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+Internet Engineering Task Force (IETF)                           T. Graf
+Request for Comments: 9487                                      Swisscom
+Category: Standards Track                                      B. Claise
+ISSN: 2070-1721                                                   Huawei
+                                                             P. Francois
+                                                               INSA-Lyon
+                                                           November 2023
+
+
+ Export of Segment Routing over IPv6 Information in IP Flow Information
+                             Export (IPFIX)
+
+Abstract
+
+   This document introduces new IP Flow Information Export (IPFIX)
+   Information Elements (IEs) to identify a set of information related
+   to Segment Routing over IPv6 (SRv6) such as data contained in a
+   Segment Routing Header (SRH), the SRv6 control plane, and the SRv6
+   Endpoint behavior that traffic is being forwarded with.
+
+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/rfc9487.
+
+Copyright Notice
+
+   Copyright (c) 2023 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.  Terminology
+   3.  New IPFIX IPv6 SRH Information Elements
+   4.  Sample Use Cases
+   5.  IANA Considerations
+     5.1.  IPFIX Information Elements Registry
+       5.1.1.  srhFlagsIPv6
+       5.1.2.  srhTagIPv6
+       5.1.3.  srhSegmentIPv6
+       5.1.4.  srhActiveSegmentIPv6
+       5.1.5.  srhSegmentIPv6BasicList
+       5.1.6.  srhSegmentIPv6ListSection
+       5.1.7.  srhSegmentsIPv6Left
+       5.1.8.  srhIPv6Section
+       5.1.9.  srhIPv6ActiveSegmentType
+       5.1.10. srhSegmentIPv6LocatorLength
+       5.1.11. srhSegmentIPv6EndpointBehavior
+     5.2.  New IPFIX IPv6 SRH Segment Type (Value 500) Subregistry
+   6.  Operational Considerations
+     6.1.  SRv6 Segment List
+     6.2.  Compressed SRv6 Segment List Decomposition
+   7.  Security Considerations
+   8.  References
+     8.1.  Normative References
+     8.2.  Informative References
+   Appendix A.  IPFIX Encoding Examples
+     A.1.  Three Observed SRH Headers and Their Routing Protocols
+       A.1.1.  Template Record and Data Set with Segment Basic List
+       A.1.2.  Template Record and Data Set with Segment List Section
+       A.1.3.  Template Record and Data Set with SRH Section
+     A.2.  Options Template Record and Data Set for SRv6 Segment
+           Endpoint Behavior and Locator Length
+   Acknowledgements
+   Authors' Addresses
+
+1.  Introduction
+
+   A dedicated Routing Extension Header, called "Segment Routing Header
+   (SRH)", is defined in [RFC8754] for use of Segment Routing over IPv6
+   (SRv6) data plane.
+
+   Also, three routing protocol extensions, OSPFv3 [OSPFV3-SRV6-EXT],
+   IS-IS [RFC9352], and BGP Prefix Segment Identifiers (Prefix-SIDs)
+   [RFC8669]; the Path Computation Element Communication Protocol (PCEP)
+   Extension [PCEP-SRV6-EXT]; and the Segment Routing Policy [RFC9256]
+   are defined to propagate Segment Identifiers (SIDs).
+
+   SRv6 Segment Endpoint behaviors describe how packets should be
+   processed by SRv6 Segment Endpoint Nodes.  Such behaviors are defined
+   in [RFC8986].
+
+   This document specifies eleven new IPFIX Information Elements (IEs)
+   and one new subregistry within the "IPFIX Information Elements"
+   registry [RFC7012], for SRv6 purposes.
+
+   These IEs are used to export the SRv6 active segment and its control
+   plane protocol, the SRv6 Segment List, the next SRv6 node and its
+   type, and the numbers of SRv6 segments left.
+
+   Some examples are provided in Appendix A.
+
+2.  Terminology
+
+   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.
+
+   This document makes use of the terms defined in [RFC7011], [RFC8402],
+   and [RFC8754].
+
+   The following terms are used as defined in [RFC7011]:
+
+   *  IPFIX
+
+   *  IPFIX Information Elements
+
+   *  Template
+
+   *  Template Record
+
+   *  Options Template
+
+   *  Options Template Record
+
+   *  Data Record
+
+   *  Data Set
+
+   The following terms are used as defined in [RFC8402]:
+
+   *  Segment Routing (SR)
+
+   *  Segment
+
+   *  Segment List
+
+   *  Active Segment
+
+   *  Segment Identifier (SID)
+
+   *  SRv6
+
+   *  SRv6 SID
+
+   The following terms are used as defined in [RFC8754]:
+
+   *  Segment Routing Header (SRH)
+
+   *  SR Source Node
+
+   *  Transit Node
+
+   *  SR Segment Endpoint Node
+
+   *  Reduced SRH
+
+   *  Segments Left
+
+   *  Last Entry
+
+3.  New IPFIX IPv6 SRH Information Elements
+
+   This section specifies the new IPFIX IPv6 SRH IEs.
