   described in the Simplified BSD License.Table of Contents   1.  Introduction   2.  Abbreviations and Terminology   3.  Security Considerations for DetNet Component Design     3.1.  Resource Allocation       3.1.1.  Inviolable Flows       3.1.2.  Design Trade-Off Considerations in the Use Cases               Continuum       3.1.3.  Documenting the Security Properties of a Component       3.1.4.  Fail-Safe Component Behavior       3.1.5.  Flow Aggregation Example     3.2.  Explicit Routes     3.3.  Redundant Path Support     3.4.  Timing (or Other) Violation Reporting   4.  DetNet Security Considerations Compared with Diffserv Security           Considerations   5.  Security Threats     5.1.  Threat Taxonomy     5.2.  Threat Analysis       5.2.1.  Delay       5.2.2.  DetNet Flow Modification or Spoofing       5.2.3.  Resource Segmentation (Inter-segment Attack)               Vulnerability       5.2.4.  Packet Replication and Elimination         5.2.4.1.  Replication: Increased Attack Surface         5.2.4.2.  Replication-Related Header Manipulation       5.2.5.  Controller Plane         5.2.5.1.  Path Choice Manipulation         5.2.5.2.  Compromised Controller       5.2.6.  Reconnaissance       5.2.7.  Time-Synchronization Mechanisms     5.3.  Threat Summary   6.  Security Threat Impacts     6.1.  Delay Attacks       6.1.1.  Data Plane Delay Attacks       6.1.2.  Controller Plane Delay Attacks     6.2.  Flow Modification and Spoofing       6.2.1.  Flow Modification       6.2.2.  Spoofing         6.2.2.1.  Data Plane Spoofing         6.2.2.2.  Controller Plane Spoofing     6.3.  Segmentation Attacks (Injection)       6.3.1.  Data Plane Segmentation       6.3.2.  Controller Plane Segmentation     6.4.  Replication and Elimination       6.4.1.  Increased Attack Surface       6.4.2.  Header Manipulation at Elimination Routers     6.5.  Control or Signaling Packet Modification     6.6.  Control or Signaling Packet Injection     6.7.  Reconnaissance     6.8.  Attacks on Time-Synchronization Mechanisms     6.9.  Attacks on Path Choice   7.  Security Threat Mitigation     7.1.  Path Redundancy     7.2.  Integrity Protection     7.3.  DetNet Node Authentication     7.4.  Synthetic Traffic Insertion     7.5.  Encryption       7.5.1.  Encryption Considerations for DetNet     7.6.  Control and Signaling Message Protection     7.7.  Dynamic Performance Analytics     7.8.  Mitigation Summary   8.  Association of Attacks to Use Cases     8.1.  Association of Attacks to Use Case Common Themes       8.1.1.  Sub-network Layer       8.1.2.  Central Administration       8.1.3.  Hot Swap       8.1.4.  Data Flow Information Models       8.1.5.  L2 and L3 Integration       8.1.6.  End-to-End Delivery       8.1.7.  Replacement for Proprietary Fieldbuses and               Ethernet-Based Networks       8.1.8.  Deterministic vs. Best-Effort Traffic       8.1.9.  Deterministic Flows       8.1.10. Unused Reserved Bandwidth       8.1.11. Interoperability       8.1.12. Cost Reductions       8.1.13. Insufficiently Secure Components       8.1.14. DetNet Network Size       8.1.15. Multiple Hops       8.1.16. Level of Service       8.1.17. Bounded Latency       8.1.18. Low Latency       8.1.19. Bounded Jitter (Latency Variation)       8.1.20. Symmetrical Path Delays       8.1.21. Reliability and Availability       8.1.22. Redundant Paths       8.1.23. Security Measures     8.2.  Summary of Attack Types per Use Case Common Theme   9.  Security Considerations for OAM Traffic   10. DetNet Technology-Specific Threats     10.1.  IP     10.2.  MPLS   11. IANA Considerations   12. Security Considerations   13. Privacy Considerations   14. References     14.1.  Normative References     14.2.  Informative References   Contributors   Authors' Addresses1.  Introduction   A deterministic IP network ("Deterministic Networking Architecture"   [RFC8655]) can carry data flows for real-time applications with   extremely low data loss rates and bounded latency.  The bounds on   latency defined by DetNet (as described in [RFC9016]) include both   worst-case latency (Maximum Latency, Section 5.9.2 of [RFC9016]) and   worst-case jitter (Maximum Latency Variation, Section 5.9.3 of   [RFC9016]).  Data flows with deterministic properties are well   established for Ethernet networks (see Time-Sensitive Networking   (TSN), [IEEE802.1BA]); DetNet brings these capabilities to the IP   network.   Deterministic IP networks have been successfully deployed in real-   time Operational Technology (OT) applications for some years;   however, such networks are typically isolated from external access,   and thus the security threat from external attackers is low.  An   example of such an isolated network is a network deployed within an   aircraft, which is "air gapped" from the outside world.  DetNet   specifies a set of technologies that enable creation of deterministic   flows on IP-based networks of a potentially wide area (on the scale   of a corporate network), potentially merging OT traffic with best-   effort Information Technology (IT) traffic, and placing OT network   components into contact with IT network components, thereby exposing   the OT traffic and components to security threats that were not   present in an isolated OT network.   These DetNet (OT-type) technologies may not have previously been   deployed on a wide area IP-based network that also carries IT   traffic, and thus they can present security considerations that may   be new to IP-based wide area network designers; this document   provides insight into such system-level security considerations.  In   addition, designers of DetNet components (such as routers) face new   security-related challenges in providing DetNet services, for   example, maintaining reliable isolation between traffic flows in an   environment where IT traffic co-mingles with critical reserved-   bandwidth OT traffic; this document also examines security   implications internal to DetNet components.   Security is of particularly high importance in DetNet because many of   the use cases that are enabled by DetNet [RFC8578] include control of   physical devices (power grid devices, industrial controls, building   controls, etc.) that can have high operational costs for failure and   present potentially attractive targets for cyber attackers.   This situation is even more acute given that one of the goals of   DetNet is to provide a "converged network", i.e., one that includes   both IT traffic and OT traffic, thus exposing potentially sensitive   OT devices to attack in ways that were not previously common (usually   because they were under a separate control system or otherwise   isolated from the IT network, for example [ARINC664P7]).  Security   considerations for OT networks are not a new area, and there are many   OT networks today that are connected to wide area networks or the   Internet; this document focuses on the issues that are specific to   the DetNet technologies and use cases.   Given the above considerations, securing a DetNet starts with a   scrupulously well-designed and well-managed engineered network   following industry best practices for security at both the data plane   and controller plane, as well as for any Operations, Administration,   and Maintenance (OAM) implementation; this is the assumed starting   point for the considerations discussed herein.  Such assumptions also   depend on the network components themselves upholding the security-   related properties that are to be assumed by DetNet system-level   designers; for example, the assumption that network traffic   associated with a given flow can never affect traffic associated with   a different flow is only true if the underlying components make it   so.  Such properties, which may represent new challenges to component   designers, are also considered herein.   Starting with a "well-managed network", as noted above, enables us to   exclude some of the more powerful adversary capabilities from the   Internet Threat Model of [BCP72], such as the ability to arbitrarily   drop or delay any or all traffic.  Given this reduced attacker   capability, we can present security considerations based on attacker   capabilities that are more directly relevant to a DetNet.   In this context, we view the "conventional" (i.e., non-time-   sensitive) network design and management aspects of network security   as being primarily concerned with preventing denial of service, i.e.,   they must ensure that DetNet traffic goes where it's supposed to and   that an external attacker can't inject traffic that disrupts the   delivery timing assurance of the DetNet.  The time-specific aspects   of DetNet security presented here take up where those "conventional"   design and management aspects leave off.   However, note that "conventional" methods for mitigating (among all   the others) denial-of-service attacks (such as throttling) can only   be effectively used in a DetNet when their use does not compromise   the required time-sensitive or behavioral properties required for the   OT flows on the network.  For example, a "retry" protocol is   typically not going to be compatible with a low-latency (worst-case   maximum latency) requirement; however, if in a specific use case and   implementation such a retry protocol is able to meet the timing   constraints, then it may well be used in that context.  Similarly, if   common security protocols such as TLS/DTLS or IPsec are to be used,   it must be verified that their implementations are able to meet the   timing and behavioral requirements of the time-sensitive network as   implemented for the given use case.  An example of "behavioral   properties" might be that dropping of more than a specific number of   packets in a row is not acceptable according to the service level   agreement.   The exact security requirements for any given DetNet are necessarily   specific to the use cases handled by that network.  Thus, the reader   is assumed to be familiar with the specific security requirements of   their use cases, for example, those outlined in the DetNet Use Cases   [RFC8578] and the Security Considerations sections of the DetNet   documents applicable to the network technologies in use, for example,   [RFC8939] for an IP data plane and [RFC8964] for an MPLS data plane.   Readers can find a general introduction to the DetNet Architecture in   [RFC8655], the DetNet Data Plane in [RFC8938], and the Flow   Information Model in [RFC9016].   The DetNet technologies include ways to:   *  Assign data plane resources for DetNet flows in some or all of the      intermediate nodes (routers) along the path of the flow   *  Provide explicit routes for DetNet flows that do not dynamically      change with the network topology in ways that affect the quality      of service received by the affected flow(s)   *  Distribute data from DetNet flow packets over time and/or space to      ensure delivery of the data in each packet in spite of the loss of      a path   This document includes sections considering DetNet component design   as well as system design.  The latter includes a taxonomy and   analysis of threats, threat impacts and mitigations, and an   association of attacks with use cases (based on Section 11 of   [RFC8578]).   This document is based on the premise that there will be a very broad   range of DetNet applications and use cases, ranging in size and scope   from individual industrial machines to networks that span an entire   country [RFC8578].  Thus, no single set of prescriptions (such as   exactly which mitigation should be applied to which segment of a   DetNet) can be applicable to all of them, and indeed any single one   that we might prescribe would inevitably prove impractical for some   use case, perhaps one that does not even exist at the time of this   writing.  Thus, we are not prescriptive here; we are stating the   desired end result, with the understanding that most DetNet use cases   will necessarily differ from each other, and there is no "one size   fits all".2.  Abbreviations and Terminology   Information Technology (IT):  The application of computers to store,      study, retrieve, transmit, and manipulate data or information,      often in the context of a business or other enterprise [IT-DEF].   Operational Technology (OT):  The hardware and software dedicated to      detecting or causing changes in physical processes through direct      monitoring and/or control of physical devices such as valves,      pumps, etc.  [OT-DEF].   Component:  A component of a DetNet system -- used here to refer to      any hardware or software element of a DetNet that implements      DetNet-specific functionality, for example, all or part of a      router, switch, or end system.   Device:  Used here to refer to a physical entity controlled by the      DetNet, for example, a motor.   Resource Segmentation:  Used as a more general form for Network      Segmentation (the act or practice of splitting a computer network      into sub-networks, each being a network segment [NS-DEF]).   Controller Plane:  In DetNet, the Controller Plane corresponds to the      aggregation of the Control and Management Planes (see [RFC8655],      Section 4.4.2).3.  Security Considerations for DetNet Component Design   This section provides guidance for implementers of components to be   used in a DetNet.   As noted above, DetNet provides resource allocation, explicit routes,   and redundant path support.  Each of these has associated security   implications, which are discussed in this section, in the context of   component design.  Detection, reporting and appropriate action in the   case of packet arrival-time violations are also discussed.3.1.  Resource Allocation3.1.1.  Inviolable Flows   A DetNet system security designer relies on the premise that any   resources allocated to a resource-reserved (OT-type) flow are   inviolable; in other words, there is no physical possibility within a   DetNet component that resources allocated to a given DetNet flow can   be compromised by any type of traffic in the network.  This includes   malicious traffic as well as inadvertent traffic such as might be   produced by a malfunctioning component, or due to interactions   between components that were not sufficiently tested for   interoperability.  From a security standpoint, this is a critical   assumption, for example, when designing against DoS attacks.  In   other words, with correctly designed components and security   mechanisms, one can prevent malicious activities from impacting other   resources.   However, achieving the goal of absolutely inviolable flows may not be   technically or economically feasible for any given use case, given   the broad range of possible use cases (e.g., [RFC8578]) and their   associated security considerations as outlined in this document.  It   can be viewed as a continuum of security requirements, from isolated   ultra-low latency systems that may have little security vulnerability   (such as an industrial machine) to broadly distributed systems with   many possible attack vectors and OT security concerns (such as a   utility network).  Given this continuum, the design principle   employed in this document is to specify the desired end results,   without being overly prescriptive in how the results are achieved,   reflecting the understanding that no individual implementation is   likely to be appropriate for every DetNet use case.3.1.2.  Design Trade-Off Considerations in the Use Cases Continuum   For any given DetNet use case and its associated security   requirements, it is important for the DetNet system designer to   understand the interaction and design trade-offs that inevitably need   to be reconciled between the desired end results and the DetNet   protocols, as well as the DetNet system and component design.   For any given component, as designed for any given use case (or scope   of use cases), it is the responsibility of the component designer to   ensure that the premise of inviolable flows is supported to the   extent that they deem necessary to support their target use cases.   For example, the component may include traffic shaping and policing   at the ingress to prevent corrupted, malicious, or excessive packets   from entering the network, thereby decreasing the likelihood that any   traffic will interfere with any DetNet OT flow.  The component may   include integrity protection for some or all of the header fields   such as those used for flow ID, thereby decreasing the likelihood   that a packet whose flow ID has been compromised might be directed   into a different flow path.  The component may verify every single   packet header at every forwarding location, or only at certain   points.  In any of these cases, the component may use dynamic   performance analytics (Section 7.7) to cause action to be initiated   to address the situation in an appropriate and timely manner, either   at the data plane or controller plane, or both in concert.  The   component's software and hardware may include measures to ensure the   integrity of the resource allocation/deallocation process.  Other   design aspects of the component may help ensure that the adverse   effects of malicious traffic are more limited, for example, by   protecting network control interfaces or minimizing cascade failures.   