RFC 9085
Border Gateway Protocol - Link State (BGP-LS) Extensions for Segment Routing
RFC 9085: Border Gateway Protocol - Link State (BGP-LS) Extensions for Segment Routing 🌸 (Part 1 of 6)
Okay bestie, the title block first! 💖 This is an Internet Standards Track doc from the IETF, published August 2021 (ISSN 2070-1721). The authors are S. Previdi (Huawei Technologies), K. Talaulikar, Ed. (Cisco Systems, Inc.), C. Filsfils (Cisco Systems, Inc.), H. Gredler (RtBrick Inc.), and M. Chen (Huawei Technologies). Nothing in this title block says it obsoletes or updates any other RFC, so it's a standalone release. 🧚
Abstract ✨
Segment Routing (SR) is giving flexible end-to-end paths 🦋. You encode a path as a sequence of topological subpaths, which are called "segments". Routing protocols advertise these segments. The link-state routing protocols (IS-IS, OSPFv2, and OSPFv3) do this inside IGP topologies.
This document defines extensions to the Border Gateway Protocol - Link State (BGP-LS) address family, so BGP can carry SR information. 🔥
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). For more info on Internet Standards, check Section 2 of RFC 7841. ✨
You can find info about the current status of this document, any errata, and how to send feedback at https://www.rfc-editor.org/info/rfc9085. 🌈
Copyright Notice 🎀
Copyright (c) 2021 IETF Trust and the persons identified as the document authors. All rights reserved. 🫶
This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) as they stand on the date of publication. Please read these carefully, because they spell out your rights and restrictions for this document. 🙈 Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions. They're provided without warranty, as described in the Simplified BSD License. 💀
Table of Contents 🍓
1. Introduction
1.1. Requirements Language
2. BGP-LS Extensions for Segment Routing
2.1. Node Attribute TLVs
2.1.1. SID/Label TLV
2.1.2. SR Capabilities TLV
2.1.3. SR-Algorithm TLV
2.1.4. SR Local Block TLV
2.1.5. SRMS Preference TLV
2.2. Link Attribute TLVs
2.2.1. Adjacency SID TLV
2.2.2. LAN Adjacency SID TLV
2.2.3. L2 Bundle Member Attributes TLV
2.3. Prefix Attribute TLVs
2.3.1. Prefix-SID TLV
2.3.2. Prefix Attribute Flags TLV
2.3.3. Source Router Identifier TLV
2.3.4. Source OSPF Router-ID TLV
2.3.5. Range TLV
2.4. Equivalent IS-IS Segment Routing TLVs/Sub-TLVs
2.5. Equivalent OSPFv2/OSPFv3 Segment Routing TLVs/Sub-TLVs
3. IANA Considerations
3.1. TLV/Sub-TLV Code Points Summary
4. Manageability Considerations
5. Security Considerations
6. References
6.1. Normative References
6.2. Informative References
Acknowledgements
Contributors
Authors' Addresses1. Introduction ✨
Segment Routing (SR) lets you build flexible end-to-end paths by combining subpaths called "segments" 💖. A segment can represent any instruction, whether it's topological or service based. It can have a local meaning to one SR node, or a global meaning across a whole domain. Inside IGP topologies, an SR path is encoded as a sequence of topological subpaths called "IGP segments". The link-state routing protocols (IS-IS, OSPFv2, and OSPFv3) advertise these segments. 🦋
[RFC8402] defines the link-state IGP segments: prefix, node, anycast, and adjacency segments 🔥. By default, a prefix segment represents an ECMP-aware shortest path to a prefix, based on the state of the IGP topology. An adjacency segment represents a hop over one specific adjacency between two nodes in the IGP. A prefix segment is usually a multi-hop path, while an adjacency segment is usually a one-hop path. Node and anycast segments are variations of the prefix segment, with their own special characteristics. 🌸
When SR is enabled in an IGP domain, segments get advertised as Segment Identifiers (SIDs) 🧚. The IGP link-state routing protocols have been extended to advertise SIDs and other SR-related info. The extensions are described for IS-IS [RFC8667], OSPFv2 [RFC8665], and OSPFv3 [RFC8666]. With these extensions, SR can be enabled within an IGP domain. ✨
SR allows advertisement of single-hop or multi-hop paths 💅. The flooding scope for the IGP extensions for SR is IGP area-wide. That means the contents of a Link-State Database (LSDB) or a Traffic Engineering Database (TED) only have the scope of one IGP area. So using the IGP alone isn't enough to construct segments across multiple IGP area or Autonomous System (AS) boundaries. 😭
Some applications need topological visibility across IGP areas, or even across ASes, so the BGP-LS address family and subaddress family were defined to let BGP carry link-state information 🌈. The BGP Network Layer Reachability Information (NLRI) encoding format for BGP-LS, plus a new BGP Path Attribute called the "BGP-LS Attribute", are defined in [RFC7752] 🎀. The identifying key of each link-state object (a node, link, or prefix) is encoded in the NLRI. The properties of that object are encoded in the BGP-LS Attribute. 💜
+------------+
| Consumer |
+------------+
^
|
v
+-------------------+
| BGP Speaker | +-----------+
| (Route Reflector) | | Consumer |
+-------------------+ +-----------+
^ ^ ^ ^
| | | |
+---------------+ | +-------------------+ |
| | | |
v v v v
+-----------+ +-----------+ +-----------+
| BGP | | BGP | | BGP |
| Speaker | | Speaker | . . . | Speaker |
+-----------+ +-----------+ +-----------+
^ ^ ^
| | |
IGP IGP IGP
Figure 1: Link-State Information CollectionFigure 1 shows a typical deployment 🦋. In each IGP area, one or more nodes are configured with BGP-LS. These BGP speakers form an Internal BGP (IBGP) mesh by connecting to one or more route reflectors. That way, all BGP speakers (especially the route reflectors) get link-state info from all IGP areas, and from other ASes through External BGP (EBGP) peers 👑. An external component connects to the route reflector to get this info. That might be filtered by a policy about what information is or isn't advertised to the external component, as described in [RFC7752] 🙈.
