Internet Engineering Task Force (IETF)                           H. SongRequest for Comments: 9326                                     FutureweiCategory: Standards Track                                       B. GafniISSN: 2070-1721                                                   Nvidia                                                            F. Brockners                                                                   Cisco                                                             S. Bhandari                                                             Thoughtspot                                                              T. Mizrahi                                                                  Huawei                                                           November 2022   In Situ Operations, Administration, and Maintenance (IOAM) Direct                               ExportingAbstract   In situ Operations, Administration, and Maintenance (IOAM) is used   for recording and collecting operational and telemetry information.   Specifically, IOAM allows telemetry data to be pushed into data   packets while they traverse the network.  This document introduces a   new IOAM option type (denoted IOAM-Option-Type) called the "IOAM   Direct Export (DEX) Option-Type".  This Option-Type is used as a   trigger for IOAM data to be directly exported or locally aggregated   without being pushed into in-flight data packets.  The exporting   method and format are outside the scope of this document.Status of This Memo   This is an Internet Standards Track document.   This document is a product of the Internet Engineering Task Force   (IETF).  It represents the consensus of the IETF community.  It has   received public review and has been approved for publication by the   Internet Engineering Steering Group (IESG).  Further information on   Internet Standards is available in Section 2 of RFC 7841.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained at   https://www.rfc-editor.org/info/rfc9326.Copyright Notice   Copyright (c) 2022 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject to BCP 78 and the IETF Trust's Legal   Provisions Relating to IETF Documents   (https://trustee.ietf.org/license-info) in effect on the date of   publication of this document.  Please review these documents   carefully, as they describe your rights and restrictions with respect   to this document.  Code Components extracted from this document must   include Revised BSD License text as described in Section 4.e of the   Trust Legal Provisions and are provided without warranty as described   in the Revised BSD License.Table of Contents   1.  Introduction   2.  Conventions     2.1.  Requirements Language     2.2.  Terminology   3.  The Direct Exporting (DEX) IOAM-Option-Type     3.1.  Overview       3.1.1.  DEX Packet Selection       3.1.2.  Responding to the DEX Trigger     3.2.  The DEX Option-Type Format   4.  IANA Considerations     4.1.  IOAM Type     4.2.  IOAM DEX Flags     4.3.  IOAM DEX Extension-Flags   5.  Performance Considerations   6.  Security Considerations   7.  References     7.1.  Normative References     7.2.  Informative References   Appendix A.  Notes about the History of This Document   Acknowledgments   Contributors   Authors' Addresses1.  Introduction   IOAM [RFC9197] is used for monitoring traffic in the network and for   incorporating IOAM data fields (denoted IOAM-Data-Fields) into in-   flight data packets.   IOAM makes use of four possible IOAM-Option-Types, defined in   [RFC9197]: Pre-allocated Trace, Incremental Trace, Proof of Transit   (POT), and Edge-to-Edge.   This document defines a new IOAM-Option-Type called the "IOAM Direct   Export (DEX) Option-Type".  This Option-Type is used as a trigger for   IOAM nodes to locally aggregate and process IOAM data and/or to   export it to a receiving entity (or entities).  Throughout the   document, this functionality is referred to as "collection" and/or   "exporting".  In this context, a "receiving entity" is an entity that   resides within the IOAM domain such as a collector, analyzer,   controller, decapsulating node, or software module in one of the IOAM   nodes.   Note that even though the IOAM-Option-Type is called "Direct Export",   it depends on the deployment whether the receipt of a packet with a   DEX Option-Type leads to the creation of another packet.  Some   deployments might simply use the packet with the DEX Option-Type to   trigger local processing of Operations, Administration, and   Maintenance (OAM) data.  The functionality of this local processing   is not within the scope of this document.2.  Conventions2.1.  Requirements Language   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and   "OPTIONAL" in this document are to be interpreted as described in   BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all   capitals, as shown here.2.2.  