Border Gateway Protocol - Link State (BGP-LS) Extensions for Segment Routing Huawei Technologies
Rome Italy stefano@previdi.net
Cisco Systems, Inc.
India ketant@cisco.com
Cisco Systems, Inc.
Brussels Belgium cfilsfil@cisco.com
RtBrick Inc.
hannes@rtbrick.com
Huawei Technologies
Huawei Building, No. 156 Beiqing Rd. Beijing 100095 China mach.chen@huawei.com
Routing Inter-Domain Routing BGP-LS Segment Routing SID MPLS Label advertisement IS-IS OSPF OSPFv3 Segment Routing (SR) allows for a flexible definition of end-to-end paths by encoding paths as sequences of topological subpaths, called "segments". These segments are advertised by routing protocols, e.g., by the link-state routing protocols (IS-IS, OSPFv2, and OSPFv3) within IGP topologies. This document defines extensions to the Border Gateway Protocol - Link State (BGP-LS) address family in order to carry SR information via BGP.
Status of This Memo This is an Internet Standards Track document. This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 7841. Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at .
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Table of Contents
  • .  Introduction
    • .  Requirements Language
  • .  BGP-LS Extensions for Segment Routing
    • .  Node Attribute TLVs
      • .  SID/Label TLV
      • .  SR Capabilities TLV
      • .  SR-Algorithm TLV
      • .  SR Local Block TLV
      • .  SRMS Preference TLV
    • .  Link Attribute TLVs
      • .  Adjacency SID TLV
      • .  LAN Adjacency SID TLV
      • .  L2 Bundle Member Attributes TLV
    • .  Prefix Attribute TLVs
      • .  Prefix-SID TLV
      • .  Prefix Attribute Flags TLV
      • .  Source Router Identifier TLV
      • .  Source OSPF Router-ID TLV
      • .  Range TLV
    • .  Equivalent IS-IS Segment Routing TLVs/Sub-TLVs
    • .  Equivalent OSPFv2/OSPFv3 Segment Routing TLVs/Sub-TLVs
  • .  IANA Considerations
    • .  TLV/Sub-TLV Code Points Summary
  • .  Manageability Considerations
  • .  Security Considerations
  • .  References
    • .  Normative References
    • .  Informative References
  • Acknowledgements
  • Contributors
  • Authors' Addresses
Introduction Segment Routing (SR) allows for a flexible definition of end-to-end paths by combining subpaths called "segments". A segment can represent any instruction: topological or service based. A segment can have a local semantic to an SR node or global semantic within a domain. Within IGP topologies, an SR path is encoded as a sequence of topological subpaths, called "IGP segments". These segments are advertised by the link-state routing protocols (IS-IS, OSPFv2, and OSPFv3). defines the link-state IGP segments -- prefix, node, anycast, and adjacency segments. Prefix segments, by default, represent an ECMP-aware shortest-path to a prefix, as per the state of the IGP topology. Adjacency segments represent a hop over a specific adjacency between two nodes in the IGP. A prefix segment is typically a multi-hop path while an adjacency segment, in most of the cases, is a one-hop path. Node and anycast segments are variations of the prefix segment with their specific characteristics. When SR is enabled in an IGP domain, segments are advertised in the form of Segment Identifiers (SIDs). The IGP link-state routing protocols have been extended to advertise SIDs and other SR-related information. IGP extensions are described for: IS-IS, OSPFv2, and OSPFv3. Using these extensions, SR can be enabled within an IGP domain. SR allows advertisement of single or multi-hop paths. The flooding scope for the IGP extensions for SR is IGP area-wide. Consequently, the contents of a Link-State Database (LSDB) or a Traffic Engineering Database (TED) has the scope of an IGP area; therefore, by using the IGP alone, it is not enough to construct segments across multiple IGP area or Autonomous System (AS) boundaries. In order to address the need for applications that require topological visibility across IGP areas, or even across ASes, the BGP-LS address family / subaddress family have been defined to allow BGP to carry link-state information. The BGP Network Layer Reachability Information (NLRI) encoding format for BGP-LS and a new BGP Path Attribute called the "BGP-LS Attribute" are defined in . The identifying key of each link-state object, namely a node, link, or prefix, is encoded in the NLRI, and the properties of the object are encoded in the BGP-LS Attribute.
