RFC 8754

IPv6 Segment Routing Header (SRH)

📅 published March 2020, from ietf

IPv6 Segment Routing Header (SRH) 🦋

okay bestie, this is RFC 8754, and the title is "IPv6 Segment Routing Header (SRH)" 💖 It's a Standards Track document from the IETF, published in March 2020, with ISSN 2070-1721. The editors are C. Filsfils and D. Dukes (both Ed.) from Cisco Systems, Inc. Then S. Previdi from Huawei, J. Leddy writing as an Individual, S. Matsushima from SoftBank, and D. Voyer from Bell Canada 🫶 The title block doesn't list any documents this one obsoletes or updates, so it's standing on its own ✨

Abstract 🌸

So the big idea is that Segment Routing can run on the IPv6 data plane using a brand new kind of Routing Extension Header, called the Segment Routing Header (SRH) 🧚 This doc explains what the SRH is and how nodes that are Segment Routing (SR) capable actually use it.

Status of This Memo 📜

This is an Internet Standards Track document 🔥

It's a product of the Internet Engineering Task Force (IETF), so it reflects what the IETF community agrees on. It got public review and was 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 the current status, any errata, and how to send feedback, go to https://www.rfc-editor.org/info/rfc8754 💅

Copyright (c) 2020 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 stood on the publication date. Please actually read these, because they spell out your rights and restrictions. Code Components pulled out of this document must include Simplified BSD License text, as described in Section 4.e of the Trust Legal Provisions, and they come with no warranty, as the Simplified BSD License describes 🙈

Table of Contents 🗺️

1.  Introduction
  1.1.  Terminology
  1.2.  Requirements Language
2.  Segment Routing Header
  2.1.  SRH TLVs
    2.1.1.  Padding TLVs
    2.1.2.  HMAC TLV
3.  SR Nodes
  3.1.  SR Source Node
  3.2.  Transit Node
  3.3.  SR Segment Endpoint Node
4.  Packet Processing
  4.1.  SR Source Node
    4.1.1.  Reduced SRH
  4.2.  Transit Node
  4.3.  SR Segment Endpoint Node
    4.3.1.  FIB Entry Is a Locally Instantiated SRv6 SID
    4.3.2.  FIB Entry Is a Local Interface
    4.3.3.  FIB Entry Is a Nonlocal Route
    4.3.4.  FIB Entry Is a No Match
5.  Intra-SR-Domain Deployment Model
  5.1.  Securing the SR Domain
  5.2.  SR Domain as a Single System with Delegation among
        Components
  5.3.  MTU Considerations
  5.4.  ICMP Error Processing
  5.5.  Load Balancing and ECMP
  5.6.  Other Deployments
6.  Illustrations
  6.1.  Abstract Representation of an SRH
  6.2.  Example Topology
  6.3.  SR Source Node
    6.3.1.  Intra-SR-Domain Packet
    6.3.2.  Inter-SR-Domain Packet -- Transit
    6.3.3.  Inter-SR-Domain Packet -- Internal to External
  6.4.  Transit Node
  6.5.  SR Segment Endpoint Node
  6.6.  Delegation of Function with HMAC Verification
    6.6.1.  SID List Verification
7.  Security Considerations
  7.1.  SR Attacks
  7.2.  Service Theft
  7.3.  Topology Disclosure
  7.4.  ICMP Generation
  7.5.  Applicability of AH
8.  IANA Considerations
  8.1.  Segment Routing Header Flags Registry
  8.2.  Segment Routing Header TLVs Registry
9.  References
  9.1.  Normative References
  9.2.  Informative References
Acknowledgements
Contributors
Authors' Addresses

1. Introduction ✨

Segment Routing (SR) can run on the IPv6 data plane using a new type of routing header, the Segment Routing Header (SRH) 💜 This document covers what the SRH is and how SR capable nodes use it.

"Segment Routing Architecture" [RFC8402] is the one that explains Segment Routing and how it shows up in two data planes: MPLS and IPv6 🦋

The encoding of IPv6 segments in the SRH is defined right here in this document 💅

1.1. Terminology 📖

This document uses the terms Segment Routing (SR), SR domain, SR over IPv6 (SRv6), Segment Identifier (SID), SRv6 SID, Active Segment, and SR Policy, all as defined in [RFC8402] 🫶

1.2. Requirements Language 🔑

Okay, this part matters a lot 😭 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" are to be read as described in BCP 14 [RFC2119] [RFC8174], but only when they're written in all capitals, exactly like that. That's the whole deal 🔥

2. Segment Routing Header 🎀

Routing headers are defined in [RFC8200] 💖 The SRH gets a brand new Routing Type, which is 4 ✨

Here's how the SRH is 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
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Next Header   |  Hdr Ext Len  | Routing Type  | Segments Left |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |  Last Entry   |     Flags     |              Tag              |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                                                               |
 |            Segment List[0] (128-bit IPv6 address)             |
 |                                                               |
 |                                                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                                                               |
 |                                                               |
                               ...
 |                                                               |
 |                                                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                                                               |
 |            Segment List[n] (128-bit IPv6 address)             |
 |                                                               |
 |                                                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 //                                                             //
 //         Optional Type Length Value objects (variable)       //
 //                                                             //
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Here's what each field means 👀

  • Next Header: Defined in [RFC8200], Section 4.4.
  • Hdr Ext Len: Defined in [RFC8200], Section 4.4.
  • Routing Type: 4.
  • Segments Left: Defined in [RFC8200], Section 4.4.
  • Last Entry: the index (zero based) in the Segment List of the last element in the Segment List 🫶
  • Flags: 8 bits of flags 🚩 Section 8.1 sets up an IANA registry for new flags that get defined later. For now, these are the flags defined:
  0 1 2 3 4 5 6 7
 +-+-+-+-+-+-+-+-+
 |U U U U U U U U|
 +-+-+-+-+-+-+-+-+
  • U: Unused and reserved for future use. It MUST be 0 on transmission and ignored on receipt 💀
  • Tag: This tags a packet as part of a class or group of packets, like packets that share the same set of properties 🏷️ If the source isn't using Tag, it MUST be set to zero on transmission. If Tag isn't used during SRH processing, it SHOULD be ignored. Tag isn't used when processing the SID defined in Section 4.3.1. It MAY be used when processing other SIDs that this document doesn't define. How tags get allocated and used is outside the scope of this document 🌸
  • Segment List[0..n]: 128-bit IPv6 addresses for the nth segment in the Segment List. The list is encoded starting from the last segment of the SR Policy. So Segment List[0] holds the last segment of the SR Policy, the second element holds the penultimate segment, and so on 🧚
  • TLV: Type Length Value (TLV), described in Section 2.1 🍓