+
+   srhFlagsIPv6
+      The 8-bit Flags field defined in the SRH (Section 2 of [RFC8754]).
+
+   srhTagIPv6
+      The 16-bit Tag field defined in the SRH (Section 2 of [RFC8754]).
+      A tag is used to mark a packet as part of a class or group of
+      packets sharing the same set of properties.
+
+   srhSegmentIPv6
+      The 128-bit IPv6 address that represents an SRv6 segment.
+
+   srhActiveSegmentIPv6
+      The 128-bit IPv6 address that represents the active SRv6 segment.
+
+   srhSegmentIPv6BasicList
+      The ordered basicList [RFC6313] of zero or more 128-bit IPv6
+      addresses in the SRH that represents the SRv6 Segment List.  As
+      specified in Section 2 of [RFC8754], the Segment List is encoded
+      starting from the last segment of the SR Policy.  That is, the
+      first element of the Segment List (Segment List[0]) contains the
+      last segment of the SR Policy, the second element contains the
+      penultimate segment of the SR Policy, and so on.
+
+   srhSegmentIPv6ListSection
+      The SRH Segment List as defined in Section 2 of [RFC8754] as a
+      series of octets in IPFIX.
+
+   srhSegmentsIPv6Left
+      The 8-bit unsigned integer that defines the number of segments
+      remaining to reach the end of the Segment List from the SRH, as
+      specified by the "Segments Left" field in Section 4.4 of [RFC8200]
+      and as mentioned in the SRH part of Section 2 of [RFC8754].
+
+   srhIPv6Section
+      The SRH and its TLVs as specified in Section 2 of [RFC8754] as a
+      series of octets in IPFIX.
+
+   srhIPv6ActiveSegmentType
+      The designator of the routing protocol or PCEP extension where the
+      active SRv6 segment has been learned from.
+
+   srhSegmentIPv6LocatorLength
+      The length of the SRH segment IPv6 locator specified as the number
+      of significant bits.  Together with srhSegmentIPv6, it enables the
+      calculation of the SRv6 Locator.
+
+   srhSegmentIPv6EndpointBehavior
+      The 16-bit unsigned integer that represents an SRv6 Endpoint
+      behavior as per Section 4 of [RFC8986].
+
+   Note that the srhSegmentIPv6, srhSegmentIPv6LocatorLength, and
+   srhSegmentIPv6EndpointBehavior IPFIX IEs are generic fields to be
+   used in the context of IPFIX Options Templates or IPFIX Structured
+   Data [RFC6313].
+
+4.  Sample Use Cases
+
+   The IPFIX IEs srhSegmentIPv6BasicList (496) or alternatively
+   srhSegmentIPv6ListSection (497), srhActiveSegmentIPv6 (495),
+   srhSegmentsIPv6Left (498), srhIPv6ActiveSegmentType (500), and
+   forwardingStatus (89) [RFC7270] [IANA-IPFIX] as well as some existing
+   counter information [IANA-IPFIX] provide answers to the following
+   questions (amongst others):
+
+   *  How many packets steered with an SR policy are forwarded or
+      dropped using SRv6 in a network?
+
+   *  If dropped, for which reasons?
+
+   *  What is the current active segment and its associated control
+      plane protocol?
+
+   *  What is the SRv6 Segment List?
+
+   *  What is the next SRv6 node and its type?
+
+   *  How many SRv6 segments are left?
+
+5.  IANA Considerations
+
+5.1.  IPFIX Information Elements Registry
+
+   IANA has added the following new IEs to the "IPFIX Information
+   Elements" registry [RFC7012] at [IANA-IPFIX]:
+
+              +===========+================================+
+              | ElementID | Name                           |
+              +===========+================================+
+              | 492       | srhFlagsIPv6                   |
+              +-----------+--------------------------------+
+              | 493       | srhTagIPv6                     |
+              +-----------+--------------------------------+
+              | 494       | srhSegmentIPv6                 |
+              +-----------+--------------------------------+
+              | 495       | srhActiveSegmentIPv6           |
+              +-----------+--------------------------------+
+              | 496       | srhSegmentIPv6BasicList        |
+              +-----------+--------------------------------+
+              | 497       | srhSegmentIPv6ListSection      |
+              +-----------+--------------------------------+
+              | 498       | srhSegmentsIPv6Left            |
+              +-----------+--------------------------------+
+              | 499       | srhIPv6Section                 |
+              +-----------+--------------------------------+
+              | 500       | srhIPv6ActiveSegmentType       |
+              +-----------+--------------------------------+
+              | 501       | srhSegmentIPv6LocatorLength    |
+              +-----------+--------------------------------+
+              | 502       | srhSegmentIPv6EndpointBehavior |
+              +-----------+--------------------------------+
+
+               Table 1: IPFIX Information Elements Registry
+
+5.1.1.  srhFlagsIPv6
+
+   ElementID:  492
+   Name:  srhFlagsIPv6
+   Abstract Data Type:  unsigned8
+   Data Type Semantics:  flags
+   Description:  The 8-bit Flags field defined in the SRH (Section 2 of
+      [RFC8754]).  Assigned flags and their meanings are provided in the
+      "Segment Routing Header Flags" IANA registry.