The component may include features specific to a given use case, such   as configuration of the response to a given sequential packet loss   count.   Ultimately, due to cost and complexity factors, the security   properties of a component designed for low-cost systems may be (by   design) far inferior to a component with similar intended   functionality, but designed for highly secure or otherwise critical   applications, perhaps at substantially higher cost.  Any given   component is designed for some set of use cases and accordingly will   have certain limitations on its security properties and   vulnerabilities.  It is thus the responsibility of the system   designer to assure themselves that the components they use in their   design are capable of satisfying their overall system security   requirements.3.1.3.  Documenting the Security Properties of a Component   In order for the system designer to adequately understand the   security-related behavior of a given component, the designer of any   component intended for use with DetNet needs to clearly document the   security properties of that component.  For example, to address the   case where a corrupted packet in which the flow identification   information is compromised and thus may incidentally match the flow   ID of another ("victim") DetNet flow, resulting in additional   unauthorized traffic on the victim, the documentation might state   that the component employs integrity protection on the flow   identification fields.3.1.4.  Fail-Safe Component Behavior   Even when the security properties of a component are understood and   well specified, if the component malfunctions, for example, due to   physical circumstances unpredicted by the component designer, it may   be difficult or impossible to fully prevent malfunction of the   network.  The degree to which a component is hardened against various   types of failures is a distinguishing feature of the component and   its design, and the overall system design can only be as strong as   its weakest link.   However, all networks are subject to this level of uncertainty; it is   not unique to DetNet.  Having said that, DetNet raises the bar by   changing many added latency scenarios from tolerable annoyances to   unacceptable service violations.  That in turn underscores the   importance of system integrity, as well as correct and stable   configuration of the network and its nodes, as discussed in   Section 1.3.1.5.  Flow Aggregation Example   As another example regarding resource allocation implementation,   consider the implementation of Flow Aggregation for DetNet flows (as   discussed in [RFC8938]).  In this example, say there are N flows that   are to be aggregated; thus, the bandwidth resources of the aggregate   flow must be sufficient to contain the sum of the bandwidth   reservation for the N flows.  However, if one of those flows were to   consume more than its individually allocated bandwidth, this could   cause starvation of the other flows.  Thus, simply providing and   enforcing the calculated aggregate bandwidth may not be a complete   solution; the bandwidth for each individual flow must still be   guaranteed, for example, via ingress policing of each flow (i.e.,   before it is aggregated).  Alternatively, if by some other means each   flow to be aggregated can be trusted not to exceed its allocated   bandwidth, the same goal can be achieved.3.2.  Explicit Routes   The DetNet-specific purpose for constraining the ability of the   DetNet to reroute OT traffic is to maintain the specified service   parameters (such as upper and lower latency boundaries) for a given   flow.  For example, if the network were to reroute a flow (or some   part of a flow) based exclusively on statistical path usage metrics,   or due to malicious activity, it is possible that the new path would   have a latency that is outside the required latency bounds that were   designed into the original TE-designed path, thereby violating the   quality of service for the affected flow (or part of that flow).   However, it is acceptable for the network to reroute OT traffic in   such a way as to maintain the specified latency bounds (and any other   specified service properties) for any reason, for example, in   response to a runtime component or path failure.   So from a DetNet security standpoint, the DetNet system designer can   expect that any component designed for use in a DetNet will deliver   the packets within the agreed-upon service parameters.  For the   component designer, this means that in order for a component to   achieve that expectation, any component that is involved in   controlling or implementing any change of the initially TE-configured   flow routes must prevent rerouting of OT flows (whether malicious or   accidental) that might adversely affect delivering the traffic within   the specified service parameters.3.3.  Redundant Path Support   The DetNet provision for redundant paths (i.e., PREOF, or "Packet   Replication, Elimination, and Ordering Functions"), as defined in the   DetNet Architecture [RFC8655], provides the foundation for high   reliability of a DetNet by virtually eliminating packet loss (i.e.,   to a degree that is implementation dependent) through hitless   redundant packet delivery.      |  Note: At the time of this writing, PREOF is not defined for the      |  IP data plane.   It is the responsibility of the system designer to determine the   level of reliability required by their use case and to specify   redundant paths sufficient to provide the desired level of   reliability (in as much as that reliability can be provided through   the use of redundant paths).  It is the responsibility of the   component designer to ensure that the relevant PREOF operations are   executed reliably and securely to avoid potentially catastrophic   situations for the operational technology relying on them.   However, note that not all PREOF operations are necessarily   implemented in every network; for example, a packet reordering   function may not be necessary if the packets are either not required   to be in order or if the ordering is performed in some other part of   the network.   Ideally, a redundant path for a flow could be specified from end to   end; however, given that this is not always possible (as described in   [RFC8655]), the system designer will need to consider the resulting   end-to-end reliability and security resulting from any given   arrangement of network segments along the path, each of which   provides its individual PREOF implementation and thus its individual   level of reliability and security.   At the data plane, the implementation of PREOF depends on the correct   assignment and interpretation of packet sequence numbers, as well as   the actions taken based on them, such as elimination (including   elimination of packets with spurious sequence numbers).  Thus, the   integrity of these values must be maintained by the component as they   are assigned by the DetNet Data Plane Service sub-layer and   transported by the Forwarding sub-layer.  This is no different than   the integrity of the values in any header used by the DetNet (or any   other) data plane and is not unique to redundant paths.  The   integrity protection of header values is technology dependent; for   example, in Layer 2 networks, the integrity of the header fields can   be protected by using MACsec [IEEE802.1AE-2018].  Similarly, from the   sequence number injection perspective, it is no different from any   other protocols that use sequence numbers; for particulars of   integrity protection via IPsec Authentication Headers, useful   insights are provided by Section 3 of [RFC4302].3.4.  Timing (or Other) Violation Reporting   A task of the DetNet system designer is to create a network such that   for any incoming packet that arrives with any timing or bandwidth   violation, an appropriate action can be taken in order to prevent   damage to the system.  The reporting step may be accomplished through   dynamic performance analysis (see Section 7.7) or by any other means   as implemented in one or more components.  The action to be taken for   any given circumstance within any given application will depend on   the use case.  The action may involve intervention from the   controller plane, or it may be taken "immediately" by an individual   component, for example, if a very fast response is required.   The definitions and selections of the actions that can be taken are   properties of the components.  The component designer implements   these options according to their expected use cases, which may vary   widely from component to component.  Clearly, selecting an   inappropriate response to a given condition may cause more problems   than it is intending to mitigate; for example, a naive approach might   be to have the component shut down the link if a packet arrives   outside of its prescribed time window.  However, such a simplistic   action may serve the attacker better than it serves the network.   Similarly, simple logging of such issues may not be adequate since a   delay in response could result in material damage, for example, to   mechanical devices controlled by the network.  Thus, a breadth of   possible and effective security-related actions and their   configuration is a positive attribute for a DetNet component.   Some possible violations that warrant detection include cases where a   packet arrives:   *  Outside of its prescribed time window   *  Within its time window but with a compromised timestamp that makes      it appear that it is not within its window   *  Exceeding the reserved flow bandwidth   Some possible direct actions that may be taken at the data plane   include traffic policing and shaping functions (e.g., those described   in [RFC2475]), separating flows into per-flow rate-limited queues,   and potentially applying active queue management [RFC7567].  However,   if those (or any other) actions are to be taken, the system designer   must ensure that the results of such actions do not compromise the   continued safe operation of the system.  For example, the network   (i.e., the controller plane and data plane working together) must   mitigate in a timely fashion any potential adverse effect on   mechanical devices controlled by the network.4.  DetNet Security Considerations Compared with Diffserv Security    Considerations   DetNet is designed to be compatible with Diffserv [RFC2474] as   applied to IT traffic in the DetNet.  DetNet also incorporates the   use of the 6-bit value of the Differentiated Services Code Point   (DSCP) field of the Type of Service (IPv4) and Traffic Class (IPv6)   bytes for flow identification.  However, the DetNet interpretation of   the DSCP value for OT traffic is not equivalent to the per-hop   behavior (PHB) selection behavior as defined by Diffserv.   Thus, security considerations for DetNet have some aspects in common   with Diffserv, in fact overlapping 100% with respect to IP IT   traffic.  Security considerations for these aspects are part of the   existing literature on IP network security, specifically the Security   Considerations sections of [RFC2474] and [RFC2475].  However, DetNet   also introduces timing and other considerations that are not present   in Diffserv, so the Diffserv security considerations are a subset of   the DetNet security considerations.   In the case of DetNet OT traffic, the DSCP value is interpreted   differently than in Diffserv and contributes to determination of the   service provided to the packet.  In DetNet, there are similar   consequences to Diffserv for lack of detection of, or incorrect   handling of, packets with mismarked DSCP values, and many of the   points made in the Diffserv Security discussions (Section 6.1 of   [RFC2475], Section 7 of [RFC2474], and Section 3.3.2.1 of [RFC6274])   are also relevant to DetNet OT traffic though perhaps in modified   form.  For example, in DetNet, the effect of an undetected or   incorrectly handled maliciously mismarked DSCP field in an OT packet   is not identical to affecting the PHB of that packet, since DetNet   does not use the PHB concept for OT traffic.  Nonetheless, the   service provided to the packet could be affected, so mitigation   measures analogous to those prescribed by Diffserv would be   appropriate for DetNet.  For example, mismarked DSCP values should   not cause failure of network nodes.  The remarks in [RFC2474]   regarding IPsec and Tunneling Interactions are also relevant (though   this is not to say that other sections are less relevant).   In this discussion, interpretation (and any possible intentional re-   marking) of the DSCP values of packets destined for DetNet OT flows   is expected to occur at the ingress to the DetNet domain; once inside   the domain, maintaining the integrity of the DSCP values is subject   to the same handling considerations as any other field in the packet.5.  Security Threats   This section presents a taxonomy of threats and analyzes the possible   threats in a DetNet-enabled network.  The threats considered in this   section are independent of any specific technologies used to   implement the DetNet; Section 10 considers attacks that are   associated with the DetNet technologies encompassed by [RFC8938].   We distinguish controller plane threats from data plane threats.  The   attack surface may be the same, but the types of attacks, as well as   the motivation behind them, are different.  For example, a Delay   attack is more relevant to the data plane than to the controller   plane.  There is also a difference in terms of security solutions;   the way you secure the data plane is often different than the way you   secure the controller plane.5.1.  Threat Taxonomy   This document employs organizational elements of the threat models of   [RFC7384] and [RFC7835].  This model classifies attackers based on   two criteria:   Internal vs. external:      Internal attackers either have access to a trusted segment of the      network or possess the encryption or authentication keys.      External attackers, on the other hand, do not have the keys and      have access only to the encrypted or authenticated traffic.   On-path vs. off-path:      On-path attackers are located in a position that allows      interception, modification, or dropping of in-flight protocol      packets, whereas off-path attackers can only attack by generating      protocol packets.   Regarding the boundary between internal vs. external attackers as   defined above, note that in this document we do not make concrete   recommendations regarding which specific segments of the network are   to be protected in any specific way, for example, via encryption or   authentication.  As a result, the boundary as defined above is not   unequivocally specified here.  Given that constraint, the reader can   view an internal attacker as one who can operate within the perimeter   defined by the DetNet Edge Nodes (as defined in the DetNet   Architecture [RFC8655]), allowing that the specifics of what is   encrypted or authenticated within this perimeter will vary depending   on the implementation.   Care has also been taken to adhere to Section 5 of [RFC3552], both   with respect to which attacks are considered out of scope for this   document, and also which are considered to be the most common threats   (explored further in Section 5.2).  Most of the direct threats to   DetNet are active attacks (i.e., attacks that modify DetNet traffic),   but it is highly suggested that DetNet application developers take   appropriate measures to protect the content of the DetNet flows from   passive attacks (i.e., attacks that observe but do not modify DetNet   traffic), for example, through the use of TLS or DTLS.   DetNet-Service, one of the service scenarios described in   [DETNET-SERVICE-MODEL], is the case where a service connects DetNet   islands, i.e., two or more otherwise independent DetNets are   connected via a link that is not intrinsically part of either   network.  This implies that there could be DetNet traffic flowing   over a non-DetNet link, which may provide an attacker with an   advantageous opportunity to tamper with DetNet traffic.  The security   properties of non-DetNet links are outside of the scope of DetNet   Security, but it should be noted that use of non-DetNet services to   interconnect DetNets merits security analysis to ensure the integrity   of the networks involved.5.2.  Threat Analysis5.2.1.  Delay   An attacker can maliciously delay DetNet data flow traffic.  By   delaying the traffic, the attacker can compromise the service of   applications that are sensitive to high delays or to high delay   variation.  The delay may be constant or modulated.5.2.2.  DetNet Flow Modification or Spoofing   An attacker can modify some header fields of en route packets in a   way that causes the DetNet flow identification mechanisms to   misclassify the flow.  Alternatively, the attacker can inject traffic   that is tailored to appear as if it belongs to a legitimate DetNet   flow.  The potential consequence is that the DetNet flow resource   allocation cannot guarantee the performance that is expected when the   flow identification works correctly.5.2.3.  