Terminology   Abbreviations used in this document:   IOAM:   In situ Operations, Administration, and Maintenance   OAM:    Operations, Administration, and Maintenance [RFC6291]   DEX:    Direct Exporting3.  The Direct Exporting (DEX) IOAM-Option-Type3.1.  Overview   The DEX Option-Type is used as a trigger for collecting IOAM data   locally or exporting it to a receiving entity (or entities).   Specifically, the DEX Option-Type can be used as a trigger for   collecting IOAM data by an IOAM node and locally aggregating it;   thus, this aggregated data can be periodically pushed to a receiving   entity or pulled by a receiving entity on-demand.   This Option-Type is incorporated into data packets by an IOAM   encapsulating node and removed by an IOAM decapsulating node, as   illustrated in Figure 1.  The Option-Type can be read, but not   modified, by transit nodes.  Note that the terms "IOAM encapsulating   node", "IOAM decapsulating node", and "IOAM transit node" are as   defined in [RFC9197].                                      ^                                      |Exported IOAM data                                      |                                      |                                      |                +--------------+------+-------+--------------+                |              |              |              |                |              |              |              |  User      +---+----+     +---+----+     +---+----+     +---+----+  packets   |Encapsu-|     | Transit|     | Transit|     |Decapsu-|  --------->|lating  |====>| Node   |====>| Node   |====>|lating  |---->            |Node    |     | A      |     | B      |     |Node    |            +--------+     +--------+     +--------+     +--------+            Insert DEX       Export         Export       Remove DEX            option and      IOAM data      IOAM data     option and            export data                                  export data                        Figure 1: DEX Architecture   The DEX Option-Type is used as a trigger to collect and/or export   IOAM data.  The trigger applies to transit nodes, the decapsulating   node, and the encapsulating node:   *  An IOAM encapsulating node configured to incorporate the DEX      Option-Type encapsulates the packets (or possibly a subset of the      packets) it forwards with the DEX Option-Type and MAY export and/      or collect the requested IOAM data immediately.  Only IOAM      encapsulating nodes are allowed to add the DEX Option-Type to a      packet.  An IOAM encapsulating node can generate probe packets      that incorporate the DEX Option-Type.  These probe packets can be      generated periodically or on-demand (for example, triggered by the      management plane).  The specification of such probe packets is      outside the scope of this document.   *  A transit node that processes a packet with the DEX Option-Type      MAY export and/or collect the requested IOAM data.   *  An IOAM decapsulating node that processes a packet with the DEX      Option-Type MAY export and/or collect the requested IOAM data and      MUST decapsulate the IOAM header.   As in [RFC9197], the DEX Option-Type can be incorporated into all or   a subset of the traffic that is forwarded by the encapsulating node,   as further discussed in Section 3.1.1.  Moreover, IOAM nodes respond   to the DEX trigger by exporting and/or collecting IOAM data either   for all traversing packets that carry the DEX Option-Type or   selectively only for a subset of these packets, as further discussed   in Section 3.1.2.3.1.1.  DEX Packet Selection   If an IOAM encapsulating node incorporates the DEX Option-Type into   all the traffic it forwards, it may lead to an excessive amount of   exported data, which may overload the network and the receiving   entity.  Therefore, an IOAM encapsulating node that supports the DEX   Option-Type MUST support the ability to incorporate the DEX Option-   Type selectively into a subset of the packets that are forwarded by   the IOAM encapsulating node.   Various methods of packet selection and sampling have been previously   defined, such as [RFC7014] and [RFC5475].  Similar techniques can be   applied by an IOAM encapsulating node to apply DEX to a subset of the   forwarded traffic.   The subset of traffic that is forwarded or transmitted with a DEX   Option-Type SHOULD NOT exceed 1/N of the interface capacity on any of   the IOAM encapsulating node's interfaces.  It is noted that this   requirement applies to the total traffic that incorporates a DEX   Option-Type, including traffic that is forwarded by the IOAM   encapsulating node and probe packets that are generated by the IOAM   encapsulating node.  In this context, N is a parameter that can be   configurable by network operators.  