This document describes extensions to BGP-LS so it can advertise SR info 💖. An external component, like a controller, can collect SR information from across an SR domain (as described in [RFC8402]). Then it can build the end-to-end path, with its associated SIDs, that needs to be applied to an incoming packet to get the forwarding you want 🔥. SR operates within a trusted domain made of a single AS, or multiple ASes managed by the same administrative entity, such as one provider network. 🫶
1.1. Requirements Language 💅
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here. 🎀
2. BGP-LS Extensions for Segment Routing 🎀
This document defines SR extensions to BGP-LS 🌸. It specifies the TLVs and sub-TLVs for advertising SR information within the BGP-LS Attribute. Sections 2.4 and 2.5 list the equivalent TLVs and sub-TLVs in the IS-IS, OSPFv2, and OSPFv3 protocols. ✨
BGP-LS [RFC7752] defines the BGP-LS NLRI, which can be a Node NLRI, a Link NLRI, or a Prefix NLRI. It also defines the TLVs that map link-state info to BGP-LS NLRI within the BGP-LS Attribute. This document adds more BGP-LS Attribute TLVs to encode SR information. It does not introduce any changes to the encoding of the BGP-LS NLRIs. 💜
2.1. Node Attribute TLVs 🦋
These Node Attribute TLVs are defined 🧚:
+======+=================+===============+
| Type | Description | Section |
+======+=================+===============+
| 1161 | SID/Label | Section 2.1.1 |
+------+-----------------+---------------+
| 1034 | SR Capabilities | Section 2.1.2 |
+------+-----------------+---------------+
| 1035 | SR Algorithm | Section 2.1.3 |
+------+-----------------+---------------+
| 1036 | SR Local Block | Section 2.1.4 |
+------+-----------------+---------------+
| 1037 | SRMS Preference | Section 2.1.5 |
+------+-----------------+---------------+
Table 1: Node Attribute TLVsThese TLVs should only be added to the BGP-LS Attribute associated with the Node NLRI that describes the IGP node originating the corresponding IGP TLV/sub-TLV described below. 🌈
2.1.1. SID/Label TLV 💖
okay bestie, the SID/Label TLV is the little helper that gets tucked inside the SR Capabilities (Section 2.1.2) and Segment Routing Local Block (SRLB) (Section 2.1.4) TLVs as a sub-TLV 🎀 The info comes from whatever the protocol-specific advertisements already say ✨
- IS-IS, as defined by the SID/Label Sub-TLV in Section 2.3 of [RFC8667].
- OSPFv2/OSPFv3, as defined by the SID/Label Sub-TLV in Section 2.1 of [RFC8665] and Section 3.1 of [RFC8666].
here's the 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SID/Label (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+Figure 2: SID/Label TLV Format
here's what each piece means:
Type:1161🦋Length: variable, either3or4octets, depending on whether the value is encoded as a label or as an index/SID 🧚SID/Label: if the length is3, the 20 rightmost bits are a label (total TLV size is 7) and the 4 leftmost bits are set to0💅 If the length is4, the value is a 32-bit SID (total TLV size is 8) 🔥
2.1.2. SR Capabilities TLV 👑
the SR Capabilities TLV is how a node advertises its SR capabilities, including its Segment Routing Global Base (SRGB) range(s) 🌈 For IS-IS, the capabilities also cover IPv4 and IPv6 support for the SR-MPLS forwarding plane 💜 Again, the info is derived from the protocol-specific advertisements ✨
- IS-IS, as defined by the SR-Capabilities Sub-TLV in Section 3.1 of [RFC8667].
- OSPFv2/OSPFv3, as defined by the SID/Label Range TLV in Section 3.2 of [RFC8665]. OSPFv3 leverages the same TLV as defined for OSPFv2.
the format is giving structure 🎀
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Range Size 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SID/Label Sub-TLV 1 //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Range Size N |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SID/Label Sub-TLV N //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+Figure 3: SR Capabilities TLV Format
the field breakdown 🧁
Type:1034🌸Length: variable, minimum length is 12 octets 💖Flags: 1 octet of flags as defined in Section 3.1 of [RFC8667] for IS-IS. The flags are not currently defined for OSPFv2 and OSPFv3, and they MUST be set to 0 and ignored on receipt 🙈Reserved: 1 octet that MUST be set to 0 and ignored on receipt 💀
then you get one or more entries, each with this format ✨
Range Size: 3 octets with a non-zero value, indicating the number of labels in the range.SID/Label TLV: (as defined in Section 2.1.1) used as a sub-TLV, which encodes the first label in the range. Since the SID/Label TLV is used to indicate the first label of the SRGB range, only label encoding is valid under the SR Capabilities TLV 🫶
2.1.3. SR-Algorithm TLV 🦋
the SR-Algorithm TLV advertises which SR algorithms the node supports 💅 Same deal, the info comes from the protocol-specific advertisements 🌈
- IS-IS, as defined by the SR-Algorithm Sub-TLV in Section 3.2 of [RFC8667].
- OSPFv2/OSPFv3, as defined by the SR-Algorithm TLV in Section 3.1 of [RFC8665]. OSPFv3 leverages the same TLV as defined for OSPFv2.
format time ✨
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Algorithm 1 | Algorithm... | Algorithm N |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+Figure 4: SR-Algorithm TLV Format
Type:1035🍓Length: variable, minimum length is 1 octet and the maximum can be 256 💜Algorithm: one or more fields of 1 octet each that identify the algorithm 🔥
2.1.4. SR Local Block TLV 🧚
the SRLB TLV carries the range(s) of labels the node has reserved for local SIDs 🌸 Local SIDs show up in IGPs (IS-IS, OSPF) for things like Adjacency SIDs, and they can also be allocated by components other than IGP protocols 💖 For example, an application or a controller might tell a node to allocate a specific local SID 👀 So, so that those applications or controllers know which local SIDs are available, the node is required to advertise its SRLB 🫶
the info is derived from the protocol-specific advertisements ✨
- IS-IS, as defined by the SRLB Sub-TLV in Section 3.3 of [RFC8667].