Link-State Information Collection +------------+ | Consumer | +------------+ ^ | v +-------------------+ | BGP Speaker | +-----------+ | (Route Reflector) | | Consumer | +-------------------+ +-----------+ ^ ^ ^ ^ | | | | +---------------+ | +-------------------+ | | | | | v v v v +-----------+ +-----------+ +-----------+ | BGP | | BGP | | BGP | | Speaker | | Speaker | . . . | Speaker | +-----------+ +-----------+ +-----------+ ^ ^ ^ | | | IGP IGP IGP
denotes a typical deployment scenario. 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. This way, all BGP speakers (specifically the route reflectors) obtain link-state information from all IGP areas (and from other ASes from External BGP (EBGP) peers). An external component connects to the route reflector to obtain this information (perhaps moderated by a policy regarding what information is or isn't advertised to the external component) as described in . This document describes extensions to BGP-LS to advertise the SR information. An external component (e.g., a controller) can collect SR information from across an SR domain (as described in ) and construct the end-to-end path (with its associated SIDs) that needs to be applied to an incoming packet to achieve the desired end-to-end forwarding. SR operates within a trusted domain consisting of a single AS or multiple ASes managed by the same administrative entity, e.g., within a single provider network.
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 when, and only when, they appear in all capitals, as shown here.
BGP-LS Extensions for Segment Routing This document defines SR extensions to BGP-LS and specifies the TLVs and sub-TLVs for advertising SR information within the BGP-LS Attribute. Sections and list the equivalent TLVs and sub-TLVs in the IS-IS, OSPFv2, and OSPFv3 protocols. BGP-LS defines the BGP-LS NLRI that can be a Node NLRI, a Link NLRI, or a Prefix NLRI, and it defines the TLVs that map link-state information to BGP-LS NLRI within the BGP-LS Attribute. This document adds additional BGP-LS Attribute TLVs in order to encode SR information. It does not introduce any changes to the encoding of the BGP-LS NLRIs.
Node Attribute TLVs The following Node Attribute TLVs are defined: Node Attribute TLVs
Type Description Section
1161 SID/Label
1034 SR Capabilities
1035 SR Algorithm
1036 SR Local Block
1037 SRMS Preference
These TLVs should only be added to the BGP-LS Attribute associated with the Node NLRI that describes the IGP node that is originating the corresponding IGP TLV/sub-TLV described below.
SID/Label TLV The SID/Label TLV is used as a sub-TLV by the SR Capabilities () and Segment Routing Local Block (SRLB) () TLVs. This information is derived from the protocol-specific advertisements.
  • IS-IS, as defined by the SID/Label Sub-TLV in .
  • OSPFv2/OSPFv3, as defined by the SID/Label Sub-TLV in and .
The TLV has the following format:
SID/Label TLV 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) // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Where:
Type:
1161
Length:
Variable. Either 3 or 4 octets depending on whether the value is encoded as a label or as an index/SID.
SID/Label:
If the length is set to 3, then the 20 rightmost bits represent a label (the total TLV size is 7), and the 4 leftmost bits are set to 0. If the length is set to 4, then the value represents a 32-bit SID (the total TLV size is 8).
SR Capabilities TLV The SR Capabilities TLV is used in order to advertise the node's SR capabilities including its Segment Routing Global Base (SRGB) range(s). In the case of IS-IS, the capabilities also include the IPv4 and IPv6 support for the SR-MPLS forwarding plane. This information is derived from the protocol-specific advertisements.
  • IS-IS, as defined by the SR-Capabilities Sub-TLV in .
  • OSPFv2/OSPFv3, as defined by the SID/Label Range TLV in . OSPFv3 leverages the same TLV as defined for OSPFv2.
The SR Capabilities TLV has the following format:
SR Capabilities TLV 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Range Size 1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SID/Label Sub-TLV 1 // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Range Size N | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SID/Label Sub-TLV N // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Where:
Type:
1034
Length:
Variable. The minimum length is 12 octets.
Flags:
1 octet of flags as defined in for IS-IS. The flags are not currently defined for OSPFv2 and OSPFv3 and MUST be set to 0 and ignored on receipt.
Reserved:
1 octet that MUST be set to 0 and ignored on receipt.
One or more entries, each of which have the following format:
Range Size:
3 octets with a non-zero value indicating the number of labels in the range.
SID/Label TLV:
(as defined in ) 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.
SR-Algorithm TLV The SR-Algorithm TLV is used in order to advertise the SR algorithms supported by the node. This information is derived from the protocol-specific advertisements.
  • IS-IS, as defined by the SR-Algorithm Sub-TLV in .