In the SRH, the Next Header, Hdr Ext Len, Routing Type, and Segments Left fields are defined in Section 4.4 of [RFC8200]. Based on the constraints in that section, Next Header, Hdr Ext Len, and Routing Type are not mutable, while Segments Left is mutable 🔄

The mutability of the TLV value is set by the most significant bit in the type, as specified in Section 2.1 ✨

Section 4.3 defines the mutability of the remaining SRH fields (Flags, Tag, Segment List) in the context of the SID defined in this document 🦋

New SIDs defined in the future MUST specify the mutability properties of the Flags, Tag, and Segment List, and they MUST indicate how the Hashed Message Authentication Code (HMAC) TLV (Section 2.1.2) verification works. Note that, in effect, these fields are mutable 👑

Consistent with the SR model, the source of the SRH always knows how to set the Segment List, Flags, Tag, and TLVs of the SRH for use within the SR domain. How it does that is outside the scope of this document. It can be based on topology, available SIDs and their mutability properties, the SRH mutability requirements of the destination, or any other information 💜

2.1. SRH TLVs ✨

okay so this section is all about TLVs of the Segment Routing Header 🎀 A TLV is basically little metadata sticky note for segment processing, and this doc only defines two of them: the HMAC (Section 2.1.2) and the padding ones (Section 2.1.1). 💅 When a node processes the SID from Section 4.3.1, it ignores every TLV unless local configuration says otherwise (Section 4.3.1.1.1). So TLV and HMAC support is optional for any implementation, BUT if you're adding or parsing TLVs you MUST support PAD TLVs 🫶 Other docs can define extra TLVs and their own processing rules, so the party doesn't end here 🎉

TLVs are present when the Hdr Ext Len is greater than (Last Entry+1)*2 🦋

Now the boundary drama 😭 While a segment endpoint is processing TLVs, every TLV MUST be fully contained inside the SRH, as decided by Hdr Ext Len. If a TLV pokes out past that boundary, you get an ICMP Parameter Problem, Code 0, sent to the Source Address, pointing at the Hdr Ext Len field of the SRH, and the packet gets discarded 💀 Yikes, don't be that TLV.

An implementation MAY limit how many TLVs it processes or how long they are, based on local configuration. It MAY limit:

  • the number of consecutive Pad1 (Section 2.1.1.1) options to 1. If padding of more than one byte is required, then PadN (Section 2.1.1.2) should be used.
  • The length in PadN to 5.
  • The maximum number of non-Pad TLVs to be processed.
  • The maximum length of all TLVs to be processed.

And if those limits get exceeded, the implementation MAY stop processing any more TLVs in the SRH 🌸

Here's the TLV layout, bestie 🍓

    0                   1
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-----------------------
   |     Type      |    Length     | Variable-length data
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-----------------------
  • Type: an 8-bit codepoint from the "Segment Routing Header TLVs" [IANA-SRHTLV]. Unrecognized Types MUST be ignored on receipt. 🙈
  • Length: the length of the variable-length data field, in bytes.
  • Variable-length data: data that's specific to the Type.

TLV entries hold OPTIONAL info that the node sitting in the Destination Address (DA) of the packet might use 🧚 Every TLV has its own length, format, and semantic. The codepoint IANA hands out for each TLV Type decides both its format AND its meaning, and you can encode multiple TLVs in the same SRH 💜

The highest-order bit of the TLV type (bit 0) tells you whether that TLV's data can change on the way to the packet's final destination:

  • 0: TLV data does not change en route
  • 1: TLV data does change en route

Every TLV spells out its alignment using the xn+y format, which comes from [RFC8200]. SR source nodes use those xn+y alignment rules for TLVs and Padding TLVs when they build an SRH ✨

The Length field is what lets a node skip over a TLV it doesn't support or recognize. It counts the TLV length in octets, NOT including the Type and Length fields themselves. 🎀

So these are the TLVs defined in this doc:

  • Padding TLVs
  • HMAC TLV

More may show up in the future 🌈

2.1.1. Padding TLVs

There are two flavours of Padding TLVs, Pad1 and PadN, and everything below applies to both 💖

  • Padding TLVs are used for meeting the alignment requirement of the subsequent TLVs.
  • Padding TLVs are used to pad the SRH to a multiple of 8 octets.
  • Padding TLVs are ignored by a node processing the SRH TLV.
  • Multiple Padding TLVs MAY be used in one SRH.

2.1.1.1. Pad1

Alignment requirement: none 🧚

   0 1 2 3 4 5 6 7
  +-+-+-+-+-+-+-+-+
  |     Type      |
  +-+-+-+-+-+-+-+-+
  • Type: 0

A single Pad1 TLV MUST be used when a single byte of padding is required. A Pad1 TLV MUST NOT be used if more than one consecutive byte of padding is required. 💅

2.1.1.2. PadN

Alignment requirement: none 🌸

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Type      |    Length     |      Padding (variable)       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   //                    Padding (variable)                       //
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  • Type: 4
  • Length: 0 to 5. The length of the Padding field, in bytes.
  • Padding: padding bits have no semantic. They MUST be set to 0 on transmission and ignored on receipt. 🙌

The PadN TLV MUST be used when more than one byte of padding is required 🔥

2.1.2. HMAC TLV

Alignment requirement: 8n 🔐

The keyed Hashed Message Authentication Code (HMAC) TLV is OPTIONAL and 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      Type     |     Length    |D|        RESERVED             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      HMAC Key ID (4 octets)                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                              //
   |                      HMAC (variable)                         //
   |                                                              //
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

where:

  • Type: 5.
  • Length: the length of the variable-length data, in bytes.
  • D: 1 bit. 1 means Destination Address verification is disabled because a reduced Segment List is in use (see Section 4.1.1).
  • RESERVED: 15 bits. MUST be 0 on transmission.
  • HMAC Key ID: a 4-octet opaque number that uniquely identifies the pre-shared key and algorithm used to generate the HMAC.
  • HMAC: keyed HMAC, in multiples of 8 octets, at most 32 octets.

