Movatterモバイル変換

Network Working Group                                       L. Fang, Ed.Request for Comments: 4111                                    AT&T Labs.Category: Informational                                        July 2005Security Framework forProvider-Provisioned Virtual Private Networks (PPVPNs)Status of This Memo   This memo provides information for the Internet community.  It does   not specify an Internet standard of any kind.  Distribution of this   memo is unlimited.Copyright Notice   Copyright (C) The Internet Society (2005).Abstract   This document addresses security aspects pertaining to Provider-   Provisioned Virtual Private Networks (PPVPNs).  First, it describes   the security threats in the context of PPVPNs and defensive   techniques to combat those threats.  It considers security issues   deriving both from malicious behavior of anyone and from negligent or   incorrect behavior of the providers.  It also describes how these   security attacks should be detected and reported.  It then discusses   possible user requirements for security of a PPVPN service.  These   user requirements translate into corresponding provider requirements.   In addition, the provider may have additional requirements to make   its network infrastructure secure to a level that can meet the PPVPN   customer's expectations.  Finally, this document defines a template   that may be used to describe and analyze the security characteristics   of a specific PPVPN technology.Table of Contents1.  Introduction .................................................22.  Terminology ..................................................43.  Security Reference Model .....................................44.  Security Threats .............................................64.1.  Attacks on the Data Plane ..............................74.2.  Attacks on the Control Plane ...........................95.  Defensive Techniques for PPVPN Service Providers .............115.1.  Cryptographic Techniques ...............................125.2.  Authentication .........................................205.3.  Access Control Techniques ..............................225.4.  Use of Isolated Infrastructure .........................27Fang                         Informational                      [Page 1]

RFC 4111                PPVPN Security Framework               July 20055.5.  Use of Aggregated Infrastructure .......................275.6.  Service Provider Quality Control Processes .............285.7.  Deployment of Testable PPVPN Service ...................286.  Monitoring, Detection, and Reporting of Security Attacks .....287.  User Security Requirements ...................................297.1.  Isolation ..............................................307.2.  Protection .............................................307.3.  Confidentiality ........................................317.4.  CE Authentication ......................................317.5.  Integrity ..............................................317.6.  Anti-replay ............................................328.  Provider Security Requirements ...............................328.1.  Protection within the Core Network .....................328.2.  Protection on the User Access Link .....................348.3.  General Requirements for PPVPN Providers ...............369.  Security Evaluation of PPVPN Technologies ....................379.1.  Evaluating the Template ................................379.2.  Template ...............................................3710. Security Considerations ......................................4011. Contributors .................................................4112. Acknowledgement ..............................................4213. Normative References .........................................4214. Informative References .......................................431.  Introduction   Security is an integral aspect of Provider-Provisioned Virtual   Private Network (PPVPN) services.  The motivation and rationale for   both Provider-Provisioned Layer-2 VPN and Provider-Provisioned   Layer-3 VPN services are provided by [RFC4110] and [RFC4031].  These   documents acknowledge that security is an important and integral   aspect of PPVPN services, for both VPN customers and VPN service   providers.  Both will benefit from a PPVPN Security Framework   document that lists the customer and provider security requirements   related to PPVPN services, and that can be used to assess how much a   particular technology protects against security threats and fulfills   the security requirements.   First, we describe the security threats that are relevant in the   context of PPVPNs, and the defensive techniques that can be used to   combat those threats.  We consider security issues deriving both from   malicious or incorrect behavior of users and other parties and from   negligent or incorrect behavior of the providers.  An important part   of security defense is the detection and report of a security attack,Fang                         Informational                      [Page 2]

RFC 4111                PPVPN Security Framework               July 2005   which is also addressed in this document.  Special considerations   engendered by IP mobility within PPVPNs are not in the scope of this   document.   Then, we discuss the possible user and provider security requirements   for a PPVPN service.  Users expectations must be met for the security   characteristics of a VPN service.  These user requirements translate   into corresponding requirements for the providers offering the   service.  Furthermore, providers have security requirements to   protect their network infrastructure, securing it to the level   required to provide the PPVPN services in addition to other services.   Finally, we define a template that may be used to describe the   security characteristics of a specific PPVPN technology in a manner   consistent with the security framework described in this document.   It is not within the scope of this document to analyze the security   properties of specific technologies.  Instead, our intention is to   provide a common tool, in the form of a checklist, that may be used   in other documents dedicated to an in-depth security analysis of   individual PPVPN technologies to describe their security   characteristics in a comprehensive and coherent way, thereby   providing a common ground for comparison between different   technologies.   It is important to clarify that this document is limited to   describing users' and providers' security requirements that pertain   to PPVPN services.  It is not the intention to formulate precise   "requirements" on each specific technology by defining the mechanisms   and techniques that must be implemented to satisfy such users' and   providers' requirements.   This document is organized as follows.Section 2 defines the   terminology used in the document.Section 3 defines the security   reference model for security in PPVPN networks.Section 4 describes   the security threats that are specific of PPVPNs.Section 5 reviews   defense techniques that may be used against those threats.Section 6   describes how attacks may be detected and reported.Section 7   discusses the user security requirements that apply to PPVPN   services.Section 8 describes additional security requirements on   the provider to guarantee the security of the network infrastructure   providing PPVPN services.  InSection 9, we provide a template that   may be used to describe the security characteristics of specific   PPVPN technologies.  Finally,Section 10 discusses security   considerations.Fang                         Informational                      [Page 3]

RFC 4111                PPVPN Security Framework               July 20052.  Terminology   This document uses PPVPN-specific terminology.  Definitions and   details specific to PPVPN terminology can be found in [RFC4026] and   [RFC4110].  The most important definitions are repeated in this   section; for other definitions, the reader is referred to   [RFC4026] and [RFC4110].      CE: Customer Edge device, a router or a switch in the customer         network interfacing with the service provider's network.      P: Provider Router.  The Provider Router is a router in the         service provider's core network that does not have interfaces         directly toward the customer.  A P router is used to         interconnect the PE routers.  A P router does not have to         maintain VPN state and is thus VPN unaware.      PE: Provider Edge device, the equipment in the service provider's         network that interfaces with the equipment in the customer's         network.      PPVPN: Provider-Provisioned Virtual Private Network, a VPN that is         configured and managed by the service provider (and thus not by         the customer itself).      SP: Service Provider.      VPN: Virtual Private Network, which restricts communication         between a set of sites using an IP backbone shared by traffic         that is not going to or coming from those sites.3.  Security Reference Model   This section defines a reference model for security in PPVPN   networks.   A PPVPN core network is the central network infrastructure (P and PE   routers) over which PPVPN services are delivered.  A PPVPN core   network consists of one or more SP networks.  All network elements in   the core are under the operational control of one or more PPVPN   service providers.  Even if the PPVPN core is provided by several   service providers, it appears to the PPVPN users as a single zone of   trust.  However, several service providers providing a common PPVPN   core still have to secure themselves against the other providers.   PPVPN services can also be delivered over the Internet, in which case   the Internet forms a logical part of the PPVPN core.Fang                         Informational                      [Page 4]

RFC 4111                PPVPN Security Framework               July 2005   A PPVPN user is a company, institution or residential client of the   PPVPN service provider.   A PPVPN service is a private network service made available by a   service provider to a PPVPN user.  The service is implemented using   virtual constructs built on a shared PPVPN core network.  A PPVPN   service interconnects sites of a PPVPN user.   Extranets are VPNs in which multiple sites are controlled by   different (legal) entities.  Extranets are another example of PPVPN   deployment scenarios wherein restricted and controlled communication   is allowed between trusted zones, often via well-defined transit   points.   This document defines each PPVPN as a trusted zone and the PPVPN core   as another trusted zone.  A primary concern is security aspects that   relate to breaches of security from the "outside" of a trusted zone   to the "inside" of this zone.  Figure 1 depicts the concept of   trusted zones within the PPVPN framework.      +------------+                             +------------+      | PPVPN      +-----------------------------+      PPVPN |      | user           PPVPN                             user |      | site       +---------------------XXX-----+       site |      +------------+  +------------------XXX--+  +------------+                      |   PPVPN core     | |  |                      +------------------| |--+                                         | |                                         | +------\                                         +--------/  Internet                   Figure 1: The PPVPN trusted zone model   In principle, the trusted zones should be separate.  However, PPVPN   core networks often offer Internet access, in which case a transit   point (marked "XXX" in the figure) is defined.   The key requirement of a "virtual private" network (VPN) is that the   security of the trusted zone of the VPN is not compromised by sharing   the core infrastructure with other VPNs.   Security against threats that originate within the same trusted zone   as their targets (for example, attacks from a user in a PPVPN to   other users within the same PPVPN, or attacks entirely within the   core network) is outside the scope of this document.   Also outside the scope are all aspects of network security that are   independent of whether a network is a PPVPN network or a privateFang                         Informational                      [Page 5]

RFC 4111                PPVPN Security Framework               July 2005   network.  For example, attacks from the Internet to a web server   inside a given PPVPN will not be considered here, unless the   provisioning of the PPVPN network could make a difference to the   security of this server.4.  Security Threats   This section discusses the various network security threats that may   endanger PPVPNs.  The discussion is limited to threats that are   unique to PPVPNs, or that affect PPVPNs in unique ways.  A successful   attack on a particular PPVPN or on a service provider's PPVPN   infrastructure may cause one or more of the following ill effects:   -  observation, modification, or deletion of PPVPN user data,   -  replay of PPVPN user data,   -  injection of non-authentic data into a PPVPN,   -  traffic pattern analysis on PPVPN traffic,   -  disruption of PPVPN connectivity, or   -  degradation of PPVPN service quality.   It is useful to consider that threats to a PPVPN, whether malicious   or accidental, may come from different categories of sources.  For   example they may come from:   -  users of other PPVPNs provided by the same PPVPN service provider,   -  the PPVPN service provider or persons working for it,   -  other persons who obtain physical access to a service provider      site,   -  other persons who use social engineering methods to influence      behavior of service provider personnel,   -  users of the PPVPN itself, i.e., intra-VPN threats (such threats      are beyond the scope of this document), or   -  others, i.e., attackers from the Internet at large.   In the case of PPVPNs, some parties may be in more advantageous   positions that enable them to launch types of attacks not available   to others.  For example, users of different PPVPNs provided by theFang                         Informational                      [Page 6]