If there is an upper bound, M, on   the number of IOAM transit nodes in any path in the network, then it   is RECOMMENDED to use an N such that N >> M (i.e., N is much greater   than M).  The rationale is that a packet that includes a DEX Option-   Type may trigger an exported packet from each IOAM transit node along   the path for a total of M exported packets.  Thus, if N >> M, then   the number of exported packets is significantly lower than the number   of data packets forwarded by the IOAM encapsulating node.  If there   is no prior knowledge about the network topology or size, it is   RECOMMENDED to use N>100.3.1.2.  Responding to the DEX Trigger   The DEX Option-Type specifies which IOAM-Data-Fields should be   exported and/or collected, as specified in Section 3.2.  As mentioned   above, the data can be locally collected, aggregated, and/or exported   to a receiving entity proactively or on-demand.  If IOAM data is   exported, the format and encapsulation of the packet that contains   the exported data is not within the scope of the current document.   For example, the export format can be based on [IOAM-RAWEXPORT].   An IOAM node that performs DEX-triggered exporting MUST support the   ability to limit the rate of the exported packets.  The rate of   exported packets SHOULD be limited so that the number of exported   packets is significantly lower than the number of packets that are   forwarded by the device.  The exported data rate SHOULD NOT exceed 1/   N of the interface capacity on any of the IOAM node's interfaces.  It   is RECOMMENDED to use N>100.  Depending on the IOAM node's   architecture considerations, the export rate may be limited to a   lower number in order to avoid loading the IOAM node.  An IOAM node   MAY maintain a counter or a set of counters that count the events in   which the IOAM node receives a packet with the DEX Option-Type and   does not collect and/or export data due to the rate limits.   IOAM nodes SHOULD NOT be configured to export packets over a path or   a tunnel that is subject to IOAM direct exporting.  Furthermore, IOAM   encapsulating nodes that can identify a packet as an IOAM exported   packet MUST NOT push a DEX Option-Type into such a packet.  This   requirement is intended to prevent nested exporting and/or exporting   loops.   A transit or decapsulating IOAM node that receives an unknown IOAM-   Option-Type ignores it (as defined in [RFC9197]); specifically, nodes   that do not support the DEX Option-Type ignore it.  As per [RFC9197],   note that a decapsulating node removes the IOAM encapsulation and all   its IOAM-Option-Types.  Specifically, this applies to the case where   one of these options is a (possibly unknown) DEX Option-Type.  The   ability to skip over a (possibly unknown) DEX Option-Type in the   parsing or in the decapsulation procedure is dependent on the   specific encapsulation, which is outside the scope of this document.   For example, when IOAM is encapsulated in IPv6 [IOAM-IPV6-OPTIONS],   the DEX Option-Type is incorporated either in a Hop-by-Hop options   header or in a Destination options header; thus, it can be skipped   using the length field in the options header.3.2.  The DEX Option-Type Format   The format of the DEX Option-Type is depicted in Figure 2.  The   length of the DEX Option-Type is at least 8 octets.  The DEX Option-   Type MAY include one or more optional fields.  The existence of the   optional fields is indicated by the corresponding flags in the   Extension-Flags field.  Two optional fields are defined in this   document: the Flow ID and Sequence Number fields.  Every optional   field MUST be exactly 4 octets long.  Thus, the Extension-Flags field   explicitly indicates the length of the DEX Option-Type.  Defining a   new optional field requires an allocation of a corresponding flag in   the Extension-Flags field, as specified in Section 4.2.       0                   1                   2                   3       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      |        Namespace-ID           |     Flags     |Extension-Flags|      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      |               IOAM-Trace-Type                 |   Reserved    |      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      |                         Flow ID (Optional)                    |      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      |                     Sequence Number  (Optional)               |      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                      Figure 2: DEX Option-Type Format   Namespace-ID:      A 16-bit identifier of the IOAM namespace, as defined in      [RFC9197].   Flags:      An 8-bit field, comprised of 8 1-bit subfields.  Flags are      allocated by IANA, as defined in Section 4.2.   Extension-Flags:      An 8-bit field, comprised of 8 1-bit subfields.  Extension-Flags      are allocated by IANA, as defined in Section 4.3.  