The HMAC TLV is how you verify that the SRH on a packet was picked by an authorized party, and that the segment list hasn't been messed with since it was generated 🕵️‍♀️ It also lets you check that the current segment (because it's in the authorized Segment List) is allowed to be used. The SR domain makes sure the source node is allowed to use the source address in the packet, using ingress filtering from BCP 84 [RFC3704] or other strategies that fit 🦋

2.1.2.1. HMAC Generation and Verification

Local configuration decides when to check for an HMAC. That config is outside the scope of this doc 🙈 It may be based on the active segment at an SR Segment endpoint node, or on the result of an Access Control List (ACL) that looks at the incoming interface, the HMAC Key ID, or other packet fields.

An implementation that supports generating and verifying the HMAC gets the following default behavior, as defined in the rest of this section ✨

HMAC verification starts by checking that the current segment equals the IPv6 header's destination address. The check passes when either:

  • HMAC D bit is 1 and Segments Left is greater than Last Entry, or
  • HMAC Segments Left is less than or equal to Last Entry, and the destination address is equal to Segment List[Segments Left].

The HMAC field is the output of the HMAC computation defined in [RFC2104], using:

  • key: the pre-shared key identified by the HMAC Key ID
  • HMAC algorithm: identified by the HMAC Key ID
  • Text: a concatenation of the following fields from the IPv6 header and the SRH, as they'd be received at the node doing the verifying:
    • IPv6 header: Source address (16 octets)
    • SRH: Last Entry (1 octet)
    • SRH: Flags (1 octet)
    • SRH: HMAC 16 bits following Length
    • SRH: HMAC Key ID (4 octets)
    • SRH: All addresses in the Segment List (variable octets)

The HMAC digest gets truncated to 32 octets and placed in the HMAC field of the HMAC TLV 💜

For HMAC algorithms that make digests shorter than 32 octets, the digest goes in the lowest-order octets of the HMAC field. The remaining octets MUST be set to zero so the HMAC length is a multiple of 8 octets. 🔢

If HMAC verification succeeds, processing carries on as normal 🎉

If HMAC verification fails, an ICMP error message (parameter problem, error code 0, pointing to the HMAC TLV) SHOULD be generated (but rate limited) and logged, and the packet SHOULD be discarded. > Yikes, a failed check means the packet is getting tossed, so keep that rate limit on the ICMP side 😭

2.1.2.2. HMAC Pre-shared Key Algorithm

The HMAC Key ID field lets several hash algorithms (SHA-256, SHA3-256 ... or future ones) and pre-shared keys exist at the same time 🌈

The HMAC Key ID field is opaque, which means it has no syntax or semantic except as an identifier for the right combo of pre-shared key and hash algorithm 🔑

At both the HMAC TLV generating and verifying nodes, the Key ID uniquely identifies the pre-shared key and HMAC algorithm.

At the HMAC TLV generating node, the Text for the HMAC computation is set to the IPv6 header fields and SRH fields as they would appear at the verification node(s). That's not necessarily the same as the source node that sends a packet with the HMAC TLV, so don't mix those up 🙃

Pre-shared key rollover works by having two key IDs in use while the HMAC TLV generating node and verifying node converge on a new key 💫

The HMAC TLV generating node may need to revoke an SRH it previously generated an HMAC for. Revocation happens by allocating a new key and key ID, then rolling over the key ID associated with the SRH being revoked. The HMAC TLV verifying node drops packets with the revoked SRH 🚫

An implementation supporting HMAC can support multiple hash functions. An implementation supporting HMAC MUST implement SHA-2 [FIPS180-4] in its SHA-256 variant. 💜

Picking the pre-shared key and algorithm, and distributing them, is outside the scope of this doc. Some options include:

  • setting these items in the configuration of the HMAC generating or verifying nodes, either by static configuration or any SDN-oriented approach
  • dynamically using a trusted key distribution protocol such as [RFC6407]

Key management is outside the scope of this doc too, but the recommendations of BCP 107 [RFC4107] should be considered when choosing the key management system 🧠

3. SR Nodes ✨

There are different types of nodes that can show up in segment routing networks 🌸 SR source nodes originate packets with a segment in the IPv6 header's destination address. Transit nodes forward packets destined for a remote segment. SR segment endpoint nodes process a local segment in the destination address of an IPv6 header. Ooh, three different roles, all with their own vibe 💅

3.1. SR Source Node

An SR source node is any node that originates an IPv6 packet with a segment (i.e., SRv6 SID) in the destination address of the IPv6 header 🦋 The packet leaving the SR source node may or may not contain an SRH. That covers either:

  • A host originating an IPv6 packet, or
  • An SR domain ingress router encapsulating a received packet in an outer IPv6 header, followed by an optional SRH.