  • OSPFv2/OSPFv3, as defined by the SR-Algorithm TLV in . OSPFv3 leverages the same TLV as defined for OSPFv2.
The SR-Algorithm TLV has the following format:
SR-Algorithm TLV 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Algorithm 1 | Algorithm... | Algorithm N | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Where:
Type:
1035
Length:
Variable. The minimum length is 1 octet and the maximum can be 256.
Algorithm:
One or more fields of 1 octet each that identifies the algorithm.
SR Local Block TLV The SRLB TLV contains the range(s) of labels the node has reserved for local SIDs. Local SIDs are used, e.g., in IGP (IS-IS, OSPF) for Adjacency SIDs and may also be allocated by components other than IGP protocols. As an example, an application or a controller may instruct a node to allocate a specific local SID. Therefore, in order for such applications or controllers to know the range of local SIDs available, the node is required to advertise its SRLB. This information is derived from the protocol-specific advertisements.
  • IS-IS, as defined by the SRLB Sub-TLV in .
  • OSPFv2/OSPFv3, as defined by the SR Local Block TLV in . OSPFv3 leverages the same TLV as defined for OSPFv2.
The SRLB TLV has the following format:
SRLB TLV 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 // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Where:
Type:
1036
Length:
Variable. The minimum length is 12 octets.
Flags:
1 octet of flags. The flags are as defined in for IS-IS. The flags are not currently defined for OSPFv2 and OSPFv3 and MUST be set to 0 and ignored on receipt.
Reserved:
1 octet that MUST be set to 0 and ignored on receipt.
One or more entries corresponding to a sub-range(s), each of which have the following format:
Range Size:
3-octet value indicating the number of labels in the range.
SID/Label TLV:
(as defined in ) 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.
SRMS Preference TLV The Segment Routing Mapping Server (SRMS) Preference TLV is used in order to associate a preference with SRMS advertisements from a particular source. specifies the SRMS functionality along with the SRMS preference of the node advertising the SRMS Prefix-to-SID mapping ranges. This information is derived from the protocol-specific advertisements.
  • IS-IS, as defined by the SRMS Preference Sub-TLV in .
  • OSPFv2/OSPFv3, as defined by the SRMS Preference TLV in . OSPFv3 leverages the same TLV as defined for OSPFv2.
The SRMS Preference TLV has the following format:
SRMS Preference TLV 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 | +-+-+-+-+-+-+-+-+
Where:
Type:
1037
Length:
1 octet
Preference:
1 octet carrying an unsigned 8-bit SRMS preference.
Link Attribute TLVs The following Link Attribute TLVs are defined: Link Attribute TLVs
Type Description Section
1099 Adjacency SID TLV
1100 LAN Adjacency SID TLV
1172 L2 Bundle Member Attributes TLV
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.
Adjacency SID TLV The Adjacency SID TLV is used in order to advertise information related to an Adjacency SID. This information is derived from the Adj-SID Sub-TLV of IS-IS (), OSPFv2 (), and OSPFv3 (). The Adjacency SID TLV has the following format:
Adjacency SID TLV 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 | Weight | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SID/Label/Index (variable) // +---------------------------------------------------------------+
Where:
Type:
1099
Length:
Variable. Either 7 or 8 octets depending on the label or index encoding of the SID.
Flags:
1-octet value that should be set as:
  • IS-IS Adj-SID flags as defined in .
  • OSPFv2 Adj-SID flags as defined in .
  • OSPFv3 Adj-SID flags as defined in .
Weight:
1 octet carrying the weight used for load-balancing purposes. The use of weight is described in .
Reserved:
2 octets that MUST be set to 0 and ignored on receipt.
SID/Index/Label:

IS-IS:
Label or index value as defined in .
OSPFv2:
Label or index value as defined in .
OSPFv3:
Label or index value as defined in .
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 Link NLRI is used to determine the underlying protocol specification for parsing these fields.
LAN Adjacency SID TLV For a LAN, normally a node only announces its adjacency to the IS-IS pseudonode (or the equivalent OSPF Designated and Backup Designated Routers). The LAN Adjacency SID TLV allows a node to announce adjacencies to all other nodes attached to the LAN in a single instance of the BGP-LS Link NLRI. Without this TLV, the corresponding BGP-LS Link NLRI would need to be originated for each additional adjacency in order to advertise the SR TLVs for these neighbor adjacencies. This information is derived from the LAN-Adj-SID Sub-TLV of IS-IS (), the LAN Adj-SID Sub-TLV of OSPFv2 (), and the LAN Adj-SID Sub-TLV of OSPFv3 (). The LAN Adjacency SID TLV has the following format:
LAN Adjacency SID TLV 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 | Weight | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | OSPF Neighbor ID / IS-IS System ID | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SID/Label/Index (variable) // +---------------------------------------------------------------+
Where:
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:
  • IS-IS LAN Adj-SID flags as defined in .
