Swisscom

Binzring 17 Zurich 8045 Switzerland thomas.graf@swisscom.com

Huawei

benoit.claise@huawei.com

INSA-Lyon

Lyon France pierre.francois@insa-lyon.fr

ops opsawg 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 .

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 () 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

• .  Introduction
• .  Terminology
• .  New IPFIX IPv6 SRH Information Elements
• .  Sample Use Cases
• .  IANA Considerations
  • .  IPFIX Information Elements Registry
    • .  srhFlagsIPv6
    • .  srhTagIPv6
    • .  srhSegmentIPv6
    • .  srhActiveSegmentIPv6
    • .  srhSegmentIPv6BasicList
    • .  srhSegmentIPv6ListSection
    • .  srhSegmentsIPv6Left
    • .  srhIPv6Section
    • .  srhIPv6ActiveSegmentType
    • . srhSegmentIPv6LocatorLength
    • . srhSegmentIPv6EndpointBehavior
  • .  New IPFIX IPv6 SRH Segment Type (Value 500) Subregistry
• .  Operational Considerations
  • .  SRv6 Segment List
  • .  Compressed SRv6 Segment List Decomposition
• .  Security Considerations
• .  References
  • .  Normative References
  • .  Informative References
• .  IPFIX Encoding Examples
  • .  Three Observed SRH Headers and Their Routing Protocols
    • .  Template Record and Data Set with Segment Basic List
    • .  Template Record and Data Set with Segment List Section
    • .  Template Record and Data Set with SRH Section
  • .  Options Template Record and Data Set for SRv6 Segment Endpoint Behavior and Locator Length
• Acknowledgements
• Authors' Addresses

Introduction A dedicated Routing Extension Header, called "Segment Routing Header (SRH)", is defined in for use of Segment Routing over IPv6 (SRv6) data plane. Also, three routing protocol extensions, OSPFv3, IS-IS, and BGP Prefix Segment Identifiers (Prefix-SIDs); the Path Computation Element Communication Protocol (PCEP) Extension; and the Segment Routing Policy 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 . This document specifies eleven new IPFIX Information Elements (IEs) and one new subregistry within the "IPFIX Information Elements" registry , 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 .

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 when, and only when, they appear in all capitals, as shown here. This document makes use of the terms defined in , , and . The following terms are used as defined in :

• IPFIX
• IPFIX Information Elements
• Template
• Template Record
• Options Template
• Options Template Record
• Data Record
• Data Set

The following terms are used as defined in :

• Segment Routing (SR)
• Segment
• Segment List
• Active Segment
• Segment Identifier (SID)
• SRv6
• SRv6 SID

The following terms are used as defined in :

• Segment Routing Header (SRH)
• SR Source Node
• Transit Node
• SR Segment Endpoint Node
• Reduced SRH
• Segments Left
• Last Entry

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 ().

srhTagIPv6

The 16-bit Tag field defined in the SRH (). 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 of zero or more 128-bit IPv6 addresses in the SRH that represents the SRv6 Segment List. As specified in , 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 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 and as mentioned in the SRH part of .

srhIPv6Section

The SRH and its TLVs as specified in 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 .

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 .

Sample Use Cases The IPFIX IEs srhSegmentIPv6BasicList (496) or alternatively srhSegmentIPv6ListSection (497), srhActiveSegmentIPv6 (495), srhSegmentsIPv6Left (498), srhIPv6ActiveSegmentType (500), and forwardingStatus (89) as well as some existing counter information 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?

IANA Considerations

IPFIX Information Elements Registry IANA has added the following new IEs to the "IPFIX Information Elements" registry at : IPFIX Information Elements Registry

ElementID	Name
492	srhFlagsIPv6
493	srhTagIPv6
494	srhSegmentIPv6
495	srhActiveSegmentIPv6
496	srhSegmentIPv6BasicList
497	srhSegmentIPv6ListSection
498	srhSegmentsIPv6Left
499	srhIPv6Section
500	srhIPv6ActiveSegmentType
501	srhSegmentIPv6LocatorLength
502	srhSegmentIPv6EndpointBehavior

srhFlagsIPv6

ElementID:

492

Name:

srhFlagsIPv6

Abstract Data Type:

unsigned8

Data Type Semantics:

flags

Description:

The 8-bit Flags field defined in the SRH (). 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 . See also for the SRH specification.

Reference:

RFC 9487

srhTagIPv6

ElementID:

493

Name:

srhTagIPv6

Abstract Data Type:

unsigned16

Data Type Semantics:

identifier

Description:

The 16-bit Tag field defined in the SRH (). 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 for more details about the Tag.

Reference:

RFC 9487

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 and mentioned in "Segment List" in .

Reference:

RFC 9487

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 for the definition of "active segment".

Reference:

RFC 9487

srhSegmentIPv6BasicList

ElementID:

496

Name:

srhSegmentIPv6BasicList

Abstract Data Type:

basicList

Data Type Semantics:

list

Description:

The ordered basicList of zero or more 128-bit IPv6 addresses in the SRH that represents the SRv6 Segment List. As specified in , 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 for more details about the SRv6 Segment List.