+   Additional Information:  See the assignments in the "Segment Routing
+      Header Flags" registry at <https://www.iana.org/assignments/
+      ipv6-parameters>.  See also [RFC8754] for the SRH specification.
+   Reference:  RFC 9487
+
+5.1.2.  srhTagIPv6
+
+   ElementID:  493
+   Name:  srhTagIPv6
+   Abstract Data Type:  unsigned16
+   Data Type Semantics:  identifier
+   Description:  The 16-bit Tag field defined in the SRH (Section 2 of
+      [RFC8754]).  A tag is used to mark a packet as part of a class or
+      group of packets sharing the same set of properties.
+   Additional Information:  See Section 2 of [RFC8754] for more details
+      about the Tag.
+   Reference:  RFC 9487
+
+5.1.3.  srhSegmentIPv6
+
+   ElementID:  494
+   Name:  srhSegmentIPv6
+   Abstract Data Type:  ipv6Address
+   Data Type Semantics:  default
+   Description:  The 128-bit IPv6 address that represents an SRv6
+      segment.
+   Additional Information:  Specified in Section 1 of [RFC8402] and
+      mentioned in "Segment List" in Section 2 of [RFC8754].
+   Reference:  RFC 9487
+
+5.1.4.  srhActiveSegmentIPv6
+
+   ElementID:  495
+   Name:  srhActiveSegmentIPv6
+   Abstract Data Type:  ipv6Address
+   Data Type Semantics:  default
+   Description:  The 128-bit IPv6 address that represents the active
+      SRv6 segment.
+   Additional Information:  See Section 2 of [RFC8402] for the
+      definition of "active segment".
+   Reference:  RFC 9487
+
+5.1.5.  srhSegmentIPv6BasicList
+
+   ElementID:  496
+   Name:  srhSegmentIPv6BasicList
+   Abstract Data Type:  basicList
+   Data Type Semantics:  list
+   Description:  The ordered basicList [RFC6313] of zero or more 128-bit
+      IPv6 addresses in the SRH that represents the SRv6 Segment List.
+      As specified in Section 2 of [RFC8754], the Segment List is
+      encoded starting from the last segment of the SR Policy.  That is,
+      the first element of the Segment List (Segment List[0]) contains
+      the last segment of the SR Policy, the second element contains the
+      penultimate segment of the SR Policy, and so on.
+   Additional Information:  See Section 2 of [RFC8754] for more details
+      about the SRv6 Segment List.
+   Reference:  RFC 9487
+
+5.1.6.  srhSegmentIPv6ListSection
+
+   ElementID:  497
+   Name:  srhSegmentIPv6ListSection
+   Abstract Data Type:  octetArray
+   Data Type Semantics:  default
+   Description:  The SRv6 Segment List as defined in Section 2 of
+      [RFC8754] as a series of octets in IPFIX.
+   Additional Information:  See Section 2 of [RFC8754] for more details
+      about the SRv6 Segment List.
+   Reference:  RFC 9487
+
+5.1.7.  srhSegmentsIPv6Left
+
+   ElementID:  498
+   Name:  srhSegmentsIPv6Left
+   Abstract Data Type:  unsigned8
+   Data Type Semantics:  quantity
+   Description:  The 8-bit unsigned integer defining the number of
+      segments remaining to reach the end of the Segment List from the
+      SRH.
+   Additional Information:  Specified by the "Segments Left" field in
+      Section 4.4 of [RFC8200] and mentioned in Section 2 of [RFC8754].
+   Reference:  RFC 9487
+
+5.1.8.  srhIPv6Section
+
+   ElementID:  499
+   Name:  srhIPv6Section
+   Abstract Data Type:  octetArray
+   Data Type Semantics:  default
+   Description:  The SRH and its TLVs as defined in Section 2 of
+      [RFC8754] as a series of octets in IPFIX.
+   Additional Information:  See Section 2 of [RFC8754] for more details
+      about the structure of an SRH.
+   Reference:  RFC 9487
+
+5.1.9.  srhIPv6ActiveSegmentType
+
+   ElementID:  500
+   Name:  srhIPv6ActiveSegmentType
+   Abstract Data Type:  unsigned8
+   Data Type Semantics:  identifier
+   Description:  The designator of the routing protocol or PCEP
+      extension where the active SRv6 segment has been learned from.
+      Values for this Information Element are listed in the "IPFIX IPv6
+      SRH Segment Type (Value 500)" subregistry.
+   Additional Information:  See the assigned types in the "IPFIX IPv6
+      SRH Segment (Value 500)" registry at
+      <https://www.iana.org/assignments/ipfix>.