  • OSPFv2 LAN Adj-SID flags as defined in .
  • OSPFv3 LAN Adj-SID flags as defined in .
Weight:
1 octet carrying the weight used for load-balancing purposes. The use of weight is described in .
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:

IS-IS:
Label or index value as defined in .
OSPFv2:
Label or index value as defined in .
OSPFv3:
Label or index value as defined in .
The Neighbor ID, 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 Link NLRI is used to determine the underlying protocol specification for parsing these fields.
L2 Bundle Member Attributes TLV The L2 Bundle Member Attributes TLV identifies an L2 Bundle Member link, which in turn is associated with a parent L3 link. The L3 link is described by the Link NLRI defined in , and the L2 Bundle Member Attributes TLV is associated with the Link NLRI. The TLV MAY include sub-TLVs that describe attributes associated with the bundle member. The identified bundle member represents a unidirectional path from the originating router to the neighbor specified in the parent L3 link. Multiple L2 Bundle Member Attributes TLVs MAY be associated with a Link NLRI. This information is derived from L2 Bundle Member Attributes TLV of IS-IS (). The equivalent functionality has not been specified as yet for OSPF. The L2 Bundle Member Attributes TLV has the following format:
L2 Bundle Member Attributes TLV 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | L2 Bundle Member Descriptor | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Link Attribute Sub-TLVs(variable) // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Where:
Type:
1172
Length:
Variable.
L2 Bundle Member Descriptor:
4-octet field that carries a link-local identifier as defined in .
Link attributes for L2 Bundle Member links are advertised as sub-TLVs of the L2 Bundle Member Attributes TLV. The sub-TLVs are identical to existing BGP-LS TLVs as identified in the table below. BGP-LS Attribute TLVs are also used as sub-TLVs of the L2 Bundle Member Attributes TLV
TLV Code Point Description Reference Document
1088 Administrative group (color)
1089 Maximum link bandwidth
1090 Max. reservable link bandwidth
1091 Unreserved bandwidth
1092 TE default metric
1093 Link protection type
1099 Adjacency Segment Identifier (Adj-SID) TLV
1100 LAN Adjacency Segment Identifier (Adj-SID) TLV
1114 Unidirectional link delay
1115 Min/Max Unidirectional link delay
1116 Unidirectional Delay Variation
1117 Unidirectional Link Loss
1118 Unidirectional residual bandwidth
1119 Unidirectional available bandwidth
1120 Unidirectional Utilized Bandwidth
Prefix Attribute TLVs The following Prefix Attribute TLVs are defined: Prefix Attribute TLVs
Type Description Section
1158 Prefix-SID
1159 Range
1170 Prefix Attribute Flags
1171 Source Router Identifier
1174 Source OSPF Router-ID
These TLVs should only be added to the BGP-LS Attribute associated with the Prefix NLRI that describes the prefix of the IGP node that is originating the corresponding IGP TLV/sub-TLV described below.
Prefix-SID TLV The Prefix-SID TLV is used in order to advertise information related to a Prefix-SID. This information is derived from the Prefix-SID Sub-TLV of IS-IS (), the Prefix-SID Sub-TLV of OSPFv2 (), and the Prefix-SID Sub-TLV of OSPFv3 (). The Prefix-SID TLV has the following format:
Prefix-SID TLV 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 | Algorithm | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SID/Index/Label (variable) // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Where:
Type:
1158
Length:
Variable. 7 or 8 octets depending on the label or index encoding of the SID.
Flags:
1-octet value that should be set as:
  • IS-IS Prefix-SID flags as defined in .
  • OSPFv2 Prefix-SID flags as defined in .
  • OSPFv3 Prefix-SID flags as defined in .
Algorithm:
1-octet value identifies the algorithm. The semantics of the algorithm are described in .
Reserved:
2 octets that MUST be set to 0 and ignored on receipt.
SID/Index/Label:
IS-IS:
Label or index value as defined in .
OSPFv2:
Label or index value as defined in .
OSPFv3:
Label or index value as defined in .
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.