- OSPFv2/OSPFv3, as defined by the SR Local Block TLV in Section 3.3 of [RFC8665]. OSPFv3 leverages the same TLV as defined for OSPFv2.
here's the 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-Range Size 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SID/Label Sub-TLV 1 //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-Range Size N |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SID/Label Sub-TLV N //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+Figure 5: SRLB TLV Format
the field breakdown 🍓
Type:1036🌈Length: variable, minimum length is 12 octets 💅Flags: 1 octet of flags. The flags are as defined in Section 3.3 of [RFC8667] for IS-IS. The flags are not currently defined for OSPFv2 and OSPFv3, and they MUST be set to 0 and ignored on receipt 🙈Reserved: 1 octet that MUST be set to 0 and ignored on receipt 💀
then come one or more entries corresponding to sub-range(s), each with this format ✨
Range Size: 3-octet value indicating the number of labels in the range.SID/Label TLV: (as defined in Section 2.1.1) used as a sub-TLV, which encodes the first label in the sub-range. Since the SID/Label TLV is used to indicate the first label of the SRLB sub-range, only label encoding is valid under the SR Local Block TLV 🦋
2.1.5. SRMS Preference TLV 🌸
the Segment Routing Mapping Server (SRMS) Preference TLV associates a preference with SRMS advertisements from a particular source 💖 [RFC8661] specifies the SRMS functionality, along with the SRMS preference of the node advertising the SRMS Prefix-to-SID mapping ranges 🧚
this info is derived from the protocol-specific advertisements too ✨
- IS-IS, as defined by the SRMS Preference Sub-TLV in Section 3.4 of [RFC8667].
- OSPFv2/OSPFv3, as defined by the SRMS Preference TLV in Section 3.4 of [RFC8665]. OSPFv3 leverages the same TLV as defined for OSPFv2.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Preference |
+-+-+-+-+-+-+-+-+Figure 6: SRMS Preference TLV Format
Type:1037🦋Length:1octet 💜Preference: 1 octet carrying an unsigned 8-bit SRMS preference 🫶
2.2. Link Attribute TLVs 🌈
the following Link Attribute TLVs are defined 💅
+======+=================================+===============+
| Type | Description | Section |
+======+=================================+===============+
| 1099 | Adjacency SID TLV | Section 2.2.1 |
+------+---------------------------------+---------------+
| 1100 | LAN Adjacency SID TLV | Section 2.2.2 |
+------+---------------------------------+---------------+
| 1172 | L2 Bundle Member Attributes TLV | Section 2.2.3 |
+------+---------------------------------+---------------+Table 2: Link Attribute TLVs
these TLVs should only be added to the BGP-LS Attribute associated with the Link NLRI that describes the link of the IGP node that is originating the corresponding IGP TLV/sub-TLV described below 👀
2.2.1. Adjacency SID TLV ✨
okay so the Adjacency SID TLV is how we advertise info about an Adjacency SID 🦋 This info is pulled from the Adj-SID Sub-TLV in IS-IS (Section 2.2.1 of [RFC8667]), OSPFv2 (Section 6.1 of [RFC8665]), and OSPFv3 (Section 7.1 of [RFC8666]). It's giving copy-paste from the source protocols, just packaged for BGP-LS 💅
Here's the layout, bestie:
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags | Weight | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SID/Label/Index (variable) //
+---------------------------------------------------------------+Figure 7: Adjacency SID TLV Format 🎀
Here's what each field means:
- Type: 1099 🌸
- Length: Variable. It's either 7 or 8 octets depending on the label or index encoding of the SID.
- Flags: 1-octet value that should be set as:
- Weight: 1 octet carrying the weight used for load-balancing purposes. The use of weight is described in Section 3.4 of [RFC8402].
- Reserved: 2 octets that MUST be set to 0 and ignored on receipt. 🙈
- SID/Index/Label:
The Flags and, as an extension, the SID/Index/Label fields of this TLV get interpreted according to whichever underlying protocol applies: IS-IS, OSPFv2, or OSPFv3. The Protocol-ID of the BGP-LS Link NLRI tells you which protocol spec to use for parsing these fields. Main character energy, literally 👑
2.2.2. LAN Adjacency SID TLV 🌈
okay so on a LAN, a node normally only announces its adjacency to the IS-IS pseudonode (or the OSPF Designated and Backup Designated Routers, the OSPF equivalent). The LAN Adjacency SID TLV lets a node announce adjacencies to all the other nodes on the LAN in one single instance of the BGP-LS Link NLRI 🧚 Without this TLV, you'd have to originate a BGP-LS Link NLRI for every extra adjacency just to advertise the SR TLVs for those neighbors. Nobody has time for that, fr fr 💀
This info is derived from the LAN-Adj-SID Sub-TLV of IS-IS (Section 2.2.2 of [RFC8667]), the LAN Adj-SID Sub-TLV of OSPFv2 (Section 6.2 of [RFC8665]), and the LAN Adj-SID Sub-TLV of OSPFv3 (Section 7.2 of [RFC8666]).
The LAN Adjacency SID TLV is laid out 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags | Weight | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OSPF Neighbor ID / IS-IS System ID |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SID/Label/Index (variable) //
+---------------------------------------------------------------+Figure 8: LAN Adjacency SID TLV Format 🦋
And the deets:
- Type: 1100 🍓
- Length: Variable. For IS-IS, it would be 13 or 14 octets depending on the label or index encoding of the SID. For OSPF, it would be 11 or 12 octets depending on the label or index encoding of the SID.
- Flags: 1-octet value that should be set as:
- Weight: 1 octet carrying the weight used for load-balancing purposes. The use of weight is described in Section 3.4 of [RFC8402].
- Reserved: 2 octets that MUST be set to 0 and ignored on receipt. 💅
- Neighbor ID: 6 octets for IS-IS for the System ID, and 4 octets for OSPF for the OSPF Router-ID of the neighbor.