+   Reference:  RFC 9487
+
+5.1.10.  srhSegmentIPv6LocatorLength
+
+   ElementID:  501
+   Name:  srhSegmentIPv6LocatorLength
+   Data Type Semantics:  default
+   Description:  The length of the SRH segment IPv6 locator specified as
+      the number of significant bits.  Together with srhSegmentIPv6, it
+      enables the calculation of the SRv6 Locator.
+   Additional Information:  See Section 3.1 of [RFC8986] for more
+      details about the SID format.
+   Reference:  RFC 9487
+
+5.1.11.  srhSegmentIPv6EndpointBehavior
+
+   ElementID:  502
+   Name:  srhSegmentIPv6EndpointBehavior
+   Abstract Data Type:  unsigned16
+   Data Type Semantics:  identifier
+   Description:  The 16-bit unsigned integer that represents an SRv6
+      Endpoint behavior as per Section 4 of [RFC8986].  Assigned values
+      and their meanings are provided in the "SRv6 Endpoint Behaviors"
+      registry.
+   Additional Information:  See the assigned behaviors in the "SRv6
+      Endpoint Behaviors" registry at <https://www.iana.org/assignments/
+      segment-routing>.  See Section 4 of [RFC8986] for more details
+      about the processing of endpoint behaviors.
+   Reference:  RFC 9487
+
+5.2.  New IPFIX IPv6 SRH Segment Type (Value 500) Subregistry
+
+   IANA has created a new subregistry called "IPFIX IPv6 SRH Segment
+   Type (Value 500)" under the "IPFIX Information Elements" registry
+   [RFC7012] at [IANA-IPFIX].
+
+   The allocation policy of this new subregistry is Expert Review
+   (Section 4.5 of [RFC8126]).
+
+   The designated experts for this registry should be familiar with SRH.
+   The guidelines that are being followed by the designated experts for
+   the "IPFIX Information Elements" registry should be followed for this
+   subregistry.  In particular, criteria that should be applied by the
+   designated experts include determining whether the proposed
+   registration duplicates existing entries and whether the registration
+   description is clear and fits the purpose of this registry.  Within
+   the review period, the designated experts will either approve or deny
+   the registration request, communicating this decision to IANA.
+   Denials should include an explanation and, if applicable, suggestions
+   as to how to make the request successful.
+
+   Initial values in the registry are defined in Table 2.
+
+    +=======+==========================+=============================+
+    | Value | Description              | Reference                   |
+    +=======+==========================+=============================+
+    | 0     | Unknown                  | RFC 9487                    |
+    +-------+--------------------------+-----------------------------+
+    | 1     | Segment Routing Policy   | RFC 9487, [RFC9256]         |
+    +-------+--------------------------+-----------------------------+
+    | 2     | Path Computation Element | RFC 9487, [PCEP-SRV6-EXT]   |
+    +-------+--------------------------+-----------------------------+
+    | 3     | OSPFv3 Segment Routing   | RFC 9487, [OSPFV3-SRV6-EXT] |
+    +-------+--------------------------+-----------------------------+
+    | 4     | IS-IS Segment Routing    | RFC 9487, [RFC9352]         |
+    +-------+--------------------------+-----------------------------+
+    | 5     | BGP Segment Routing      | RFC 9487, [RFC8669]         |
+    |       | Prefix-SID               |                             |
+    +-------+--------------------------+-----------------------------+
+
+       Table 2: IPFIX IPv6 SRH Segment Type (Value 500) Subregistry
+
+6.  Operational Considerations
+
+6.1.  SRv6 Segment List
+
+   The zero or more 128-bit IPv6 addresses in the SRH [RFC8754] can be
+   exported in two different ways, with two different IPFIX IEs:
+
+   *  srhSegmentIPv6BasicList
+
+   *  srhSegmentIPv6ListSection
+
+   The srhSegmentIPv6BasicList encodes the SRv6 Segment List with a
+   basicList, specified in the IPFIX Structured Data [RFC6313].  This
+   encoding is an advantage for data collection since the different IPv6
+   addresses are already structured as a list, without the need of post-
+   processing.  However, this method requires some extra processing on
+   the exporter to realize the basicList data mapping.
+
+   The srhSegmentIPv6ListSection, on the other hand, encodes the list of
+   IPv6 addresses as an octetArray.  This doesn't impose any data flow
+   manipulation on the exporter, facilitating the immediate export.
+   However, the data collection MUST be able to decode the IPv6
+   addresses according to the SR specifications.  Compared to the
+   srhSegmentIPv6BasicList, the srhSegmentIPv6ListSection flow records
+   length is slightly reduced.
+
+   It is not expected that an exporter would support both
+   srhSegmentIPv6BasicList and srhSegmentIPv6ListSection at the same
+   time.