RFC 4111                PPVPN Security Framework               July 2005   same service provider may be able to launch attacks that those who   are completely outside the network cannot.   Given that security is generally a compromise between expense and   risk, it is also useful to consider the likelihood of different   attacks.  There is at least a perceived difference in the likelihood   of most types of attacks being successfully mounted in different   environments, such as   -  in a PPVPN contained within one service provider's network, or   -  in a PPVPN transiting the public Internet.   Most types of attacks become easier to mount, and hence more likely,   as the shared infrastructure that provides VPN service expands from a   single service provider to multiple cooperating providers, and then   to the global Internet.  Attacks that may not be sufficiently likely   to warrant concern in a closely controlled environment often merit   defensive measures in broader, more open environments.   The following sections discuss specific types of exploits that   threaten PPVPNs.4.1.  Attacks on the Data Plane   This category encompasses attacks on the PPVPN user's data, as viewed   by the service provider.  Note that from the PPVPN user's point of   view, some of this might be control plane traffic, e.g., routing   protocols running from PPVPN user site to PPVPN user site via an L2   PPVPN.4.1.1.  Unauthorized Observation of Data Traffic   This refers to "sniffing" VPN packets and examining their contents.   This can result in exposure of confidential information.  It can also   be a first step in other attacks (described below) in which the   recorded data is modified and re-inserted, or re-inserted unchanged.4.1.2.  Modification of Data Traffic   This refers to modifying the contents of packets as they traverse the   VPN.4.1.3.  Insertion of Non-authentic Data Traffic: Spoofing and Replay   This refers to the insertion into the VPN (or "spoofing") of packets   that do not belong there, with the objective of having them accepted   as legitimate by the recipient.  Also included in this category isFang                         Informational                      [Page 7]

RFC 4111                PPVPN Security Framework               July 2005   the insertion of copies of once-legitimate packets that have been   recorded and replayed.4.1.4.  Unauthorized Deletion of Data Traffic   This refers to causing packets to be discarded as they traverse the   VPN.  This is a specific type of Denial-of-Service attack.4.1.5.  Unauthorized Traffic Pattern Analysis   This refers to "sniffing" VPN packets and examining aspects or meta-   aspects of them that may be visible even when the packets themselves   are encrypted.  An attacker might gain useful information based on   the amount and timing of traffic, packet sizes, source and   destination addresses, etc.  For most PPVPN users, this type of   attack is generally considered significantly less of a concern than   are the other types discussed in this section.4.1.6.  Denial-of-Service Attacks on the VPN   Denial-of-Service (DoS) attacks are those in which an attacker   attempts to disrupt or prevent the use of a service by its legitimate   users.  Taking network devices out of service, modifying their   configuration, or overwhelming them with requests for service are   several of the possible avenues for DoS attack.   Overwhelming the network with requests for service, otherwise known   as a "resource exhaustion" DoS attack, may target any resource in the   network, e.g., link bandwidth, packet forwarding capacity, session   capacity for various protocols, and CPU power.   DoS attacks of the resource exhaustion type can be mounted against   the data plane of a particular PPVPN by attempting to insert (spoof)   an overwhelming quantity of non-authentic data into the VPN from   outside of that VPN.  Potential results might be to exhaust the   bandwidth available to that VPN or to overwhelm the cryptographic   authentication mechanisms of the VPN.   Data plane resource exhaustion attacks can also be mounted by   overwhelming the service provider's general (VPN-independent)   infrastructure with traffic.  These attacks on the general   infrastructure are not usually a PPVPN-specific issue, unless the   attack is mounted by another PPVPN user from a privileged position.   For example, a PPVPN user might be able to monopolize network data   plane resources and thus to disrupt other PPVPNs.)Fang                         Informational                      [Page 8]

RFC 4111                PPVPN Security Framework               July 20054.2.  Attacks on the Control Plane   This category encompasses attacks on the control structures operated   by the PPVPN service provider.4.2.1.  Denial-of-Service Attacks on Network Infrastructure   Control plane DoS attacks can be mounted specifically against the   mechanisms that the service provider uses to provide PPVPNs (e.g.,   IPsec, MPLS) or against the general infrastructure of the service   provider (e.g., P routers or shared aspects of PE routers.)   Attacks   against the general infrastructure are within the scope of this   document only if the attack happens in relation to the VPN service;   otherwise, they are not a PPVPN-specific issue.   Of special concern for PPVPNs is denial of service to one PPVPN user   caused by the activities of another.  This can occur, for example, if   one PPVPN user's activities are allowed to consume excessive network   resources of any sort that are also needed to serve other PPVPN   users.   The attacks described in the following sections may each have denial   of service as one of their effects.  Other DoS attacks are also   possible.4.2.2.  Attacks on Service Provider Equipment via Management        Interfaces   This includes unauthorized access to service provider infrastructure   equipment, in order, for example, to reconfigure the equipment or to   extract information (statistics, topology, etc.) about one or more   PPVPNs.   This can be accomplished through malicious entrance of the systems,   or as an inadvertent consequence of inadequate inter-VPN isolation in   a PPVPN user self-management interface.  (The former is not   necessarily a PPVPN-specific issue.)4.2.3.  Social Engineering Attacks on Service Provider        Infrastructure   Attacks in which the service provider network is reconfigured or   damaged, or in which confidential information is improperly   disclosed, may be mounted through manipulation of service provider   personnel.  These types of attacks are PPVPN-specific if they affect   PPVPN-serving mechanisms.  It may be observed that the organizational   split (customer, service provider) that is inherent in PPVPNs may   make it easier to mount such attacks against provider-provisionedFang                         Informational                      [Page 9]

RFC 4111                PPVPN Security Framework               July 2005   VPNs than against VPNs that are self-provisioned by the customer at   the IP layer.4.2.4.  Cross-Connection of Traffic between PPVPNs   This refers to events where expected isolation between separate   PPVPNs is breached.  This includes cases such as:   -  a site being connected into the "wrong" VPN,   -  two or more VPNs being improperly merged,   -  a point-to-point VPN connecting the wrong two points, or   -  any packet or frame being improperly delivered outside the VPN it      is sent in.   Misconnection or cross-connection of VPNs may be caused by service   provider or equipment vendor error, or by the malicious action of an   attacker.  The breach may be physical (e.g., PE-CE links   misconnected) or logical (improper device configuration).   Anecdotal evidence suggests that the cross-connection threat is one   of the largest security concerns of PPVPN users (or would-be users).4.2.5.  Attacks against PPVPN Routing Protocols   This encompasses attacks against routing protocols that are run by   the service provider and that directly support the PPVPN service.  In   layer 3 VPNs this, typically relates to membership discovery or to   the distribution of per-VPN routes.  In layer 2 VPNs, this typically   relates to membership and endpoint discovery.  Attacks against the   use of routing protocols for the distribution of backbone (non-VPN)   routes are beyond the scope of this document.  Specific attacks   against popular routing protocols have been widely studied and are   described in [RFC3889].4.2.6.  Attacks on Route Separation   "Route separation" refers here to keeping the per-VPN topology and   reachability information for each PPVPN separate from, and   unavailable to, any other PPVPN (except as specifically intended by   the service provider).  This concept is only a distinct security   concern for layer-3 VPN types for which the service provider is   involved with the routing within the VPN (i.e., VR, BGP-MPLS, routed   version of IPsec).  A breach in the route separation can reveal   topology and addressing information about a PPVPN.  It can also causeFang                         Informational                     [Page 10]

RFC 4111                PPVPN Security Framework               July 2005   black hole routing or unauthorized data plane cross-connection   between PPVPNs.4.2.7.  Attacks on Address Space Separation   In layer-3 VPNs, the IP address spaces of different VPNs have to be   kept separate.  In layer-2 VPNs, the MAC address and VLAN spaces of   different VPNs have to be kept separate.  A control plane breach in   this addressing separation may result in unauthorized data plane   cross-connection between VPNs.4.2.8.  Other Attacks on PPVPN Control Traffic   Besides routing and management protocols (covered separately in the   previous sections), a number of other control protocols may be   directly involved in delivering the PPVPN service (e.g., for   membership discovery and tunnel establishment in various PPVPN   approaches).  These include but may not be limited to:   -  MPLS signaling (LDP, RSVP-TE),   -  IPsec signaling (IKE) ,   -  L2TP,   -  BGP-based membership discovery, and   -  Database-based membership discovery (e.g., RADIUS-based).   Attacks might subvert or disrupt the activities of these protocols,   for example, via impersonation or DoS attacks.5.  Defensive Techniques for PPVPN Service Providers   The defensive techniques discussed in this document are intended to   describe methods by which some security threats can be addressed.   They are not intended as requirements for all PPVPN implementations.   The PPVPN provider should determine the applicability of these   techniques to the provider's specific service offerings, and the   PPVPN user may wish to assess the value of these techniques in regard   to the user's VPN requirements.   The techniques discussed here include encryption, authentication,   filtering, firewalls, access control, isolation, aggregation, and   other techniques.   Nothing is ever 100% secure.  Defense therefore protects against   those attacks that are most likely to occur or that could have the   most dire consequences.  Absolute protection against these attacks is   seldom achievable; more often it is sufficient to make the cost of a   successful attack greater than what the adversary would be willing to   expend.Fang                         Informational                     [Page 11]