- SID/Index/Label:
The Neighbor ID, Flags, and, as an extension, the SID/Index/Label fields of this TLV get interpreted according to the underlying IS-IS, OSPFv2, or OSPFv3 protocol. Same deal as before: the Protocol-ID of the BGP-LS Link NLRI decides which protocol spec you use for parsing ✨
2.2.3. L2 Bundle Member Attributes TLV 🫶
so the L2 Bundle Member Attributes TLV identifies an L2 Bundle Member link. That link belongs to a parent L3 link, which is described by the Link NLRI defined in [RFC7752], and this TLV gets associated with that Link NLRI. The TLV MAY include sub-TLVs that describe attributes of the bundle member. The bundle member it identifies is a unidirectional path from the originating router to the neighbor named in the parent L3 link. You're also allowed to have multiple L2 Bundle Member Attributes TLVs attached to one Link NLRI, so it MAY get busy in there 🌸
This info is derived from the L2 Bundle Member Attributes TLV of IS-IS (Section 2 of [RFC8668]). The equivalent functionality hasn't been specified for OSPF yet 🙈
The L2 Bundle Member Attributes TLV 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| L2 Bundle Member Descriptor |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link Attribute Sub-TLVs(variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+Figure 9: L2 Bundle Member Attributes TLV Format 🧚
Where:
- Type: 1172 🌈
- Length: Variable.
- L2 Bundle Member Descriptor: 4-octet field that carries a link-local identifier as defined in [RFC4202].
Link attributes for L2 Bundle Member links get advertised as sub-TLVs of the L2 Bundle Member Attributes TLV. These sub-TLVs are identical to existing BGP-LS TLVs, as you can see in the table below 🍓
+================+==========================+====================+
| TLV Code Point | Description | Reference Document |
+================+==========================+====================+
| 1088 | Administrative group | [RFC7752] |
| | (color) | |
+----------------+--------------------------+--------------------+
| 1089 | Maximum link bandwidth | [RFC7752] |
+----------------+--------------------------+--------------------+
| 1090 | Max. reservable link | [RFC7752] |
| | bandwidth | |
+----------------+--------------------------+--------------------+
| 1091 | Unreserved bandwidth | [RFC7752] |
+----------------+--------------------------+--------------------+
| 1092 | TE default metric | [RFC7752] |
+----------------+--------------------------+--------------------+
| 1093 | Link protection type | [RFC7752] |
+----------------+--------------------------+--------------------+
| 1099 | Adjacency Segment | Section 2.2.1 |
| | Identifier (Adj-SID) TLV | |
+----------------+--------------------------+--------------------+
| 1100 | LAN Adjacency Segment | Section 2.2.2 |
| | Identifier (Adj-SID) TLV | |
+----------------+--------------------------+--------------------+
| 1114 | Unidirectional link | [RFC8571] |
| | delay | |
+----------------+--------------------------+--------------------+
| 1115 | Min/Max Unidirectional | [RFC8571] |
| | link delay | |
+----------------+--------------------------+--------------------+
| 1116 | Unidirectional Delay | [RFC8571] |
| | Variation | |
+----------------+--------------------------+--------------------+
| 1117 | Unidirectional Link Loss | [RFC8571] |
+----------------+--------------------------+--------------------+
| 1118 | Unidirectional residual | [RFC8571] |
| | bandwidth | |
+----------------+--------------------------+--------------------+
| 1119 | Unidirectional available | [RFC8571] |
| | bandwidth | |
+----------------+--------------------------+--------------------+
| 1120 | Unidirectional Utilized | [RFC8571] |
| | Bandwidth | |
+----------------+--------------------------+--------------------+Table 3: BGP-LS Attribute TLVs are also used as sub-TLVs of the L2 Bundle Member Attributes TLV ✨
2.3. Prefix Attribute TLVs 🌸
okay now we're on to the Prefix Attribute TLVs 💖 These are the following ones that are defined:
+======+==========================+===============+
| Type | Description | Section |
+======+==========================+===============+
| 1158 | Prefix-SID | Section 2.3.1 |
+------+--------------------------+---------------+
| 1159 | Range | Section 2.3.5 |
+------+--------------------------+---------------+
| 1170 | Prefix Attribute Flags | Section 2.3.2 |
+------+--------------------------+---------------+
| 1171 | Source Router Identifier | Section 2.3.3 |
+------+--------------------------+---------------+
| 1174 | Source OSPF Router-ID | Section 2.3.4 |
+------+--------------------------+---------------+Table 4: Prefix Attribute TLVs 🦋
These TLVs should only be added to the BGP-LS Attribute associated with the Prefix NLRI that describes the prefix of the IGP node originating the corresponding IGP TLV/sub-TLV described below. Basically, only attach them to the right node's prefix, bestie 🫶
2.3.1. Prefix-SID TLV 🎀
okay so the Prefix-SID TLV is how we advertise info about a Prefix-SID 💖 It's built from the Prefix-SID Sub-TLV in IS-IS (Section 2.1 of [RFC8667]), the Prefix-SID Sub-TLV in OSPFv2 (Section 5 of [RFC8665]), and the Prefix-SID Sub-TLV in OSPFv3 (Section 6 of [RFC8666]). the way they all get stitched together is so iconic 🧚
The Prefix-SID TLV 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags | Algorithm | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SID/Index/Label (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 10: Prefix-SID TLV FormatHere's the rundown 👇
Type: 1158Length: Variable. 7 or 8 octets depending on the label or index encoding of the SID.Flags: 1-octet value that should be set as:Algorithm: 1-octet value that identifies the algorithm. The semantics of the algorithm are described in Section 3.1.1 of [RFC8402].Reserved: 2 octets that MUST be set to 0 and ignored on receipt. 🙈SID/Index/Label:
The Flags and, as an extension, the SID/Index/Label fields of this TLV are interpreted according to the respective underlying IS-IS, OSPFv2, or OSPFv3 protocol. The Protocol-ID of the BGP-LS Prefix NLRI is used to determine the underlying protocol specification for parsing these fields. the protocol ID is the key that unlocks everything 🔑
2.3.2. Prefix Attribute Flags TLV 🦋
The Prefix Attribute Flags TLV carries IPv4/IPv6 prefix attribute flags information. These flags are defined for OSPFv2 in Section 2.1 of [RFC7684], OSPFv3 in Appendix A.4.1.1 of [RFC5340], and IS-IS in Section 2.1 of [RFC7794]. it's giving organized 📚
The Prefix Attribute Flags TLV 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 11: Prefix Attribute Flags TLV FormatWhere:
Type: 1170Length: Variable.Flags: a variable-length Flag field (according to the Length field). Flags are routing protocol specific and are to be set as below:- IS-IS flags correspond to the IPv4/IPv6 Extended Reachability Attribute Flags defined in Section 2.1 of [RFC7794]. In the case of the X-flag when associated with IPv6 prefix reachability, the setting corresponds to the setting of the X-flag in the fixed format of IS-IS TLVs 236 [RFC5308] and 237 [RFC5120].