+
+6.2.  Compressed SRv6 Segment List Decomposition
+
+   The SRv6 Segment List in the IPFIX IEs srhSegmentIPv6BasicList,
+   srhSegmentIPv6ListSection, and destinationIPv6Address could contain
+   compressed-SID containers as described in [SRV6-SRH-COM].  The SR
+   Endpoint Flavors, as described in Section 4 of [SRV6-SRH-COM], define
+   new flavors for SID Endpoint behaviors and determine wherever the
+   Segment List encoding is compressed, along with the flavor.  The SID
+   Locator, as described in Section 3.1 of [RFC8986], determines the
+   common most significant bits.  By using described information from
+   srhSegmentIPv6EndpointBehavior and srhSegmentIPv6LocatorLength, the
+   compressed-SID containers can be decoded at the data collection.
+
+7.  Security Considerations
+
+   There are no additional security considerations regarding allocation
+   of these new IPFIX IEs compared to [RFC7012].
+
+   The IEs described in this document export provider plane data metrics
+   on how packets are being forwarded within an SRv6 network.
+   Applications and operators using the IEs described in this document
+   must evaluate the sensitivity of this information in their
+   implementation context and apply the data-at-rest storage guidance in
+   Section 11.8 of [RFC7011] as appropriate.
+
+8.  References
+
+8.1.  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>.
+
+   [RFC6313]  Claise, B., Dhandapani, G., Aitken, P., and S. Yates,
+              "Export of Structured Data in IP Flow Information Export
+              (IPFIX)", RFC 6313, DOI 10.17487/RFC6313, July 2011,
+              <https://www.rfc-editor.org/info/rfc6313>.
+
+   [RFC7011]  Claise, B., Ed., Trammell, B., Ed., and P. Aitken,
+              "Specification of the IP Flow Information Export (IPFIX)
+              Protocol for the Exchange of Flow Information", STD 77,
+              RFC 7011, DOI 10.17487/RFC7011, September 2013,
+              <https://www.rfc-editor.org/info/rfc7011>.
+
+   [RFC7012]  Claise, B., Ed. and B. Trammell, Ed., "Information Model
+              for IP Flow Information Export (IPFIX)", RFC 7012,
+              DOI 10.17487/RFC7012, September 2013,
+              <https://www.rfc-editor.org/info/rfc7012>.
+
+   [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>.
+
+   [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>.
+
+   [RFC8200]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
+              (IPv6) Specification", STD 86, RFC 8200,
+              DOI 10.17487/RFC8200, July 2017,
+              <https://www.rfc-editor.org/info/rfc8200>.
+
+   [RFC8754]  Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J.,
+              Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header
+              (SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020,
+              <https://www.rfc-editor.org/info/rfc8754>.
+
+8.2.  Informative References
+
+   [IANA-IPFIX]
+              IANA, "IP Flow Information Export (IPFIX) Entities",
+              <https://www.iana.org/assignments/ipfix>.
+
+   [OSPFV3-SRV6-EXT]
+              Li, Z., Hu, Z., Talaulikar, K., Ed., and P. Psenak,
+              "OSPFv3 Extensions for SRv6", Work in Progress, Internet-
+              Draft, draft-ietf-lsr-ospfv3-srv6-extensions-15, 21 June
+              2023, <https://datatracker.ietf.org/doc/html/draft-ietf-
+              lsr-ospfv3-srv6-extensions-15>.
+
+   [PCEP-SRV6-EXT]
+              Li, C., Kaladharan, P., Sivabalan, S., Koldychev, M., and
+              Y. Zhu, "Path Computation Element Communication Protocol
+              (PCEP) Extensions for Segment Routing leveraging the IPv6
+              dataplane", Work in Progress, Internet-Draft, draft-ietf-
+              pce-segment-routing-ipv6-20, 8 September 2023,
+              <https://datatracker.ietf.org/doc/html/draft-ietf-pce-
+              segment-routing-ipv6-20>.
+
+   [RFC7270]  Yourtchenko, A., Aitken, P., and B. Claise, "Cisco-
+              Specific Information Elements Reused in IP Flow
+              Information Export (IPFIX)", RFC 7270,
+              DOI 10.17487/RFC7270, June 2014,
+              <https://www.rfc-editor.org/info/rfc7270>.
+
+   [RFC8402]  Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
+              Decraene, B., Litkowski, S., and R. Shakir, "Segment
+              Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
+              July 2018, <https://www.rfc-editor.org/info/rfc8402>.
+
+   [RFC8669]  Previdi, S., Filsfils, C., Lindem, A., Ed., Sreekantiah,
+              A., and H. Gredler, "Segment Routing Prefix Segment
+              Identifier Extensions for BGP", RFC 8669,
+              DOI 10.17487/RFC8669, December 2019,
+              <https://www.rfc-editor.org/info/rfc8669>.
+
+   [RFC8986]  Filsfils, C., Ed., Camarillo, P., Ed., Leddy, J., Voyer,
+              D., Matsushima, S., and Z. Li, "Segment Routing over IPv6
+              (SRv6) Network Programming", RFC 8986,
+              DOI 10.17487/RFC8986, February 2021,
+              <https://www.rfc-editor.org/info/rfc8986>.