RFC 4111                PPVPN Security Framework               July 2005   Successful defense against an attack does not necessarily mean that   the attack must be prevented from happening or from reaching its   target.  In many cases, the network can instead be designed to   withstand the attack.  For example, the introduction of non-authentic   packets could be defended against by preventing their introduction in   the first place, or by making it possible to identify and eliminate   them before delivery to the PPVPN user's system.  The latter is   frequently a much easier task.5.1.  Cryptographic Techniques   PPVPN defenses against a wide variety of attacks can be enhanced by   the proper application of cryptographic techniques.  These are the   same cryptographic techniques that are applicable to general network   communications.  In general, these techniques can provide   confidentiality (encryption) of communication between devices,   authentication of the identities of the devices, and detection of a   change of the protected data during transit.   Privacy is a key part (the middle name!) of any Virtual Private   Network.  In a PPVPN, privacy can be provided by two mechanisms:   traffic separation and encryption.  This section focuses on   encryption; traffic separation is addressed separately.   Several aspects of authentication are addressed in some detail in a   separate "Authentication" section.   Encryption adds complexity, and thus it may not be a standard   offering within every PPVPN service.  There are a few reasons for   this.  Encryption adds an additional computational burden to the   devices performing encryption and decryption.  This may reduce the   number of user VPN connections that can be handled on a device or   otherwise reduce the capacity of the device, potentially driving up   the provider's costs.  Typically, configuring encryption services on   devices adds to the complexity of the device configuration and adds   incremental labor cost.  Encrypting packets typically increases   packet lengths, thereby increasing the network traffic load and the   likelihood of packet fragmentation, with its increased overhead.   (Packet length increase can often be mitigated to some extent by data   compression techniques, but with additional computational burden.)   Finally, some PPVPN providers may employ enough other defensive   techniques, such as physical isolation or filtering/firewall   techniques, that they may not perceive additional benefit from   encryption techniques.   The trust model among the PPVPN user, the PPVPN provider, and other   parts of the network is a key element in determining the   applicability of encryption for any specific PPVPN implementation.Fang                         Informational                     [Page 12]

RFC 4111                PPVPN Security Framework               July 2005   In particular, it determines where encryption should be applied, as   follows.      -  If the data path between the user's site and the provider's PE         is not trusted, then encryption may be used on the PE-CE link.      -  If some part of the backbone network is not trusted,         particularly in implementations where traffic may travel across         the Internet or multiple provider networks, then the PE-PE         traffic may be encrypted.      -  If the PPVPN user does not trust any zone outside of its         premises, it may require end-to-end or CE-CE encryption         service.  This service fits within the scope of this PPVPN         security framework when the CE is provisioned by the PPVPN         provider.      -  If the PPVPN user requires remote access to a PPVPN from a         system that is not at a PPVPN customer location (for example,         access by a traveler), there may be a requirement for         encrypting the traffic between that system and an access point         on the PPVPN or at a customer site.  If the PPVPN provider         provides the access point, then the customer must cooperate         with the provider to handle the access control services for the         remote users.  These access control services are usually         implemented by using encryption, as well.   Although CE-CE encryption provides confidentiality against third-   party interception, if the PPVPN provider has complete management   control over the CE (encryption) devices, then it may be possible for   the provider to gain access to the user's VPN traffic or internal   network.  Encryption devices can potentially be configured to use   null encryption, to bypass encryption processing altogether, or to   provide some means of sniffing or diverting unencrypted traffic.   Thus, a PPVPN implementation using CE-CE encryption has to consider   the trust relationship between the PPVPN user and provider.  PPVPN   users and providers may wish to negotiate a service level agreement   (SLA) for CE-CE encryption that will provide an acceptable   demarcation of responsibilities for management of encryption on the   CE devices.   The demarcation may also be affected by the capabilities of the CE   devices.  For example, the CE might support some partitioning of   management or a configuration lock-down ability, or it might allow   both parties to verify the configuration.  In general, if the managed   CE-CE model is used, the PPVPN user has to have a fairly high level   of trust that the PPVPN provider will properly provision and manage   the CE devices.Fang                         Informational                     [Page 13]

RFC 4111                PPVPN Security Framework               July 20055.1.1.  IPsec in PPVPNs   IPsec [RFC2401] [RFC2402] [RFC2406] [RFC2407] [RFC2411] is the   security protocol of choice for encryption at the IP layer (Layer 3),   as discussed in [RFC3631].  IPsec provides robust security for IP   traffic between pairs of devices.  Non-IP traffic must be converted   to IP packets, or it cannot be transported over IPsec.  Encapsulation   is a common conversion method.   In the PPVPN model, IPsec can be employed to protect IP traffic   between PEs, between a PE and a CE, or from CE to CE.  CE-to-CE IPsec   may be employed in either a provider-provisioned or a user-   provisioned model.  The user-provisioned CE-CE IPsec model is outside   the scope of this document and outside the scope of the PPVPN Working   Group.  Likewise, data encryption that is performed within the user's   site is outside the scope of this document, as it is simply handled   as user data by the PPVPN.  IPsec can also be used to protect IP   traffic between a remote user and the PPVPN.   IPsec does not itself specify an encryption algorithm.  It can use a   variety of encryption algorithms with various key lengths, such as   AES encryption.  There are trade-offs between key length,   computational burden, and the level of security of the encryption.  A   full discussion of these trade-offs is beyond the scope of this   document.  In order to assess the level of security offered by a   particular IPsec-based PPVPN service, some PPVPN users may wish to   know the specific encryption algorithm and effective key length used   by the PPVPN provider.  However, in practice, any currently   recommended IPsec encryption offers enough security to substantially   reduce the likelihood of being directly targeted by an attacker.   Other, weaker, links in the chain of security are likely to be   attacked first.  PPVPN users may wish to use a Service Level   Agreement (SLA) specifying the service provider's responsibility for   ensuring data confidentiality rather than to analyze the specific   encryption techniques used in the PPVPN service.   For many of the PPVPN provider's network control messages and some   PPVPN user requirements, cryptographic authentication of messages   without encryption of the contents of the message may provide   acceptable security.  With IPsec, authentication of messages is   provided by the Authentication Header (AH) or by the Encapsulating   Security Protocol (ESP) with authentication only.  Where control   messages require authentication but do not use IPsec, other   cryptographic authentication methods are available.  Message   authentication methods currently considered to be secure are based on   hashed message authentication codes (HMAC) [RFC2104] implemented with   a secure hash algorithm such as Secure Hash Algorithm 1 (SHA-1)   [RFC3174].Fang                         Informational                     [Page 14]

RFC 4111                PPVPN Security Framework               July 2005   One recommended mechanism for providing a combination   confidentiality, data origin authentication, and connectionless   integrity is the use of AES in Cipher Block Chaining (CBC) Mode, with   an explicit Initialization Vector (IV) [RFC3602], as the IPsec ESP.   PPVPNs that provide differentiated services based on traffic type may   encounter some conflicts with IPsec encryption of traffic.  As   encryption hides the content of the packets, it may not be possible   to differentiate the encrypted traffic in the same manner as   unencrypted traffic.  Although DiffServ markings are copied to the   IPsec header and can provide some differentiation, not all traffic   types can be accommodated by this mechanism.5.1.2.  Encryption for Device Configuration and Management   For configuration and management of PPVPN devices, encryption and   authentication of the management connection at a level comparable to   that provided by IPsec is desirable.   Several methods of transporting PPVPN device management traffic offer   security and confidentiality.   -  Secure Shell (SSH) offers protection for TELNET [STD8] or      terminal-like connections to allow device configuration.   -  SNMP v3 [STD62] provides encrypted and authenticated protection      for SNMP-managed devices.   -  Transport Layer Security (TLS) [RFC2246] and the closely-related      Secure Sockets Layer (SSL) are widely used for securing HTTP-based      communication, and thus can provide support for most XML- and      SOAP-based device management approaches.   -  As of 2004, extensive work is proceeding in several organizations      (OASIS, W3C, WS-I, and others) on securing device management      traffic within a "Web Services" framework.  This work uses a wide      variety of security models and supports multiple security token      formats, multiple trust domains, multiple signature formats, and      multiple encryption technologies.   -  IPsec provides the services with security and confidentiality at      the network layer.  With regard to device management, its current      use is primarily focused on in-band management of user-managed      IPsec gateway devices.Fang                         Informational                     [Page 15]

RFC 4111                PPVPN Security Framework               July 20055.1.3.  Cryptographic Techniques in Layer-2 PPVPNs   Layer-2 PPVPNs will generally not be able to use IPsec to provide   encryption throughout the entire network.  They may be able to use   IPsec for PE-PE traffic where it is encapsulated in IP packets, but   IPsec will generally not be applicable for CE-PE traffic in Layer-2   PPVPNs.   Encryption techniques for Layer-2 links are widely available but are   not within the scope of this document or IETF documents in general.   Layer-2 encryption could be applied to the links from CE to PE, or it   could be applied from CE to CE, as long as the encrypted Layer-2   packets can be handled properly by the intervening PE devices.  In   addition, the upper-layer traffic transported by the Layer-2 VPN can   be encrypted by the user.  In this case, confidentiality will be   maintained; however, this is transparent to the PPVPN provider and is   outside the scope of this document.5.1.4.  End-to-End vs. Hop-by-Hop Encryption Tradeoffs in PPVPNs   In PPVPNs, encryption could potentially be applied to the VPN traffic   at several different places.  This section discusses some of the   tradeoffs in implementing encryption in several different connection   topologies among different devices within a PPVPN.   Encryption typically involves a pair of devices that encrypt the   traffic passing between them.  The devices may be directly connected   (over a single "hop"), or there may be intervening devices that   transport the encrypted traffic between the pair of devices.  The   extreme cases involve hop-by-hop encryption between every adjacent   pair of devices along a given path or "end-to-end" encryption only   between the end devices along a given path.  To keep this discussion   within the scope of PPVPNs, we consider the "end to end" case to be   CE to CE rather than fully end to end.   Figure 2 depicts a simplified PPVPN topology, showing the Customer   Edge (CE) devices, the Provider Edge (PE) devices, and a variable   number (three are shown) of Provider core (P) devices that might be   present along the path between two sites in a single VPN, operated by   a single service provider (SP).          Site_1---CE---PE---P---P---P---PE---CE---Site_2                  Figure 2: Simplified PPVPN topologyFang                         Informational                     [Page 16]