Resource Segmentation (Inter-segment Attack) Vulnerability   DetNet components are expected to split their resources between   DetNet flows in a way that prevents traffic from one DetNet flow from   affecting the performance of other DetNet flows and also prevents   non-DetNet traffic from affecting DetNet flows.  However, perhaps due   to implementation constraints, some resources may be partially   shared, and an attacker may try to exploit this property.  For   example, an attacker can inject traffic in order to exhaust network   resources such that DetNet packets that share resources with the   injected traffic may be dropped or delayed.  Such injected traffic   may be part of DetNet flows or non-DetNet traffic.   Another example of a Resource Segmentation attack is the case in   which an attacker is able to overload the exception path queue on the   router, i.e., a "slow path" typically taken by control or OAM packets   that are diverted from the data plane because they require processing   by a CPU.  DetNet OT flows are typically configured to take the "fast   path" through the data plane to minimize latency.  However, if there   is only one queue from the forwarding Application-Specific Integrated   Circuit (ASIC) to the exception path, and for some reason the system   is configured such that any DetNet packets must be handled on this   exception path, then saturating the exception path could result in   the delaying or dropping of DetNet packets.5.2.4.  Packet Replication and Elimination5.2.4.1.  Replication: Increased Attack Surface   Redundancy is intended to increase the robustness and survivability   of DetNet flows, and replication over multiple paths can potentially   mitigate an attack that is limited to a single path.  However, the   fact that packets are replicated over multiple paths increases the   attack surface of the network, i.e., there are more points in the   network that may be subject to attacks.5.2.4.2.  Replication-Related Header Manipulation   An attacker can manipulate the replication-related header fields.   This capability opens the door for various types of attacks.  For   example:   Forward both replicas:      Malicious change of a packet SN (Sequence Number) can cause both      replicas of the packet to be forwarded.  Note that this attack has      a similar outcome to a replay attack.   Eliminate both replicas:      SN manipulation can be used to cause both replicas to be      eliminated.  In this case, an attacker that has access to a single      path can cause packets from other paths to be dropped, thus      compromising some of the advantage of path redundancy.   Flow hijacking:      An attacker can hijack a DetNet flow with access to a single path      by systematically replacing the SNs on the given path with higher      SN values.  For example, an attacker can replace every SN value S      with a higher value S+C, where C is a constant integer.  Thus, the      attacker creates a false illusion that the attacked path has the      lowest delay, causing all packets from other paths to be      eliminated in favor of the attacked path.  Once the flow from the      compromised path is favored by the eliminating bridge, the flow      has effectively been hijacked by the attacker.  It is now possible      for the attacker to either replace en route packets with malicious      packets, or to simply inject errors into the packets, causing the      packets to be dropped at their destination.   Amplification:      An attacker who injects packets into a flow that is to be      replicated will have their attack amplified through the      replication process.  This is no different than any attacker who      injects packets that are delivered through multicast, broadcast,      or other point-to-multi-point mechanisms.5.2.5.  Controller Plane5.2.5.1.  Path Choice Manipulation5.2.5.1.1.  Control or Signaling Packet Modification   An attacker can maliciously modify en route control packets in order   to disrupt or manipulate the DetNet path/resource allocation.5.2.5.1.2.  Control or Signaling Packet Injection   An attacker can maliciously inject control packets in order to   disrupt or manipulate the DetNet path/resource allocation.5.2.5.1.3.  Increased Attack Surface   One of the possible consequences of a Path Manipulation attack is an   increased attack surface.  Thus, when the attack described in the   previous subsection is implemented, it may increase the potential of   other attacks to be performed.5.2.5.2.  Compromised Controller   An attacker can subvert a legitimate controller (or subvert another   component such that it represents itself as a legitimate controller)   with the result that the network nodes incorrectly believe it is   authorized to instruct them.   The presence of a compromised node or controller in a DetNet is not a   threat that arises as a result of determinism or time sensitivity;   the same techniques used to prevent or mitigate against compromised   nodes in any network are equally applicable in the DetNet case.  The   act of compromising a controller may not even be within the   capabilities of our defined attacker types -- in other words, it may   not be achievable via packet traffic at all, whether internal or   external, on path or off path.  It might be accomplished, for   example, by a human with physical access to the component, who could   upload bogus firmware to it via a USB stick.  All of this underscores   the requirement for careful overall system security design in a   DetNet, given that the effects of even one bad actor on the network   can be potentially catastrophic.   Security concerns specific to any given controller plane technology   used in DetNet will be addressed by the DetNet documents associated   with that technology.5.2.6.  Reconnaissance   A passive eavesdropper can identify DetNet flows and then gather   information about en route DetNet flows, e.g., the number of DetNet   flows, their bandwidths, their schedules, or other temporal or   statistical properties.  The gathered information can later be used   to invoke other attacks on some or all of the flows.   DetNet flows are typically uniquely identified by their 6-tuple,   i.e., fields within the L3 or L4 header.  However, in some   implementations, the flow ID may also be augmented by additional per-   flow attributes known to the system, e.g., above L4.  For the purpose   of this document, we assume any such additional fields used for flow   ID are encrypted and/or integrity protected from external attackers.   Note however that existing OT protocols designed for use on dedicated   secure networks may not intrinsically provide such protection, in   which case IPsec or transport-layer security mechanisms may be   needed.5.2.7.  Time-Synchronization Mechanisms   An attacker can use any of the attacks described in [RFC7384] to   attack the synchronization protocol, thus affecting the DetNet   service.5.3.  Threat Summary   A summary of the attacks that were discussed in this section is   presented in Table 1.  For each attack, the table specifies the type   of attackers that may invoke the attack.  In the context of this   summary, the distinction between internal and external attacks is   under the assumption that a corresponding security mechanism is being   used, and that the corresponding network equipment takes part in this   mechanism.    +======================+=========================================+    |        Attack        |              Attacker Type              |    |                      +====================+====================+    |                      |      Internal      |      External      |    |                      +=========+==========+=========+==========+    |                      | On-Path | Off-Path | On-Path | Off-Path |    +======================+=========+==========+=========+==========+    | Delay Attack         |    +    |          |    +    |          |    +----------------------+---------+----------+---------+----------+    | DetNet Flow          |    +    |    +     |         |          |    | Modification or      |         |          |         |          |    | Spoofing             |         |          |         |          |    +----------------------+---------+----------+---------+----------+    | Inter-segment Attack |    +    |    +     |    +    |    +     |    +----------------------+---------+----------+---------+----------+    | Replication:         |    +    |    +     |    +    |    +     |    | Increased Attack     |         |          |         |          |    | Surface              |         |          |         |          |    +----------------------+---------+----------+---------+----------+    | Replication-Related  |    +    |          |         |          |    | Header Manipulation  |         |          |         |          |    +----------------------+---------+----------+---------+----------+    | Path Manipulation    |    +    |    +     |         |          |    +----------------------+---------+----------+---------+----------+    | Path Choice:         |    +    |    +     |    +    |    +     |    | Increased Attack     |         |          |         |          |    | Surface              |         |          |         |          |    +----------------------+---------+----------+---------+----------+    | Control or Signaling |    +    |          |         |          |    | Packet Modification  |         |          |         |          |    +----------------------+---------+----------+---------+----------+    | Control or Signaling |    +    |    +     |         |          |    | Packet Injection     |         |          |         |          |    +----------------------+---------+----------+---------+----------+    | Reconnaissance       |    +    |          |    +    |          |    +----------------------+---------+----------+---------+----------+    | Attacks on Time-     |    +    |    +     |    +    |    +     |    | Synchronization      |         |          |         |          |    | Mechanisms           |         |          |         |          |    +----------------------+---------+----------+---------+----------+                     Table 1: Threat Analysis Summary6.  Security Threat Impacts   When designing security for a DetNet, as with any network, it may be   prohibitively expensive or technically infeasible to thoroughly   protect against every possible threat.  Thus, the security designer   must be informed (for example, by an application domain expert such   as a product manager) regarding the relative significance of the   various threats and their impact if a successful attack is carried   out.  In this section, we present an example of a possible template   for such a communication, culminating in a table (Table 2) that lists   a set of threats under consideration, and some values characterizing   their relative impact in the context of a given industry.  The   specific threats, industries, and impact values in the table are   provided only as an example of this kind of assessment and its   communication; they are not intended to be taken literally.   This section considers assessment of the relative impacts of the   attacks described in Section 5.  In this section, the impacts as   described assume that the associated mitigation is not present or has   failed.  Mitigations are discussed in Section 7.   In computer security, the impact (or consequence) of an incident can   be measured in loss of confidentiality, integrity, or availability of   information.  In the case of OT or time sensitive networks (though   not to the exclusion of IT or non-time-sensitive networks), the   impact of an exploit can also include failure or malfunction of   mechanical and/or other physical systems.   DetNet raises these stakes significantly for OT applications,   particularly those that may have been designed to run in an OT-only   environment and thus may not have been designed for security in an IT   environment with its associated components, services, and protocols.   The extent of impact of a successful vulnerability exploit varies   considerably by use case and by industry; additional insight   regarding the individual use cases is available from "Deterministic   Networking Use Cases" [RFC8578].  Each of those use cases is   represented in Table 2, including Pro Audio, Electrical Utilities,   Industrial M2M (split into two areas: M2M Data Gathering and M2M   Control Loop), and others.   Aspects of Impact (left column) include Criticality of Failure,   Effects of Failure, Recovery, and DetNet Functional Dependence.   Criticality of failure summarizes the seriousness of the impact.  The   impact of a resulting failure can affect many different metrics that   vary greatly in scope and severity.  In order to reduce the number of   variables, only the following were included: Financial, Health and   Safety, Effect on a Single Organization, and Effect on Multiple   Organizations.  Recovery outlines how long it would take for an   affected use case to get back to its pre-failure state (Recovery Time   Objective, RTO) and how much of the original service would be lost in   between the time of service failure and recovery to original state   (Recovery Point Objective, RPO).  DetNet dependence maps how much the   following DetNet service objectives contribute to impact of failure:   time dependency, data integrity, source node integrity, availability,   and latency/jitter.   The scale of the Impact mappings is low, medium, and high.  In some   use cases, there may be a multitude of specific applications in which   DetNet is used.  For simplicity, this section attempts to average the   varied impacts of different applications.  This section does not   address the overall risk of a certain impact that would require the   likelihood of a failure happening.   In practice, any such ratings will vary from case to case; the   ratings shown here are given as examples.   +==============+=====+======+======+==========+======+======+======+   |              | PRO | Util | Bldg | Wireless | Cell | M2M  | M2M  |   |              | A   |      |      |          |      | Data | Ctrl |   +==============+=====+======+======+==========+======+======+======+   | Criticality  | Med | Hi   | Low  | Med      | Med  | Med  | Med  |   +==============+=====+======+======+==========+======+======+======+   | Effects                                                          |   +==============+=====+======+======+==========+======+======+======+   | Financial    | Med | Hi   | Med  | Med      | Low  | Med  | Med  |   +--------------+-----+------+------+----------+------+------+------+   | Health/      | Med | Hi   | Hi   | Med      | Med  | Med  | Med  |   | Safety       |     |      |      |          |      |      |      |   +--------------+-----+------+------+----------+------+------+------+   | Affects 1    | Hi  | Hi   | Med  | Hi       | Med  | Med  | Med  |   | org          |     |      |      |          |      |      |      |   +--------------+-----+------+------+----------+------+------+------+   | Affects >1   | Med | Hi   | Low  | Med      | Med  | Med  | Med  |   | org          |     |      |      |          |      |      |      |   +==============+=====+======+======+==========+======+======+======+   | Recovery                                                         |   +==============+=====+======+======+==========+======+======+======+   | Recov Time   | Med | Hi   | Med  | Hi       | Hi   | Hi   | Hi   |   | Obj          |     |      |      |          |      |      |      |   +--------------+-----+------+------+----------+------+------+------+   | Recov Point  | Med | Hi   | Low  | Med      | Low  | Hi   | Hi   |   | Obj          |     |      |      |          |      |      |      |   +==============+=====+======+======+==========+======+======+======+   | DetNet Dependence                                                |   +==============+=====+======+======+==========+======+======+======+   | Time         | Hi  | Hi   | Low  | Hi       | Med  | Low  | Hi   |   | Dependence   |     |      |      |          |      |      |      |   +--------------+-----+------+------+----------+------+------+------+   | Latency/     | Hi  | Hi   | Med  | Med      | Low  | Low  | Hi   |   | Jitter       |     |      |      |          |      |      |      |   +--------------+-----+------+------+----------+------+------+------+   | Data         | Hi  | Hi   | Med  | Hi       | Low  | Hi   | Hi   |   | Integrity    |     |      |      |          |      |      |      |   +--------------+-----+------+------+----------+------+------+------+   | Src Node     | Hi  | Hi   | Med  | Hi       | Med  | Hi   | Hi   |   | Integ        |     |      |      |          |      |      |      |   +--------------+-----+------+------+----------+------+------+------+   | Availability | Hi  | Hi   | Med  | Hi       | Low  | Hi   | Hi   |   +--------------+-----+------+------+----------+------+------+------+             Table 2: Impact of Attacks by Use Case Industry   The rest of this section will cover impact of the different groups in   more detail.6.1.  Delay Attacks6.1.1.  Data Plane Delay Attacks   Note that "Delay attack" also includes the possibility of a "negative   delay" or early arrival of a packet, or possibly adversely changing   the timestamp value.   