Every bit in      the Extension-Flag field that is set to 1 indicates the existence      of a corresponding optional 4-octet field.  An IOAM node that      receives a DEX Option-Type with an unknown flag set to 1 MUST      ignore the corresponding optional field.   IOAM-Trace-Type:      A 24-bit identifier that specifies which IOAM-Data-Fields should      be exported.  The format of this field is as defined in [RFC9197].      Specifically, the bit that corresponds to the Checksum Complement      IOAM-Data-Field SHOULD be assigned to be zero by the IOAM      encapsulating node and ignored by transit and decapsulating nodes.      The reason for this is that the Checksum Complement is intended      for in-flight packet modifications and is not relevant for direct      exporting.   Reserved:      This field MUST be ignored by the receiver.   Optional fields:      The optional fields, if present, reside after the Reserved field.      The order of the optional fields is according to the order of the      respective bits, starting from the most significant bit, that are      enabled in the Extension-Flags field.  Each optional field is 4      octets long.      Flow ID:         An optional 32-bit field representing the flow identifier.  If         the actual Flow ID is shorter than 32 bits, it is zero padded         in its most significant bits.  The field is set at the         encapsulating node.  The Flow ID can be used to correlate the         exported data of the same flow from multiple nodes and from         multiple packets.  Flow ID values are expected to be allocated         in a way that avoids collisions.  For example, random         assignment of Flow ID values can be subject to collisions,         while centralized allocation can avoid this problem.  The         specification of the Flow ID allocation method is not within         the scope of this document.      Sequence Number:         An optional 32-bit sequence number starting from 0 and         incremented by 1 for each packet from the same flow at the         encapsulating node that includes the DEX option.  The Sequence         Number, when combined with the Flow ID, provides a convenient         approach to correlate the exported data from the same user         packet.4.  IANA Considerations4.1.  IOAM Type   The "IOAM Option-Type" registry is defined in Section 7.1 of   [RFC9197].  IANA has allocated the following code point from the   "IOAM Option-Type" registry as follows:   Code Point:  4   Name  IOAM Direct Export (DEX) Option-Type   Description:  Direct exporting   Reference:  This document4.2.  IOAM DEX Flags   IANA has created the "IOAM DEX Flags" registry.  This registry   includes 8 flag bits.  Allocation is based on the "IETF Review"   procedure defined in [RFC8126].   New registration requests MUST use the following template:   Bit:  Desired bit to be allocated in the 8-bit Flags field of the DEX      Option-Type.   Description:  Brief description of the newly registered bit.   Reference:  Reference to the document that defines the new bit.4.3.  IOAM DEX Extension-Flags   IANA has created the "IOAM DEX Extension-Flags" registry.  This   registry includes 8 flag bits.  Bit 0 (the most significant bit) and   bit 1 in the registry are allocated by this document and described in   Section 3.2.  Allocation of the other bits should be performed based   on the "IETF Review" procedure defined in [RFC8126].   Bit 0:  "Flow ID [RFC9326]"   Bit 1:  "Sequence Number [RFC9326]"   New registration requests MUST use the following template:   Bit:  Desired bit to be allocated in the 8-bit Extension-Flags field      of the DEX Option-Type.   Description:  Brief description of the newly registered bit.   Reference:  Reference to the document that defines the new bit.5.  Performance Considerations   The DEX Option-Type triggers IOAM data to be collected and/or   exported packets to be exported to a receiving entity (or entities).   In some cases, this may impact the receiving entity's performance or   the performance along the paths leading to it.   Therefore, the performance impact of these exported packets is   limited by taking two measures: at the encapsulating nodes by   selective DEX encapsulation (Section 3.1.1) and at the transit nodes   by limiting exporting rate (Section 3.1.2).  These two measures   ensure that direct exporting is used at a rate that does not   significantly affect the network bandwidth and does not overload the   receiving entity.  Moreover, it is possible to load balance the   exported data among multiple receiving entities, although the   exporting method is not within the scope of this document.   It should be noted that, in some networks, DEX data may be exported   over an out-of-band network in which a large volume of exported   traffic does not compromise user traffic.  