How a segment in the IPv6 destination address and the Segment List in the SRH get derived is out of the scope of this document, so we're not going there today 🙈

3.2. Transit Node 🦋

okay so a transit node is any node forwarding an IPv6 packet whose destination address is not configured locally as a segment or a local interface 🌸 it's just passing the packet along, no drama 💅 and a transit node is not required to be capable of processing a segment or SRH. pure background vibes ✨

3.3. SR Segment Endpoint Node 🧚

an SR segment endpoint node is any node that receives an IPv6 packet whose destination address is locally configured as a segment or local interface. this is the main character 👑

4. Packet Processing ✨

this section is all about SRv6 packet processing at the SR source, Transit, and SR segment endpoint nodes 💖

4.1. SR Source Node 🌈

a source node steers a packet into an SR Policy 🚀 if the SR Policy ends up with a Segment List containing a single segment, and there's no need to add anything to the SRH flag or add a TLV, then the DA is set to that single Segment List entry, and the SRH MAY be omitted. lowkey simple ✨

when the SRH is needed, it gets made like this 🎀

  • The Next Header and Hdr Ext Len fields are set as specified in [RFC8200].
  • The Routing Type field is set to 4.
  • The DA of the packet is set with the value of the first segment.
  • The first element of the SRH Segment List is the ultimate segment. The second element is the penultimate segment, and so on.
  • The Segments Left field is set to n-1, where n is the number of elements in the SR Policy.
  • The Last Entry field is set to n-1, where n is the number of elements in the SR Policy.
  • TLVs (including HMAC) may be set according to their specification.
  • The packet is forwarded toward the packet's Destination Address (the first segment).

4.1.1. Reduced SRH 🍓

when a source doesn't need the entire SID list kept in the SRH, a reduced SRH may be used. it's giving efficiency 🫶

a reduced SRH does not contain the first segment of the related SR Policy (the first segment is the one already in the DA of the IPv6 header), and the Last Entry field is set to n-2, where n is the number of elements in the SR Policy. 💜

4.2. Transit Node 🌸

as specified in [RFC8200], the only node allowed to inspect the Routing Extension Header (and therefore the SRH) is the node corresponding to the DA of the packet. so any other transit node MUST NOT inspect the underneath routing header, and it MUST forward the packet toward the DA according to its IPv6 routing table. that's the rule, bestie 🔥

when a SID is in the destination address of an IPv6 header, it gets routed through an IPv6 network as an IPv6 address 🦋 SIDs, or the prefix(es) covering SIDs, and their reachability may be distributed by means outside the scope of this document. for example, [RFC5308] or [RFC5340] may be used to advertise a prefix covering the SIDs on a node 🌈

4.3. SR Segment Endpoint Node 👑

without constraining the details of an implementation, the SR segment endpoint node creates Forwarding Information Base (FIB) entries for its local SIDs 🧚

when an SRv6-capable node receives an IPv6 packet, it does a longest-prefix-match lookup on the packet's destination address. that lookup can return any of the following 👀

  • A FIB entry that represents a locally instantiated SRv6 SID
  • A FIB entry that represents a local interface, not locally instantiated as an SRv6 SID
  • A FIB entry that represents a nonlocal route
  • No Match

4.3.1. FIB Entry Is a Locally Instantiated SRv6 SID 💖

this document and section define a single SRv6 SID. future documents may define additional SRv6 SIDs. in that case, the entire content of this section will be defined in that document 📄

if the FIB entry represents a locally instantiated SRv6 SID, process the next header chain of the IPv6 header as defined in Section 4 of [RFC8200]. Section 4.3.1.1 describes how to process an SRH; Section 4.3.1.2 describes how to process an upper-layer header or the absence of a Next Header 🎀

processing this SID modifies Segments Left and, if configured to process TLVs, it may modify the "variable-length data" of TLV types that change en route. so Segments Left is mutable, and TLVs that change en route are mutable. the rest of the SRH (Flags, Tag, Segment List, and TLVs that do not change en route) is immutable while processing this SID 🔒

4.3.1.1. SRH Processing 🌈

S01. When an SRH is processed {
S02.   If Segments Left is equal to zero {
S03.     Proceed to process the next header in the packet,
            whose type is identified by the Next Header field in
            the routing header.
S04.   }
S05.   Else {
S06.     If local configuration requires TLV processing {
S07.       Perform TLV processing (see TLV Processing)
S08.     }
S09.     max_last_entry  =  ( Hdr Ext Len /  2 ) - 1
S10.     If  ((Last Entry > max_last_entry) or
S11.          (Segments Left is greater than (Last Entry+1)) {
S12.       Send an ICMP Parameter Problem, Code 0, message to
              the Source Address, pointing to the Segments Left
              field, and discard the packet.
S13.     }
S14.     Else {
S15.       Decrement Segments Left by 1.
S16.       Copy Segment List[Segments Left] from the SRH to the
              destination address of the IPv6 header.
S17.       If the IPv6 Hop Limit is less than or equal to 1 {
S18.         Send an ICMP Time Exceeded -- Hop Limit Exceeded in
                Transit message to the Source Address and discard
                the packet.
S19.       }
S20.       Else {
S21.         Decrement the Hop Limit by 1
S22.         Resubmit the packet to the IPv6 module for transmission
                to the new destination.
S23.       }
S24.     }
S25.   }
S26. }

4.3.1.1.1. TLV Processing 🧸

local configuration determines how TLVs are processed when the Active Segment is a local SID defined in this document. the definition of local configuration is outside the scope of this document 🌷

just for illustration, here are two example local configurations that may be associated with a SID 💡

Example 1:
For any packet received from interface I2
  Skip TLV processing

Example 2:
For any packet received from interface I1
  If first TLV is HMAC {
    Process the HMAC TLV
  }
  Else {
    Discard the packet
  }

4.3.1.2. Upper-Layer Header or No Next Header 🦋

when processing the upper-layer header of a packet matching a FIB entry locally instantiated as an SRv6 SID defined in this document:

IF (Upper-layer Header is IPv4 or IPv6) and
    local configuration permits {
  Perform IPv6 decapsulation
  Resubmit the decapsulated packet to the IPv4 or IPv6 module
}
ELSE {
  Send an ICMP parameter problem message to the Source Address and
  discard the packet.  Error code (4) "SR Upper-layer
  Header Error", pointer set to the offset of the upper-layer
  header.
}

a unique error code lets an SR source node recognize an error in SID processing at an endpoint. that's iconic behaviour 🌈

4.3.2. FIB Entry Is a Local Interface 🌸

if the FIB entry represents a local interface and is not locally instantiated as an SRv6 SID, the SRH is processed as follows 🎀

  • If Segments Left is zero, the node must ignore the routing header and proceed to process the next header in the packet, whose type is identified by the Next Header field in the routing header.
  • If Segments Left is non-zero, the node must discard the packet and send an ICMP Parameter Problem, Code 0, message to the packet's Source Address, pointing to the unrecognized Routing Type.