Delayed messages in a DetNet link can result in the same behavior as   dropped messages in ordinary networks, since the services attached to   the DetNet flow are likely to have strict delivery time requirements.   For a single-path scenario, disruption within the single flow is a   real possibility.  In a multipath scenario, large delays or   instabilities in one DetNet flow can also lead to increased buffer   and processor resource consumption at the eliminating router.   A data plane Delay attack on a system controlling substantial moving   devices, for example, in industrial automation, can cause physical   damage.  For example, if the network promises a bounded latency of 2   ms for a flow, yet the machine receives it with 5 ms latency, the   control loop of the machine may become unstable.6.1.2.  Controller Plane Delay Attacks   In and of itself, this is not directly a threat to the DetNet   service, but the effects of delaying control messages can have quite   adverse effects later.   *  Delayed teardown can lead to resource leakage, which in turn can      result in failure to allocate new DetNet flows, finally giving      rise to a denial-of-service attack.   *  Failure to deliver, or severely delaying, controller plane      messages adding an endpoint to a multicast group will prevent the      new endpoint from receiving expected frames thus disrupting      expected behavior.   *  Delaying messages that remove an endpoint from a group can lead to      loss of privacy, as the endpoint will continue to receive messages      even after it is supposedly removed.6.2.  Flow Modification and Spoofing6.2.1.  Flow Modification   If the contents of a packet header or body can be modified by the   attacker, this can cause the packet to be routed incorrectly or   dropped, or the payload to be corrupted or subtly modified.  Thus,   the potential impact of a Modification attack includes disrupting the   application as well as the network equipment.6.2.2.  Spoofing6.2.2.1.  Data Plane Spoofing   Spoofing data plane messages can result in increased resource   consumption on the routers throughout the network as it will increase   buffer usage and processor utilization.  This can lead to resource   exhaustion and/or increased delay.   If the attacker manages to create valid headers, the false messages   can be forwarded through the network, using part of the allocated   bandwidth.  This in turn can cause legitimate messages to be dropped   when the resource budget has been exhausted.   Finally, the endpoint will have to deal with invalid messages being   delivered to the endpoint instead of (or in addition to) a valid   message.6.2.2.2.  Controller Plane Spoofing   A successful Controller Plane Spoofing attack will potentially have   adverse effects.  It can do virtually anything from:   *  modifying existing DetNet flows by changing the available      bandwidth   *  adding or removing endpoints from a DetNet flow   *  dropping DetNet flows completely   *  falsely creating new DetNet flows (exhausting the systems      resources or enabling DetNet flows that are outside the control of      the network engineer)6.3.  Segmentation Attacks (Injection)6.3.1.  Data Plane Segmentation   Injection of false messages in a DetNet flow could lead to exhaustion   of the available bandwidth for that flow if the routers attribute   these false messages to the resource budget of that flow.   In a multipath scenario, injected messages will cause increased   processor utilization in elimination routers.  If enough paths are   subject to malicious injection, the legitimate messages can be   dropped.  Likewise, it can cause an increase in buffer usage.  In   total, it will consume more resources in the routers than normal,   giving rise to a resource-exhaustion attack on the routers.   If a DetNet flow is interrupted, the end application will be affected   by what is now a non-deterministic flow.  Note that there are many   possible sources of flow interruptions, for example, but not limited   to, such physical-layer conditions as a broken wire or a radio link   that is compromised by interference.6.3.2.  Controller Plane Segmentation   In a successful Controller Plane Segmentation attack, control   messages are acted on by nodes in the network, unbeknownst to the   central controller or the network engineer.  This has the potential   to:   *  create new DetNet flows (exhausting resources)   *  drop existing DetNet flows (denial of service)   *  add end stations to a multicast group (loss of privacy)   *  remove end stations from a multicast group (reduction of service)   *  modify the DetNet flow attributes (affecting available bandwidth)   If an attacker can inject control messages without the central   controller knowing, then one or more components in the network may   get into a state that is not expected by the controller.  At that   point, if the controller initiates a command, the effect of that   command may not be as expected, since the target of the command may   have started from a different initial state.6.4.  Replication and Elimination   The Replication and Elimination functions are relevant only to data   plane messages as controller plane messages are not subject to   multipath routing.6.4.1.  Increased Attack Surface   The impact of an increased attack surface is that it increases the   probability that the network can be exposed to an attacker.  This can   facilitate a wide range of specific attacks, and their respective   impacts are discussed in other subsections of this section.6.4.2.  Header Manipulation at Elimination Routers   This attack can potentially cause DoS to the application that uses   the attacked DetNet flows or to the network equipment that forwards   them.  Furthermore, it can allow an attacker to manipulate the   network paths and the behavior of the network layer.6.5.  Control or Signaling Packet Modification   If control packets are subject to manipulation undetected, the   network can be severely compromised.6.6.  Control or Signaling Packet Injection   If an attacker can inject control packets undetected, the network can   be severely compromised.6.7.  Reconnaissance   Of all the attacks, this is one of the most difficult to detect and   counter.   An attacker can, at their leisure, observe over time various aspects   of the messaging and signaling, learning the intent and purpose of   the traffic flows.  Then at some later date, possibly at an important   time in the operational context, they might launch an attack based on   that knowledge.   The flow ID in the header of the data plane messages gives an   attacker a very reliable identifier for DetNet traffic, and this   traffic has a high probability of going to lucrative targets.   Applications that are ported from a private OT network to the higher   visibility DetNet environment may need to be adapted to limit   distinctive flow properties that could make them susceptible to   reconnaissance.6.8.  Attacks on Time-Synchronization Mechanisms   DetNet relies on an underlying time-synchronization mechanism;   therefore, a compromised synchronization mechanism may cause DetNet   nodes to malfunction.  Specifically, DetNet flows may fail to meet   their latency requirements and deterministic behavior, thus causing   DoS to DetNet applications.6.9.  Attacks on Path Choice   This is covered in part in Section 6.3 (Segmentation Attacks   (Injection)) and, as with Replication and Elimination (see   Section 6.4), this is relevant for data plane messages.7.  Security Threat Mitigation   This section describes a set of measures that can be taken to   mitigate the attacks described in Section 5.  These mitigations   should be viewed as a set of tools, any of which can be used   individually or in concert.  The DetNet component and/or system and/   or application designer can apply these tools as necessary based on a   system-specific threat analysis.   Some of the technology-specific security considerations and   mitigation approaches are further discussed in DetNet data plane   solution documents, such as [RFC8938], [RFC8939], [RFC8964],   [RFC9025], and [RFC9056].7.1.  Path Redundancy   Description:  Path redundancy is a DetNet flow that can be forwarded      simultaneously over multiple paths.  Packet Replication and      Elimination [RFC8655] provide resiliency to dropped or delayed      packets.  This redundancy improves the robustness to failures and      to on-path attacks.         |  Note: At the time of this writing, PREOF is not defined for         |  the IP data plane.   Related attacks:  Path redundancy can be used to mitigate various on-      path attacks, including attacks described in Sections 5.2.1,      5.2.2, 5.2.3, and 5.2.7.  However, it is also possible that      multiple paths may make it more difficult to locate the source of      an on-path attacker.      A Delay Modulation attack could result in extensively exercising      otherwise unused code paths to expose hidden flaws.  Subtle race      conditions and memory allocation bugs in error-handling paths are      classic examples of this.7.2.  Integrity Protection   Description:  Integrity protection in the scope of DetNet is the      ability to detect if a packet header has been modified      (maliciously or otherwise) and if so, take some appropriate action      (as discussed in Section 7.7).  The decision on where in the      network to apply integrity protection is part of the DetNet system      design, and the implementation of the protection method itself is      a part of a DetNet component design.      The most common technique for detecting header modification is the      use of a Message Authentication Code (MAC) (see Section 10 for      examples).  The MAC can be distributed either in line (included in      the same packet) or via a side channel.  Of these, the in-line      method is generally preferred due to the low latency that may be      required on DetNet flows and the relative complexity and      computational overhead of a sideband approach.      There are different levels of security available for integrity      protection, ranging from the basic ability to detect if a header      has been corrupted in transit (no malicious attack) to stopping a      skilled and determined attacker capable of both subtly modifying      fields in the headers as well as updating an unkeyed checksum.      Common for all are the 2 steps that need to be performed in both      ends.  The first is computing the checksum or MAC.  The      corresponding verification step must perform the same steps before      comparing the provided with the computed value.  Only then can the      receiver be reasonably sure that the header is authentic.      The most basic protection mechanism consists of computing a simple      checksum of the header fields and providing it to the next entity      in the packets path for verification.  Using a MAC combined with a      secret key provides the best protection against Modification and      Replication attacks (see Sections 5.2.2 and 5.2.4).  This MAC      usage needs to be part of a security association that is      established and managed by a security association protocol (such      as IKEv2 for IPsec security associations).  Integrity protection      in the controller plane is discussed in Section 7.6.  The secret      key, regardless of the MAC used, must be protected from falling      into the hands of unauthorized users.  Once key management becomes      a topic, it is important to understand that this is a delicate      process and should not be undertaken lightly.  BCP 107 [BCP107]      provides best practices in this regard.      DetNet system and/or component designers need to be aware of these      distinctions and enforce appropriate integrity-protection      mechanisms as needed based on a threat analysis.  Note that adding      integrity-protection mechanisms may introduce latency; thus, many      of the same considerations in Section 7.5.1 also apply here.   Packet Sequence Number Integrity Considerations:  The use of PREOF in      a DetNet implementation implies the use of a sequence number for      each packet.  There is a trust relationship between the component      that adds the sequence number and the component that removes the      sequence number.  The sequence number may be end-to-end source to      destination, or it may be added/deleted by network edge      components.  The adder and remover(s) have the trust relationship      because they are the ones that ensure that the sequence numbers      are not modifiable.  Thus, sequence numbers can be protected by      using authenticated encryption or by a MAC without using      encryption.  Between the adder and remover there may or may not be      replication and elimination functions.  The elimination functions      must be able to see the sequence numbers.  Therefore, if      encryption is done between adders and removers, it must not      obscure the sequence number.  If the sequence removers and the      eliminators are in the same physical component, it may be possible      to obscure the sequence number; however, that is a layer violation      and is not recommended practice.         |  Note: At the time of this writing, PREOF is not defined for         |  the IP data plane.   Related attacks:  Integrity protection mitigates attacks related to      modification and tampering, including the attacks described in      Sections 5.2.2 and 5.2.4.7.3.  DetNet Node Authentication   Description:  Authentication verifies the identity of DetNet nodes      (including DetNet Controller Plane nodes), and this enables      mitigation of Spoofing attacks.  While integrity protection      (Section 7.2) prevents intermediate nodes from modifying      information, authentication can provide traffic origin      verification, i.e., to verify that each packet in a DetNet flow is      from a known source.  Although node authentication and integrity      protection are two different goals of a security protocol, in most      cases, a common protocol (such as IPsec [RFC4301] or MACsec      [IEEE802.1AE-2018]) is used for achieving both purposes.   Related attacks:  DetNet node authentication is used to mitigate      attacks related to spoofing, including the attacks of Sections      5.2.2 and 5.2.4.7.4.  Synthetic Traffic Insertion   Description:  With some queuing methods such as [IEEE802.1Qch-2017],      it is possible to introduce synthetic traffic in order to      regularize the timing of packet transmission.  (Synthetic traffic      typically consists of randomly generated packets injected in the      network to mask observable transmission patterns in the flows,      which may allow an attacker to gain insight into the content of      the flows).  This can subsequently reduce the value of passive      monitoring from internal threats (see Section 5) as it will be      much more difficult to associate discrete events with particular      network packets.   Related attacks:  Removing distinctive temporal properties of      individual packets or flows can be used to mitigate against      reconnaissance attacks (Section 5.2.6).  For example, synthetic      traffic can be used to maintain constant traffic rate even when no      user data is transmitted, thus making it difficult to collect      information about the times at which users are active and the      times at which DetNet flows are added or removed.   Traffic Insertion Challenges:  Once an attacker is able to monitor      the frames traversing a network to such a degree that they can      differentiate between best-effort traffic and traffic belonging to      a specific DetNet flow, it becomes difficult to not reveal to the      attacker whether a given frame is valid traffic or an inserted      frame.  Thus, having the DetNet components generate and remove the      synthetic traffic may or may not be a viable option unless certain      challenges are solved; for example, but not limited to:      *  Inserted traffic must be indistinguishable from valid stream         traffic from the viewpoint of the attacker.      *  DetNet components must be able to safely identify and remove         all inserted traffic (and only inserted traffic).      *  The controller plane must manage where to insert and remove         synthetic traffic, but this information must not be revealed to         an attacker.         An alternative design is to have the insertion and removal of         synthetic traffic be performed at the application layer rather         than by the DetNet itself.  For example, the use of RTP padding         to reduce information leakage from variable-bit-rate audio         transmission via the Secure Real-time Transport Protocol (SRTP)         is discussed in [RFC6562].7.5.  Encryption   Description:  Reconnaissance attacks (Section 5.2.6) can be mitigated      to some extent through the use of encryption, thereby preventing      the attacker from accessing the packet header or contents.      Specific encryption protocols will depend on the lower layers that      DetNet is forwarded over.  For example, IP flows may be forwarded      over IPsec [RFC4301], and Ethernet flows may be secured using      MACsec [IEEE802.1AE-2018].      However, despite the use of encryption, a reconnaissance attack      can provide the attacker with insight into the network, even      without visibility into the packet.  