RFC 4111                PPVPN Security Framework               July 2005   Within this simplified topology and assuming that P devices are not   to be involved with encryption, there are four basic feasible   configurations for implementing encryption on connections among the   devices:      1) Site-to-site (CE-to-CE): Encryption can be configured between         the two CE devices, so that traffic will be encrypted         throughout the SP's network.      2) Provider edge-to-edge (PE-to-PE): Encryption can be configured         between the two PE devices.  Unencrypted traffic is received at         one PE from the customer's CE; then it is encrypted for         transmission through the SP's network to the other PE, where it         is decrypted and sent to the other CE.      3) Access link (CE-to-PE): Encryption can be configured between         the CE and PE, on each side (or on only one side).      4) Configurations 2) and 3) can be combined, with encryption         running from CE to PE, then from PE to PE, and then from PE to         CE.   Among the four feasible configurations, key tradeoffs in considering   encryption include the following:   -  Vulnerability to link eavesdropping: Assuming that an attacker can      observe the data in transit on the links, would it be protected by      encryption?   -  Vulnerability to device compromise: Assuming an attacker can get      access to a device (or freely alter its configuration), would the      data be protected?   -  Complexity of device configuration and management: Given Nce, the      number of sites per VPN customer, and Npe, the number of PEs      participating in a given VPN, how many device configurations have      to be created or maintained and how do those configurations scale?   -  Processing load on devices: How many encryption or decryption      operations must be done, given P packets?  This influences      considerations of device capacity and perhaps end-to-end delay.   -  Ability of SP to provide enhanced services (QoS, firewall,      intrusion detection, etc.): Can the SP inspect the data in order      to provide these services?   These tradeoffs are discussed below for each configuration.Fang                         Informational                     [Page 17]

RFC 4111                PPVPN Security Framework               July 2005   1) Site-to-site (CE-to-CE) Configurations      o  Link eavesdropping: Protected on all links.      o  Device compromise: Vulnerable to CE compromise.      o  Complexity: Single administration, responsible for one device         per site (Nce devices), but overall configuration per VPN         scales as Nce**2.      o  Processing load: on each of two CEs, each packet is either         encrypted or decrypted (2P).      o  Enhanced services: Severely limited; typically only DiffServ         markings are visible to SP, allowing some QoS services.   2) Provider edge-to-edge (PE-to-PE) Configurations      o  Link eavesdropping: Vulnerable on CE-PE links; protected on         SP's network links.      o  Device compromise: Vulnerable to CE or PE compromise.      o  Complexity: Single administration; Npe devices to configure.         (Multiple sites may share a PE device, so Npe is typically much         less than Nce.)  Scalability of the overall configuration         depends on the PPVPN type: If the encryption is separate per         VPN context, it scales as Npe**2 per customer VPN.  If the         encryption is per PE, it scales as Npe**2 for all customer VPNs         combined.      o  Processing load: On each of two PEs, each packet is either         encrypted or decrypted (2P).      o  Enhanced services: Full; SP can apply any enhancements based on         detailed view of traffic.   3) Access link (CE-to-PE) Configuration      o  Link eavesdropping: Protected on CE-PE link; vulnerable on SP's         network links.      o  Device compromise: Vulnerable to CE or PE compromise.      o  Complexity: Two administrations (customer and SP) with device         configuration on each side (Nce + Npe devices to configure),         but as there is no mesh, the overall configuration scales as         Nce.Fang                         Informational                     [Page 18]

RFC 4111                PPVPN Security Framework               July 2005      o  Processing load: On each of two CEs, each packet is either         encrypted or decrypted.  On each of two PEs, each packet is         either encrypted or decrypted (4P).      o  Enhanced services: Full; SP can apply any enhancements based on         detailed view of traffic.   4) Combined Access link and PE-to-PE (essentially hop-by-hop).      o  Link eavesdropping: Protected on all links.      o  Device compromise: Vulnerable to CE or PE compromise.      o  Complexity: Two administrations (customer and SP), with device         configuration on each side (Nce + Npe devices to configure).         Scalability of the overall configuration depends on the PPVPN         type.  If the encryption is separate per VPN context, it scales         as Npe**2 per customer VPN.  If the encryption is per-PE, it         scales as Npe**2 for all customer VPNs combined.      o  Processing load: On each of two CEs, each packet is either         encrypted or decrypted.  On each of two PEs, each packet is         both encrypted and decrypted (6P).      o  Enhanced services: Full; SP can apply any enhancements based on         detailed view of traffic.   Given the tradeoffs discussed above, a few conclusions can be   reached.   -  Configurations 2 and 3, which are subsets of 4, may be appropriate      alternatives to 4 under certain threat models.  The remainder of      these conclusions compare 1 (CE-to-CE) with 4 (combined access      links and PE-to-PE).   -  If protection from link eavesdropping is most important, then      configurations 1 and 4 are equivalent.   -  If protection from device compromise is most important and the      threat is to the CE devices, both cases are equivalent; if the      threat is to the PE devices, configuration 1 is best.   -  If reducing complexity is most important and the size of the      network is very small, configuration 1 is the best.  Otherwise,      the comparison between options 1 and 4 is relatively complex ,      based on a number of issues such as, how close the CE to CE      communication is to a full mesh, and what tools are used for key      management.  Option 1 requires configuring keys for each CE-CEFang                         Informational                     [Page 19]

RFC 4111                PPVPN Security Framework               July 2005      pair that is communicating directly.  Option 4 requires      configuring keys on both CE and PE devices but may offer benefit      from the fact that the number of PEs is generally much smaller      than the number of CEs.      Also, under some PPVPN approaches, the scaling of 4 is further      improved by sharing the same PE-PE mesh across all VPN contexts.      The scaling characteristics of 4 may be increased or decreased in      any given situation if the CE devices are simpler to configure      than the PE devices, or vice versa.  Furthermore, with option 4,      the impact of operational error may be significantly increased.   -  If the overall processing load is a key factor, then 1 is best.   -  If the availability of enhanced services support from the SP is      most important, then 4 is best.   As a quick overall conclusion, CE-to-CE encryption provides greater   protection against device compromise, but it comes at the cost of   enhanced services and with additional operational complexity due to   the Order(n**2) scaling of the mesh.   This analysis of site-to-site vs. hop-by-hop encryption tradeoffs   does not explicitly include cases where multiple providers cooperate   to provide a PPVPN service, public Internet VPN connectivity, or   remote access VPN service, but many of the tradeoffs will be similar.5.2.  Authentication   In order to prevent security issues from some denial-of-service   attacks or from malicious misconfiguration, it is critical that   devices in the PPVPN should only accept connections or control   messages from valid sources.  Authentication refers to methods for   ensuring that message sources are properly identified by the PPVPN   devices with which they communicate.  This section focuses on   identifying the scenarios in which sender authentication is required,   and it recommends authentication mechanisms for these scenarios.   Cryptographic techniques (authentication and encryption) do not   protect against some types of denial-of-service attacks,   specifically, resource exhaustion attacks based on CPU or bandwidth   exhaustion.  In fact, the processing required to decrypt or check   authentication may in some cases increase the effect of these   resource exhaustion attacks.  Cryptographic techniques may, however,   be useful against resource exhaustion attacks based on exhaustion of   state information (e.g., TCP SYN attacks).Fang                         Informational                     [Page 20]

RFC 4111                PPVPN Security Framework               July 20055.2.1.  VPN Member Authentication   This category includes techniques for the CEs to verify that they are   connected to the expected VPN.  It includes techniques for CE-PE   authentication, to verify that each specific CE and PE is actually   communicating with its expected peer.5.2.2.  Management System Authentication   Management system authentication includes the authentication of a PE   to a centrally-managed directory server when directory-based "auto-   discovery" is used.  It also includes authentication of a CE to its   PPVPN configuration server when a configuration server system is   used.5.2.3.  Peer-to-Peer Authentication   Peer-to-peer authentication includes peer authentication for network   control protocols (e.g., LDP, BGP), and other peer authentication   (i.e., authentication of one IPsec security gateway by another).5.2.4.  Authenticating Remote Access VPN Members   This section describes methods for authentication of remote access   users connecting to a VPN.   Effective authentication of individual connections is a key   requirement for enabling remote access to a PPVPN from an arbitrary   Internet address (for instance, by a traveler).   There are several widely used standards-based protocols to support   remote access authentication.  These include RADIUS [RFC2865] and   DIAMETER [RFC3588].  Digital certificate systems also provide   authentication.  In addition, there has been extensive development   and deployment of mechanisms for securely transporting individual   remote access connections within tunneling protocols, including L2TP   [RFC2661] and IPsec.   Remote access involves connection to a gateway device, which provides   access to the PPVPN.  The gateway device may be managed by the user   at a user site, or by the PPVPN provider at any of several possible   locations in the network.  The user-managed case is of limited   interest within the PPVPN security framework, and it is not   considered at this time.   When a PPVPN provider manages authentication at the remote access   gateway, this implies that authentication databases, which are   usually extremely confidential user-managed systems, will have to beFang                         Informational                     [Page 21]

RFC 4111                PPVPN Security Framework               July 2005   referenced in a secure manner by the PPVPN provider.  This can be   accomplished through proxy authentication services, which accept an   encrypted authentication credential from the remote access user, pass   it to the PPVPN user's authentication system, and receive a yes/no   response as to whether the user has been authenticated.  Thus, the   PPVPN provider does not have access to the actual authentication   database, but it can use it on behalf of the PPVPN user to provide   remote access authentication.   Specific cryptographic techniques for handling authentication are   described in the following sections.5.2.5.  Cryptographic Techniques for Authenticating Identity   Cryptographic techniques offer several mechanisms for authenticating   the identity of devices or individuals.  These include the use of   shared secret keys, one-time keys generated by accessory devices or   software, user-ID and password pairs, and a range of public-private   key systems.  Another approach is to use a hierarchical Certificate   Authority system to provide digital certificates.   This section describes or provides references to the specific   cryptographic approaches for authenticating identity.  These   approaches provide secure mechanisms for most of the authentication   scenarios required in operating a PPVPN.5.3.  Access Control Techniques   Access control techniques include packet-by-packet or packet flow -   by - packet flow access control by means of filters and firewalls, as   well as by means of admitting a "session" for a   control/signaling/management protocol that is being used to implement   PPVPNs.  Enforcement of access control by isolated infrastructure   addresses is discussed elsewhere in this document.   We distinguish between filtering and firewalls primarily by the   direction of traffic flow.  We define filtering as being applicable   to unidirectional traffic, whereas a firewall can analyze and control   both sides of a conversation.   There are two significant corollaries of this definition:   -  Routing or traffic flow symmetry: A firewall typically requires      routing symmetry, which is usually enforced by locating a firewall      where the network topology assures that both sides of a      conversation will pass through the firewall.  A filter can then      operate upon traffic flowing in one direction without considering      traffic in the reverse direction.Fang                         Informational                     [Page 22]