Prefix Attribute Flags TLV The Prefix Attribute Flags TLV carries IPv4/IPv6 prefix attribute flags information. These flags are defined for OSPFv2 in , OSPFv3 in , and IS-IS in . The Prefix Attribute Flags TLV has the following format:
Prefix Attribute Flags TLV 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 (variable) // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Where:
Type:
1170
Length:
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 . 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 and 237 .
  • OSPFv2 flags correspond to the Flags field of the OSPFv2 Extended Prefix TLV defined in .
  • OSPFv3 flags map to the Prefix Options field defined in and extended in .
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.
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 . For the OSPF protocol, this is derived from the Prefix Source Router Address Sub-TLV as defined in . The Source Router Identifier TLV has the following format:
Source Router Identifier TLV 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 4- or 16-octet Router Identifier // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Where:
Type:
1171
Length:
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.
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 . The Source OSPF Router-ID TLV has the following format:
Source OSPF Router-ID TLV 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 4-octet OSPF Router-ID // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Where:
Type:
1174
Length:
4 octets
OSPF Router-ID:
the OSPF Router-ID of the node originating the prefix.
Range TLV The Range TLV is used in order to advertise a range of prefix-to-SID mappings as part of the SRMS functionality , as defined in the respective underlying IGP SR extensions: , , and . 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 format of the Range TLV is as follows:
Range TLV 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 | Range Size | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | sub-TLVs // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Where:
Type:
1159
Length:
Variable. 11 or 12 octets depending on the label or index encoding of the SID.
Flags:
1-octet value that should be set as:
  • IS-IS SID/Label Binding TLV flags as defined in .
  • OSPFv2 OSPF Extended Prefix Range TLV flags as defined in .
  • OSPFv3 Extended Prefix Range TLV flags as defined in .
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 .
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. For each BGP-LS TLV, the following table illustrates its equivalence in IS-IS. IS-IS Segment Routing Extensions TLVs/Sub-TLVs
Description IS-IS TLV/sub-TLV Reference
SR Capabilities SR-Capabilities Sub-TLV (2)
SR Algorithm SR-Algorithm Sub-TLV (19)
SR Local Block SR Local Block Sub-TLV (22)
SRMS Preference SRMS Preference Sub-TLV (19)
Adjacency SID Adj-SID Sub-TLV (31)
LAN Adjacency SID LAN-Adj-SID Sub-TLV (32)
Prefix-SID Prefix-SID Sub-TLV (3)
Range SID/Label Binding TLV (149)
SID/Label SID/Label Sub-TLV (1)
Prefix Attribute Flags Prefix Attribute Flags Sub-TLV (4)
Source Router Identifier IPv4/IPv6 Source Router ID Sub-TLV (11/12)
L2 Bundle Member Attributes L2 Bundle Member Attributes TLV (25)
Equivalent OSPFv2/OSPFv3 Segment Routing TLVs/Sub-TLVs This section illustrates the OSPFv2 and OSPFv3 Segment Routing Extensions TLVs and sub-TLVs mapped to the ones defined in this document. For each BGP-LS TLV, the following tables illustrate its equivalence in OSPFv2 and OSPFv3. OSPFv2 Segment Routing Extensions TLVs/Sub-TLVs
Description OSPFv2 TLV/sub-TLV Reference
SR Capabilities SID/Label Range TLV (9)
SR Algorithm SR-Algorithm TLV (8)
SR Local Block SR Local Block TLV (14)
SRMS Preference SRMS Preference TLV (15)
Adjacency SID Adj-SID Sub-TLV (2)
LAN Adjacency SID LAN Adj-SID Sub-TLV (3)
Prefix-SID Prefix-SID Sub-TLV (2)
Range OSPF Extended Prefix Range TLV (2)
SID/Label SID/Label Sub-TLV (1)
Prefix Attribute Flags Flags of OSPFv2 Extended Prefix TLV (1)
Source Router Identifier Prefix Source Router Address Sub-TLV (5)
Source OSPF Router-ID Prefix Source OSPF Router-ID Sub-TLV (4)
OSPFv3 Segment Routing Extensions TLVs/Sub-TLVs
Description OSPFv3 TLV/sub-TLV Reference
SR Capabilities SID/Label Range TLV (9)
SR Algorithm SR-Algorithm TLV (8)
SR Local Block SR Local Block TLV (14)
SRMS Preference SRMS Preference TLV (15)
Adjacency SID Adj-SID Sub-TLV (5)
LAN Adjacency SID LAN Adj-SID Sub-TLV (6)
Prefix-SID Prefix-SID Sub-TLV (4)
Range OSPFv3 Extended Prefix Range TLV (9)
SID/Label SID/Label Sub-TLV (7)
Prefix Attribute Flags Prefix Option Fields of Prefix TLV types 3,5,6
Source OSPF Router Identifier Prefix Source Router Address Sub-TLV (28)
Source OSPF Router-ID Prefix Source OSPF Router-ID Sub-TLV (27)
IANA Considerations 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 . The column "IS-IS TLV/Sub-TLV" defined in the registry does not require any value and should be left empty.