- OSPFv2 flags correspond to the Flags field of the OSPFv2 Extended Prefix TLV defined in Section 2.1 of [RFC7684].
- OSPFv3 flags map to the Prefix Options field defined in Appendix A.4.1.1 of [RFC5340] and extended in Section 3.1 of [RFC8362].
The Flags field of this TLV is interpreted according to the respective underlying IS-IS, OSPFv2, or OSPFv3 protocol. The Protocol-ID of the BGP-LS Prefix NLRI is used to determine the underlying protocol specification for parsing this field. same energy as the Prefix-SID TLV, just with flags 🚩
2.3.3. Source Router Identifier TLV 🌸
The Source Router Identifier TLV contains the IPv4 or IPv6 Router Identifier of the originator of the prefix. For the IS-IS protocol, this is derived from the IPv4/IPv6 Source Router ID Sub-TLV as defined in Section 2.2 of [RFC7794]. For the OSPF protocol, this is derived from the Prefix Source Router Address Sub-TLV as defined in Section 2.2 of [RFC9084].
The Source Router Identifier TLV 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 4- or 16-octet Router Identifier //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 12: Source Router Identifier TLV FormatWhere:
Type: 1171Length: Variable. 4 or 16 octets for the IPv4 or IPv6 prefix, respectively.Router-ID: the IPv4 or IPv6 Router-ID in the case of IS-IS, and the IPv4 or IPv6 Router Address in the case of OSPF.
2.3.4. Source OSPF Router-ID TLV 🍓
The Source OSPF Router-ID TLV is applicable only for the OSPF protocol and contains the OSPF Router-ID of the originator of the prefix. It is derived from the Prefix Source OSPF Router-ID Sub-TLV as defined in Section 2.1 of [RFC9084]. this one's OSPF-only, so no drama 💅
The Source OSPF Router-ID TLV 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 4-octet OSPF Router-ID //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 13: Source OSPF Router-ID TLV FormatWhere:
Type: 1174Length: 4 octetsOSPF Router-ID: the OSPF Router-ID of the node originating the prefix.
2.3.5. Range TLV 🧚♀️
The Range TLV is used to advertise a range of prefix-to-SID mappings as part of the SRMS functionality [RFC8661], as defined in the respective underlying IGP SR extensions: Section 4 of [RFC8665], Section 5 of [RFC8666], and Section 2.4 of [RFC8667]. The information advertised in the Range TLV is derived from the SID/Label Binding TLV in the case of IS-IS and the OSPFv2/OSPFv3 Extended Prefix Range TLV in the case of OSPFv2/OSPFv3.
A Prefix NLRI, that has been advertised with a Range TLV, is considered a normal routing prefix (i.e., prefix reachability) only when there is also an IGP metric TLV (TLV 1095) associated it. Otherwise, it is considered only as the first prefix in the range for prefix-to-SID mapping advertisement. the first prefix has a special job here, bestie 👑
The Range TLV 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags | Reserved | Range Size |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| sub-TLVs //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 14: Range TLV FormatWhere:
Type: 1159Length: Variable. 11 or 12 octets depending on the label or index encoding of the SID.Flags: 1-octet value that should be set as:Reserved: 1 octet that MUST be set to 0 and ignored on receipt.Range Size: 2 octets that carry the number of prefixes that are covered by the advertisement.
The Flags field of this TLV is interpreted according to the respective underlying IS-IS, OSPFv2, or OSPFv3 protocol. The Protocol-ID of the BGP-LS Prefix NLRI is used to determine the underlying protocol specification for parsing this field.
The prefix-to-SID mappings are advertised using sub-TLVs as below:
IS-IS:
SID/Label Range TLV
Prefix-SID Sub-TLV
OSPFv2/OSPFv3:
OSPFv2/OSPFv3 Extended Prefix Range TLV
Prefix-SID Sub-TLV
BGP-LS:
Range TLV
Prefix-SID TLV (used as a sub-TLV in this context)The prefix-to-SID mapping information for the BGP-LS Prefix-SID TLV (used as a sub-TLV in this context) is encoded as described in Section 2.3.1. 🫶
2.4. Equivalent IS-IS Segment Routing TLVs/Sub-TLVs 🌈
This section illustrates the IS-IS Segment Routing Extensions TLVs and sub-TLVs mapped to the ones defined in this document. basically a cheat sheet so you can match everything up 📝
For each BGP-LS TLV, the following table illustrates its equivalence in IS-IS.