+
+   [RFC9256]  Filsfils, C., Talaulikar, K., Ed., Voyer, D., Bogdanov,
+              A., and P. Mattes, "Segment Routing Policy Architecture",
+              RFC 9256, DOI 10.17487/RFC9256, July 2022,
+              <https://www.rfc-editor.org/info/rfc9256>.
+
+   [RFC9352]  Psenak, P., Ed., Filsfils, C., Bashandy, A., Decraene, B.,
+              and Z. Hu, "IS-IS Extensions to Support Segment Routing
+              over the IPv6 Data Plane", RFC 9352, DOI 10.17487/RFC9352,
+              February 2023, <https://www.rfc-editor.org/info/rfc9352>.
+
+   [SRV6-SRH-COM]
+              Cheng, W., Ed., Filsfils, C., Li, Z., Decraene, B., and F.
+              Clad, Ed., "Compressed SRv6 Segment List Encoding", Work
+              in Progress, Internet-Draft, draft-ietf-spring-srv6-srh-
+              compression-09, 23 October 2023,
+              <https://datatracker.ietf.org/doc/html/draft-ietf-spring-
+              srv6-srh-compression-09>.
+
+Appendix A.  IPFIX Encoding Examples
+
+   This appendix represents three different encodings for the newly
+   introduced IEs, for the example values in Table 3.  The three
+   different encodings use the following IEs, respectively:
+   srhSegmentIPv6BasicList, srhSegmentIPv6ListSection, and
+   srhIPv6Section.
+
+    +========+=======+=====+==============+==========================+
+    | SRH Nr | SRH   | SRH | Active       | Segment List             |
+    |        | Flags | Tag | Segment Type |                          |
+    +========+=======+=====+==============+==========================+
+    | 1      | 0     | 123 | IS-IS [4]    | 2001:db8::1,             |
+    |        |       |     |              | 2001:db8::2, 2001:db8::3 |
+    +--------+-------+-----+--------------+--------------------------+
+    | 2      | 0     | 456 | IS-IS [4]    | 2001:db8::4, 2001:db8::5 |
+    +--------+-------+-----+--------------+--------------------------+
+    | 3      | 0     | 789 | IS-IS [4]    | 2001:db8::6              |
+    +--------+-------+-----+--------------+--------------------------+
+
+         Table 3: Three Observed SRH Headers and Their Associated
+                            Routing Protocols
+
+A.1.  Three Observed SRH Headers and Their Routing Protocols
+
+A.1.1.  Template Record and Data Set with Segment Basic List
+
+   With encoding in Figure 1, the examples in Table 3 are represented
+   with the following IEs, where "=>" is used to indicate which IE is
+   mapped to given information:
+
+   *  SRH Flags => srhFlagsIPv6 (492)
+
+   *  SRH Tag => srhTagIPv6 (493)
+
+   *  Active Segment Type => srhIPv6ActiveSegmentType (500)
+
+   *  Segment List => srhSegmentIPv6BasicList (496)
+
+      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
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |          SET ID = 2           |       Length = 24             |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |      Template ID = 256        |      Field Count = 4          |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |0|     srhFlagsIPv6 = 492      |      Field Length = 1         |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |0|      srhTagIPv6 = 493       |      Field Length = 2         |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |0|srhIPv6ActiveSegmentType= 500|      Field Length = 1         |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |0|srhSegmentIPv6BasicList = 496|      Field Length = 0xFFFF    |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+
+         Figure 1: Template Record with Basic List Encoding Format
+
+   In this example, the Template ID is 256, which will be used in the
+   Data Record.  The field length for srhSegmentIPv6BasicList is 0xFFFF,
+   which means the length of this IE is variable, and the actual length
+   of this IE is indicated by the List Length field in the basicList
+   format as per [RFC6313].