TLV/Sub-TLV Code Points Summary This section contains the global table of all TLVs/sub-TLVs defined in this document. Summary of TLV/Sub-TLV Code Points
TLV Code Point Description Reference
1034 SR Capabilities
1035 SR Algorithm
1036 SR Local Block
1037 SRMS Preference
1099 Adjacency SID
1100 LAN Adjacency SID
1158 Prefix-SID
1159 Range
1161 SID/Label
1170 Prefix Attribute Flags
1171 Source Router Identifier
1172 L2 Bundle Member Attributes
1174 Source OSPF Router-ID
Manageability Considerations This section is structured as recommended in . The new protocol extensions introduced in this document augment the existing IGP topology information that is distributed via . Procedures and protocol extensions defined in this document do not affect the BGP protocol operations and management other than as discussed in the Manageability Considerations section of . Specifically, the malformed attribute tests for syntactic checks in the Fault Management section of now encompass 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 and of ). The handling of semantic or content errors by the consumer would be dictated by the nature of its application usage and hence is 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 . The manageability aspects of the underlying SR features are covered by , , and .
Security Considerations The new protocol extensions introduced in this document augment the existing IGP topology information that is distributed via . The advertisement of the SR link attribute information defined in this document presents similar risk as associated with the existing set of link attribute information as described in . The Security Considerations section of also applies to these extensions. The procedures and new TLVs defined in this document, by themselves, do not affect the BGP-LS security model discussed in . The TLVs introduced in this document are used to propagate IGP-defined information (see , , and ). These TLVs represent the SR information associated with the IGP node, link, and prefix. The IGP instances originating these TLVs are assumed to support all the required security and authentication mechanisms (as described in , , and ) in order to prevent any security issue when propagating the TLVs into BGP-LS. BGP-LS SR extensions enable traffic engineering use cases within the SR domain. SR operates within a trusted domain , and its security considerations also apply to BGP-LS sessions when carrying SR information. The SR traffic engineering policies using the 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). Therefore, precaution is necessary to ensure that the link-state information (including SR information) advertised via BGP-LS sessions is limited to consumers in a secure manner within this trusted SR domain. BGP peering sessions for address families other than link state may be set up to routers outside the SR domain. The isolation of BGP-LS peering sessions is recommended to ensure that BGP-LS topology information (including the newly added SR information) is not advertised to an external BGP peering session outside the SR domain.
References Normative References Key words for use in RFCs to Indicate Requirement Levels In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. Routing Extensions in Support of Generalized Multi-Protocol Label Switching (GMPLS) This document specifies routing extensions in support of carrying link state information for Generalized Multi-Protocol Label Switching (GMPLS). This document enhances the routing extensions required to support MPLS Traffic Engineering (TE). [STANDARDS-TRACK] M-ISIS: Multi Topology (MT) Routing in Intermediate System to Intermediate Systems (IS-ISs) This document describes an optional mechanism within Intermediate System to Intermediate Systems (IS-ISs) used today by many ISPs for IGP routing within their clouds. This document describes how to run, within a single IS-IS domain, a set of independent IP topologies that we call Multi-Topologies (MTs). This MT extension can be used for a variety of purposes, such as an in-band management network "on top" of the original IGP topology, maintaining separate IGP routing domains for isolated multicast or IPv6 islands within the backbone, or forcing a subset of an address space to follow a different topology. [STANDARDS-TRACK] Routing IPv6 with IS-IS This document specifies a method for exchanging IPv6 routing information using the IS-IS routing protocol. The described method utilizes two new TLVs: a reachability TLV and an interface address TLV to distribute the necessary IPv6 information throughout a routing domain. Using this method, one can route IPv6 along with IPv4 and OSI using a single intra-domain routing protocol. [STANDARDS-TRACK] OSPF for IPv6 This document describes the modifications to OSPF to support version 6 of the Internet Protocol (IPv6). The fundamental mechanisms of OSPF (flooding, Designated Router (DR) election, area support, Short Path First (SPF) calculations, etc.) remain unchanged. However, some changes have been