+========================+==============================+===========+
| Description | IS-IS TLV/sub-TLV | Reference |
+========================+==============================+===========+
| SR Capabilities | SR-Capabilities Sub-TLV (2) | [RFC8667] |
+------------------------+------------------------------+-----------+
| SR Algorithm | SR-Algorithm Sub-TLV (19) | [RFC8667] |
+------------------------+------------------------------+-----------+
| SR Local Block | SR Local Block Sub-TLV (22) | [RFC8667] |
+------------------------+------------------------------+-----------+
| SRMS Preference | SRMS Preference Sub-TLV (19) | [RFC8667] |
+------------------------+------------------------------+-----------+
| Adjacency SID | Adj-SID Sub-TLV (31) | [RFC8667] |
+------------------------+------------------------------+-----------+
| LAN Adjacency SID | LAN-Adj-SID Sub-TLV (32) | [RFC8667] |
+------------------------+------------------------------+-----------+
| Prefix-SID | Prefix-SID Sub-TLV (3) | [RFC8667] |
+------------------------+------------------------------+-----------+
| Range | SID/Label Binding TLV (149) | [RFC8667] |
+------------------------+------------------------------+-----------+
| SID/Label | SID/Label Sub-TLV (1) | [RFC8667] |
+------------------------+------------------------------+-----------+
| Prefix Attribute | Prefix Attribute Flags Sub- | [RFC7794] |
| Flags | TLV (4) | |
+------------------------+------------------------------+-----------+
| Source Router | IPv4/IPv6 Source Router ID | [RFC7794] |
| Identifier | Sub-TLV (11/12) | |
+------------------------+------------------------------+-----------+
| L2 Bundle Member | L2 Bundle Member Attributes | [RFC8668] |
| Attributes | TLV (25) | |
+------------------------+------------------------------+-----------+
Table 5: IS-IS Segment Routing Extensions TLVs/Sub-TLVs2.5. Equivalent OSPFv2/OSPFv3 Segment Routing TLVs/Sub-TLVs ✨
okay so this section is basically the cheat sheet 📝💖 it shows which OSPFv2 and OSPFv3 Segment Routing TLVs and sub-TLVs line up with the ones we defined in this document. bestie, it's so useful for matching things up across protocols 🫶
for each BGP-LS TLV, the tables below show its equivalent in OSPFv2 and OSPFv3 🦋
+===================+==========================+===========+
| Description | OSPFv2 TLV/sub-TLV | Reference |
+===================+==========================+===========+
| SR Capabilities | SID/Label Range TLV (9) | [RFC8665] |
+-------------------+--------------------------+-----------+
| SR Algorithm | SR-Algorithm TLV (8) | [RFC8665] |
+-------------------+--------------------------+-----------+
| SR Local Block | SR Local Block TLV (14) | [RFC8665] |
+-------------------+--------------------------+-----------+
| SRMS Preference | SRMS Preference TLV (15) | [RFC8665] |
+-------------------+--------------------------+-----------+
| Adjacency SID | Adj-SID Sub-TLV (2) | [RFC8665] |
+-------------------+--------------------------+-----------+
| LAN Adjacency SID | LAN Adj-SID Sub-TLV (3) | [RFC8665] |
+-------------------+--------------------------+-----------+
| Prefix-SID | Prefix-SID Sub-TLV (2) | [RFC8665] |
+-------------------+--------------------------+-----------+
| Range | OSPF Extended Prefix | [RFC8665] |
| | Range TLV (2) | |
+-------------------+--------------------------+-----------+
| SID/Label | SID/Label Sub-TLV (1) | [RFC8665] |
+-------------------+--------------------------+-----------+
| Prefix Attribute | Flags of OSPFv2 Extended | [RFC7684] |
| Flags | Prefix TLV (1) | |
+-------------------+--------------------------+-----------+
| Source Router | Prefix Source Router | [RFC9084] |
| Identifier | Address Sub-TLV (5) | |
+-------------------+--------------------------+-----------+
| Source OSPF | Prefix Source OSPF | [RFC9084] |
| Router-ID | Router-ID Sub-TLV (4) | |
+-------------------+--------------------------+-----------+
Table 6: OSPFv2 Segment Routing Extensions TLVs/Sub-TLVsand here's the OSPFv3 version, same vibe but with its own numbers 💅🌈
+===================+==========================+===========+
| Description | OSPFv3 TLV/sub-TLV | Reference |
+===================+==========================+===========+
| SR Capabilities | SID/Label Range TLV (9) | [RFC8665] |
+-------------------+--------------------------+-----------+
| SR Algorithm | SR-Algorithm TLV (8) | [RFC8665] |
+-------------------+--------------------------+-----------+
| SR Local Block | SR Local Block TLV (14) | [RFC8665] |
+-------------------+--------------------------+-----------+
| SRMS Preference | SRMS Preference TLV (15) | [RFC8665] |
+-------------------+--------------------------+-----------+
| Adjacency SID | Adj-SID Sub-TLV (5) | [RFC8666] |
+-------------------+--------------------------+-----------+
| LAN Adjacency SID | LAN Adj-SID Sub-TLV (6) | [RFC8666] |
+-------------------+--------------------------+-----------+
| Prefix-SID | Prefix-SID Sub-TLV (4) | [RFC8666] |
+-------------------+--------------------------+-----------+
| Range | OSPFv3 Extended Prefix | [RFC8666] |
| | Range TLV (9) | |
+-------------------+--------------------------+-----------+
| SID/Label | SID/Label Sub-TLV (7) | [RFC8666] |
+-------------------+--------------------------+-----------+
| Prefix Attribute | Prefix Option Fields of | [RFC8362] |
| Flags | Prefix TLV types 3,5,6 | |
+-------------------+--------------------------+-----------+
| Source OSPF | Prefix Source Router | [RFC9084] |
| Router Identifier | Address Sub-TLV (28) | |
+-------------------+--------------------------+-----------+
| Source OSPF | Prefix Source OSPF | [RFC9084] |
| Router-ID | Router-ID Sub-TLV (27) | |
+-------------------+--------------------------+-----------+
Table 7: OSPFv3 Segment Routing Extensions TLVs/Sub-TLVs3. IANA Considerations 🎀
okay the IANA part is where the registry stuff happens 🙈 IANA has registered the following code points in the "BGP-LS Node Descriptor, Link Descriptor, Prefix Descriptor, and Attribute TLVs" registry under the "Border Gateway Protocol - Link State (BGP-LS) Parameter" registry, based on Table 8. the column "IS-IS TLV/Sub-TLV" defined in the registry does not require any value and should be left empty 💖
3.1. TLV/Sub-TLV Code Points Summary 📋
this section has the global table of every TLV and sub-TLV defined in this document, so it's basically the master list 🌸
+================+=============================+===============+
| TLV Code Point | Description | Reference |
+================+=============================+===============+
| 1034 | SR Capabilities | Section 2.1.2 |
+----------------+-----------------------------+---------------+
| 1035 | SR Algorithm | Section 2.1.3 |
+----------------+-----------------------------+---------------+
| 1036 | SR Local Block | Section 2.1.4 |
+----------------+-----------------------------+---------------+
| 1037 | SRMS Preference | Section 2.1.5 |
+----------------+-----------------------------+---------------+
| 1099 | Adjacency SID | Section 2.2.1 |
+----------------+-----------------------------+---------------+
| 1100 | LAN Adjacency SID | Section 2.2.2 |
+----------------+-----------------------------+---------------+
| 1158 | Prefix-SID | Section 2.3.1 |
+----------------+-----------------------------+---------------+
| 1159 | Range | Section 2.3.5 |
+----------------+-----------------------------+---------------+
| 1161 | SID/Label | Section 2.1.1 |
+----------------+-----------------------------+---------------+
| 1170 | Prefix Attribute Flags | Section 2.3.2 |
+----------------+-----------------------------+---------------+
| 1171 | Source Router Identifier | Section 2.3.3 |
+----------------+-----------------------------+---------------+
| 1172 | L2 Bundle Member Attributes | Section 2.2.3 |
+----------------+-----------------------------+---------------+
| 1174 | Source OSPF Router-ID | Section 2.3.4 |
+----------------+-----------------------------+---------------+
Table 8: Summary of TLV/Sub-TLV Code Points4. Manageability Considerations 🔥
okay manageability is all about how operators keep this stuff running smoothly 🧚 this section is structured as recommended in [RFC5706].
