RFC 9487

Export of Segment Routing over IPv6 Information in IP Flow Information Export (IPFIX)

📅 published November 2023, from ietf

Export of Segment Routing over IPv6 Information in IP Flow Information Export (IPFIX) 💖

okay bestie, this is RFC 9487 🎀 and it's all about getting SRv6 info exported through IPFIX so you can actually see what's going on in your network 👀. Here's the title block tea ☕: it's a Standards Track document (ISSN 2070-1721) dated November 2023. The authors are T. Graf from Swisscom, B. Claise from Huawei, and P. Francois from INSA-Lyon 🧚. The title block doesn't list any RFCs under "Obsoletes" or "Updates," so this one doesn't obsolete or update anything 🌸.

Abstract ✨

okay so this document adds new IP Flow Information Export (IPFIX) Information Elements (IEs) 🦋. They help you identify stuff about Segment Routing over IPv6 (SRv6), like the data inside 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 went through public review and got approved for publication by the Internet Engineering Steering Group (IESG). If you want more info on Internet Standards, check out Section 2 of RFC 7841 🎀.

For info on the current status of this document, any errata, and how to send feedback, head to https://www.rfc-editor.org/info/rfc9487 🔗.

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) as they stand on the date this document was published. Please read these carefully, because they spell out your rights and restrictions for this document 🙈. Code Components pulled out of this document must include Revised BSD License text, as described in Section 4.e of the Trust Legal Provisions, and they come 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 🦋

okay first things first: a dedicated Routing Extension Header called "Segment Routing Header (SRH)" is defined in [RFC8754] for the SRv6 data plane 💖.

Then there are three routing protocol extensions 🌈: OSPFv3 [OSPFV3-SRV6-EXT], IS-IS [RFC9352], and BGP Prefix Segment Identifiers (Prefix-SIDs) [RFC8669]. On top of those, the Path Computation Element Communication Protocol (PCEP) Extension [PCEP-SRV6-EXT] and the Segment Routing Policy [RFC9256] are also defined to propagate Segment Identifiers (SIDs) ✨.

SRv6 Segment Endpoint behaviors describe how packets get processed by SRv6 Segment Endpoint Nodes 🧚. Those 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], all 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 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 interpreted as described in BCP 14 [RFC2119] [RFC8174], but only when they appear in all capitals, as shown here 🙈.

This document uses 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 spells out 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 marks a packet as part of a class or group of packets that share 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 represent the SRv6 Segment List. As Section 2 of [RFC8754] specifies, the Segment List is encoded starting from the last segment of the SR Policy. So the first element, Segment List[0], holds the last segment of the SR Policy, the second element holds the penultimate segment, and so on 📜.
  • srhSegmentIPv6ListSection: the SRH Segment List as defined in Section 2 of [RFC8754], written as a series of octets in IPFIX 🧾.
  • srhSegmentsIPv6Left: the 8-bit unsigned integer that counts the segments remaining to reach the end of the Segment List from the SRH. It follows the "Segments Left" field in Section 4.4 of [RFC8200] and the SRH part of Section 2 of [RFC8754] 🔢.
  • srhIPv6Section: the SRH and its TLVs as specified in Section 2 of [RFC8754], written as a series of octets in IPFIX 📦.
  • srhIPv6ActiveSegmentType: the designator of the routing protocol or PCEP extension where the active SRv6 segment was learned from 🔍.
  • srhSegmentIPv6LocatorLength: the length of the SRH segment IPv6 locator, counted as the number of significant bits. Together with srhSegmentIPv6, it lets you calculate the SRv6 Locator 📏.
  • srhSegmentIPv6EndpointBehavior: the 16-bit unsigned integer that represents an SRv6 Endpoint behavior, as per Section 4 of [RFC8986] 🌟.

Note that srhSegmentIPv6, srhSegmentIPv6LocatorLength, and srhSegmentIPv6EndpointBehavior are generic fields. They're meant for use in 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], plus some existing counter information [IANA-IPFIX], answer questions like these (amongst others) 🔥:

  • How many packets steered with an SR policy get forwarded or dropped using SRv6 in a network? 📊
  • If they get dropped, for what reasons? 💀
  • What's 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 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

Okay bestie, let's keep going! 🦋

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.

+=======+==========================+=============================+

ValueDescriptionReference

+=======+==========================+=============================+

0UnknownRFC 9487

+-------+--------------------------+-----------------------------+

1Segment Routing PolicyRFC 9487, [RFC9256]

+-------+--------------------------+-----------------------------+

2Path Computation ElementRFC 9487, [PCEP-SRV6-EXT]

+-------+--------------------------+-----------------------------+

3OSPFv3 Segment RoutingRFC 9487, [OSPFV3-SRV6-EXT]

+-------+--------------------------+-----------------------------+

4IS-IS Segment RoutingRFC 9487, [RFC9352]

+-------+--------------------------+-----------------------------+

5BGP Segment RoutingRFC 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 🧚

okay so this appendix is where we get to see three different ways to encode the brand new IEs 🔥. All three use the same example values from Table 3, just packaged differently. The three encodings use these IEs, in this order: 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 🌸

so with the encoding in Figure 1, the Table 3 examples get represented with these IEs. The => arrow just shows which IE each piece of info maps to 💅:

  • 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, and that's the one the Data Record uses 🎀. The field length for srhSegmentIPv6BasicList is 0xFFFF, which basically means the length is variable 🦋. The real length of this IE is in the List Length field of the basicList format, as per [RFC6313].

the data set looks like this 👑:

      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

okay so this part is where the template finally shows up, and I'm obsessed 😭🎀 With encoding in Figure 3, the examples in Table 3 get represented with these IEs, and the => just means "this IE holds that info" 💅

  • 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

okay the template ID here is 257, and that's the one the Data Record uses 🦋 The field length for srhSegmentIPv6ListSection is 0xFFFF, which means the length is variable and the actual length lives in the Data Set instead ✨ Also, when the actual length is inferior to 255 in the Data Record example, the length field gets encoded in 8 bits (Section 7 of [RFC7011]). big brain stuff, bestie 🧠💜

and here's the data, all laid out 👑

  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

that's the whole vibe of the segment list section, periodt 💜🫶

A.1.3. Template Record and Data Set with SRH Section ✨

okay so this is where the examples get spicy 🌶️💅 With the encoding in Figure 5, the examples in Table 3 get mapped onto these IEs. The => arrow shows which IE holds which info:

  • 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, and it gets used in the Data Record. The field length for srhIPv6Section in the Template Record is 0xFFFF, which means the length is variable. Its actual length gets 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 like this:

      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 gives an SRv6 Endpoint Behavior Options Template example, using the values from 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 gets used in the Data Record 🦋

The data set looks like this 💅

     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 want 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 a huge 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

📦 where this page comes from