4.3.3. FIB Entry Is a Nonlocal Route 🍓

processing is not changed by this document 🙌

4.3.4. FIB Entry Is a No Match 🫧

processing is not changed by this document either 💅

5. Intra-SR-Domain Deployment Model 👑

the use of SIDs exclusively within the SR domain, and solely for packets of the SR domain, is an important deployment model 🏰

this enables the SR domain to act as a single routing system 🌟

this section covers 💜

  • securing the SR domain from external attempts to use its SIDs
  • using the SR domain as a single system with delegation between components
  • handling packets of the SR domain

5.1. Securing the SR Domain 🔐

nodes outside the SR domain are not trusted: they cannot directly use the SIDs of the domain. this is enforced by two levels of access control lists 🚧

  1. Any packet entering the SR domain and destined to a SID within the SR domain is dropped. this may be realized with the following logic. other methods with equivalent outcome are considered compliant:
    • Allocate all the SIDs from a block S/s
    • Configure each external interface of each edge node of the domain with an inbound infrastructure access list (IACL) that drops any incoming packet with a destination address in S/s
    • Failure to implement this method of ingress filtering exposes the SR domain to source-routing attacks, as described and referenced in [RFC5095] 😱 this one is serious, bestie, do not skip it 🚨
  2. The distributed protection in #1 is complemented with per-node protection, dropping packets to SIDs from source addresses outside the SR domain. this may be realized with the following logic. other methods with equivalent outcome are considered compliant:
    • Assign all interface addresses from prefix A/a
    • At node k, all SIDs local to k are assigned from prefix Sk/sk
    • Configure each internal interface of each SR node k in the SR domain with an inbound IACL that drops any incoming packet with a destination address in Sk/sk if the source address is not in A/a

5.2. SR Domain as a Single System with Delegation among Components 🧚

all intra-SR-domain packets are of the SR domain. the IPv6 header is originated by a node of the SR domain and is destined to a node of the SR domain 💖

all interdomain packets are encapsulated for the part of the packet journey that is within the SR domain. the outer IPv6 header is originated by a node of the SR domain and is destined to a node of the SR domain 🌈

so, as a consequence, any packet within the SR domain is of the SR domain. ✨

the SR domain is a system where the operator may want to distribute or delegate different operations of the outermost header to different nodes within the system 🎀

an operator of an SR domain may choose to delegate SRH addition to a host node within the SR domain, and delegate validation of the contents of any SRH to a more trusted router or switch attached to the host. picture this: a top-of-rack switch T connected to host H via interface I 🏢 H receives an SRH (SRH1) with a computed HMAC via some SDN method outside the scope of this document. H classifies traffic it sources and adds SRH1 to traffic requiring a specific Service Level Agreement (SLA). T is configured with an IACL on I requiring verification of the SRH for any packet destined to the SID block of the SR domain (S/s). T checks and verifies that SRH1 is valid and contains an HMAC TLV; T then verifies the HMAC 🔍 very teamwork-coded, honestly 🫶

an operator of the SR domain may choose to have all segments in the SR domain verify the HMAC. this mechanism would verify that the SRH Segment List is not modified while traversing the SR domain 🔒🦋

5.3. MTU Considerations 🎀

Okay, so the SR domain ingress edge node is the one wrapping up packets to travel across the SR domain, which means it has to think about the MTU of the whole domain 🧚. Inside the domain, well-known mitigation techniques are RECOMMENDED, like deploying a bigger MTU inside the domain than at the ingress edges. Total glow-up energy ✨

Encapsulating with an outer IPv6 header and SRH has the same MTU and fragmentation vibes as the IPv6 tunnels in [RFC2473] 🦋. If you want to go deeper on how different tunneling methods (IPv6 tunnels included) hold up, check [INTAREA-TUNNELS]. Operators SHOULD consider that when they're thinking about MTU inside the SR domain 💜

5.4. ICMP Error Processing 🙈

ICMP error packets generated inside the SR domain get sent back to source nodes inside the SR domain. The invoking packet in the ICMP error message might have an SRH, and the destination address of a packet with an SRH changes every time a segment gets processed. So it might not match the destination the socket or application that made the packet was using. Plot twist 💀

For the source of the invoking packet to process the ICMP error message, the ultimate destination address in the IPv6 header might be needed. Here's the logic for figuring out the destination address for protocol-error handlers:

  • Walk all extension headers of the invoking IPv6 packet to the routing extension header preceding the upper-layer header.
    • If routing header is type 4 Segment Routing Header (SRH)
      • The SID at Segment List[0] may be used as the destination address of the invoking packet.

After that, ICMP errors get processed by upper-layer transports as defined in [RFC4443] 🌸

For IP packets encapsulated in an outer IPv6 header, ICMP error handling is as defined in [RFC2473] 🫶

5.5. Load Balancing and ECMP 💖

For any interdomain packet, the SR source node MUST impose a flow label computed based on the inner packet. Computing the flow label is as recommended in [RFC6438] for the sending Tunnel End Point 🔥

For any intradomain packet, the SR source node SHOULD impose a flow label computed as described in [RFC6437]. That helps ECMP load balancing at transit nodes that can't compute a 5-tuple beyond the SRH 🍓

At any transit node inside an SR domain, the flow label MUST be used as defined in [RFC6438] to calculate the ECMP hash toward the destination address. If there's no flow label, the transit node would likely hash all packets between a pair of SR Edge nodes onto the same link, and nobody wants that 😭

At an SR segment endpoint node, the flow label MUST be used as defined in [RFC6438] to calculate any ECMP hash used to forward the processed packet to the next segment 👑

5.6. Other Deployments 🧚

Other deployment models and what they mean for security, MTU, HMAC, ICMP error processing, and interaction with other extension headers are outside the scope of this document. Not our problem today, bestie 💅

6. Illustrations 🌈

This section has illustrations of SRv6 packet processing at SR source, transit, and SR segment endpoint nodes. Let's get visual 🦋

6.1. Abstract Representation of an SRH 💜

For a node k, its IPv6 address is represented as Ak, and its SRv6 SID is represented as Sk.