+
+   The data set is represented as follows:
+
+      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
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |         SET ID = 256          |           Length = 136        |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     | srhFlagsIPv6  |        srhTagIPv6 = 123        |srhIPv6Active |
+     | = 0           |                                |SegmentType= 4|
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |      255      |        List Length = 53       |semantic=      |
+     |               |                               |ordered        |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |     srhSegmentIPv6 = 494      |        Field Length = 16      |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |             Segment List[0] = 2001:db8::1                     |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |                              ...                              |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |                              ...                              |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |                              ...                              |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |             Segment List[1] = 2001:db8::2                     |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |                              ...                              |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |                              ...                              |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |                              ...                              |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |             Segment List[2] = 2001:db8::3                     |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |                              ...                              |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |                              ...                              |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |                              ...                              |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     | srhFlagsIPv6  |        srhTagIPv6 = 456       | srhIPv6Active |
+     | = 0           |                               | SegmentType= 4|
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |      255      |        List Length = 37       |semantic=      |
+     |               |                               |ordered        |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |     srhSegmentIPv6 = 494      |        Field Length = 16      |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |             Segment List[0] = 2001:db8::4                     |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |                              ...                              |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |                              ...                              |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |                              ...                              |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |             Segment List[1] = 2001:db8::5  (16 bytes)         |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |                              ...                              |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |                              ...                              |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |                              ...                              |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     | srhFlagsIPv6  |        srhTagIPv6 = 789       | srhIPv6Active |
+     | = 0           |                               | SegmentType= 4|
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |      255      |        List Length = 21       |semantic=      |
+     |               |                               |ordered        |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |     srhSegmentIPv6 = 494      |        Field Length = 16      |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |             Segment List[0] = 2001:db8::6  ...                |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |                              ...                              |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |                              ...                              |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |                              ...                              |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+
+             Figure 2: Data Set Encoding Format for Basic List
+
+A.1.2.  Template Record and Data Set with Segment List Section
+
+   With encoding in Figure 3, the examples in Table 3 are represented
+   with the following IEs, where "=>" is used to indicate which IE is
+   mapped to given information:
+
+   *  SRH Flags => srhFlagsIPv6 (492)
+
+   *  SRH Tag => srhTagIPv6 (493)
+
+   *  Active Segment Type => srhIPv6ActiveSegmentType (500)
+
+   *  Segment List => srhSegmentIPv6ListSection (497)
+
+      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
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |          SET ID = 2           |       Length = 24             |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |      Template ID = 257        |      Field Count = 4          |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |0|     srhFlagsIPv6 = 492      |      Field Length = 1         |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |0|      srhTagIPv6 = 493       |      Field Length = 2         |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |0|srhIPv6ActiveSegmentType= 500|      Field Length = 1         |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |0|srhSegmentIPv6ListSection=497|      Field Length = 0xFFFF    |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+
+    Figure 3: Template Record with Segment List Section Encoding Format
+
+   In this example, the Template ID is 257, which will be used in the
+   Data Record.  The field length for srhSegmentIPv6ListSection in the
+   Template Record is 0xFFFF, which means that the length of this IE is
+   variable: its actual length is encoded in the Data Set. Note that,
+   with an actual length inferior to 255 in the Data Record example, the
+   length field is encoded in 8 bits (Section 7 of [RFC7011]).
+
+   The data can be represented as follows:
+
+      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
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |         SET ID = 257          |           Length = 116        |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     | srhFlagsIPv6  |        srhTagIPv6 = 123       | srhIPv6Active |
+     | = 0           |                               | SegmentType= 4|
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     | Length = 48   |   2001:db8::1                                 |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |                              ...                              |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |                              ...                              |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |                              ...                              |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |      ...      |   2001:db8::2                                 |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |                              ...                              |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |                              ...                              |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |                              ...                              |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |      ...      |   2001:db8::3                                 |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |                              ...                              |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |                              ...                              |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |                              ...                              |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |      ...      | srhFlagsIPv6  |        srhTagIPv6 = 456       |
+     |               | = 0           |                               |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     | srhIPv6Active | Length = 32   |   2001:db8::4                 |
+     | SegmentType= 4|               |                               |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |                              ...                              |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |                              ...                              |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |                              ...                              |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |      ...                      |   2001:db8::5                 |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |                              ...                              |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |                              ...                              |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |                              ...                              |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |      ...                      |srhFlagsIPv6=0 | srhTagIPv6 =  |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |   789         | srhIPv6ActiveSegmentType = 4  | Length = 16   |
+     |               |                               |               |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |                        2001:db8::6 ...                        |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |                              ...                              |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |                              ...                              |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |                              ...                              |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+
+        Figure 4: Data Set Encoding Format for Segment List Section
+
+A.1.3.  Template Record and Data Set with SRH Section
+
+   With encoding in Figure 5, the examples in Table 3 are represented
+   with the following IEs, where "=>" is used to indicate which IE is
+   mapped to given information:
+
+   *  SRH Flags + SRH Tag + Segment List => srhIPv6Section (499)
+
+   *  Active Segment Type => srhIPv6ActiveSegmentType (500)
+
+      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
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |          SET ID = 2           |       Length = 16             |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |      Template ID = 258        |      Field Count = 2          |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |0|srhIPv6ActiveSegmentType= 500|      Field Length = 1         |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |0|    srhIPv6Section = 499     |      Field Length = 0xFFFF    |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+
+         Figure 5: Template Record with SRH Section Encoding Format
+
+   In this example, the Template ID is 258, which will be used in the
+   Data Record.  The field length for srhIPv6Section in the Template
+   Record is 0xFFFF, which means that the length of this IE is variable:
+   its actual length is encoded in the Data Set. Note that, with an
+   actual length inferior to 255 in the Data Record example, the length
+   field is encoded in 8 bits (Section 7 of [RFC7011]).