For example, an attacker can      observe which nodes are communicating with which other nodes,      including when, how often, and with how much data.  In addition,      the timing of packets may be correlated in time with external      events such as action of an external device.  Such information may      be used by the attacker, for example, in mapping out specific      targets for a different type of attack at a different time.      DetNet nodes do not have any need to inspect the payload of any      DetNet packets, making them data agnostic.  This means that end-      to-end encryption at the application layer is an acceptable way to      protect user data.      Note that reconnaissance is a threat that is not specific to      DetNet flows; therefore, reconnaissance mitigation will typically      be analyzed and provided by a network operator regardless of      whether DetNet flows are deployed.  Thus, encryption requirements      will typically not be defined in DetNet technology-specific      specifications, but considerations of using DetNet in encrypted      environments will be discussed in these specifications.  For      example, Section 5.1.2.3 of [RFC8939] discusses flow      identification of DetNet flows running over IPsec.   Related attacks:  As noted above, encryption can be used to mitigate      reconnaissance attacks (Section 5.2.6).  However, for a DetNet to      provide differentiated quality of service on a flow-by-flow basis,      the network must be able to identify the flows individually.  This      implies that in a reconnaissance attack, the attacker may also be      able to track individual flows to learn more about the system.7.5.1.  Encryption Considerations for DetNet   Any compute time that is required for encryption and decryption   processing ("crypto") must be included in the flow latency   calculations.  Thus, cryptographic algorithms used in a DetNet must   have bounded worst-case execution times, and these values must be   used in the latency calculations.  Fortunately, encryption and   decryption operations typically are designed to have constant   execution times in order to avoid side channel leakage.   Some cryptographic algorithms are symmetric in encode/decode time   (such as AES), and others are asymmetric (such as public key   algorithms).  There are advantages and disadvantages to the use of   either type in a given DetNet context.  The discussion in this   document relates to the timing implications of crypto for DetNet; it   is assumed that integrity considerations are covered elsewhere in the   literature.   Asymmetrical crypto is typically not used in networks on a packet-by-   packet basis due to its computational cost.  For example, if only   endpoint checks or checks at a small number of intermediate points   are required, asymmetric crypto can be used to authenticate   distribution or exchange of a secret symmetric crypto key; a   successful check based on that key will provide traffic origin   verification as long as the key is kept secret by the participants.   TLS (v1.3 [RFC8446], in particular, Section 4.1 ("Key Exchange   Messages")) and IKEv2 [RFC6071] are examples of this for endpoint   checks.   However, if secret symmetric keys are used for this purpose, the key   must be given to all relays, which increases the probability of a   secret key being leaked.  Also, if any relay is compromised or   faulty, then it may inject traffic into the flow.  Group key   management protocols can be used to automate management of such   symmetric keys; for an example in the context of IPsec, see   [IPSECME-G-IKEV2].   Alternatively, asymmetric crypto can provide traffic origin   verification at every intermediate node.  For example, a DetNet flow   can be associated with an (asymmetric) keypair, such that the private   key is available to the source of the flow and the public key is   distributed with the flow information, allowing verification at every   node for every packet.  However, this is more computationally   expensive.   In either case, origin verification also requires replay detection as   part of the security protocol to prevent an attacker from recording   and resending traffic, e.g., as a denial-of-service attack on flow   forwarding resources.   In the general case, cryptographic hygiene requires the generation of   new keys during the lifetime of an encrypted flow (e.g., see   Section 9 of [RFC4253]), and any such key generation (or key   exchange) requires additional computing time, which must be accounted   for in the latency calculations for that flow.  For modern ECDH   (Elliptical Curve Diffie-Hellman) key-exchange operations (such as   x25519 [RFC7748]), these operations can be performed in constant   (predictable) time; however, this is not universally true (for   example, for legacy RSA key exchange [RFC4432]).  Thus, implementers   should be aware of the time properties of these algorithms and avoid   algorithms that make constant-time implementation difficult or   impossible.7.6.  Control and Signaling Message Protection   Description:  Control and signaling messages can be protected through      the use of any or all of encryption, authentication, and      integrity-protection mechanisms.  Compared with data flows, the      timing constraints for controller and signaling messages may be      less strict, and the number of such packets may be fewer.  If that      is the case in a given application, then it may enable the use of      asymmetric cryptography for the signing of both payload and      headers for such messages, as well as encrypting the payload.      Given that a DetNet is managed by a central controller, the use of      a shared public key approach for these processes is well proven.      This is further discussed in Section 7.5.1.   Related attacks:  These mechanisms can be used to mitigate various      attacks on the controller plane, as described in Sections 5.2.5,      5.2.7, and 5.2.5.1.7.7.  Dynamic Performance Analytics   Description:  Incorporating Dynamic Performance Analytics (DPA)      implies that the DetNet design includes a performance monitoring      system to validate that timing guarantees are being met and to      detect timing violations or other anomalies that may be the      symptom of a security attack or system malfunction.  If this      monitoring system detects unexpected behavior, it must then cause      action to be initiated to address the situation in an appropriate      and timely manner, either at the data plane or controller plane or      both in concert.      The overall DPA system can thus be decomposed into the "detection"      and "notification" functions.  Although the time-specific DPA      performance indicators and their implementation will likely be      specific to a given DetNet, and as such are nascent technology at      the time of this writing, DPA is commonly used in existing      networks so we can make some observations on how such a system      might be implemented for a DetNet given that it would need to be      adapted to address the time-specific performance indicators.   Detection Mechanisms:  Measurement of timing performance can be done      via "passive" or "active" monitoring, as discussed below.      Examples of passive monitoring strategies include:      *  Monitoring of queue and buffer levels, e.g., via active queue         management (e.g., [RFC7567]).      *  Monitoring of per-flow counters.      *  Measurement of link statistics such as traffic volume,         bandwidth, and QoS.      *  Detection of dropped packets.      *  Use of commercially available Network Monitoring tools.      Examples of active monitoring include:      *  In-band timing measurements (such as packet arrival times),         e.g., by timestamping and packet inspection.      *  Use of OAM.  For DetNet-specific OAM considerations, see         [DETNET-IP-OAM] and [DETNET-MPLS-OAM].  Note: At the time of         this writing, specifics of DPA have not been developed for the         DetNet OAM but could be a subject for future investigation.         -  For OAM for Ethernet specifically, see also Connectivity            Fault Management (CFM [IEEE802.1Q]), which defines protocols            and practices for OAM for paths through 802.1 bridges and            LANs.      *  Out-of-band detection.  Following the data path or parts of a         data path, for example, Bidirectional Forwarding Detection         (BFD, e.g., [RFC5880]).      Note that for some measurements (e.g., packet delay), it may be      necessary to make and reconcile measurements from more than one      physical location (e.g., a source and destination), possibly in      both directions, in order to arrive at a given performance      indicator value.   Notification Mechanisms:  Making DPA measurement results available at      the right place(s) and time(s) to effect timely response can be      challenging.  Two notification mechanisms that are in general use      are NETCONF/YANG Notifications and the proprietary local telemetry      interfaces provided with components from some vendors.  The      Constrained Application Protocol (CoAP) Observe Option [RFC7641]      could also be relevant to such scenarios.      At the time of this writing, YANG Notifications are not addressed      by the DetNet YANG documents; however, this may be a topic for      future work.  It is possible that some of the passive mechanisms      could be covered by notifications from non-DetNet-specific YANG      modules; for example, if there is OAM or other performance      monitoring that can monitor delay bounds, then that could have its      own associated YANG data model, which could be relevant to DetNet,      for example, some "threshold" values for timing measurement      notifications.      At the time of this writing, there is an IETF Working Group for      network/performance monitoring (IP Performance Metrics (IPPM)).      See also previous work by the completed Remote Network Monitoring      Working Group (RMONMIB).  See also "An Overview of the IETF      Network Management Standards", [RFC6632].      Vendor-specific local telemetry may be available on some      commercially available systems, whereby the system can be      programmed (via a proprietary dedicated port and API) to monitor      and report on specific conditions, based on both passive and      active measurements.   Related attacks:  Performance analytics can be used to detect various      attacks, including the ones described in Section 5.2.1 (Delay      attack), Section 5.2.3 (Resource Segmentation attack), and      Section 5.2.7 (Time-Synchronization attack).  Once detection and      notification have occurred, the appropriate action can be taken to      mitigate the threat.      For example, in the case of data plane Delay attacks, one possible      mitigation is to timestamp the data at the source and timestamp it      again at the destination, and if the resulting latency does not      meet the service agreement, take appropriate action.  Note that      DetNet specifies packet sequence numbering; however, it does not      specify use of packet timestamps, although they may be used by the      underlying transport (for example, TSN [IEEE802.1BA]) to provide      the service.7.8.  Mitigation Summary   The following table maps the attacks of Section 5 (Security Threats)   to the impacts of Section 6 (Security Threat Impacts) and to the   mitigations of the current section.  Each row specifies an attack,   the impact of this attack if it is successfully implemented, and   possible mitigation methods.   +======================+======================+=====================+   | Attack               | Impact               | Mitigations         |   +======================+======================+=====================+   | Delay Attack         | *  Non-deterministic | *  Path redundancy  |   |                      |    delay             |                     |   |                      |                      | *  Performance      |   |                      | *  Data disruption   |    analytics        |   |                      |                      |                     |   |                      | *  Increased         |                     |   |                      |    resource          |                     |   |                      |    consumption       |                     |   +----------------------+----------------------+---------------------+   | Reconnaissance       | *  Enabler for other | *  Encryption       |   |                      |    attacks           |                     |   |                      |                      | *  Synthetic        |   |                      |                      |    traffic          |   |                      |                      |    insertion        |   +----------------------+----------------------+---------------------+   | DetNet Flow          | *  Increased         | *  Path redundancy  |   | Modification or      |    resource          |                     |   | Spoofing             |    consumption       | *  Integrity        |   |                      |                      |    protection       |   |                      | *  Data disruption   |                     |   |                      |                      | *  DetNet Node      |   |                      |                      |    authentication   |   +----------------------+----------------------+---------------------+   | Inter-segment Attack | *  Increased         | *  Path redundancy  |   |                      |    resource          |                     |   |                      |    consumption       | *  Performance      |   |                      |                      |    analytics        |   |                      | *  Data disruption   |                     |   +----------------------+----------------------+---------------------+   | Replication:         | *  All impacts of    | *  Integrity        |   | Increased Attack     |    other attacks     |    protection       |   | Resource             |                      |                     |   |                      |                      | *  DetNet Node      |   |                      |                      |    authentication   |   |                      |                      |                     |   |                      |                      | *  Encryption       |   +----------------------+----------------------+---------------------+   | Replication-Related  | *  Non-deterministic | *  Integrity        |   | Header Manipulation  |    delay             |    protection       |   |                      |                      |                     |   |                      | *  Data disruption   | *  DetNet Node      |   |                      |                      |    authentication   |   +----------------------+----------------------+---------------------+   | Path Manipulation    | *  Enabler for other | *  Control and      |   |                      |    attacks           |    signaling        |   |                      |                      |    message          |   |                      |                      |    protection       |   +----------------------+----------------------+---------------------+   | Path Choice:         | *  All impacts of    | *  Control and      |   | Increased Attack     |    other attacks     |    signaling        |   | Surface              |                      |    message          |   |                      |                      |    protection       |   +----------------------+----------------------+---------------------+   | Control or Signaling | *  Increased         | *  Control and      |   | Packet Modification  |    resource          |    signaling        |   |                      |    consumption       |    message          |   |                      |                      |    protection       |   |                      | *  Non-deterministic |                     |   |                      |    delay             |                     |   |                      |                      |                     |   |                      | *  Data disruption   |                     |   +----------------------+----------------------+---------------------+   | Control or Signaling | *  Increased         | *  Control and      |   | Packet Injection     |    resource          |    signaling        |   |                      |    consumption       |    message          |   |                      |                      |    protection       |   |                      | *  Non-deterministic |                     |   |                      |    delay             |                     |   |                      |                      |                     |   |                      | *  Data disruption   |                     |   +----------------------+----------------------+---------------------+   | Attacks on Time-     | *  Non-deterministic | *  Path redundancy  |   | Synchronization      |    delay             |                     |   | Mechanisms           |                      | *  Control and      |   |                      | *  Increased         |    signaling        |   |                      |    resource          |    message          |   |                      |    consumption       |    protection       |   |                      |                      |                     |   |                      | *  Data disruption   | *  Performance      |   |                      |                      |    analytics        |   +----------------------+----------------------+---------------------+             Table 3: Mapping Attacks to Impact and Mitigations8.  