RFC 4111                PPVPN Security Framework               July 2005   -  Statefulness: Because it receives both sides of a conversation, a      firewall may be able to obtain a significant amount of information      concerning that conversation and to use this information to      control access.  A filter can maintain some limited state      information on a unidirectional flow of packets, but it cannot      determine the state of the bi-directional conversation as      precisely as a firewall can.5.3.1.  Filtering   It is relatively common for routers to filter data packets.  That is,   routers can look for particular values in certain fields of the IP or   higher level (e.g., TCP or UDP) headers.  Packets that match the   criteria associated with a particular filter may be either discarded   or given special treatment.   In discussing filters, it is useful to separate the filter   characteristics that may be used to determine whether a packet   matches a filter from the packet actions that are applied to packets   that match a particular filter.   o  Filter Characteristics      Filter characteristics are used to determine whether a particular      packet or set of packets matches a particular filter.      In many cases, filter characteristics may be stateless.  A      stateless filter determines whether a particular packet matches a      filter based solely on the filter definition, on normal forwarding      information (such as the next hop for a packet), and on the      characteristics of that individual packet.  Typically, stateless      filters may consider the incoming and outgoing logical or physical      interface, information in the IP header, and information in higher      layer headers such as the TCP or UDP header.  Information in the      IP header to be considered may, for example, include source and      destination IP address, Protocol field, Fragment Offset, and TOS      field.  Filters may also consider fields in the TCP or UDP header      such as the Port fields and the SYN field in the TCP header.      Stateful filtering maintains packet-specific state information to      aid in determining whether a filter has been met.  For example, a      device might apply stateless filters to the first fragment of a      fragmented IP packet.  If the filter matches, then the data unit      ID may be remembered, and other fragments of the same packet may      then be considered to match the same filter.  Stateful filtering      is more commonly done in firewalls, although firewall technology      may be added to routers.Fang                         Informational                     [Page 23]

RFC 4111                PPVPN Security Framework               July 2005   o  Actions Based on Filter Results      If a packet, or a series of packets, match a specific filter, then      there are a variety of actions that may be taken based on that      filter match.  Examples of such actions include:      -  Discard         In many cases, filters may be set to catch certain undesirable         packets.  Examples may include packets with forged or invalid         source addresses, packets that are part of a DoS or DDoS         attack, or packets that are trying to access forbidden         resources (such as network management packets from an         unauthorized source).  Where such filters are activated, it is         common to silently discard the packet or set of packets         matching the filter.  The discarded packets may also be counted         and/or logged, of course.      -  Set CoS         A filter may be used to set the Class of Service associated         with the packet.      -  Count Packets and/or Bytes      -  Rate Limit         In some cases, the set of packets that match a particular         filter may be limited to a specified bandwidth.  Packets and/or         bytes would be counted and forwarded normally up to the         specified limit.  Excess packets may be discarded or marked         (for example, by setting a "discard eligible" bit in the IP ToS         field or the MPLS EXP field).      -  Forward and Copy         It is useful in some cases not only to forward some set of         packets normally, but also to send a copy to a specified other         address or interface.  For example, this may be used to         implement a lawful intercept capability, or to feed selected         packets to an Intrusion Detection System.   o  Other Issues Related to Packet Filters      There may be a very wide variation in the performance impact of      filtering.  This may occur both due to differences between      implementations, and due to differences between types or numbersFang                         Informational                     [Page 24]

RFC 4111                PPVPN Security Framework               July 2005      of filters deployed.  For filtering to be useful, the performance      of the equipment has to be acceptable in the presence of filters.      The precise definition of "acceptable" may vary from service      provider to service provider and may depend on the intended use of      the filters.  For example, for some uses a filter may be turned on      all the time in order to set CoS, to prevent an attack, or to      mitigate the effect of a possible future attack.  In this case it      is likely that the service provider will want the filter to have      minimal or no impact on performance.  In other cases, a filter may      be turned on only in response to a major attack (such as a major      DDoS attack).  In this case a greater performance impact may be      acceptable to some service providers.      A key consideration with the use of packet filters is that they      can provide few options for filtering packets carrying encrypted      data.  Because the data itself is not accessible, only packet      header information or other unencrypted fields can be used for      filtering.5.3.2.  Firewalls   Firewalls provide a mechanism for control over traffic passing   between different trusted zones in the PPVPN model, or between a   trusted zone and an untrusted zone.  Firewalls typically provide much   more functionality than filters, as they may be able to apply   detailed analysis and logical functions to flows and not just to   individual packets.  They may offer a variety of complex services,   such as threshold-driven denial-of-service attack protection, virus   scanning, or acting as a TCP connection proxy.  As with other access   control techniques, the value of firewalls depends on a clear   understanding of the topologies of the PPVPN core network, the user   networks, and the threat model.  Their effectiveness depends on a   topology with a clearly defined inside (secure) and outside (not   secure).   Within the PPVPN framework, traffic typically is not allowed to pass   between the various user VPNs.  This inter-VPN isolation is usually   not performed by a firewall, but it is a part of the basic VPN   mechanism.  An exception to the total isolation of VPNs is the case   of "extranets", which allow specific external access to a user's VPN,   potentially from another VPN.  Firewalls can be used to provide the   services required for secure extranet implementation.Fang                         Informational                     [Page 25]

RFC 4111                PPVPN Security Framework               July 2005   In a PPVPN, firewalls can be applied between the public Internet and   user VPNs, in cases where Internet access services are offered by the   provider to the VPN user sites.  In addition, firewalls may be   applied between VPN user sites and any shared network-based services   offered by the PPVPN provider.   Firewalls may be applied to help protect PPVPN core network functions   from attacks originating from the Internet or from PPVPN user sites,   but typically other defensive techniques will be used for this   purpose.   Where firewalls are employed as a service to protect user VPN sites   from the Internet, different VPN users, and even different sites of a   single VPN user, may have varying firewall requirements.  The overall   PPVPN logical and physical topology, along with the capabilities of   the devices implementing the firewall services, will have a   significant effect on the feasibility and manageability of such   varied firewall service offerings.   Another consideration with the use of firewalls is that they can   provide few options for handling packets carrying encrypted data.  As   the data itself is not accessible, only packet header information,   other unencrypted fields, or analysis of the flow of encrypted   packets can be used for making decisions on accepting or rejecting   encrypted traffic.5.3.3.  Access Control to Management Interfaces   Most of the security issues related to management interfaces can be   addressed through the use of authentication techniques described in   the section on authentication.  However, additional security may be   provided by controlling access to management interfaces in other   ways.   Management interfaces, especially console ports on PPVPN devices, may   be configured so that they are only accessible out of band, through a   system that is physically or logically separated from the rest of the   PPVPN infrastructure.   Where management interfaces are accessible in-band within the PPVPN   domain, filtering or firewalling techniques can be used to restrict   unauthorized in-band traffic from having access to management   interfaces.  Depending on device capabilities, these filtering or   firewalling techniques can be configured either on other devices   through which the traffic might pass, or on the individual PPVPN   devices themselves.Fang                         Informational                     [Page 26]

RFC 4111                PPVPN Security Framework               July 20055.4.  Use of Isolated Infrastructure   One way to protect the infrastructure used for support of VPNs is to   separate the VPN support resources from the resources used for other   purposes (such as support of Internet services).  In some cases, this   may require the use of physically separate equipment for VPN   services, or even a physically separate network.   For example, PE-based L3 VPNs may be run on a separate backbone not   connected to the Internet, or they may use separate edge routers from   those used to support Internet service.  Private IP addresses (local   to the provider and non-routable over the Internet) are sometimes   used to provide additional separation.   It is common for CE-based L3VPNs to make use of CE devices that are   dedicated to one specific VPN.  In many or most cases, CE-based VPNs   may make use of normal Internet services to interconnect CE devices.5.5.  Use of Aggregated Infrastructure   In general it is not feasible to use a completely separate set of   resources for support of each VPN.  One of the main reasons for VPN   services is to allow sharing of resources between multiple users,   including multiple VPNs.  Thus, even if VPN services make use of a   separate network from Internet services, there will still be multiple   VPN users sharing the same network resources.  In some cases, VPN   services will share the use of network resources with Internet   services or other services.   It is therefore important for VPN services to provide protection   between resource use by different VPNs.  Thus, a well-behaved VPN   user should be protected from possible misbehavior by other VPNs.   This requires that limits be placed on the amount of resources that   can be used by any one VPN.  For example, both control traffic and   user data traffic may be rate limited.  In some cases or in some   parts of the network where a sufficiently large number of queues are   available, each VPN (and, optionally, each VPN and CoS within the   VPN) may make use of a separate queue.  Control-plane resources such   as link bandwidth and CPU and memory resources may be reserved on a   per-VPN basis.   The techniques that are used to provision resource protection between   multiple VPNs served by the same infrastructure can also be used to   protect VPN services from Internet services.   The use of aggregated infrastructure allows the service provider to   benefit from stochastic multiplexing of multiple bursty flows and mayFang                         Informational                     [Page 27]