IPv6 headers are represented as the tuple of (source,destination). For example, a packet with source address A1 and destination address A2 is represented as (A1,A2). The payload of the packet is omitted, so we don't have to deal with it 🙈

An SR Policy is a list of segments. A list of segments is represented as <S1,S2,S3>, where S1 is the first SID to visit, S2 is the second SID to visit, and S3 is the last SID to visit.

(SA,DA) (S3,S2,S1; SL) represents an IPv6 packet with:

  • Source Address SA, Destination Addresses DA, and next header SRH.
  • SRH with SID list <S1,S2,S3> with SegmentsLeft = SL.
  • Note the difference between the <> and () symbols. <S1,S2,S3> represents a SID list where the leftmost segment is the first segment. In contrast, (S3,S2,S1; SL) represents the same SID list but encoded in the SRH Segment List format, where the leftmost segment is the last segment. When referring to an SR Policy in a high-level use case, it's simpler to use the <S1,S2,S3> notation. When referring to an illustration of detailed behavior, the (S3,S2,S1; SL) notation is more convenient 🎀

At its SR Policy headend, the Segment List <S1,S2,S3> results in SRH (S3,S2,S1; SL=2), represented fully as:

Segments Left=2
Last Entry=2
Flags=0
Tag=0
Segment List[0]=S3
Segment List[1]=S2
Segment List[2]=S1

6.2. Example Topology 🗺️

The following topology is used in the examples below:

        + * * * * * * * * * * * * * * * * * * * * +

        *         [8]                [9]          *
                   |                  |
        *          |                  |           *
[1]----[3]--------[5]----------------[6]---------[4]---[2]
        *          |                  |           *
                   |                  |
        *          |                  |           *
                   +--------[7]-------+
        *                                         *

        + * * * * * * *  SR domain  * * * * * * * +

                               Figure 1
  • 3 and 4 are SR domain edge routers
  • 5, 6, and 7 are all SR domain routers
  • 8 and 9 are hosts within the SR domain
  • 1 and 2 are hosts outside the SR domain
  • The SR domain implements ingress filtering as per Section 5.1, and no external packet can enter the domain with a destination address equal to a segment of the domain. Locked down 🔒

6.3. SR Source Node 💅

6.3.1. Intra-SR-Domain Packet 🦋

When host 8 sends a packet to host 9 via an SR Policy <S7,A9>, the packet is:

P1: (A8,S7)(A9,S7; SL=1)

6.3.1.1. Reduced Variant ✂️

When host 8 sends a packet to host 9 via an SR Policy <S7,A9> and wants to use a reduced SRH, the packet is:

P2: (A8,S7)(A9; SL=1)

6.3.2. Inter-SR-Domain Packet -- Transit 🌍

When host 1 sends a packet to host 2, the packet is:

P3: (A1,A2)

The SR domain ingress router 3 receives P3 and steers it to SR domain egress router 4 via an SR Policy <S7,S4>. Router 3 encapsulates the received packet P3 in an outer header with an SRH. The packet is:

P4: (A3,S7)(S4,S7; SL=1)(A1,A2)

If the SR Policy contains only one segment (the egress router 4), the ingress router 3 encapsulates P3 into an outer header (A3,S4) without SRH. The packet is:

P5: (A3,S4)(A1,A2)

6.3.2.1. Reduced Variant 🍰

The SR domain ingress router 3 receives P3 and steers it to SR domain egress router 4 via an SR Policy <S7,S4>. If router 3 wants to use a reduced SRH, it encapsulates the received packet P3 in an outer header with a reduced SRH. The packet is:

P6: (A3,S7)(S4; SL=1)(A1,A2)

6.3.3. Inter-SR-Domain Packet -- Internal to External 🏠

When host 8 sends a packet to host 1, the packet is encapsulated for the portion of its journey within the SR domain. From 8 to 3, the packet is:

P7: (A8,S3)(A8,A1)

In the opposite direction, the packet generated from 1 to 8 is:

P8: (A1,A8)

At node 3, P8 is encapsulated for the portion of its journey within the SR domain, with the outer header destined to segment S8. This results in:

P9: (A3,S8)(A1,A8)

At node 8, the outer IPv6 header is removed by S8 processing, then processed again when received by A8. Layers, layers 🧅

6.4. Transit Node 🚏

Node 5 acts as transit node for packet P1 and sends packet:

P1: (A8,S7)(A9,S7;SL=1)

on the interface toward node 7.

6.5. SR Segment Endpoint Node 🎯

Node 7 receives packet P1 and, using the logic in Section 4.3.1, sends packet:

P7: (A8,A9)(A9,S7; SL=0)

on the interface toward router 6.

6.6. Delegation of Function with HMAC Verification 🔐

This section describes how a function may be delegated within the SR domain. In the following sections, consider a host 8 connected to a top of rack 5.

6.6.1. SID List Verification ✅

An operator may prefer to apply the SRH at source 8, while 5 verifies that the SID list is valid.

For illustration purposes, an SDN controller provides 8 an SRH terminating at node 9, with Segment List <S5,S7,S6,A9>, and HMAC TLV computed for the SRH. The HMAC key ID and key associated with the HMAC TLV are shared with 5. Node 8 does not know the key 🙈 Node 5 is configured with an IACL applied to the interface connected to 8, requiring HMAC verification for any packet destined to S/s.

Node 8 originates packets with the received SRH, including HMAC TLV:

P15: (A8,S5)(A9,S6,S7,S5;SL=3;HMAC)

Node 5 receives and verifies the HMAC for the SRH, then forwards the packet to the next segment:

P16: (A8,S7)(A9,S6,S7,S5;SL=2;HMAC)

Node 6 receives:

P17: (A8,S6)(A9,S6,S7,S5;SL=1;HMAC)

Node 9 receives:

P18: (A8,A9)(A9,S6,S7,S5;SL=0;HMAC)

This use of an HMAC is particularly valuable within an enterprise-based SR domain [SRN]. Very practical, very iconic 💼

7. Security Considerations 🚨

This section is serious business, so put your sunglasses on 🕶️

This section reviews security considerations related to the SRH, given the SRH processing and deployment models discussed in this document.