the new protocol extensions in this document augment the existing IGP topology information that gets distributed via [RFC7752]. the procedures and protocol extensions defined here do not affect BGP protocol operations and management, other than as discussed in the Manageability Considerations section of [RFC7752] 💅 specifically, the malformed attribute tests for syntactic checks in the Fault Management section of [RFC7752] now cover the new BGP-LS Attribute TLVs defined in this document. the semantic or content checking for the TLVs specified in this document, and their association with the BGP-LS NLRI types or their BGP-LS Attribute, is left to the consumer of the BGP-LS information (e.g., an application or a controller) and not the BGP protocol 🫶
a consumer of the BGP-LS information retrieves this information over a BGP-LS session (refer to Sections 1 and 2 of [RFC7752]). how the consumer handles semantic or content errors is dictated by the nature of its application usage, so it's beyond the scope of this document 🦋
this document only introduces new Attribute TLVs, and any syntactic error in them would result in the BGP-LS Attribute being discarded with an error log 💀 the SR information introduced in BGP-LS by this specification may be used by BGP-LS consumer applications like an SR Path Computation Engine (PCE) to learn the SR capabilities of the nodes in the topology and the mapping of SR segments to those nodes. this can enable the SR PCE to perform path computations based on SR for traffic engineering use cases, and to steer traffic on paths different from the underlying IGP-based distributed best-path computation 🔥 errors in the encoding or decoding of the SR information may result in the unavailability of such information to the SR PCE, or incorrect information being made available to it. this may result in the SR PCE not being able to perform the desired SR-based optimization functionality, or to perform it in an unexpected or inconsistent manner 😭 the handling of such errors by applications like SR PCE may be implementation specific and out of scope of this document 🙈
the extensions specified in this document do not introduce any new configuration or monitoring aspects in BGP or BGP-LS, other than as discussed in [RFC7752] ✨ the manageability aspects of the underlying SR features are covered by [RFC9020], [ISIS-SR-YANG], and [OSPF-SR-YANG] 👑
5. Security Considerations ✨
okay bestie, security time 🔐💅 this doc's new protocol extensions are basically riding on the existing IGP topology info that [RFC7752] already passes around 🦋. The SR link attribute info advertised here carries a similar risk to the link attribute info [RFC7752] already covers, no cap. The Security Considerations section of [RFC7752] also applies to these extensions 🫶. The new procedures and TLVs in this document don't, by themselves, change the BGP-LS security model from [RFC7752] 💜.
The TLVs introduced here propagate IGP-defined information (see [RFC8665], [RFC8666], and [RFC8667]) 🧚. They carry the SR information tied to the IGP node, link, and prefix. The IGP instances that originate these TLVs are assumed to support all the required security and authentication mechanisms (as described in [RFC8665], [RFC8666], and [RFC8667]) so that no security issue shows up when those TLVs get propagated into BGP-LS 🌸.
BGP-LS SR extensions enable traffic engineering use cases within the SR domain 👑. SR operates within a trusted domain [RFC8402], and its security considerations also apply to BGP-LS sessions when they carry SR information. The SR traffic engineering policies that use SIDs advertised via BGP-LS are expected to be used entirely within this trusted SR domain (e.g., between multiple ASes/domains within a single provider network). So precaution is necessary to make sure the link-state information (including SR information) advertised via BGP-LS sessions only reaches consumers, in a secure manner, inside this trusted SR domain 🔥. BGP peering sessions for address families other than link state may be set up to routers outside the SR domain.