RFC 4111                PPVPN Security Framework               July 2005   also, in some cases, thwart traffic pattern analysis by combining the   data from multiple VPNs.5.6.  Service Provider Quality Control Processes   Deployment of provider-provisioned VPN services requires a relatively   large amount of configuration by the service provider.  For example,   the service provider has to configure which VPN each site belongs to,   as well as QoS and SLA guarantees.  This large amount of required   configuration leads to the possibility of misconfiguration.   It is important for the service provider to have operational   processes in place to reduce the potential impact of   misconfiguration.  CE-to-CE authentication may also be used to detect   misconfiguration when it occurs.5.7.  Deployment of Testable PPVPN Service   This refers to solutions that can readily be tested for correct   configuration.  For example, for a point-point VPN, checking that the   intended connectivity is working largely ensures that there is not   connectivity to some unintended site.6.  Monitoring, Detection, and Reporting of Security Attacks   A PPVPN service may be subject to attacks from a variety of security   threats.  Many threats are described in another part of this   document.  Many of the defensive techniques described in this   document and elsewhere provide significant levels of protection from   a variety of threats.  However, in addition to silently employing   defensive techniques to protect against attacks, PPVPN services can   add value for both providers and customers by implementing security-   monitoring systems that detect and report on any security attacks   that occur, regardless of whether the attacks are effective.   Attackers often begin by probing and analyzing defenses, so systems   that can detect and properly report these early stages of attacks can   provide significant benefits.   Information concerning attack incidents, especially if available   quickly, can be useful in defending against further attacks.  It can   be used to help identify attackers and their specific targets at an   early stage.  This knowledge about attackers and targets can be used   to further strengthen defenses against specific attacks or attackers,   or to improve the defensive services for specific targets on an as-   needed basis.  Information collected on attacks may also be useful in   identifying and developing defenses against novel attack types.Fang                         Informational                     [Page 28]

RFC 4111                PPVPN Security Framework               July 2005   Monitoring systems used to detect security attacks in PPVPNs will   typically operate by collecting information from Provider Edge (PE),   Customer Edge (CE), and/or Provider backbone (P) devices.  Security   monitoring systems should have the ability to actively retrieve   information from devices (e.g., SNMP get) or to passively receive   reports from devices (e.g., SNMP notifications).  The specific   information exchanged will depend on the capabilities of the devices   and on the type of VPN technology.  Particular care should be given   to securing the communications channel between the monitoring systems   and the PPVPN devices.   The CE, PE, and P devices should employ efficient methods to acquire   and communicate the information needed by the security monitoring   systems.  It is important that the communication method between PPVPN   devices and security monitoring systems be designed so that it will   not disrupt network operations.  As an example, multiple attack   events may be reported through a single message, rather than allow   each attack event to trigger a separate message, which might result   in a flood of messages, essentially becoming a denial-of-service   attack against the monitoring system or the network.   The mechanisms for reporting security attacks should be flexible   enough to meet the needs of VPN service providers, VPN customers, and   regulatory agencies.  The specific reports will depend on the   capabilities of the devices, the security monitoring system, the type   of VPN, and the service level agreements between the provider and   customer.7.  User Security Requirements   This section defines a list of security-related requirements that the   users of PPVPN services may have for their PPVPN service.  Typically,   these translate into requirements for the provider in offering the   service.   The following sections detail various requirements that ensure the   security of a given trusted zone.  Since in real life there are   various levels of security, a PPVPN may fulfill any or all of these   security requirements.  This document does not state that a PPVPN   must fulfill all of these requirements to be secure.  As mentioned in   the Introduction, it is not within the scope of this document to   define the specific requirements that each VPN technology must   fulfill in order to be secure.Fang                         Informational                     [Page 29]

RFC 4111                PPVPN Security Framework               July 20057.1.  Isolation   A virtual private network usually defines "private" as isolation from   other PPVPNs and the Internet.  More specifically, isolation has   several components, which are discussed in the following sections.7.1.1.  Address Separation   A given PPVPN can use the full Internet address range, including   private address ranges [RFC1918], without interfering with other   PPVPNs that use PPVPN services from the same service provider(s).   When Internet access is provided (e.g., by the same service provider   that is offering PPVPN service), NAT functionality may be needed.   In layer-2 VPNs, the same requirement exists for the layer 2   addressing schemes, such as MAC addresses.7.1.2.  Routing Separation   A PPVPN core must maintain routing separation between the trusted   zones.  This means that routing information must not leak from any   trusted zone to any other, unless the zones are specifically   engineered this way (e.g., for Internet access.)   In layer-2 VPNs, the switching information must be kept separate   between the trusted zones, so that switching information of one PPVPN   does not influence other PPVPNs or the PPVPN core.7.1.3.  Traffic Separation   Traffic from a given trusted zone must never leave this zone, and   traffic from another zone must never enter this zone.  Exceptions are   made where zones are is specifically engineered that way (e.g., for   extranet purposes or Internet access.)7.2.  Protection   The common perception is that a completely separated "private"   network has defined entry points and is only subject to attack or   intrusion over those entry points.  By sharing a common core, a PPVPN   appears to lose some of these clear interfaces to networks outside   the trusted zone.  Thus, one of the key security requirements of   PPVPN services is that they offer the same level of protection as   private networks.Fang                         Informational                     [Page 30]

RFC 4111                PPVPN Security Framework               July 20057.2.1.  Protection against Intrusion   An intrusion is defined here as the penetration of a trusted zone   from outside.  This could be from the Internet, another PPVPN, or the   core network itself.   The fact that a network is "virtual" must not expose it to additional   threats over private networks.  Specifically, it must not add new   interfaces to other parts outside the trusted zone.  Intrusions from   known interfaces such as Internet gateways are outside the scope of   this document.7.2.2.  Protection against Denial-of-Service Attacks   A denial-of-service (DoS) attack aims at making services or devices   unavailable to legitimate users.  In the framework of this document,   only those DoS attacks are considered that are a consequence of   providing network service through a VPN.  DoS attacks over the   standard interfaces into a trusted zone are not considered here.   The requirement is that a PPVPN is not more vulnerable against DoS   attacks than it would be if the same network were private.7.2.3.  Protection against Spoofing   It must not be possible to violate the integrity of a PPVPN by   changing the sender identification (source address, source label,   etc) of traffic in transit.  For example, if two CEs are connected to   the same PE, it must not be possible for one CE to send crafted   packets that make the PE believe those packets are coming from the   other CE, thus inserting them into the wrong PPVPN.7.3.  Confidentiality   This requirement means that data must be cryptographically secured in   transit over the PPVPN core network to avoid eavesdropping.7.4.  CE Authentication   Where CE authentication is provided, it is not possible for an   outsider to install a CE and pretend to belong to a specific PPVPN to   which this CE does not belong in reality.7.5.  Integrity   Data in transit must be secured in such a manner that it cannot be   altered or that any alteration may be detected at the receiver.Fang                         Informational                     [Page 31]

RFC 4111                PPVPN Security Framework               July 20057.6.  Anti-replay   Anti-replay means that data in transit cannot be recorded and   replayed later.  To protect against anti-replay attacks, the data   must be cryptographically secured.   Note: Even private networks do not necessarily meet the requirements   of confidentiality, integrity, and anti-reply.  Thus, when private   and "virtually private" PPVPN services are compared, these   requirements are only applicable if the comparable private service   also included these services.  However, the fact that VPNs operate   over a shared infrastructure may make some of these requirements more   important in a VPN environment than in a private network environment.8.  Provider Security Requirements   In this section, we discuss additional security requirements that the   provider may have in order to secure its network infrastructure as it   provides PPVPN services.   The PPVPN service provider requirements defined here are the   requirements for the PPVPN core in the reference model.  The core   network can be implemented with different types of network   technologies, and each core network may use different technologies to   provide the PPVPN services to users with different levels of offered   security.  Therefore, a PPVPN service provider may fulfill any number   of the security requirements listed in this section. This document   does not state that a PPVPN must fulfill all of these requirements to   be secure.   These requirements are focused on 1) how to protect the PPVPN core   from various attacks outside the core, including PPVPN users and   non-PPVPN alike, both accidentally and maliciously, and 2) how to   protect the PPVPN user VPNs and sites themselves.  Note that a PPVPN   core is not more vulnerable against attacks than a core that does not   provide PPVPNs.  However, providing PPVPN services over such a core   may lead to additional security requirements, if only because most   users are expecting higher security standards in a core delivering   PPVPN services.8.1.  Protection within the Core Network8.1.1.  Control Plane Protection   -  Protocol Authentication within the Core:      PPVPN technologies and infrastructure must support mechanisms for      authentication of the control plane.  For an IP core, IGP and BGPFang                         Informational                     [Page 32]

RFC 4111                PPVPN Security Framework               July 2005      sessions may be authenticated by using TCP MD5 or IPsec.  If an      MPLS core is used, LDP sessions may be authenticated by using TCP      MD5.  In addition, IGP and BGP authentication should also be      considered.  For a core providing layer-2 services, PE to PE      authentication may also be used via IPsec.      With the cost of authentication coming down rapidly, the      application of control plane authentication may not increase the      cost of implementation for providers significantly, and it will      improve the security of the core.  If the core is dedicated to VPN      services and there are no interconnects to third parties, then it      may reduce the requirement for authentication of the core control      plane.   -  Elements protection      Here we discuss means to hide the provider's infrastructure nodes.      A PPVPN provider may make the infrastructure routers (P and PE      routers) unreachable by outside users and unauthorized internal      users.  For example, separate address space may be used for the      infrastructure loopbacks.      Normal TTL propagation may be altered to make the backbone look      like one hop from the outside, but caution should be taken for      loop prevention.  This prevents the backbone addresses from being      exposed through trace route; however, it must also be assessed      against operational requirements for end-to-end fault tracing.      An Internet backbone core may be re-engineered to make Internet      routing an edge function, for example, by using MPLS label      switching for all traffic within the core and possibly by making      the Internet a VPN within the PPVPN core itself.  This helps      detach Internet access from PPVPN services.      PE devices may implement separate control plane, data plane, and      management plane functionality in terms of hardware and software,      to improve security.  This may help limit the problems when one      particular area is attacked, and it may allow each plane to      implement additional security measurement separately.      PEs are often more vulnerable to attack than P routers, since, by      their very nature, PEs cannot be made unreachable to outside      users.  Access to core trunk resources can be controlled on a      per-user basis by the application of inbound rate-      limiting/shaping.  This can be further enhanced on a per-Class of      Service basis (seesection 8.2.3).Fang                         Informational                     [Page 33]