+
+   The data can be represented as follows:
+
+      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
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |         SET ID = 258          |           Length = (*)        |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |        srhIPv6ActiveSegmentType = 4           |  Length = (*) |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     | Next Header   |  Hdr Ext Len  | Routing Type  | Segments Left |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |  Last Entry   |     Flags     |              Tag              |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |                           2001:db8::1                         |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |                              ...                              |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |                              ...                              |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |                              ...                              |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |                           2001:db8::2                         |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |                              ...                              |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |                              ...                              |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |                              ...                              |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |                           2001:db8::3                         |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |                              ...                              |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |                              ...                              |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |                              ...                              |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     ~          Optional Type Length Value objects (variable)        ~
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |        srhIPv6ActiveSegmentType = 4           |    0xFFFF     |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     | Next Header   |  Hdr Ext Len  | Routing Type  | Segments Left |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |  Last Entry   |     Flags     |              Tag              |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |                           2001:db8::4                         |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |                              ...                              |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |                              ...                              |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |                              ...                              |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |                           2001:db8::5                         |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |                              ...                              |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |                              ...                              |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |                              ...                              |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     ~          Optional Type Length Value objects (variable)        ~
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |        srhIPv6ActiveSegmentType = 4           |    0xFFFF     |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     | Next Header   |  Hdr Ext Len  | Routing Type  | Segments Left |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |  Last Entry   |     Flags     |              Tag              |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |                           2001:db8::6                         |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |                              ...                              |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |                              ...                              |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |                              ...                              |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     ~          Optional Type Length Value objects (variable)        ~
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+
+             Figure 6: Data Set Encoding Format for SRH Section
+
+   (*) The Length must be calculated to include the optional Type Length
+   Value objects.
+
+A.2.  Options Template Record and Data Set for SRv6 Segment Endpoint
+      Behavior and Locator Length
+
+   This appendix provides an SRv6 Endpoint Behavior Options Template
+   example, for the values presented in Table 4.  In the Options
+   Template case, the srhActiveSegmentIPv6 IE is a Scope field.
+
+    +==========+===================+================+================+
+    | Entry Nr | SRH Endpoint IPv6 | SRH Endpoint   | SRH Segment    |
+    |          |                   | Behavior       | Locator Length |
+    +==========+===================+================+================+
+    | 1        | 2001:db8::1       | End [1]        | 48             |
+    +----------+-------------------+----------------+----------------+
+    | 2        | 2001:db8::4       | End with NEXT- | 48             |
+    |          |                   | CSID [43]      |                |
+    +----------+-------------------+----------------+----------------+
+    | 3        | 2001:db8::6       | End.DX6 [16]   | 48             |
+    +----------+-------------------+----------------+----------------+
+
+         Table 4: Three Observed SRv6 Segment Endpoint Behaviors
+
+       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
+    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+    |         Set ID = 3            |          Length = 24          |
+    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+    |       Template ID 259         |        Field Count = 3        |
+    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+    |     Scope Field Count = 1     |0| srhActiveSegmentIPv6 = 495  |
+    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+    |   Scope 1 Field Length = 4    |0|srhSegmentIPv6End.Behav = 502|
+    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+    |       Field Length = 1        |0|srhSegmentIPv6Lo.Length = 501|
+    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+    |       Field Length = 4        |           Padding             |
+    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+
+        Figure 7: Segment Endpoint Behavior Options Template Record
+
+   In this example, the Template ID is 259, which will be used in the
+   Data Record.
+
+   The data set is represented as follows:
+
+      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
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |         SET ID = 259          |           Length = 28         |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |               srhActiveSegmentIPv6 = 2001:db8::1              |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |srhSegmentIPv6EndpointBehavior |srhSegmentIPv6LocatorLength= 48|
+     |= End [1]                      |                               |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |               srhActiveSegmentIPv6 = 2001:db8::4              |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |srhSegmentIPv6EndpointBehavior |srhSegmentIPv6LocatorLength= 48|
+     |= End with NEXT-CSID [43]      |                               |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |               srhActiveSegmentIPv6 = 2001:db8::6              |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |srhSegmentIPv6EndpointBehavior |srhSegmentIPv6LocatorLength= 48|
+     |= End.DX6 [16]                 |                               |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+
+     Figure 8: Data Set Encoding Format for Segment Endpoint Behaviors
+
+   (*) The Length must be calculated to include the optional Type Length
+   Value objects.
+
+Acknowledgements
+
+   The authors would like to thank Yao Liu, Eduard Vasilenko, Bruno
+   Decraene, Mohamed Boucadair, Kamran Raza, Qin Wu, Jim Guichard, Tero
+   Kivinen, Paul Aitken, Roman Danyliw, John Scudder, Éric Vyncke, Erik
+   Kline, Lars Eggert, and Andrew Alston for their reviews and valuable
+   comments.  And thank you to Paolo Lucente and Alex Huang Feng for the
+   implementation and validation.
+
+Authors' Addresses
+
+   Thomas Graf
+   Swisscom
+   Binzring 17
+   CH-8045 Zurich
+   Switzerland
+   Email: thomas.graf@swisscom.com
+
+
+   Benoit Claise
+   Huawei
+   Email: benoit.claise@huawei.com
+
+
+   Pierre Francois
+   INSA-Lyon
+   Lyon
+   France
+   Email: pierre.francois@insa-lyon.fr