In this case, an operator   may choose to disable the exporting rate limiting.6.  Security Considerations   The security considerations of IOAM in general are discussed in   [RFC9197].  Specifically, an attacker may try to use the   functionality that is defined in this document to attack the network.   An attacker may attempt to overload network devices by injecting   synthetic packets that include the DEX Option-Type.  Similarly, an   on-path attacker may maliciously incorporate the DEX Option-Type into   transit packets or maliciously remove it from packets in which it is   incorporated.   Forcing DEX, either in synthetic packets or in transit packets, may   overload the IOAM nodes and/or the receiving entity (or entities).   Since this mechanism affects multiple devices along the network path,   it potentially amplifies the effect on the network bandwidth, the   storage of the devices that collect the data, and the receiving   entity's load.   The amplification effect of DEX may be worse in wide area networks in   which there are multiple IOAM-Domains.  For example, if DEX is used   in IOAM-Domain 1 for exporting IOAM data to a receiving entity, then   the exported packets of IOAM-Domain 1 can be forwarded through IOAM-   Domain 2, in which they are subject to DEX.  In turn, the exported   packets of IOAM-Domain 2 may be forwarded through another IOAM domain   (or through IOAM-Domain 1); theoretically, this recursive   amplification may continue infinitely.   In order to mitigate the attacks described above, the following   requirements (Section 3) have been defined:   *  Selective DEX (Section 3.1.1) is applied by IOAM encapsulating      nodes in order to limit the potential impact of DEX attacks to a      small fraction of the traffic.   *  Rate limiting of exported traffic (Section 3.1.2) is applied by      IOAM nodes in order to prevent overloading attacks and to      significantly limit the scale of amplification attacks.   *  IOAM encapsulating nodes are required to avoid pushing the DEX      Option-Type into IOAM exported packets (Section 3.1.2), thus      preventing some of the amplification and export loop scenarios.   Although the exporting method is not within the scope of this   document, any exporting method MUST secure the exported data from the   IOAM node to the receiving entity in order to protect the   confidentiality and guarantee the integrity of the exported data.   Specifically, an IOAM node that performs DEX exporting MUST send the   exported data to a pre-configured trusted receiving entity that is in   the same IOAM-Domain as the exporting IOAM node.  Furthermore, an   IOAM node MUST gain explicit consent to export data to a receiving   entity before starting to send exported data.   An attacker may keep track of the information sent in DEX headers as   a means of reconnaissance.  This form of recon can be mitigated to   some extent by careful allocation of the Flow ID and Sequence Number   space in a way that does not compromise privacy aspects, such as   customer identities.   The integrity of the DEX Option-Type can be protected through a   mechanism of the encapsulating protocol.  While [IOAM-DATA-INTEGRITY]   introduces an integrity protection mechanism that protects the   integrity of IOAM-Data-Fields, the DEX Option-Type does not include   IOAM-Data-Fields; therefore, these integrity protection mechanisms   are not applicable to the DEX Option-Type.  As discussed in the   threat analysis of [IOAM-DATA-INTEGRITY], injection or modification   of IOAM-Option-Type headers are threats that are not addressed in   IOAM.   IOAM is assumed to be deployed in a restricted administrative domain,   thus limiting the scope of the threats above and their effect.  This   is a fundamental assumption with respect to the security aspects of   IOAM, as further discussed in [RFC9197].7.  References7.1.  Normative References   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate              Requirement Levels", BCP 14, RFC 2119,              DOI 10.17487/RFC2119, March 1997,              <https://www.rfc-editor.org/info/rfc2119>.   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,              May 2017, <https://www.rfc-editor.org/info/rfc8174>.   [RFC9197]  Brockners, F., Ed., Bhandari, S., Ed., and T. Mizrahi,              Ed., "Data Fields for In Situ Operations, Administration,              and Maintenance (IOAM)", RFC 9197, DOI 10.17487/RFC9197,              May 2022, <https://www.rfc-editor.org/info/rfc9197>.7.2.  Informative References   [IOAM-DATA-INTEGRITY]              Brockners, F., Bhandari, S., Mizrahi, T., and J. Iurman,              "Integrity of In-situ OAM Data Fields", Work in Progress,              Internet-Draft, draft-ietf-ippm-ioam-data-integrity-02, 5              July 2022, <https://datatracker.ietf.org/doc/html/draft-              ietf-ippm-ioam-data-integrity-02>.   [IOAM-IPV6-OPTIONS]              Bhandari, S. and F. Brockners, "In-situ OAM IPv6 Options",              Work in Progress, Internet-Draft, draft-ietf-ippm-ioam-              ipv6-options-09, 11 October 2022,              <https://datatracker.ietf.org/doc/html/draft-ietf-ippm-              ioam-ipv6-options-09>.   [IOAM-RAWEXPORT]              Spiegel, M., Brockners, F., Bhandari, S., and R.              Sivakolundu, "In-situ OAM raw data export with IPFIX",              Work in Progress, Internet-Draft, draft-spiegel-ippm-ioam-              rawexport-06, 21 February 2022,              <https://datatracker.ietf.org/doc/html/draft-spiegel-ippm-              ioam-rawexport-06>.   [POSTCARD-BASED-TELEMETRY]              Song, H., Mirsky, G., Filsfils, C., Abdelsalam, A., Zhou,              T., Li, Z., Graf, T., Mishra, G. S., Shin, J., and K. Lee,              "Marking-based Direct Export for On-path Telemetry", Work              in Progress, Internet-Draft, draft-song-ippm-postcard-              based-telemetry-14, 7 September 2022,              <https://datatracker.ietf.org/doc/html/draft-song-ippm-              postcard-based-telemetry-14>.   [RFC5475]  Zseby, T., Molina, M., Duffield, N., Niccolini, S., and F.              Raspall, "Sampling and Filtering Techniques for IP Packet              Selection", RFC 5475, DOI 10.17487/RFC5475, March 2009,              <https://www.rfc-editor.org/info/rfc5475>.   [RFC6291]  Andersson, L., van Helvoort, H., Bonica, R., Romascanu,              D., and S. Mansfield, "Guidelines for the Use of the "OAM"              Acronym in the IETF", BCP 161, RFC 6291,              DOI 10.17487/RFC6291, June 2011,              <https://www.rfc-editor.org/info/rfc6291>.   [RFC7014]  D'Antonio, S., Zseby, T., Henke, C., and L. Peluso, "Flow              Selection Techniques", RFC 7014, DOI 10.17487/RFC7014,              September 2013, <https://www.rfc-editor.org/info/rfc7014>.   [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for              Writing an IANA Considerations Section in RFCs", BCP 26,              RFC 8126, DOI 10.17487/RFC8126, June 2017,              <https://www.rfc-editor.org/info/rfc8126>.   [RFC9322]  Mizrahi, T., Brockners, F., Bhandari, S., Gafni, B., and              M. Spiegel, "In Situ Operations, Administration, and              Maintanence (IOAM) Loopback and Active Flags", RFC 9322,              DOI 10.17487/RFC9322, November 2022,              <https://www.rfc-editor.org/info/rfc9322>.Appendix A.  Notes about the History of This Document   This document evolved from combining some of the concepts of PBT-I   from [POSTCARD-BASED-TELEMETRY] with immediate exporting from early   versions of [RFC9322].   In order to help correlate and order the exported packets, it is   possible to include the Hop_Lim/Node_ID IOAM-Data-Field in exported   packets.  If the IOAM-Trace-Type [RFC9197] has the Hop_Lim/Node_ID   bit set, then exported packets include the Hop_Lim/Node_ID IOAM-Data-   Field, which contains the TTL/Hop Limit value from a lower layer   protocol.  An alternative approach was considered during the design   of this document, according to which a 1-octet Hop Count field would   be included in the DEX header (presumably by claiming some space from   the Flags field).  The Hop Limit would start from 0 at the   encapsulating node and be incremented by each IOAM transit node that   supports the DEX Option-Type.  In this approach, the Hop Count field   value would also be included in the exported packet.Acknowledgments   The authors thank Martin Duke, Tommy Pauly, Meral Shirazipour, Colin   Perkins, Stephen Farrell, Linda Dunbar, Justin Iurman, Greg Mirsky,   and other members of the IPPM working group for many helpful   comments.Contributors   The Editors would like to recognize the contributions of the   following individuals to this document.   Tianran Zhou   Huawei   156 Beiqing Rd.   Beijing   100095   China   Email: zhoutianran@huawei.com   Zhenbin Li   Huawei   156 Beiqing Rd.   Beijing   100095   China   Email: lizhenbin@huawei.com   Ramesh Sivakolundu   Cisco Systems, Inc.   170 West Tasman Dr.   San Jose, CA 95134   United States of America   Email: sramesh@cisco.comAuthors' Addresses   Haoyu Song   Futurewei   2330 Central Expressway   Santa Clara,  95050   United States of America   Email: haoyu.song@futurewei.com   Barak Gafni   Nvidia   Suite 100   350 Oakmead Parkway   Sunnyvale, CA 94085   United States of America   Email: gbarak@nvidia.com   Frank Brockners   Cisco Systems, Inc.   Hansaallee 249   40549 Duesseldorf   Germany   Email: fbrockne@cisco.com   Shwetha Bhandari   Thoughtspot   3rd Floor, Indiqube Orion, Garden Layout, HSR Layout   24th Main Rd   Bangalore 560 102   Karnataka   India   Email: shwetha.bhandari@thoughtspot.com   Tal Mizrahi   Huawei   8-2 Matam   Haifa 3190501   Israel   Email: tal.mizrahi.phd@gmail.com