necessary, either due to changes in protocol semantics between IPv4 and IPv6, or simply to handle the increased address size of IPv6. These modifications will necessitate incrementing the protocol version from version 2 to version 3. OSPF for IPv6 is also referred to as OSPF version 3 (OSPFv3). Changes between OSPF for IPv4, OSPF Version 2, and OSPF for IPv6 as described herein include the following. Addressing semantics have been removed from OSPF packets and the basic Link State Advertisements (LSAs). New LSAs have been created to carry IPv6 addresses and prefixes. OSPF now runs on a per-link basis rather than on a per-IP-subnet basis. Flooding scope for LSAs has been generalized. Authentication has been removed from the OSPF protocol and instead relies on IPv6's Authentication Header and Encapsulating Security Payload (ESP). Even with larger IPv6 addresses, most packets in OSPF for IPv6 are almost as compact as those in OSPF for IPv4. Most fields and packet- size limitations present in OSPF for IPv4 have been relaxed. In addition, option handling has been made more flexible. All of OSPF for IPv4's optional capabilities, including demand circuit support and Not-So-Stubby Areas (NSSAs), are also supported in OSPF for IPv6. [STANDARDS-TRACK] OSPFv2 Prefix/Link Attribute Advertisement OSPFv2 requires functional extension beyond what can readily be done with the fixed-format Link State Advertisements (LSAs) as described in RFC 2328. This document defines OSPFv2 Opaque LSAs based on Type-Length-Value (TLV) tuples that can be used to associate additional attributes with prefixes or links. Depending on the application, these prefixes and links may or may not be advertised in the fixed-format LSAs. The OSPFv2 Opaque LSAs are optional and fully backward compatible. North-Bound Distribution of Link-State and Traffic Engineering (TE) Information Using BGP In a number of environments, a component external to a network is called upon to perform computations based on the network topology and current state of the connections within the network, including Traffic Engineering (TE) information. This is information typically distributed by IGP routing protocols within the network. This document describes a mechanism by which link-state and TE information can be collected from networks and shared with external components using the BGP routing protocol. This is achieved using a new BGP Network Layer Reachability Information (NLRI) encoding format. The mechanism is applicable to physical and virtual IGP links. The mechanism described is subject to policy control. Applications of this technique include Application-Layer Traffic Optimization (ALTO) servers and Path Computation Elements (PCEs). IS-IS Prefix Attributes for Extended IPv4 and IPv6 Reachability This document introduces new sub-TLVs to support advertisement of IPv4 and IPv6 prefix attribute flags and the source router ID of the router that originated a prefix advertisement. Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings. OSPFv3 Link State Advertisement (LSA) Extensibility OSPFv3 requires functional extension beyond what can readily be done with the fixed-format Link State Advertisement (LSA) as described in RFC 5340. Without LSA extension, attributes associated with OSPFv3 links and advertised IPv6 prefixes must be advertised in separate LSAs and correlated to the fixed-format LSAs. This document extends the LSA format by encoding the existing OSPFv3 LSA information in Type-Length-Value (TLV) tuples and allowing advertisement of additional information with additional TLVs. Backward-compatibility mechanisms are also described. This document updates RFC 5340, "OSPF for IPv6", and RFC 5838, "Support of Address Families in OSPFv3", by providing TLV-based encodings for the base OSPFv3 unicast support and OSPFv3 address family support. Segment Routing Architecture Segment Routing (SR) leverages the source routing paradigm. A node steers a packet through an ordered list of instructions, called "segments". A segment can represent any instruction, topological or service based. A segment can have a semantic local to an SR node or global within an SR domain. SR provides a mechanism that allows a flow to be restricted to a specific topological path, while maintaining per-flow state only at the ingress node(s) to the SR domain. SR can be directly applied to the MPLS architecture with no change to the forwarding plane. A segment is encoded as an MPLS label. An ordered list of segments is encoded as a stack of labels. The segment to process is on the top of the stack. Upon completion of a segment, the related label is popped from the stack. SR can be applied to the IPv6 architecture, with a new type of routing header. A segment is encoded as an IPv6 address. An ordered list of segments is encoded as an ordered list of IPv6 addresses in the routing header. The active segment is indicated by the Destination Address (DA) of the packet. The next active segment is indicated by a pointer in the new routing header. BGP - Link