As described in Section 5, it is necessary to filter packets' ingress to the SR domain, destined to SIDs within the SR domain (i.e., bearing a SID in the destination address). This ingress filtering is via an IACL at SR domain ingress border nodes. Additional protection is applied via an IACL at each SR Segment Endpoint node, filtering packets not from within the SR domain, destined to SIDs in the SR domain. ACLs are easily supported for small numbers of seldom changing prefixes, which is why summarization is important 📦

Additionally, ingress filtering of IPv6 source addresses as recommended in BCP 38 [RFC2827] SHOULD be used 🛡️

7.1. SR Attacks ⚔️

An SR domain implements distributed and per-node protection as described in Section 5.1. Additionally, domains deny traffic with spoofed addresses by implementing the recommendations in BCP 84 [RFC3704].

Full implementation of the recommended protection blocks the attacks documented in [RFC5095] from outside the SR domain, including bypassing filtering devices, reaching otherwise-unreachable Internet systems, network topology discovery, bandwidth exhaustion, and defeating anycast. Absolutely wild that this is all preventable 😤

Failure to implement distributed and per-node protection allows attackers to bypass filtering devices and exposes the SR domain to these attacks. Do not skip this, periodt 🚫

Compromised nodes within the SR domain may mount the attacks listed above, along with other known attacks on IP networks (e.g., DoS/DDoS, topology discovery, man-in-the-middle, traffic interception/siphoning). This one's the scariest, no cap 💀

7.2. Service Theft 🦹

Service theft is defined as the use of a service offered by the SR domain by a node not authorized to use the service.

Service theft is not a concern within the SR domain, as all SR source nodes and SR segment endpoint nodes within the domain are able to utilize the services of the domain. If a node outside the SR domain learns of segments or a topological service within the SR domain, IACL filtering denies access to those segments 🙅‍♀️

7.3. Topology Disclosure 👀

The SRH is unencrypted and may contain SIDs of some intermediate SR nodes in the path towards the destination within the SR domain. If packets can be snooped within the SR domain, the SRH may reveal topology, traffic flows, and service usage. Lowkey a lot of info to leak 🫣

This is applicable within an SR domain, but the disclosure is less relevant, as an attacker has other means of learning topology, flows, and service usage. Still, good to know, iykyk 🧠

7.4. ICMP Generation 💀

Okay so, ICMPv6 error messages can get weaponized for denial-of-service attacks. Someone can send back-to-back packets with a destination address or SRH that's built to cause an error, and boom, your node is making error messages nonstop 😭. The good news: an implementation that correctly follows Section 2.4 of [RFC4443] gets protected by the ICMPv6 rate-limiting mechanism 🛡️✨. Stay safe, bestie 🫶

7.5. Applicability of AH 🦋

The SR domain is a trusted domain, as defined in Sections 2 and 8.2 of [RFC8402] 👑. The SR source is trusted to add an SRH, and it can optionally verify that the SRH came from a trusted source using the HMAC TLV from this document 🔐. Segments advertised inside the domain are trusted to be accurate and to come from trusted sources through a secure control plane 💅. Because of all that, the SR domain doesn't rely on the Authentication Header (AH) defined in [RFC4302] to secure the SRH. Main character security, no extra layer needed 🌸

The use of SRH with AH by an SR source node, and its processing at an SR segment endpoint node, are not defined in this document. Future documents may define use of SRH with AH and its processing 🔮

8. IANA Considerations 📋

This document makes the following registrations in the "Internet Protocol Version 6 (IPv6) Parameters" "Routing Types" subregistry maintained by IANA 🧚

      +-------+------------------------------+---------------+
      | Value | Description                  | Reference     |
      +=======+==============================+===============+
      | 4     | Segment Routing Header (SRH) | This document |
      +-------+------------------------------+---------------+

                     Table 1: SRH Registration

This document also makes the following registrations in the "Type 4 - Parameter Problem" message of the "Internet Control Message Protocol version 6 (ICMPv6) Parameters" registry maintained by IANA 🍓

               +------+-----------------------------+
               | Code | Name                        |
               +======+=============================+
               | 4    | SR Upper-layer Header Error |
               +------+-----------------------------+

                   Table 2: SR Upper-layer Header
                         Error Registration

8.1. Segment Routing Header Flags Registry 🚩

This document describes a new IANA-managed registry to identify SRH Flags Bits ✨. The registration procedure is "IETF Review" [RFC8126]. The registry name is "Segment Routing Header Flags". Flags are 8 bits 💜

8.2. Segment Routing Header TLVs Registry 🎀

This document describes a new IANA-managed registry to identify SRH TLVs 🦋. The registration procedure is "IETF Review". The registry name is "Segment Routing Header TLVs". A TLV is identified through an unsigned 8-bit codepoint value, with assigned values 0-127 for TLVs that do not change en route and 128-255 for TLVs that may change en route 🌈. The following codepoints are defined in this document:

       +---------+--------------------------+---------------+
       | Value   | Description              | Reference     |
       +=========+==========================+===============+
       | 0       | Pad1 TLV                 | This document |
       +---------+--------------------------+---------------+
       | 1       | Reserved                 | This document |
       +---------+--------------------------+---------------+
       | 2       | Reserved                 | This document |
       +---------+--------------------------+---------------+
       | 3       | Reserved                 | This document |
       +---------+--------------------------+---------------+
       | 4       | PadN TLV                 | This document |
       +---------+--------------------------+---------------+
       | 5       | HMAC TLV                 | This document |
       +---------+--------------------------+---------------+
       | 6       | Reserved                 | This document |
       +---------+--------------------------+---------------+
       | 124-126 | Experimentation and Test | This document |
       +---------+--------------------------+---------------+
       | 127     | Reserved                 | This document |
       +---------+--------------------------+---------------+
       | 252-254 | Experimentation and Test | This document |
       +---------+--------------------------+---------------+
       | 255     | Reserved                 | This document |
       +---------+--------------------------+---------------+

           Table 3: Segment Routing Header TLVs Registry

Values 1, 2, 3, and 6 were defined in draft versions of this specification and are Reserved for backwards compatibility with early implementations, and they should not be reassigned 🙈. Values 127 and 255 are Reserved to allow for expansion of the Type field in future specifications, if needed 🔮

9. References 📚

9.1. Normative References 💖

[FIPS180-4] National Institute of Standards and Technology (NIST), "Secure Hash Standard (SHS)", FIPS PUB 180-4, DOI 10.6028/NIST.FIPS.180-4, August 2015, <http://csrc.nist.gov/publications/fips/fips180-4/fips-180-4.pdf>.