Association of Attacks to Use Cases   Different attacks can have different impact and/or mitigation   depending on the use case, so we would like to make this association   in our analysis.  However, since there is a potentially unbounded   list of use cases, we categorize the attacks with respect to the   common themes of the use cases as identified in Section 11 of   [RFC8578].   See also Table 2 for a mapping of the impact of attacks per use case   by industry.8.1.  Association of Attacks to Use Case Common Themes   In this section, we review each theme and discuss the attacks that   are applicable to that theme, as well as anything specific about the   impact and mitigations for that attack with respect to that theme.   Table 5, Mapping between Themes and Attacks, then provides a summary   of the attacks that are applicable to each theme.8.1.1.  Sub-network Layer   DetNet is expected to run over various transmission mediums, with   Ethernet being the first identified.  Attacks such as Delay or   Reconnaissance might be implemented differently on a different   transmission medium; however, the impact on the DetNet as a whole   would be essentially the same.  We thus conclude that all attacks and   impacts that would be applicable to DetNet over Ethernet (i.e., all   those named in this document) would also be applicable to DetNet over   other transmission mediums.   With respect to mitigations, some methods are specific to the   Ethernet medium, for example, time-aware scheduling using 802.1Qbv   [IEEE802.1Qbv-2015] can protect against excessive use of bandwidth at   the ingress -- for other mediums, other mitigations would have to be   implemented to provide analogous protection.8.1.2.  Central Administration   A DetNet network can be controlled by a centralized network   configuration and control system.  Such a system may be in a single   central location, or it may be distributed across multiple control   entities that function together as a unified control system for the   network.   All attacks named in this document that are relevant to controller   plane packets (and the controller itself) are relevant to this theme,   including Path Manipulation, Path Choice, Control Packet Modification   or Injection, Reconnaissance, and Attacks on Time-Synchronization   Mechanisms.8.1.3.  Hot Swap   A DetNet network is not expected to be "plug and play"; it is   expected that there is some centralized network configuration and   control system.  However, the ability to "hot swap" components (e.g.,   due to malfunction) is similar enough to "plug and play" that this   kind of behavior may be expected in DetNet networks, depending on the   implementation.   An attack surface related to hot swap is that the DetNet network must   at least consider input at runtime from components that were not part   of the initial configuration of the network.  Even a "perfect" (or   "hitless") replacement of a component at runtime would not   necessarily be ideal, since presumably one would want to distinguish   it from the original for OAM purposes (e.g., to report hot swap of a   failed component).   This implies that an attack such as Flow Modification, Spoofing, or   Inter-segment (which could introduce packets from a "new" component,   i.e., one heretofore unknown on the network) could be used to exploit   the need to consider such packets (as opposed to rejecting them out   of hand as one would do if one did not have to consider introduction   of a new component).   To mitigate this situation, deployments should provide a method for   dynamic and secure registration of new components, and (possibly   manual) deregistration and re-keying of retired components.  This   would avoid the situation in which the network must accommodate   potentially insecure packet flows from unknown components.   Similarly, if the network was designed to support runtime replacement   of a clock component, then presence (or apparent presence) and thus   consideration of packets from a new such component could affect the   network, or the time synchronization of the network, for example, by   initiating a new Best Master Clock selection process.  These types of   attacks should therefore be considered when designing hot-swap-type   functionality (see [RFC7384]).8.1.4.  Data Flow Information Models   DetNet specifies new YANG data models [DETNET-YANG] that may present   new attack surfaces.  Per IETF guidelines, security considerations   for any YANG data model are expected to be part of the YANG data   model specification, as described in [IETF-YANG-SEC].8.1.5.  L2 and L3 Integration   A DetNet network integrates Layer 2 (bridged) networks (e.g., AVB/TSN   LAN) and Layer 3 (routed) networks (e.g., IP) via the use of well-   known protocols such as IP, MPLS Pseudowire, and Ethernet.  Various   DetNet documents address many specific aspects of Layer 2 and Layer 3   integration within a DetNet, and these are not individually   referenced here; security considerations for those aspects are   covered within those documents or within the related subsections of   the present document.   Please note that although there are no entries in the L2 and L3   Integration line of the Mapping between Themes and Attacks table   (Table 5), this does not imply that there could be no relevant   attacks related to L2-L3 integration.8.1.6.  End-to-End Delivery   Packets that are part of a resource-reserved DetNet flow are not to   be dropped by the DetNet due to congestion.  Packets may however be   dropped for intended reasons, for example, security measures.  For   example, consider the case in which a packet becomes corrupted   (whether incidentally or maliciously) such that the resulting flow ID   incidentally matches the flow ID of another DetNet flow, potentially   resulting in additional unauthorized traffic on the latter.  In such   a case, it may be a security requirement that the system report and/   or take some defined action, perhaps when a packet drop count   threshold has been reached (see also Section 7.7).   A data plane attack may force packets to be dropped, for example, as   a result of a Delay attack, Replication/Elimination attack, or Flow   Modification attack.   The same result might be obtained by a Controller plane attack, e.g.,   Path Manipulation or Signaling Packet Modification.   An attack may also cause packets that should not be delivered to be   delivered, such as by forcing packets from one (e.g., replicated)   path to be preferred over another path when they should not be   (Replication attack), or by Flow Modification, or Path Choice or   Packet Injection.  A Time-Synchronization attack could cause a system   that was expecting certain packets at certain times to accept   unintended packets based on compromised system time or time windowing   in the scheduler.8.1.7.  Replacement for Proprietary Fieldbuses and Ethernet-Based        Networks   There are many proprietary "fieldbuses" used in Industrial and other   industries, as well as proprietary non-interoperable deterministic   Ethernet-based networks.  DetNet is intended to provide an open-   standards-based alternative to such buses/networks.  In cases where a   DetNet intersects with such fieldbuses/networks or their protocols,   such as by protocol emulation or access via a gateway, new attack   surfaces can be opened.   For example, an Inter-segment or Controller plane attack such as Path   Manipulation, Path Choice, or Control Packet Modification/Injection   could be used to exploit commands specific to such a protocol or that   are interpreted differently by the different protocols or gateway.8.1.8.  Deterministic vs. Best-Effort Traffic   Most of the themes described in this document address OT (reserved)   DetNet flows -- this item is intended to address issues related to IT   traffic on a DetNet.   DetNet is intended to support coexistence of time-sensitive   operational (OT, deterministic) traffic and informational (IT, "best   effort") traffic on the same ("unified") network.   With DetNet, this coexistence will become more common, and   mitigations will need to be established.  The fact that the IT   traffic on a DetNet is limited to a corporate-controlled network   makes this a less difficult problem compared to being exposed to the   open Internet; however, this aspect of DetNet security should not be   underestimated.   An Inter-segment attack can flood the network with IT-type traffic   with the intent of disrupting the handling of IT traffic and/or the   goal of interfering with OT traffic.  Presumably, if the DetNet flow   reservation and isolation of the DetNet is well designed (better-   designed than the attack), then interference with OT traffic should   not result from an attack that floods the network with IT traffic.   The handling of IT traffic (i.e., traffic that by definition is not   guaranteed any given deterministic service properties) by the DetNet   will by definition not be given the DetNet-specific protections   provided to DetNet (resource-reserved) flows.  The implication is   that the IT traffic on the DetNet network will necessarily have its   own specific set of product (component or system) requirements for   protection against attacks such as DoS; presumably they will be less   stringent than those for OT flows, but nonetheless, component and   system designers must employ whatever mitigations will meet the   specified security requirements for IT traffic for the given   component or DetNet.   The network design as a whole also needs to consider possible   application-level dependencies of OT-type applications on services   provided by the IT part of the network; for example, does the OT   application depend on IT network services such as DNS or OAM?  If   such dependencies exist, how are malicious packet flows handled?   Such considerations are typically outside the scope of DetNet proper,   but nonetheless need to be addressed in the overall DetNet network   design for a given use case.8.1.9.  Deterministic Flows   Reserved bandwidth data flows (deterministic flows) must provide the   allocated bandwidth and must be isolated from each other.   A Spoofing or Inter-segment attack that adds packet traffic to a   bandwidth-reserved DetNet flow could cause that flow to occupy more   bandwidth than it was allocated, resulting in interference with other   DetNet flows.   A Flow Modification, Spoofing, Header Manipulation, or Control Packet   Modification attack could cause packets from one flow to be directed   to another flow, thus breaching isolation between the flows.8.1.10.  Unused Reserved Bandwidth   If bandwidth reservations are made for a DetNet flow but the   associated bandwidth is not used at any point in time, that bandwidth   is made available on the network for best-effort traffic.  However,   note that security considerations for best-effort traffic on a DetNet   network is out of scope of the present document, provided that any   such attacks on best-effort traffic do not affect performance for   DetNet OT traffic.8.1.11.  Interoperability   The DetNet specifications as a whole are intended to enable an   ecosystem in which multiple vendors can create interoperable   products, thus promoting component diversity and potentially higher   numbers of each component manufactured.  Toward that end, the   security measures and protocols discussed in this document are   intended to encourage interoperability.   Given that the DetNet specifications are unambiguously written and   that the implementations are accurate, the property of   interoperability should not in and of itself cause security concerns;   however, flaws in interoperability between components could result in   security weaknesses.  The network operator, as well as system and   component designers, can all contribute to reducing such weaknesses   through interoperability testing.8.1.12.  Cost Reductions   The DetNet network specifications are intended to enable an ecosystem   in which multiple vendors can create interoperable products, thus   promoting higher numbers of each component manufactured, promoting   cost reduction and cost competition among vendors.   This envisioned breadth of DetNet-enabled products is in general a   positive factor; however, implementation flaws in any individual   component can present an attack surface.  In addition, implementation   differences between components from different vendors can result in   attack surfaces (resulting from their interaction) that may not exist   in any individual component.   Network operators can mitigate such concerns through sufficient   product and interoperability testing.8.1.13.  Insufficiently Secure Components   The DetNet network specifications are intended to enable an ecosystem   in which multiple vendors can create interoperable products, thus   promoting component diversity and potentially higher numbers of each   component manufactured.  However, this raises the possibility that a   vendor might repurpose for DetNet applications a hardware or software   component that was originally designed for operation in an isolated   OT network and thus may not have been designed to be sufficiently   secure, or secure at all, against the sorts of attacks described in   this document.  Deployment of such a component on a DetNet network   that is intended to be highly secure may present an attack surface;   thus, the DetNet network operator may need to take specific actions   to protect such components, for example, by implementing a secure   interface (such as a firewall) to isolate the component from the   threats that may be present in the greater network.8.1.14.  DetNet Network Size   DetNet networks range in size from very small, e.g., inside a single   industrial machine, to very large, e.g., a Utility Grid network   spanning a whole country.   The size of the network might be related to how the attack is   introduced into the network.  For example, if the entire network is   local, there is a threat that power can be cut to the entire network.   If the network is large, perhaps only a part of the network is   attacked.   A Delay attack might be as relevant to a small network as to a large   network, although the amount of delay might be different.   Attacks sourced from IT traffic might be more likely in large   networks since more people might have access to the network,   presenting a larger attack surface.  Similarly, Path Manipulation,   Path Choice, and Time-Synchronization attacks seem more likely   relevant to large networks.8.1.15.  Multiple Hops   Large DetNet networks (e.g., a Utility Grid network) may involve many   "hops" over various kinds of links, for example, radio repeaters,   microwave links, fiber optic links, etc.   An attacker who has knowledge of the operation of a component or   device's internal software (such as "device drivers") may be able to   take advantage of this knowledge to design an attack that could   exploit flaws (or even the specifics of normal operation) in the   communication between the various links.   It is also possible that a large-scale DetNet topology containing   various kinds of links may not be in as common use as other more   homogeneous topologies.  This situation may present more opportunity   for attackers to exploit software and/or protocol flaws in or between   these components because these components or configurations may not   have been sufficiently tested for interoperability (in the way they   would be as a result of broad usage).  This may be of particular   concern to early adopters of new DetNet components or technologies.   Of the attacks we have defined, the ones identified in Section 8.1.14   as germane to large networks are the most relevant.8.1.16.  Level of Service   A DetNet is expected to provide means to configure the network that   include querying network path latency, requesting bounded latency for   a given DetNet flow, requesting worst-case maximum and/or minimum   latency for a given path or DetNet flow, and so on.  It is an   expected case that the network cannot provide a given requested   service level.  In such cases, the network control system should   reply that the requested service level is not available (as opposed   to accepting the parameter but then not delivering the desired   behavior).   Controller plane attacks such as Signaling Packet Modification and   Injection could be used to modify or create control traffic that   could interfere with the process of a user requesting a level of   service and/or the reply from the network.   Reconnaissance could be used to characterize flows and perhaps target   specific flows for attack via the controller plane as noted in   Section 6.7.8.1.17.  Bounded Latency   DetNet provides the expectation of guaranteed bounded latency.   Delay attacks can cause packets to miss their agreed-upon latency   boundaries.   Time-Synchronization attacks can corrupt the time reference of the   system, resulting in missed latency deadlines (with respect to the   "correct" time reference).8.1.18.  