State (BGP-LS) Advertisement of IGP Traffic Engineering Performance Metric Extensions This document defines new BGP - Link State (BGP-LS) TLVs in order to carry the IGP Traffic Engineering Metric Extensions defined in the IS-IS and OSPF protocols. OSPF Extensions for Segment Routing Segment Routing (SR) allows a flexible definition of end-to-end paths within IGP topologies by encoding paths as sequences of topological subpaths called "segments". These segments are advertised by the link-state routing protocols (IS-IS and OSPF). This document describes the OSPFv2 extensions required for Segment Routing. OSPFv3 Extensions for Segment Routing Segment Routing (SR) allows a flexible definition of end-to-end paths within IGP topologies by encoding paths as sequences of topological subpaths called "segments". These segments are advertised by the link-state routing protocols (IS-IS and OSPF). This document describes the OSPFv3 extensions required for Segment Routing with the MPLS data plane. IS-IS Extensions for Segment Routing Segment Routing (SR) allows for a flexible definition of end-to-end paths within IGP topologies by encoding paths as sequences of topological sub-paths, called "segments". These segments are advertised by the link-state routing protocols (IS-IS and OSPF). This document describes the IS-IS extensions that need to be introduced for Segment Routing operating on an MPLS data plane. Advertising Layer 2 Bundle Member Link Attributes in IS-IS There are deployments where the Layer 3 interface on which IS-IS operates is a Layer 2 interface bundle. Existing IS-IS advertisements only support advertising link attributes of the Layer 3 interface. If entities external to IS-IS wish to control traffic flows on the individual physical links that comprise the Layer 2 interface bundle, link attribute information about the bundle members is required. This document introduces the ability for IS-IS to advertise the link attributes of Layer 2 (L2) Bundle Members. OSPF Prefix Originator Extensions Informative References YANG Data Model for IS-IS Segment Routing Cisco Systems Futurewei Individual The MITRE Corporation Apstra This document defines a YANG data module that can be used to configure and manage IS-IS Segment Routing, as well as a YANG data module for the management of Signaling Maximum SID Depth (MSD) Using IS-IS. Work in Progress YANG Data Model for OSPF SR (Segment Routing) Protocol Arrcus Futurewei Juniper Networks The MITRE Corporation Cisco Systems This document defines a YANG data module that can be used to configure and manage OSPF Extensions for Segment Routing. It also defines a module for management of Signaling Maximum SID Depth (MSD) Using OSPF. Work in Progress Guidelines for Considering Operations and Management of New Protocols and Protocol Extensions New protocols or protocol extensions are best designed with due consideration of the functionality needed to operate and manage the protocols. Retrofitting operations and management is sub-optimal. The purpose of this document is to provide guidance to authors and reviewers of documents that define new protocols or protocol extensions regarding aspects of operations and management that should be considered. This memo provides information for the Internet community. Segment Routing MPLS Interworking with LDP A Segment Routing (SR) node steers a packet through a controlled set of instructions, called segments, by prepending the packet with an SR header. A segment can represent any instruction, topological or service based. SR allows enforcing a flow through any topological path while maintaining per-flow state only at the ingress node to the SR domain. The Segment Routing architecture can be directly applied to the MPLS data plane with no change in the forwarding plane. This document describes how Segment Routing MPLS operates in a network where LDP is deployed and in the case where SR-capable and non-SR-capable nodes coexist. YANG Data Model for Segment Routing This document defines three YANG data models. The first is for Segment Routing (SR) configuration and operation, which is to be augmented by different Segment Routing data planes. The next is a YANG data model that defines a collection of generic types and groupings for SR. The third module defines the configuration and operational states for the Segment Routing MPLS data plane.
Acknowledgements The authors would like to thank , , , and for their review of this document and their comments. The authors would also like to thank 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: Cisco Systems
ppsenak@cisco.com
Cisco Systems
ginsberg@cisco.com
Cisco Systems
acee@cisco.com
Individual
raysaikat@gmail.com
Apstra Inc.
jefftant.ietf@gmail.com
Authors' Addresses Huawei Technologies
Rome Italy stefano@previdi.net
Cisco Systems, Inc.
India ketant@cisco.com
Cisco Systems, Inc.
Brussels Belgium cfilsfil@cisco.com
RtBrick Inc.
hannes@rtbrick.com
Huawei Technologies
Huawei Building, No. 156 Beiqing Rd. Beijing 100095 China mach.chen@huawei.com