[IANA-SRHTLV] IANA, "Segment Routing Header TLVs", <https://www.iana.org/assignments/ipv6-parameters/>.

[RFC2104] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-Hashing for Message Authentication", RFC 2104, DOI 10.17487/RFC2104, February 1997, <https://www.rfc-editor.org/info/rfc2104>.

[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>.

[RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in IPv6 Specification", RFC 2473, DOI 10.17487/RFC2473, December 1998, <https://www.rfc-editor.org/info/rfc2473>.

[RFC2827] Ferguson, P. and D. Senie, "Network Ingress Filtering: Defeating Denial of Service Attacks which employ IP Source Address Spoofing", BCP 38, RFC 2827, DOI 10.17487/RFC2827, May 2000, <https://www.rfc-editor.org/info/rfc2827>.

[RFC3704] Baker, F. and P. Savola, "Ingress Filtering for Multihomed Networks", BCP 84, RFC 3704, DOI 10.17487/RFC3704, March 2004, <https://www.rfc-editor.org/info/rfc3704>.

[RFC4107] Bellovin, S. and R. Housley, "Guidelines for Cryptographic Key Management", BCP 107, RFC 4107, DOI 10.17487/RFC4107, June 2005, <https://www.rfc-editor.org/info/rfc4107>.

[RFC4302] Kent, S., "IP Authentication Header", RFC 4302, DOI 10.17487/RFC4302, December 2005, <https://www.rfc-editor.org/info/rfc4302>.

[RFC5095] Abley, J., Savola, P., and G. Neville-Neil, "Deprecation of Type 0 Routing Headers in IPv6", RFC 5095, DOI 10.17487/RFC5095, December 2007, <https://www.rfc-editor.org/info/rfc5095>.

[RFC6407] Weis, B., Rowles, S., and T. Hardjono, "The Group Domain of Interpretation", RFC 6407, DOI 10.17487/RFC6407, October 2011, <https://www.rfc-editor.org/info/rfc6407>.

[RFC6437] Amante, S., Carpenter, B., Jiang, S., and J. Rajahalme, "IPv6 Flow Label Specification", RFC 6437, DOI 10.17487/RFC6437, November 2011, <https://www.rfc-editor.org/info/rfc6437>.

[RFC6438] Carpenter, B. and S. Amante, "Using the IPv6 Flow Label for Equal Cost Multipath Routing and Link Aggregation in Tunnels", RFC 6438, DOI 10.17487/RFC6438, November 2011, <https://www.rfc-editor.org/info/rfc6438>.

[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>.

[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>.

9.2. Informative References 🧠

[INTAREA-TUNNELS] Touch, J. and M. Townsley, "IP Tunnels in the Internet Architecture", Work in Progress, Internet-Draft, draft-ietf-intarea-tunnels-10, 12 September 2019, <https://tools.ietf.org/html/draft-ietf-intarea-tunnels-10>.

[RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet Control Message Protocol (ICMPv6) for the Internet Protocol Version 6 (IPv6) Specification", STD 89, RFC 4443, DOI 10.17487/RFC4443, March 2006, <https://www.rfc-editor.org/info/rfc4443>.

[RFC5308] Hopps, C., "Routing IPv6 with IS-IS", RFC 5308, DOI 10.17487/RFC5308, October 2008, <https://www.rfc-editor.org/info/rfc5308>.

[RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008, <https://www.rfc-editor.org/info/rfc5340>.

[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>.

[SRN] Lebrun, D., Jadin, M., Clad, F., Filsfils, C., and O. Bonaventure, "Software Resolved Networks: Rethinking Enterprise Networks with IPv6 Segment Routing", 2018, <https://inl.info.ucl.ac.be/system/files/sosr18-final15-embedfonts.pdf>.

Acknowledgements 🫶

The authors would like to thank Ole Troan, Bob Hinden, Ron Bonica, Fred Baker, Brian Carpenter, Alexandru Petrescu, Punit Kumar Jaiswal, David Lebrun, Benjamin Kaduk, Frank Xialiang, Mirja Kühlewind, Roman Danyliw, Joe Touch, and Magnus Westerlund for their comments to this document 💕

Contributors 🌟

Kamran Raza, Zafar Ali, Brian Field, Daniel Bernier, Ida Leung, Jen Linkova, Ebben Aries, Tomoya Kosugi, Éric Vyncke, David Lebrun, Dirk Steinberg, Robert Raszuk, Dave Barach, John Brzozowski, Pierre Francois, Nagendra Kumar, Mark Townsley, Christian Martin, Roberta Maglione, James Connolly, and Aloys Augustin contributed to the content of this document 🎀

Authors' Addresses 💌

Clarence Filsfils (editor)
Cisco Systems, Inc.
Brussels
Belgium

Email: cfilsfil@cisco.com


Darren Dukes (editor)
Cisco Systems, Inc.
Ottawa
Canada

Email: ddukes@cisco.com


Stefano Previdi
Huawei
Italy

Email: stefano@previdi.net


John Leddy
Individual
United States of America

Email: john@leddy.net


Satoru Matsushima
SoftBank

Email: satoru.matsushima@g.softbank.co.jp


Daniel Voyer
Bell Canada

Email: daniel.voyer@bell.ca
📦 where this page comes from