Low Latency   Applications may require "extremely low latency"; however, depending   on the application, these may mean very different latency values.   For example, "low latency" across a Utility Grid network is on a   different time scale than "low latency" in a motor control loop in a   small machine.  The intent is that the mechanisms for specifying   desired latency include wide ranges, and that architecturally there   is nothing to prevent arbitrarily low latencies from being   implemented in a given network.   Attacks on the controller plane (as described in the Level of Service   theme; see Section 8.1.16) and Delay and Time attacks (as described   in the Bounded Latency theme; see Section 8.1.17) both apply here.8.1.19.  Bounded Jitter (Latency Variation)   DetNet is expected to provide bounded jitter (packet-to-packet   latency variation).   Delay attacks can cause packets to vary in their arrival times,   resulting in packet-to-packet latency variation, thereby violating   the jitter specification.8.1.20.  Symmetrical Path Delays   Some applications would like to specify that the transit delay time   values be equal for both the transmit and return paths.   Delay attacks can cause path delays to materially differ between   paths.   Time-Synchronization attacks can corrupt the time reference of the   system, resulting in path delays that may be perceived to be   different (with respect to the "correct" time reference) even if they   are not materially different.8.1.21.  Reliability and Availability   DetNet-based systems are expected to be implemented with essentially   arbitrarily high availability (for example, 99.9999% up time, or even   12 nines).  The intent is that the DetNet designs should not make any   assumptions about the level of reliability and availability that may   be required of a given system and should define parameters for   communicating these kinds of metrics within the network.   Any attack on the system, of any type, can affect its overall   reliability and availability; thus, in the mapping table (Table 5),   we have marked every attack.  Since every DetNet depends to a greater   or lesser degree on reliability and availability, this essentially   means that all networks have to mitigate all attacks, which to a   greater or lesser degree defeats the purpose of associating attacks   with use cases.  It also underscores the difficulty of designing   "extremely high reliability" networks.   In practice, network designers can adopt a risk-based approach in   which only those attacks are mitigated whose potential cost is higher   than the cost of mitigation.8.1.22.  Redundant Paths   This document expects that each DetNet system will be implemented to   some essentially arbitrary level of reliability and/or availability,   depending on the use case.  A strategy used by DetNet for providing   extraordinarily high levels of reliability when justified is to   provide redundant paths between which traffic can be seamlessly   switched, all the while maintaining the required performance of that   system.   Replication-related attacks are by definition applicable here.   Controller plane attacks can also interfere with the configuration of   redundant paths.8.1.23.  Security Measures   If any of the security mechanisms that protect the DetNet are   attacked or subverted, this can result in malfunction of the network.   Thus, the security systems themselves need to be robust against   attacks.   The general topic of protection of security mechanisms is not unique   to DetNet; it is identical to the case of securing any security   mechanism for any network.  This document addresses these concerns   only to the extent that they are unique to DetNet.8.2.  Summary of Attack Types per Use Case Common Theme   The List of Attacks table (Table 4) lists the attacks described in   Section 5, Security Threats, assigning a number to each type of   attack.  That number is then used as a short form identifier for the   attack in Table 5, Mapping between Themes and Attacks.            +====+============================================+            |    | Attack                                     |            +====+============================================+            | 1  | Delay Attack                               |            +----+--------------------------------------------+            | 2  | DetNet Flow Modification or Spoofing       |            +----+--------------------------------------------+            | 3  | Inter-segment Attack                       |            +----+--------------------------------------------+            | 4  | Replication: Increased Attack Surface      |            +----+--------------------------------------------+            | 5  | Replication-Related Header Manipulation    |            +----+--------------------------------------------+            | 6  | Path Manipulation                          |            +----+--------------------------------------------+            | 7  | Path Choice: Increased Attack Surface      |            +----+--------------------------------------------+            | 8  | Control or Signaling Packet Modification   |            +----+--------------------------------------------+            | 9  | Control or Signaling Packet Injection      |            +----+--------------------------------------------+            | 10 | Reconnaissance                             |            +----+--------------------------------------------+            | 11 | Attacks on Time-Synchronization Mechanisms |            +----+--------------------------------------------+                          Table 4: List of Attacks   The Mapping between Themes and Attacks table (Table 5) maps the use   case themes of [RFC8578] (as also enumerated in this document) to the   attacks of Table 4.  Each row specifies a theme, and the attacks   relevant to this theme are marked with a "+".  The row items that   have no threats associated with them are included in the table for   completeness of the list of Use Case Common Themes and do not have   DetNet-specific threats associated with them.   +====================+=============================================+   |       Theme        |                    Attack                   |   |                    +===+===+===+===+===+===+===+===+===+====+====+   |                    | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 |   +====================+===+===+===+===+===+===+===+===+===+====+====+   | Network Layer -    | + | + | + | + | + | + | + | + | + | +  | +  |   | AVB/TSN Eth.       |   |   |   |   |   |   |   |   |   |    |    |   +--------------------+---+---+---+---+---+---+---+---+---+----+----+   | Central            |   |   |   |   |   | + | + | + | + | +  | +  |   | Administration     |   |   |   |   |   |   |   |   |   |    |    |   +--------------------+---+---+---+---+---+---+---+---+---+----+----+   | Hot Swap           |   | + | + |   |   |   |   |   |   |    | +  |   +--------------------+---+---+---+---+---+---+---+---+---+----+----+   | Data Flow          |   |   |   |   |   |   |   |   |   |    |    |   | Information Models |   |   |   |   |   |   |   |   |   |    |    |   +--------------------+---+---+---+---+---+---+---+---+---+----+----+   | L2 and L3          |   |   |   |   |   |   |   |   |   |    |    |   | Integration        |   |   |   |   |   |   |   |   |   |    |    |   +--------------------+---+---+---+---+---+---+---+---+---+----+----+   | End-to-End         | + | + | + | + | + | + | + | + |   | +  |    |   | Delivery           |   |   |   |   |   |   |   |   |   |    |    |   +--------------------+---+---+---+---+---+---+---+---+---+----+----+   | Proprietary        |   |   | + |   |   | + | + | + | + |    |    |   | Deterministic      |   |   |   |   |   |   |   |   |   |    |    |   | Ethernet Networks  |   |   |   |   |   |   |   |   |   |    |    |   +--------------------+---+---+---+---+---+---+---+---+---+----+----+   | Replacement for    |   |   | + |   |   |   |   |   |   |    |    |   | Proprietary        |   |   |   |   |   |   |   |   |   |    |    |   | Fieldbuses         |   |   |   |   |   |   |   |   |   |    |    |   +--------------------+---+---+---+---+---+---+---+---+---+----+----+   | Deterministic vs.  | + | + | + |   | + | + |   | + |   |    |    |   | Best-Effort        |   |   |   |   |   |   |   |   |   |    |    |   | Traffic            |   |   |   |   |   |   |   |   |   |    |    |   +--------------------+---+---+---+---+---+---+---+---+---+----+----+   | Deterministic      | + | + | + |   | + | + |   | + |   |    |    |   | Flows              |   |   |   |   |   |   |   |   |   |    |    |   +--------------------+---+---+---+---+---+---+---+---+---+----+----+   | Unused Reserved    |   | + | + |   |   |   |   | + | + |    |    |   | Bandwidth          |   |   |   |   |   |   |   |   |   |    |    |   +--------------------+---+---+---+---+---+---+---+---+---+----+----+   | Interoperability   |   |   |   |   |   |   |   |   |   |    |    |   +--------------------+---+---+---+---+---+---+---+---+---+----+----+   | Cost Reductions    |   |   |   |   |   |   |   |   |   |    |    |   +--------------------+---+---+---+---+---+---+---+---+---+----+----+   | Insufficiently     |   |   |   |   |   |   |   |   |   |    |    |   | Secure Components  |   |   |   |   |   |   |   |   |   |    |    |   +--------------------+---+---+---+---+---+---+---+---+---+----+----+   | DetNet Network     | + |   |   |   |   | + | + |   |   |    | +  |   | Size               |   |   |   |   |   |   |   |   |   |    |    |   +--------------------+---+---+---+---+---+---+---+---+---+----+----+   | Multiple Hops      | + | + |   |   |   | + | + |   |   |    | +  |   +--------------------+---+---+---+---+---+---+---+---+---+----+----+   | Level of Service   |   |   |   |   |   |   |   | + | + | +  |    |   +--------------------+---+---+---+---+---+---+---+---+---+----+----+   | Bounded Latency    | + |   |   |   |   |   |   |   |   |    | +  |   +--------------------+---+---+---+---+---+---+---+---+---+----+----+   | Low Latency        | + |   |   |   |   |   |   | + | + |    | +  |   +--------------------+---+---+---+---+---+---+---+---+---+----+----+   | Bounded Jitter     | + |   |   |   |   |   |   |   |   |    |    |   +--------------------+---+---+---+---+---+---+---+---+---+----+----+   | Symmetric Path     | + |   |   |   |   |   |   |   |   |    | +  |   | Delays             |   |   |   |   |   |   |   |   |   |    |    |   +--------------------+---+---+---+---+---+---+---+---+---+----+----+   | Reliability and    | + | + | + | + | + | + | + | + | + | +  | +  |   | Availability       |   |   |   |   |   |   |   |   |   |    |    |   +--------------------+---+---+---+---+---+---+---+---+---+----+----+   | Redundant Paths    |   |   |   | + | + |   |   | + | + |    |    |   +--------------------+---+---+---+---+---+---+---+---+---+----+----+   | Security Measures  |   |   |   |   |   |   |   |   |   |    |    |   +--------------------+---+---+---+---+---+---+---+---+---+----+----+               Table 5: Mapping between Themes and Attacks9.  Security Considerations for OAM Traffic   This section considers DetNet-specific security considerations for   packet traffic that is generated and transmitted over a DetNet as   part of OAM (Operations, Administration, and Maintenance).  For the   purposes of this discussion, OAM traffic falls into one of two basic   types:   *  OAM traffic generated by the network itself.  The additional      bandwidth required for such packets is added by the network      administration, presumably transparent to the customer.  Security      considerations for such traffic are not DetNet specific (apart      from such traffic being subject to the same DetNet-specific      security considerations as any other DetNet data flow) and are      thus not covered in this document.   *  OAM traffic generated by the customer.  From a DetNet security      point of view, DetNet security considerations for such traffic are      exactly the same as for any other customer data flows.   From the perspective of an attack, OAM traffic is indistinguishable   from DetNet traffic, and the network needs to be secure against   injection, removal, or modification of traffic of any kind, including   OAM traffic.  A DetNet is sensitive to any form of packet injection,   removal, or manipulation, and in this respect DetNet OAM traffic is   no different.  Techniques for securing a DetNet against these threats   have been discussed elsewhere in this document.10.  DetNet Technology-Specific Threats   Section 5, Security Threats, describes threats that are independent   of a DetNet implementation.  This section considers threats   specifically related to the IP- and MPLS-specific aspects of DetNet   implementations.   The primary security considerations for the data plane specifically   are to maintain the integrity of the data and the delivery of the   associated DetNet service traversing the DetNet network.   The primary relevant differences between IP and MPLS implementations   are in flow identification and OAM methodologies.   As noted in [RFC8655], DetNet operates at the IP layer [RFC8939] and   delivers service over sub-layer technologies such as MPLS [RFC8964]   and IEEE 802.1 Time-Sensitive Networking (TSN) [RFC9023].   Application flows can be protected through whatever means are   provided by the layer and sub-layer technologies.  For example,   technology-specific encryption may be used for IP flows (IPsec   [RFC4301]).  For IP-over-Ethernet (Layer 2) flows using an underlying   sub-net, MACsec [IEEE802.1AE-2018] may be appropriate.  For some use   cases, packet integrity protection without encryption may be   sufficient.   However, if the DetNet nodes cannot decrypt IPsec traffic, then   DetNet flow identification for encrypted IP traffic flows must be   performed in a different way than it would be for unencrypted IP   DetNet flows.  The DetNet IP data plane identifies unencrypted flows   via a 6-tuple that consists of two IP addresses, the transport   protocol ID, two transport protocol port numbers, and the DSCP in the   IP header.  When IPsec is used, the transport header is encrypted and   the next protocol ID is an IPsec protocol, usually Encapsulating   Security Payload (ESP), and not a transport protocol, leaving only   three components of the 6-tuple, which are the two IP addresses and   the DSCP.  If the IPsec sessions are established by a controller,   then this controller could also transmit (in the clear) the Security   Parameter Index (SPI) and thus the SPI could be used (in addition to   the pair of IP addresses) for flow identification.  Identification of   DetNet flows over IPsec is further discussed in Section 5.1.2.3 of   [RFC8939].   Sections below discuss threats specific to IP and MPLS in more   detail.10.1.  IP   IP has a long history of security considerations and architectural   protection mechanisms.  From a data plane perspective, DetNet does   not add or modify any IP header information, so the carriage of   DetNet traffic over an IP data plane does not introduce any new   security issues that were not there before, apart from those already   described in the data-plane-independent threats section (Section 5).   Thus, the security considerations for a DetNet based on an IP data   plane are purely inherited from the rich IP security literature and   code/application base, and the data-plane-independent section of this   document.   Maintaining security for IP segments of a DetNet may be more   challenging than for the MPLS segments of the network given that the   IP segments of the network may reach the edges of the network, which   are more likely to involve interaction with potentially malevolent   outside actors.  Conversely, MPLS is inherently more secure than IP   since it is internal to routers and it is well known how to protect   it from outside influence.   Another way to look at DetNet IP security is to consider it in the   light of VPN security.  As an industry, we have a lot of experience   with VPNs running through networks with other VPNs -- it is well   known how to secure the network for that.  However, for a DetNet, we   have the additional subtlety that any possible interaction of one   packet with another can have a potentially deleterious effect on the   time properties of the flows.  So the network must provide sufficient   isolation between flows, for example, by protecting the forwarding   bandwidth and related resources so that they are available to DetNet   traffic, by whatever means are appropriate for the data plane of that   network, for example, through the use of queuing mechanisms.   In a VPN, bandwidth is generally guaranteed over a period of time   whereas in DetNet, it is not aggregated over time.  This implies that   any VPN-type protection mechanism must also maintain the DetNet   timing constraints.10.2.  MPLS   An MPLS network carrying DetNet traffic is expected to be a "well-   managed" network.  Given that this is the case, it is difficult for   an attacker to pass a raw MPLS-encoded packet into a network because   operators have considerable experience at excluding such packets at   the network boundaries as well as excluding MPLS packets being   inserted through the use of a tunnel.   