Reference:

RFC 9487

srhSegmentIPv6ListSection

ElementID:

497

Name:

srhSegmentIPv6ListSection

Abstract Data Type:

octetArray

Data Type Semantics:

default

Description:

The SRv6 Segment List as defined in as a series of octets in IPFIX.

Additional Information:

See for more details about the SRv6 Segment List.

Reference:

RFC 9487

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 and mentioned in .

Reference:

RFC 9487

srhIPv6Section

ElementID:

499

Name:

srhIPv6Section

Abstract Data Type:

octetArray

Data Type Semantics:

default

Description:

The SRH and its TLVs as defined in as a series of octets in IPFIX.

Additional Information:

See for more details about the structure of an SRH.

Reference:

RFC 9487

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 .

Reference:

RFC 9487

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 for more details about the SID format.

Reference:

RFC 9487

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 . 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 . See for more details about the processing of endpoint behaviors.

Reference:

RFC 9487

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 at . The allocation policy of this new subregistry is Expert Review (). 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 . IPFIX IPv6 SRH Segment Type (Value 500) Subregistry

Value	Description	Reference
0	Unknown	RFC 9487
1	Segment Routing Policy	RFC 9487,
2	Path Computation Element	RFC 9487,
3	OSPFv3 Segment Routing	RFC 9487,
4	IS-IS Segment Routing	RFC 9487,
5	BGP Segment Routing Prefix-SID	RFC 9487,

Operational Considerations

SRv6 Segment List The zero or more 128-bit IPv6 addresses in the SRH 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 . 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.

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 . The SR Endpoint Flavors, as described in Section 4 of , 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 , 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.

Security Considerations There are no additional security considerations regarding allocation of these new IPFIX IEs compared to . 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 as appropriate.

References Normative References In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. This document specifies an extension to the IP Flow Information Export (IPFIX) protocol specification in RFC 5101 and the IPFIX information model specified in RFC 5102 to support hierarchical structured data and lists (sequences) of Information Elements in data records. This extension allows definition of complex data structures such as variable-length lists and specification of hierarchical containment relationships between Templates. Finally, the semantics are provided in order to express the relationship among multiple list elements in a structured data record. [STANDARDS-TRACK] This document specifies the IP Flow Information Export (IPFIX) protocol, which serves as a means for transmitting Traffic Flow information over the network. In order to transmit Traffic Flow information from an Exporting Process to a Collecting Process, a common representation of flow data and a standard means of communicating them are required. This document describes how the IPFIX Data and Template Records are carried over a number of transport protocols from an IPFIX Exporting Process to an IPFIX Collecting Process. This document obsoletes RFC 5101. This document defines the data types and management policy for the information model for the IP Flow Information Export (IPFIX) protocol. This information model is maintained as the IANA "IPFIX Information Elements" registry, the initial contents of which were defined by RFC 5102. This information model is used by the IPFIX protocol for encoding measured traffic information and information related to the traffic Observation Point, the traffic Metering Process, and the Exporting Process. Although this model was developed for the IPFIX protocol, it is defined in an open way that allows it to be easily used in other protocols, interfaces, and applications. This document obsoletes RFC 5102. Many protocols make use of points of extensibility that use constants to identify various protocol parameters. To ensure that the values in these fields do not have conflicting uses and to promote interoperability, their allocations are often coordinated by a central record keeper. For IETF protocols, that role is filled by the Internet Assigned Numbers Authority (IANA). To make assignments in a given registry prudently, guidance describing the conditions under which new values should be assigned, as well as when and how modifications to existing values can be made, is needed. This document defines a framework for the documentation of these guidelines by specification authors, in order to assure that the provided guidance for the IANA Considerations is clear and addresses the various issues that are likely in the operation of a registry. This is the third edition of this document; it obsoletes RFC 5226. RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings. This document specifies version 6 of the Internet Protocol (IPv6). It obsoletes RFC 2460. Segment Routing can be applied to the IPv6 data plane using a new type of Routing Extension Header called the Segment Routing Header (SRH). This document describes the SRH and how it is used by nodes that are Segment Routing (SR) capable. Informative References IANA Huawei Technologies Huawei Technologies Cisco Systems Cisco Systems Work in Progress Huawei Technologies RtBrick Inc Ciena Corporation Cisco Systems, Inc. China Telecom Segment Routing (SR) can be used to steer packets through an IPv6 or MPLS network using the source routing paradigm. SR enables any head- end node to select any path without relying on a hop-by-hop signaling technique (e.g., LDP or RSVP-TE). A Segment Routed Path can be derived from a variety of mechanisms, including an IGP Shortest Path Tree (SPT), explicit configuration, or a PCE. Since SR can be applied to both MPLS and IPv6 forwarding planes, a PCE should be able to compute SR-Path for both MPLS and IPv6 forwarding planes. The PCEP extension and mechanisms to support SR- MPLS have been defined. This document describes the extensions required for SR support for IPv6 data plane in the Path Computation Element communication Protocol (PCEP). Work in Progress This document describes some additional IP Flow Information Export (IPFIX) Information Elements in the range of 1-127, which is the range compatible with field types used by NetFlow version 9 in RFC 3954, as specified in the IPFIX Information Model in RFC 7012. Segment Routing (SR) leverages the source routing paradigm. A node steers a packet through an ordered list of instructions, called "segments". A segment can represent any instruction, topological or service based. A segment can have a semantic local to an SR node or global within an SR domain. SR provides a mechanism that allows a flow to be restricted to a specific topological path, while maintaining per-flow state only at the ingress node(s) to the SR domain. SR can be directly applied to the MPLS architecture with no change to the forwarding plane. A segment is encoded as an MPLS label. An ordered list of segments is encoded as a stack of labels. The segment to process is on the top of the stack. Upon completion of a segment, the related label is popped from the stack. SR can be applied to the IPv6 architecture, with a new type of routing header. A segment is encoded as an IPv6 address. An ordered list of segments is encoded as an ordered list of IPv6 addresses in the routing header. The active segment is indicated by the Destination Address (DA) of the packet. The next active segment is indicated by a pointer in the new routing header. Segment Routing (SR) leverages the source-routing paradigm. A node steers a packet through an ordered list of instructions called "segments". A segment can represent any instruction, topological or service based. The ingress node prepends an SR header to a packet containing a set of segment identifiers (SIDs). Each SID represents a topological or service-based instruction. Per-flow state is maintained only on the ingress node of the SR domain. An "SR domain" is defined as a single administrative domain for global SID assignment. This document defines an optional, transitive BGP attribute for announcing information about BGP Prefix Segment Identifiers (BGP Prefix-SIDs) and the specification for SR-MPLS SIDs. The Segment Routing over IPv6 (SRv6) Network Programming framework enables a network operator or an application to specify a packet processing program by encoding a sequence of instructions in the IPv6 packet header. Each instruction is implemented on one or several nodes in the network and identified by an SRv6 Segment Identifier in the packet. This document defines the SRv6 Network Programming concept and specifies the base set of SRv6 behaviors that enables the creation of interoperable overlays with underlay optimization. Segment Routing (SR) allows a node to steer a packet flow along any path. Intermediate per-path states are eliminated thanks to source routing. SR Policy is an ordered list of segments (i.e., instructions) that represent a source-routed policy. Packet flows are steered into an SR Policy on a node where it is instantiated called a headend node. The packets steered into an SR Policy carry an ordered list of segments associated with that SR Policy. This document updates RFC 8402 as it details the concepts of SR Policy and steering into an SR Policy. The Segment Routing (SR) architecture allows a flexible definition of the end-to-end path by encoding it as a sequence of topological elements called "segments". It can be implemented over the MPLS or the IPv6 data plane. This document describes the IS-IS extensions required to support SR over the IPv6 data plane. This document updates RFC 7370 by modifying an existing registry. China Mobile Cisco Systems, Inc. Huawei Technologies Orange Cisco Systems, Inc. Work in Progress