RFC 4111                PPVPN Security Framework               July 2005      In the PE, using separate routing processes for Internet and PPVPN      service may help improve the PPVPN security and better protect VPN      customers.  Furthermore, if the resources, such as CPU and memory,      may be further separated based on applications, or even on      individual VPNs, it may help provide improved security and      reliability to individual VPN customers.      Many of these were not particular issues when an IP core was      designed to support Internet services only.  Providing PPVPN      services introduces new security requirements for VPN services.      Similar consideration apply to L2 VPN services.8.1.2.  Data Plane Protection   PPVPN using IPsec technologies provides VPN users with encryption of   secure user data.   In today's MPLS, ATM, and Frame Relay networks, encryption is not   provided as a basic feature.  Mechanisms can be used to secure the   MPLS data plane and to secure the data carried over the MPLS core.   Additionally, if the core is dedicated to VPN services and there are   no external interconnects to third party networks, then there is no   obvious need for encryption of the user data plane.   Inter-working IPsec/L3 PPVPN technologies or IPsec/L2 PPVPN   technologies may be used to provide PPVPN users with end-to-end PPVPN   services.8.2.  Protection on the User Access Link   Peer/Neighbor protocol authentication may be used to enhance   security.  For example, BGP MD5 authentication may be used to enhance   security on PE-CE links using eBGP.  In the case of an inter-provider   connection, authentication/encryption mechanisms between ASes, such   as IPsec, may be used.   WAN link address space separation for VPN and non-VPN users may be   implemented to improve security in order to protect VPN customers if   multiple services are provided on the same PE platform.   Firewall/Filtering: Access control mechanisms can be used to filter   out any packets destined for the service provider's infrastructure   prefix or to eliminate routes identified as illegitimate.Fang                         Informational                     [Page 34]

RFC 4111                PPVPN Security Framework               July 2005   Rate limiting may be applied to the user interface/logical interfaces   against DDoS bandwidth attack.  This is very helpful when the PE   device is supporting both VPN services and Internet services,   especially when it supports VPN and Internet services on the same   physical interfaces through different logical interfaces.8.2.1.  Link Authentication   Authentication mechanisms can be employed to validate site access to   the PPVPN network via fixed or logical (e.g., L2TP, IPsec)   connections.  When the user wishes to hold the 'secret' associated to   acceptance of the access and site into the VPN, then PPVPN based   solutions require the flexibility for either direct authentication by   the PE itself or interaction with a customer PPVPN authentication   server.  Mechanisms are required in the latter case to ensure that   the interaction between the PE and the customer authentication server   is controlled, for example, by limiting it simply to an exchange in   relation to the authentication phase and with other attributes (e.g.,   optional filtering of RADIUS).8.2.2.  Access Routing   Mechanisms may be used to provide control at a routing protocol level   (e.g., RIP, OSPF, BGP) between the CE and PE.  Per-neighbor and per-   VPN routing policies may be established to enhance security and   reduce the impact of a malicious or non-malicious attack on the PE,   in particular, the following mechanisms should be considered:   -  Limiting the number of prefixes that may be advertised into the PE      on a per-access basis .  Appropriate action may be taken should a      limit be exceeded; for example, the PE might shut down the peer      session to the CE.   -  Applying route dampening at the PE on received routing updates.   -  Definition of a per-VPN prefix limit, after which additional      prefixes will not be added to the VPN routing table.   In the case of inter-provider connection, access protection, link   authentication, and routing policies as described above may be   applied.  Both inbound and outbound firewall/filtering mechanism may   be applied between ASes.  Proper security procedures must be   implemented in inter-provider VPN interconnection to protect the   providers' network infrastructure and their customer VPNs.  This may   be custom designed for each inter-Provider VPN peering connection,   and both providers must agree on it.Fang                         Informational                     [Page 35]

RFC 4111                PPVPN Security Framework               July 20058.2.3.  Access QoS   PPVPN providers offering QoS-enabled services require mechanisms to   ensure that individual accesses are validated against their   subscribed QOS profile and are granted access to core resources that   match their service profile.  Mechanisms such as per-Class of Service   rate limiting/traffic shaping on ingress to the PPVPN core are one   option in providing this level of control.  Such mechanisms may   require the per-Class of Service profile to be enforced by marking,   remarking, or discarding traffic that is outside of the profile.8.2.4.  Customer VPN Monitoring Tools   End users requiring visibility of VPN-specific statistics on the core   (e.g., routing table, interface status, QoS statistics) impose   requirements for mechanisms at the PE both to validate the incoming   user and to limit the views available to that particular user's VPN.   Mechanisms should also be considered to ensure that such access   cannot be used to create a DoS attack (either malicious or   accidental) on the PE itself.  This could be accomplished either   through separation of these resources within the PE itself or via the   capability to rate-limit such traffic on a per-VPN basis.8.3.  General Requirements for PPVPN Providers   The PPVPN providers must support the users' security requirements as   listed inSection 7.  Depending on the technologies used, these   requirements may include the following.   -  User control plane separation: Routing isolation.   -  User address space separation: Supporting overlapping addresses      from different VPNs.   -  User data plane separation: One VPN traffic cannot be intercepted      by other VPNs or any other users.   -  Protection against intrusion, DoS attacks and spoofing.   -  Access Authentication.   -  Techniques highlighted through this document identify      methodologies for the protection of PPVPN resources and      infrastructure.   Hardware or software bugs in equipment that lead to security breaches   are outside the scope of this document.Fang                         Informational                     [Page 36]

RFC 4111                PPVPN Security Framework               July 20059.  Security Evaluation of PPVPN Technologies   This section presents a brief template that may be used to evaluate   and summarize how a given PPVPN approach (solution) measures up   against the PPVPN Security Framework.  An evaluation using this   template should appear in the applicability statement for each PPVPN   approach.9.1.  Evaluating the Template   The first part of the template is in the form of a list of security   assertions.  For each assertion the approach is assessed and one or   more of the following ratings is assigned:   -  The requirement is not applicable to the VPN approach because ...      (fill in reason).   -  The base VPN approach completely addresses the requirement by ...      (fill in technique).   -  The base VPN approach partially addresses the requirement by ...      (fill in technique and extent to which it addresses the      requirement).   -  An optional extension to the VPN approach completely addresses the      requirement by ...  (fill in technique).   -  An optional extension to the VPN approach partially addresses the      requirement by ...  (fill in technique and extent to which it      addresses the requirement).   -  The requirement is addressed in a way that is beyond the scope of      the VPN approach.  (Explain.)  (One example of this would be a VPN      approach in which some aspect, such as membership discovery, is      done via configuration.  The protection afforded to the      configuration would be beyond the scope of the VPN approach.).   -  The VPN approach does not meet the requirement.9.2.  Template   The following assertions solicit responses of the types listed in the   previous section.   1.  The approach provides complete IP address space separation for       each L3 VPN.Fang                         Informational                     [Page 37]

RFC 4111                PPVPN Security Framework               July 2005   2.  The approach provides complete L2 address space separation for       each L2 VPN.   3.  The approach provides complete VLAN ID space separation for each       L2 VPN.   4.  The approach provides complete IP route separation for each L3       VPN.   5.  The approach provides complete L2 forwarding separation for each       L2 VPN.   6.  The approach provides a means to prevent improper cross-       connection of sites in separate VPNs.   7.  The approach provides a means to detect improper cross-connection       of sites in separate VPNs.   8.  The approach protects against the introduction of unauthorized       packets into each VPN         a. in the CE-PE link,         b. in a single- or multi-provider PPVPN backbone, or         c. in the Internet used as PPVPN backbone.   9.  The approach provides confidentiality (secrecy) protection for       PPVPN user data         a. in the CE-PE link,         b. in a single- or multi-provider PPVPN backbone, or         c. in the Internet used as PPVPN backbone.   10. The approach provides sender authentication for PPVPN user data.         a. in the CE-PE link,         b. in a single- or multi-provider PPVPN backbone, or         c. in the Internet used as PPVPN backbone.   11. The approach provides integrity protection for PPVPN user data         a. in the CE-PE link,         b. in a single- or multi- provider PPVPN backbone, or         c. in the Internet used as PPVPN backbone.   12. The approach provides protection against replay attacks for PPVPN       user data         a. in the CE-PE link,         b. in a single- or multi-provider PPVPN backbone, or         c. in the Internet used as PPVPN backbone.Fang                         Informational                     [Page 38]

RFC 4111                PPVPN Security Framework               July 2005   13. The approach provides protection against unauthorized traffic       pattern analysis for PPVPN user data         a. in the CE-PE link,         b. in a single- or multi-provider PPVPN backbone, or         c. in the Internet used as PPVPN backbone.   14. The control protocol(s) used for each of the following functions       provides message integrity and peer authentication         a. VPN membership discovery.         b. Tunnel establishment.         c. VPN topology and reachability advertisement:            i.  PE-PE.            ii. PE-CE.         d. VPN provisioning and management.         e. VPN monitoring, attack detection, and reporting.         f. Other VPN-specific control protocols, if any (list).   The following questions solicit free-form answers.   15. Describe the protection, if any, the approach provides against       PPVPN-specific DoS attacks (i.e., inter-trusted-zone DoS       attacks):         a. Protection of the service provider infrastructure against            Data Plane or Control Plane DoS attacks originated in a            private (PPVPN user) network and aimed at PPVPN mechanisms.         b. Protection of the service provider infrastructure against            Data Plane or Control Plane DoS attacks originated in the            Internet and aimed at PPVPN mechanisms.         c. Protection of PPVPN users against Data Plane or Control            Plane DoS attacks originated from the Internet or from other            PPVPN users and aimed at PPVPN mechanisms.   16. Describe the protection, if any, the approach provides against       unstable or malicious operation of a PPVPN user network         a. Protection against high levels of, or malicious design of,            routing traffic from PPVPN user networks to the service            provider network.         b. Protection against high levels of, or malicious design of,            network management traffic from PPVPN user networks to the            service provider network.Fang                         Informational                     [Page 39]