MPLS security is discussed extensively in [RFC5920] ("Security   Framework for MPLS and GMPLS Networks") to which the reader is   referred.   [RFC6941] builds on [RFC5920] by providing additional security   considerations that are applicable to the MPLS-TP extensions   appropriate to the MPLS Transport Profile [RFC5921] and thus to the   operation of DetNet over some types of MPLS network.   [RFC5921] introduces to MPLS new Operations, Administration, and   Maintenance (OAM) capabilities; a transport-oriented path protection   mechanism; and strong emphasis on static provisioning supported by   network management systems.   The operation of DetNet over an MPLS network builds on MPLS and   pseudowire encapsulation.  Thus, for guidance on securing the DetNet   elements of DetNet over MPLS, the reader is also referred to the   security considerations of [RFC4385], [RFC5586], [RFC3985],   [RFC6073], and [RFC6478].   Having attended to the conventional aspects of network security, it   is necessary to attend to the dynamic aspects.  The closest   experience that the IETF has with securing protocols that are   sensitive to manipulation of delay are the two-way time transfer   (TWTT) protocols, which are NTP [RFC5905] and the Precision Time   Protocol [IEEE1588].  The security requirements for these are   described in [RFC7384].   One particular problem that has been observed in operational tests of   TWTT protocols is the ability for two closely but not completely   synchronized flows to beat and cause a sudden phase hit to one of the   flows.  This can be mitigated by the careful use of a scheduling   system in the underlying packet transport.   Some investigations into protection of MPLS systems against dynamic   attacks exist, such as [MPLS-OPP-ENCRYPT]; perhaps deployment of   DetNets will encourage additional such investigations.11.  IANA Considerations   This document has no IANA actions.12.  Security Considerations   The security considerations of DetNet networks are presented   throughout this document.13.  Privacy Considerations   Privacy in the context of DetNet is maintained by the base   technologies specific to the DetNet and user traffic.  For example,   TSN can use MACsec, IP can use IPsec, and applications can use IP   transport protocol-provided methods, e.g., TLS and DTLS.  MPLS   typically uses L2/L3 VPNs combined with the previously mentioned   privacy methods.   However, note that reconnaissance threats such as traffic analysis   and monitoring of electrical side channels can still cause there to   be privacy considerations even when traffic is encrypted.14.  References14.1.  Normative References   [RFC8655]  Finn, N., Thubert, P., Varga, B., and J. Farkas,              "Deterministic Networking Architecture", RFC 8655,              DOI 10.17487/RFC8655, October 2019,              <https://www.rfc-editor.org/info/rfc8655>.   [RFC8938]  Varga, B., Ed., Farkas, J., Berger, L., Malis, A., and S.              Bryant, "Deterministic Networking (DetNet) Data Plane              Framework", RFC 8938, DOI 10.17487/RFC8938, November 2020,              <https://www.rfc-editor.org/info/rfc8938>.   [RFC8939]  Varga, B., Ed., Farkas, J., Berger, L., Fedyk, D., and S.              Bryant, "Deterministic Networking (DetNet) Data Plane:              IP", RFC 8939, DOI 10.17487/RFC8939, November 2020,              <https://www.rfc-editor.org/info/rfc8939>.   [RFC8964]  Varga, B., Ed., Farkas, J., Berger, L., Malis, A., Bryant,              S., and J. Korhonen, "Deterministic Networking (DetNet)              Data Plane: MPLS", RFC 8964, DOI 10.17487/RFC8964, January              2021, <https://www.rfc-editor.org/info/rfc8964>.14.2.  Informative References   [ARINC664P7]              ARINC, "Aircraft Data Network Part 7 Avionics Full-Duplex              Switched Ethernet Network", ARINC 664 P7, September 2009.   [BCP107]   Bellovin, S. and R. Housley, "Guidelines for Cryptographic              Key Management", BCP 107, RFC 4107, June 2005.              <https://www.rfc-editor.org/info/bcp107>   [BCP72]    Rescorla, E. and B. Korver, "Guidelines for Writing RFC              Text on Security Considerations", BCP 72, RFC 3552, July              2003.              <https://www.rfc-editor.org/info/bcp72>   [DETNET-IP-OAM]              Mirsky, G., Chen, M., and D. Black, "Operations,              Administration and Maintenance (OAM) for Deterministic              Networks (DetNet) with IP Data Plane", Work in Progress,              Internet-Draft, draft-ietf-detnet-ip-oam-02, 30 March              2021, <https://datatracker.ietf.org/doc/html/draft-ietf-              detnet-ip-oam-02>.   [DETNET-MPLS-OAM]              Mirsky, G. and M. Chen, "Operations, Administration and              Maintenance (OAM) for Deterministic Networks (DetNet) with              MPLS Data Plane", Work in Progress, Internet-Draft, draft-              ietf-detnet-mpls-oam-03, 30 March 2021,              <https://datatracker.ietf.org/doc/html/draft-ietf-detnet-              mpls-oam-03>.   [DETNET-SERVICE-MODEL]              Varga, B., Ed. and J. Farkas, "DetNet Service Model", Work              in Progress, Internet-Draft, draft-varga-detnet-service-              model-02, May 2017,              <https://datatracker.ietf.org/doc/html/draft-varga-detnet-              service-model-02>.   [DETNET-YANG]              Geng, X., Chen, M., Ryoo, Y., Fedyk, D., Rahman, R., and              Z. Li, "Deterministic Networking (DetNet) YANG Model",              Work in Progress, Internet-Draft, draft-ietf-detnet-yang-              12, 19 May 2021, <https://datatracker.ietf.org/doc/html/              draft-ietf-detnet-yang-12>.   [IEEE1588] IEEE, "IEEE 1588 Standard for a Precision Clock              Synchronization Protocol for Networked Measurement and              Control Systems", IEEE Std. 1588-2008,              DOI 10.1109/IEEESTD.2008.4579760, July 2008,              <https://doi.org/10.1109/IEEESTD.2008.4579760>.   [IEEE802.1AE-2018]              IEEE, "IEEE Standard for Local and metropolitan area              networks-Media Access Control (MAC) Security", IEEE Std.               802.1AE-2018, DOI 10.1109/IEEESTD.2018.8585421, December              2018, <https://ieeexplore.ieee.org/document/8585421>.   [IEEE802.1BA]              IEEE, "IEEE Standard for Local and metropolitan area              networks--Audio Video Bridging (AVB) Systems", IEEE Std.               802.1BA-2011, DOI 10.1109/IEEESTD.2011.6032690, September              2011, <https://ieeexplore.ieee.org/document/6032690>.   [IEEE802.1Q]              IEEE, "IEEE Standard for Local and metropolitan area              networks--Bridges and Bridged Networks", IEEE Std. 802.1Q-              2014, DOI 10.1109/IEEESTD.2014.6991462, December 2014,              <https://ieeexplore.ieee.org/document/6991462>.   [IEEE802.1Qbv-2015]              IEEE, "IEEE Standard for Local and metropolitan area              networks -- Bridges and Bridged Networks - Amendment 25:              Enhancements for Scheduled Traffic", IEEE Std. 802.1Qbv-              2015, DOI 10.1109/IEEESTD.2016.8613095, March 2016,              <https://ieeexplore.ieee.org/document/8613095>.   [IEEE802.1Qch-2017]              IEEE, "IEEE Standard for Local and metropolitan area              networks--Bridges and Bridged Networks--Amendment 29:              Cyclic Queuing and Forwarding", IEEE Std. 802.1Qch-2017,              DOI 10.1109/IEEESTD.2017.7961303, June 2017,              <https://ieeexplore.ieee.org/document/7961303>.   [IETF-YANG-SEC]              IETF, "YANG module security considerations", October 2018,              <https://trac.ietf.org/trac/ops/wiki/yang-security-              guidelines>.   [IPSECME-G-IKEV2]              Smyslov, V. and B. Weis, "Group Key Management using              IKEv2", Work in Progress, Internet-Draft, draft-ietf-              ipsecme-g-ikev2-02, 11 January 2021,              <https://datatracker.ietf.org/doc/html/draft-ietf-ipsecme-              g-ikev2-02>.   [IT-DEF]   Wikipedia, "Information technology", March 2020,              <https://en.wikiquote.org/w/              index.php?title=Information_technology&oldid=2749907>.   [MPLS-OPP-ENCRYPT]              Farrel, A. and S. Farrell, "Opportunistic Security in MPLS              Networks", Work in Progress, Internet-Draft, draft-ietf-              mpls-opportunistic-encrypt-03, 28 March 2017,              <https://datatracker.ietf.org/doc/html/draft-ietf-mpls-              opportunistic-encrypt-03>.   [NS-DEF]   Wikipedia, "Network segmentation", December 2020,              <https://en.wikipedia.org/w/              index.php?title=Network_segmentation&oldid=993163264>.   [OT-DEF]   Wikipedia, "Operational technology", March 2021,              <https://en.wikipedia.org/w/              index.php?title=Operational_technology&oldid=1011704361>.   [RFC2474]  Nichols, K., Blake, S., Baker, F., and D. Black,              "Definition of the Differentiated Services Field (DS              Field) in the IPv4 and IPv6 Headers", RFC 2474,              DOI 10.17487/RFC2474, December 1998,              <https://www.rfc-editor.org/info/rfc2474>.   [RFC2475]  Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z.,              and W. Weiss, "An Architecture for Differentiated              Services", RFC 2475, DOI 10.17487/RFC2475, December 1998,              <https://www.rfc-editor.org/info/rfc2475>.   [RFC3985]  Bryant, S., Ed. and P. Pate, Ed., "Pseudo Wire Emulation              Edge-to-Edge (PWE3) Architecture", RFC 3985,              DOI 10.17487/RFC3985, March 2005,              <https://www.rfc-editor.org/info/rfc3985>.   [RFC4253]  Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH)              Transport Layer Protocol", RFC 4253, DOI 10.17487/RFC4253,              January 2006, <https://www.rfc-editor.org/info/rfc4253>.   [RFC4301]  Kent, S. and K. Seo, "Security Architecture for the              Internet Protocol", RFC 4301, DOI 10.17487/RFC4301,              December 2005, <https://www.rfc-editor.org/info/rfc4301>.   [RFC4302]  Kent, S., "IP Authentication Header", RFC 4302,              DOI 10.17487/RFC4302, December 2005,              <https://www.rfc-editor.org/info/rfc4302>.   [RFC4385]  Bryant, S., Swallow, G., Martini, L., and D. McPherson,              "Pseudowire Emulation Edge-to-Edge (PWE3) Control Word for              Use over an MPLS PSN", RFC 4385, DOI 10.17487/RFC4385,              February 2006, <https://www.rfc-editor.org/info/rfc4385>.   [RFC4432]  Harris, B., "RSA Key Exchange for the Secure Shell (SSH)              Transport Layer Protocol", RFC 4432, DOI 10.17487/RFC4432,              March 2006, <https://www.rfc-editor.org/info/rfc4432>.   [RFC5586]  Bocci, M., Ed., Vigoureux, M., Ed., and S. Bryant, Ed.,              "MPLS Generic Associated Channel", RFC 5586,              DOI 10.17487/RFC5586, June 2009,              <https://www.rfc-editor.org/info/rfc5586>.   [RFC5880]  Katz, D. and D. Ward, "Bidirectional Forwarding Detection              (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010,              <https://www.rfc-editor.org/info/rfc5880>.   [RFC5905]  Mills, D., Martin, J., Ed., Burbank, J., and W. Kasch,              "Network Time Protocol Version 4: Protocol and Algorithms              Specification", RFC 5905, DOI 10.17487/RFC5905, June 2010,              <https://www.rfc-editor.org/info/rfc5905>.   [RFC5920]  Fang, L., Ed., "Security Framework for MPLS and GMPLS              Networks", RFC 5920, DOI 10.17487/RFC5920, July 2010,              <https://www.rfc-editor.org/info/rfc5920>.   [RFC5921]  Bocci, M., Ed., Bryant, S., Ed., Frost, D., Ed., Levrau,              L., and L. Berger, "A Framework for MPLS in Transport              Networks", RFC 5921, DOI 10.17487/RFC5921, July 2010,              <https://www.rfc-editor.org/info/rfc5921>.   [RFC6071]  Frankel, S. and S. Krishnan, "IP Security (IPsec) and              Internet Key Exchange (IKE) Document Roadmap", RFC 6071,              DOI 10.17487/RFC6071, February 2011,              <https://www.rfc-editor.org/info/rfc6071>.   [RFC6073]  Martini, L., Metz, C., Nadeau, T., Bocci, M., and M.              Aissaoui, "Segmented Pseudowire", RFC 6073,              DOI 10.17487/RFC6073, January 2011,              <https://www.rfc-editor.org/info/rfc6073>.   [RFC6274]  Gont, F., "Security Assessment of the Internet Protocol              Version 4", RFC 6274, DOI 10.17487/RFC6274, July 2011,              <https://www.rfc-editor.org/info/rfc6274>.   [RFC6478]  Martini, L., Swallow, G., Heron, G., and M. Bocci,              "Pseudowire Status for Static Pseudowires", RFC 6478,              DOI 10.17487/RFC6478, May 2012,              <https://www.rfc-editor.org/info/rfc6478>.   [RFC6562]  Perkins, C. and JM. Valin, "Guidelines for the Use of              Variable Bit Rate Audio with Secure RTP", RFC 6562,              DOI 10.17487/RFC6562, March 2012,              <https://www.rfc-editor.org/info/rfc6562>.   [RFC6632]  Ersue, M., Ed. and B. Claise, "An Overview of the IETF              Network Management Standards", RFC 6632,              DOI 10.17487/RFC6632, June 2012,              <https://www.rfc-editor.org/info/rfc6632>.   [RFC6941]  Fang, L., Ed., Niven-Jenkins, B., Ed., Mansfield, S., Ed.,              and R. Graveman, Ed., "MPLS Transport Profile (MPLS-TP)              Security Framework", RFC 6941, DOI 10.17487/RFC6941, April              2013, <https://www.rfc-editor.org/info/rfc6941>.   [RFC7384]  Mizrahi, T., "Security Requirements of Time Protocols in              Packet Switched Networks", RFC 7384, DOI 10.17487/RFC7384,              October 2014, <https://www.rfc-editor.org/info/rfc7384>.   [RFC7567]  Baker, F., Ed. and G. Fairhurst, Ed., "IETF              Recommendations Regarding Active Queue Management",              BCP 197, RFC 7567, DOI 10.17487/RFC7567, July 2015,              <https://www.rfc-editor.org/info/rfc7567>.   [RFC7641]  Hartke, K., "Observing Resources in the Constrained              Application Protocol (CoAP)", RFC 7641,              DOI 10.17487/RFC7641, September 2015,              <https://www.rfc-editor.org/info/rfc7641>.   [RFC7748]  Langley, A., Hamburg, M., and S. Turner, "Elliptic Curves              for Security", RFC 7748, DOI 10.17487/RFC7748, January              2016, <https://www.rfc-editor.org/info/rfc7748>.   [RFC7835]  Saucez, D., Iannone, L., and O. Bonaventure, "Locator/ID              Separation Protocol (LISP) Threat Analysis", RFC 7835,              DOI 10.17487/RFC7835, April 2016,              <https://www.rfc-editor.org/info/rfc7835>.   [RFC8446]  Rescorla, E., "The Transport Layer Security (TLS) Protocol              Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,              <https://www.rfc-editor.org/info/rfc8446>.   [RFC8578]  Grossman, E., Ed., "Deterministic Networking Use Cases",              RFC 8578, DOI 10.17487/RFC8578, May 2019,              <https://www.rfc-editor.org/info/rfc8578>.   [RFC9016]  Varga, B., Farkas, J., Cummings, R., Jiang, Y., and D.              Fedyk, "Flow and Service Information Model for              Deterministic Networking (DetNet)", RFC 9016,              DOI 10.17487/RFC9016, March 2021,              <https://www.rfc-editor.org/info/rfc9016>.   [RFC9023]  Varga, B., Ed., Farkas, J., Malis, A., and S. Bryant,              "Deterministic Networking (DetNet) Data Plane: IP over              IEEE 802.1 Time-Sensitive Networking (TSN)", RFC 9023,              DOI 10.17487/RFC9023, June 2021,              <https://www.rfc-editor.org/info/rfc9023>.   [RFC9025]  Varga, B., Ed., Farkas, J., Berger, L., Malis, A., and S.              Bryant, "Deterministic Networking (DetNet) Data Plane:              MPLS over UDP/IP", RFC 9025, DOI 10.17487/RFC9025, April              2021, <https://www.rfc-editor.org/info/rfc9025>.   [RFC9056]  Varga, B., Ed., Berger, L., Fedyk, D., Bryant, S., and J.              Korhonen, "Deterministic Networking (DetNet) Data Plane:              IP over MPLS", RFC 9056, DOI 10.17487/RFC9056, June 2021,              <https://www.rfc-editor.org/info/rfc9056>.Contributors   The Editor would like to recognize the contributions of the following   individuals to this document.   Stewart Bryant   Futurewei Technologies   Email: sb@stewartbryant.com   David Black   Dell EMC   176 South Street   Hopkinton, Massachusetts 01748   United States of America   Henrik Austad   SINTEF Digital   Klaebuveien 153   7037 Trondheim   Norway   Email: henrik@austad.us   John Dowdell   Airbus Defence and Space   Celtic Springs   Newport, NP10 8FZ   United Kingdom   Email: john.dowdell.ietf@gmail.com   Norman Finn   3101 Rio Way   Spring Valley, California 91977   United States of America   Email: nfinn@nfinnconsulting.com   Subir Das   Applied Communication Sciences   150 Mount Airy Road   Basking Ridge, New Jersey 07920   United States of America   Email: sdas@appcomsci.com   Carsten Bormann   Universitat Bremen TZI   Postfach 330440 D-28359 Bremen   Germany   Email: cabo@tzi.orgAuthors' Addresses   Ethan Grossman (editor)   Dolby Laboratories, Inc.   1275 Market Street   San Francisco, CA 94103   United States of America   Email: ethan@ieee.org   URI:   https://www.dolby.com   Tal Mizrahi   Huawei   Email: tal.mizrahi.phd@gmail.com   Andrew J. Hacker   Thought LLC   Harrisburg, PA   United States of America   Email: andrew@thought.live