🚨 bestie, this is the big one: the isolation of BGP-LS peering sessions is recommended so that BGP-LS topology information (including the newly added SR information) is never advertised to an external BGP peering session outside the SR domain. Keep that wall up 🙈
6. References
6.1. Normative References
- [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997,
https://www.rfc-editor.org/info/rfc2119. - [RFC4202] Kompella, K., Ed. and Y. Rekhter, Ed., "Routing Extensions in Support of Generalized Multi-Protocol Label Switching (GMPLS)", RFC 4202, DOI 10.17487/RFC4202, October 2005,
https://www.rfc-editor.org/info/rfc4202. - [RFC5120] Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi Topology (MT) Routing in Intermediate System to Intermediate Systems (IS-ISs)", RFC 5120, DOI 10.17487/RFC5120, February 2008,
https://www.rfc-editor.org/info/rfc5120. - [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. - [RFC7684] Psenak, P., Gredler, H., Shakir, R., Henderickx, W., Tantsura, J., and A. Lindem, "OSPFv2 Prefix/Link Attribute Advertisement", RFC 7684, DOI 10.17487/RFC7684, November 2015,
https://www.rfc-editor.org/info/rfc7684. - [RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and S. Ray, "North-Bound Distribution of Link-State and Traffic Engineering (TE) Information Using BGP", RFC 7752, DOI 10.17487/RFC7752, March 2016,
https://www.rfc-editor.org/info/rfc7752. - [RFC7794] Ginsberg, L., Ed., Decraene, B., Previdi, S., Xu, X., and U. Chunduri, "IS-IS Prefix Attributes for Extended IPv4 and IPv6 Reachability", RFC 7794, DOI 10.17487/RFC7794, March 2016,
https://www.rfc-editor.org/info/rfc7794. - [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. - [RFC8362] Lindem, A., Roy, A., Goethals, D., Reddy Vallem, V., and F. Baker, "OSPFv3 Link State Advertisement (LSA) Extensibility", RFC 8362, DOI 10.17487/RFC8362, April 2018,
https://www.rfc-editor.org/info/rfc8362. - [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. - [RFC8571] Ginsberg, L., Ed., Previdi, S., Wu, Q., Tantsura, J., and C. Filsfils, "BGP - Link State (BGP-LS) Advertisement of IGP Traffic Engineering Performance Metric Extensions", RFC 8571, DOI 10.17487/RFC8571, March 2019,
https://www.rfc-editor.org/info/rfc8571. - [RFC8665] Psenak, P., Ed., Previdi, S., Ed., Filsfils, C., Gredler, H., Shakir, R., Henderickx, W., and J. Tantsura, "OSPF Extensions for Segment Routing", RFC 8665, DOI 10.17487/RFC8665, December 2019,
https://www.rfc-editor.org/info/rfc8665. - [RFC8666] Psenak, P., Ed. and S. Previdi, Ed., "OSPFv3 Extensions for Segment Routing", RFC 8666, DOI 10.17487/RFC8666, December 2019,
https://www.rfc-editor.org/info/rfc8666. - [RFC8667] Previdi, S., Ed., Ginsberg, L., Ed., Filsfils, C., Bashandy, A., Gredler, H., and B. Decraene, "IS-IS Extensions for Segment Routing", RFC 8667, DOI 10.17487/RFC8667, December 2019,
https://www.rfc-editor.org/info/rfc8667. - [RFC8668] Ginsberg, L., Ed., Bashandy, A., Filsfils, C., Nanduri, M., and E. Aries, "Advertising Layer 2 Bundle Member Link Attributes in IS-IS", RFC 8668, DOI 10.17487/RFC8668, December 2019,
https://www.rfc-editor.org/info/rfc8668. - [RFC9084] Wang, A., Lindem, A., Dong, J., Psenak, P., and K. Talaulikar, Ed., "OSPF Prefix Originator Extensions", RFC 9084, DOI 10.17487/RFC9084, August 2021,
https://www.rfc-editor.org/info/rfc9084.
6.2. Informative References
- [ISIS-SR-YANG] Litkowski, S., Qu, Y., Sarkar, P., Chen, I., and J. Tantsura, "YANG Data Model for IS-IS Segment Routing", Work in Progress, Internet-Draft, draft-ietf-isis-sr-yang-10, 21 February 2021,
https://datatracker.ietf.org/doc/html/draft-ietf-isis-sr-yang-10. - [OSPF-SR-YANG] Yeung, D., Qu, Y., Zhang, J., Chen, I., and A. Lindem, "YANG Data Model for OSPF SR (Segment Routing) Protocol", Work in Progress, Internet-Draft, draft-ietf-ospf-sr-yang-15, 2 July 2021,
https://datatracker.ietf.org/doc/html/draft-ietf-ospf-sr-yang-15. - [RFC5706] Harrington, D., "Guidelines for Considering Operations and Management of New Protocols and Protocol Extensions", RFC 5706, DOI 10.17487/RFC5706, November 2009,
https://www.rfc-editor.org/info/rfc5706. - [RFC8661] Bashandy, A., Ed., Filsfils, C., Ed., Previdi, S., Decraene, B., and S. Litkowski, "Segment Routing MPLS Interworking with LDP", RFC 8661, DOI 10.17487/RFC8661, December 2019,
https://www.rfc-editor.org/info/rfc8661. - [RFC9020] Litkowski, S., Qu, Y., Lindem, A., Sarkar, P., and J. Tantsura, "YANG Data Model for Segment Routing", RFC 9020, DOI 10.17487/RFC9020, May 2021,
https://www.rfc-editor.org/info/rfc9020.
Acknowledgements 🙏
The authors would like to thank Jeffrey Haas, Aijun Wang, Robert Raszuk, and Susan Hares for their review of this document and their comments. The authors would also like to thank Alvaro Retana for his extensive review and comments, which helped correct issues and improve the document 🌈.
Contributors 💖
The following people have substantially contributed to the editing of this document:
- Peter Psenak, Cisco Systems, Email:
ppsenak@cisco.com - Les Ginsberg, Cisco Systems, Email:
ginsberg@cisco.com - Acee Lindem, Cisco Systems, Email:
acee@cisco.com - Saikat Ray, Individual, Email:
raysaikat@gmail.com - Jeff Tantsura, Apstra Inc., Email:
jefftant.ietf@gmail.com
Authors' Addresses 🎀
- Stefano Previdi, Huawei Technologies, Rome, Italy, Email:
stefano@previdi.net - Ketan Talaulikar (editor), Cisco Systems, Inc., India, Email:
ketant@cisco.com - Clarence Filsfils, Cisco Systems, Inc., Brussels, Belgium, Email:
cfilsfil@cisco.com - Hannes Gredler, RtBrick Inc., Email:
hannes@rtbrick.com - Mach(Guoyi) Chen, Huawei Technologies, Huawei Building, No. 156 Beiqing Rd., Beijing, 100095, China, Email:
mach.chen@huawei.com
📦 where this page comes from
- ietf: rfc9085 2021-08
- 💖 girlified by claude-haiku-5-5 on : a language model's rewrite of the original, under its terms