IPFIX Encoding Examples This appendix represents three different encodings for the newly introduced IEs, for the example values in . The three different encodings use the following IEs, respectively: srhSegmentIPv6BasicList, srhSegmentIPv6ListSection, and srhIPv6Section. Three Observed SRH Headers and Their Associated Routing Protocols

SRH Nr	SRH Flags	SRH Tag	Active Segment Type	Segment List
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

Three Observed SRH Headers and Their Routing Protocols

Template Record and Data Set with Segment Basic List With encoding in , the examples in 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)

Template Record with Basic List Encoding Format 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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 . The data set is represented as follows:

Data Set Encoding Format for Basic List 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 ... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Template Record and Data Set with Segment List Section With encoding in , the examples in 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)

Template Record with Segment List Section Encoding Format 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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 (). The data can be represented as follows:

Data Set Encoding Format for Segment List Section 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 ... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Template Record and Data Set with SRH Section With encoding in , the examples in 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)

Template Record with SRH Section Encoding Format 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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 (). The data can be represented as follows:

Data Set Encoding Format for SRH Section 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) ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

(*) The Length must be calculated to include the optional Type Length Value objects.

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 . In the Options Template case, the srhActiveSegmentIPv6 IE is a Scope field. Three Observed SRv6 Segment Endpoint Behaviors

Entry Nr	SRH Endpoint IPv6	SRH Endpoint Behavior	SRH Segment Locator Length
1	2001:db8::1	End [1]	48
2	2001:db8::4	End with NEXT-CSID [43]	48
3	2001:db8::6	End.DX6 [16]	48

Segment Endpoint Behavior Options Template Record 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

In this example, the Template ID is 259, which will be used in the Data Record. The data set is represented as follows:

Data Set Encoding Format for 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 = 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] | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

(*) The Length must be calculated to include the optional Type Length Value objects.

Acknowledgements The authors would like to thank , , , , , , , , , , , , , , and for their reviews and valuable comments. And thank you to and for the implementation and validation.

Authors' Addresses Swisscom

Binzring 17 Zurich 8045 Switzerland thomas.graf@swisscom.com

Huawei

benoit.claise@huawei.com

INSA-Lyon

Lyon France pierre.francois@insa-lyon.fr