RFC 4111                PPVPN Security Framework               July 2005         c. Protection against worms and probes originated in the PPVPN            user networks, sent toward the service provider network.   17. Is the approach subject to any approach-specific vulnerabilities       not specifically addressed by this template?  If so, describe the       defense or mitigation, if any, that the approach provides for       each.10.  Security Considerations   Security considerations constitute the sole subject of this memo and   hence are discussed throughout.  Here we recap what has been   presented and explain at a very high level the role of each type of   consideration in an overall secure PPVPN system.  The document   describes a number of potential security threats.  Some of these   threats have already been observed occurring in running networks;   others are largely theoretical at this time.   DoS attacks and intrusion attacks from the Internet against service   provider infrastructure have been seen.  DoS "attacks" (typically not   malicious) have also been seen in which CE equipment overwhelms PE   equipment with high quantities or rates of packet traffic or routing   information.  Operational/provisioning errors are cited by service   providers as one of their prime concerns.   The document describes a variety of defensive techniques that may be   used to counter the suspected threats.  All of the techniques   presented involve mature and widely implemented technologies that are   practical to implement.   The document describes the importance of detecting, monitoring, and   reporting both successful and unsuccessful attacks.  These activities   are essential for "understanding one's enemy", mobilizing new   defenses, and obtaining metrics about how secure the PPVPN service   is.  As such, they are vital components of any complete PPVPN   security system.   The document evaluates PPVPN security requirements from a customer   perspective and from a service provider perspective.  These sections   re-evaluate the identified threats from the perspectives of the   various stakeholders and are meant to assist equipment vendors and   service providers, who must ultimately decide what threats to protect   against in any given equipment or service offering.   Finally, the document includes a template for use by authors of PPVPN   technical solutions for evaluating how those solutions measure up   against the security considerations presented in this memo.Fang                         Informational                     [Page 40]

RFC 4111                PPVPN Security Framework               July 200511.  Contributors   The following people made major contributions to writing this   document:  Michael Behringer, Ross Callon, Fabio Chiussi, Jeremy De   Clerque, Paul Hitchen, and Paul Knignt.   Michael Behringer   Cisco   Village d'Entreprises Green Side,  Phone: +33.49723-2652   400, Avenue Roumanille, Bat. T 3   EMail: mbehring@cisco.com   06410 Biot, Sophia Antipolis   France   Ross Callon   Juniper Networks   10 Technology Park Drive           Phone: 978-692-6724   Westford, MA  01886                EMail: rcallon@juniper.net   Fabio Chiussi                      Phone: 1 978 367-8965   Airvana                            EMail: fabio@airvananet.com   19 Alpha Road   Chelmsford, Massachusetts 01824   Jeremy De Clercq   Alcatel   Fr. Wellesplein 1, 2018 Antwerpen  EMail: jeremy.de_clercq@alcatel.be   Belgium   Mark Duffy   Sonus Networks   250 Apollo Drive                   Phone: 1 978-614-8748   Chelmsford, MA 01824               EMail: mduffy@sonusnet.com   Paul Hitchen   BT   BT Adastral Park   Martlesham Heath                   Phone: 44-1473-606-344   Ipswich IP53RE                     EMail: paul.hitchen@bt.com   UK   Paul Knight   Nortel   600 Technology Park Drive          Phone: 978-288-6414   Billerica, MA 01821                EMail: paul.knight@nortel.comFang                         Informational                     [Page 41]

RFC 4111                PPVPN Security Framework               July 200512.  Acknowledgement   The author and contributors would also like to acknowledge the   helpful comments and suggestions from Paul Hoffman, Eric Gray, Ron   Bonica, Chris Chase, Jerry Ash, and Stewart Bryant.13.  Normative References   [RFC1918]    Rekhter, Y., Moskowitz, B., Karrenberg, D., de Groot,                G., and E. Lear, "Address Allocation for Private                Internets",BCP 5,RFC 1918, February 1996.   [RFC2246]    Dierks, T. and C. Allen, "The TLS Protocol Version 1.0",RFC 2246, January 1999.   [RFC2401]    Kent, S. and R. Atkinson, "Security Architecture for the                Internet Protocol",RFC 2401, November 1998.   [RFC2402]    Kent, S. and R. Atkinson, "IP Authentication Header",RFC 2402, November 1998.   [RFC2406]    Kent, S. and R. Atkinson, "IP Encapsulating Security                Payload (ESP)",RFC 2406, November 1998.   [RFC2407]    Piper, D., "The Internet IP Security Domain of                Interpretation for ISAKMP",RFC 2407, November 1998.   [RFC2661]    Townsley, W., Valencia, A., Rubens, A., Pall, G., Zorn,                G., and B. Palter, "Layer Two Tunneling Protocol                "L2TP"",RFC 2661, August 1999.   [RFC2865]    Rigney, C., Willens, S., Rubens, A., and W. Simpson,                "Remote Authentication Dial In User Service (RADIUS)",RFC 2865, June 2000.   [RFC3588]    Calhoun, P., Loughney, J., Guttman, E., Zorn, G., and J.                Arkko, "Diameter Base Protocol",RFC 3588, September                2003.   [RFC3602]    Frankel, S., Glenn, R., and S. Kelly, "The AES-CBC                Cipher Algorithm and Its Use with IPsec",RFC 3602,                September 2003.Fang                         Informational                     [Page 42]

RFC 4111                PPVPN Security Framework               July 2005   [STD62]      Harrington, D., Presuhn, R., and B. Wijnen, "An                Architecture for Describing Simple Network Management                Protocol (SNMP) Management Frameworks", STD 62,RFC3411, December 2002.                Case, J., Harrington, D., Presuhn, R., and B. Wijnen,                "Message Processing and Dispatching for the Simple                Network Management Protocol (SNMP)", STD 62,RFC 3412,                December 2002.                Levi, D., Meyer, P., and B. Stewart, "Simple Network                Management Protocol (SNMP) Applications", STD 62,RFC3413, December 2002.                Blumenthal, U. and B. Wijnen, "User-based Security Model                (USM) for version 3 of the Simple Network Management                Protocol (SNMPv3)", STD 62,RFC 3414, December 2002.                Wijnen, B., Presuhn, R., and K. McCloghrie, "View-based                Access Control Model (VACM) for the Simple Network                Management Protocol (SNMP)", STD 62,RFC 3415, December                2002.                Presuhn, R., "Version 2 of the Protocol Operations for                the Simple Network Management Protocol (SNMP)", STD 62,RFC 3416, December 2002.                Presuhn, R., "Transport Mappings for the Simple Network                Management Protocol (SNMP)", STD 62,RFC 3417, December                2002.                Presuhn, R., "Management Information Base (MIB) for the                Simple Network Management Protocol (SNMP)", STD 62,RFC3418, December 2002.   [STD8]       Postel, J. and J. Reynolds, "Telnet Protocol                Specification", STD 8,RFC 854, May 1983.14.  Informative References   [RFC2104]    Krawczyk, H., Bellare, M., and R. Canetti, "HMAC:                Keyed-Hashing for Message Authentication",RFC 2104,                February 1997.   [RFC2411]    Thayer, R., Doraswamy, N., and R. Glenn, "IP Security                Document Roadmap",RFC 2411, November 1998.Fang                         Informational                     [Page 43]

RFC 4111                PPVPN Security Framework               July 2005   [RFC3174]    Eastlake 3rd, D. and P. Jones, "US Secure Hash Algorithm                1 (SHA1)",RFC 3174, September 2001.   [RFC3631]    Bellovin, S., Schiller, J., and C. Kaufman, "Security                Mechanisms for the Internet",RFC 3631, December 2003.   [RFC3889]    Barbir, A., Murphy, S., and Y. Yang, "Generic Threats to                Routing Protocols",RFC 3889, October 2004.   [RFC4026]    Andersson, L. and T. Madsen, "Provider Provisioned                Virtual Private Network (VPN) Terminology",RFC 4026,                March 2005.   [RFC4031]    Carugi, M. and D. McDysan, Eds., "Service Requirements                for Layer 3 Provider Provisioned Virtual Private                Networks (PPVPNs)",RFC 4031, April 2005.   [RFC4110]    Callon, R. and M. Suzuki, "A Framework for Layer 3                Provider Provisioned Virtual Private Networks",RFC4110, July 2005.Author's Address   Luyuan Fang   AT&T Labs.   200 Laurel Avenue, Room C2-3B35   Middletown, NJ 07748   Phone: 732-420-1921   EMail: luyuanfang@att.comFang                         Informational                     [Page 44]

RFC 4111                PPVPN Security Framework               July 2005Full Copyright Statement   Copyright (C) The Internet Society (2005).   This document is subject to the rights, licenses and restrictions   contained inBCP 78, and except as set forth therein, the authors   retain all their rights.   This document and the information contained herein are provided on an   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET   ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,   INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE   INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.Intellectual Property   The IETF takes no position regarding the validity or scope of any   Intellectual Property Rights or other rights that might be claimed to   pertain to the implementation or use of the technology described in   this document or the extent to which any license under such rights   might or might not be available; nor does it represent that it has   made any independent effort to identify any such rights.  Information   on the procedures with respect to rights in RFC documents can be   found inBCP 78 andBCP 79.   Copies of IPR disclosures made to the IETF Secretariat and any   assurances of licenses to be made available, or the result of an   attempt made to obtain a general license or permission for the use of   such proprietary rights by implementers or users of this   specification can be obtained from the IETF on-line IPR repository athttp://www.ietf.org/ipr.   The IETF invites any interested party to bring to its attention any   copyrights, patents or patent applications, or other proprietary   rights that may cover technology that may be required to implement   this standard.  Please address the information to the IETF at ietf-   ipr@ietf.org.Acknowledgement   Funding for the RFC Editor function is currently provided by the   Internet Society.Fang                         Informational                     [Page 45]