Distribution of Link-State and Traffic Engineering Information Using BGP Cisco Systems
India ketant.ietf@gmail.com
Routing Inter-Domain Routing In many environments, a component external to a network is called upon to perform computations based on the network topology and the 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 BGP Network Layer Reachability Information (NLRI) encoding format. The mechanism applies to physical and virtual (e.g., tunnel) 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). This document obsoletes RFC 7752 by completely replacing that document. It makes some small changes and clarifications to the previous specification. This document also obsoletes RFC 9029 by incorporating the updates that it made to RFC 7752.
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
  • .  Motivation and Applicability
    • .  MPLS-TE with PCE
    • .  ALTO Server Network API
  • .  BGP Speaker Roles for BGP-LS
  • .  Advertising IGP Information into BGP-LS
  • .  Carrying Link-State Information in BGP
    • .  TLV Format
    • .  The Link-State NLRI
      • .  Node Descriptors
      • .  Link Descriptors
      • .  Prefix Descriptors
    • .  The BGP-LS Attribute
      • .  Node Attribute TLVs
      • .  Link Attribute TLVs
      • .  Prefix Attribute TLVs
    • .  Private Use
    • .  BGP Next-Hop Information
    • .  Inter-AS Links
    • .  OSPF Virtual Links and Sham Links
    • .  OSPFv2 Type 4 Summary-LSA & OSPFv3 Inter-Area-Router-LSA
    • .  Handling of Unreachable IGP Nodes
    • . Router-ID Anchoring Example: ISO Pseudonode
    • . Router-ID Anchoring Example: OSPF Pseudonode
    • . Router-ID Anchoring Example: OSPFv2 to IS-IS Migration
  • .  Link to Path Aggregation
    • .  Example: No Link Aggregation
    • .  Example: ASBR to ASBR Path Aggregation
    • .  Example: Multi-AS Path Aggregation
  • .  IANA Considerations
    • .  BGP-LS Registries
      • .  BGP-LS NLRI Types Registry
      • .  BGP-LS Protocol-IDs Registry
      • .  BGP-LS Well-Known Instance-IDs Registry
      • .  BGP-LS Node Flags Registry
      • .  BGP-LS MPLS Protocol Mask Registry
      • .  BGP-LS IGP Prefix Flags Registry
      • .  BGP-LS TLVs Registry
    • .  Guidance for Designated Experts
  • .  Manageability Considerations
    • .  Operational Considerations
      • .  Operations
      • .  Installation and Initial Setup
      • .  Migration Path
      • .  Requirements for Other Protocols and Functional Components
      • .  Impact on Network Operation
      • .  Verifying Correct Operation
    • .  Management Considerations
      • .  Management Information
      • .  Fault Management
      • .  Configuration Management
      • .  Accounting Management
      • .  Performance Management
      • .  Security Management
  • .  TLV/Sub-TLV Code Points Summary
  • . Security Considerations
  • . References
    • .  Normative References
    • .  Informative References
  • .  Changes from RFC 7752
  • Acknowledgements
  • Contributors
  • Author's Address
Introduction The contents of a Link-State Database (LSDB) or of an IGP's Traffic Engineering Database (TED) describe only the links and nodes within an IGP area. Some applications, such as end-to-end Traffic Engineering (TE), would benefit from visibility outside one area or Autonomous System (AS) to make better decisions. The IETF has defined the Path Computation Element (PCE) as a mechanism for achieving the computation of end-to-end TE paths that crosses the visibility of more than one TED or that requires CPU-intensive or coordinated computations. The IETF has also defined the ALTO server as an entity that generates an abstracted network topology and provides it to network-aware applications. Both a PCE and an ALTO server need to gather information about the topologies and capabilities of the network to be able to fulfill their function. 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 BGP Network Layer Reachability Information (NLRI) encoding format. The mechanism applies to physical and virtual (e.g., tunnel) links. The mechanism described is subject to policy control. A router maintains one or more databases for storing link-state information about nodes and links in any given area. Link attributes stored in these databases include: local/remote IP addresses, local/remote interface identifiers, link IGP metric, link TE metric, link bandwidth, reservable bandwidth, per Class-of-Service (CoS) class reservation state, preemption, and Shared Risk Link Groups (SRLGs). The router's BGP - Link State (BGP-LS) process can retrieve topology from these LSDBs and distribute it to a consumer, either directly or via a peer BGP Speaker (typically a dedicated route reflector), using the encoding specified in this document. An illustration of the collection of link-state and TE information and its distribution to consumers is shown in below.
Collection of Link-State and TE Information +-----------+ | Consumer | +-----------+ ^ | +-----------+ +-----------+ | BGP | | BGP | | Speaker |<----------->| Speaker | +-----------+ | RR1 | | RRm | | Consumer | +-----------+ +-----------+ +-----------+ ^ ^ ^ ^ | | | | +-----+ +---------+ +---------+ | | | | | +-----------+ +-----------+ +-----------+ | BGP | | BGP | | BGP | | Speaker | | Speaker | . . . | Speaker | | R1 | | R2 | | Rn | +-----------+ +-----------+ +-----------+ ^ ^ ^ | | | IGP IGP IGP
A BGP Speaker may apply a configurable policy to the information that it distributes. Thus, it may distribute the real physical topology from the LSDB or the TED. Alternatively, it may create an abstracted topology, where virtual, aggregated nodes are connected by virtual paths. Aggregated nodes can be created, for example, out of multiple routers in a Point of Presence (POP). Abstracted topology can also be a mix of physical and virtual nodes and physical and virtual links. Furthermore, the BGP Speaker can apply policy to determine when information is updated to the consumer so that there is a reduction in information flow from the network to the consumers. Mechanisms through which topologies can be aggregated or virtualized are outside the scope of this document. This document focuses on the specifications related to the origination of IGP-derived information and their propagation via BGP-LS. It also describes the advertisement into BGP-LS of information, either configured or derived, that is local to a node. In general, the procedures in this document form part of the base BGP-LS protocol specification and apply to information from other sources that are introduced into BGP-LS. This document obsoletes by completely replacing that document. It makes some small changes and clarifications to the previous specification as documented in .
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.
Motivation and Applicability This section describes use cases from which the requirements can be derived.
MPLS-TE with PCE As described in , a PCE can be used to compute MPLS-TE paths within a "domain" (such as an IGP area) or across multiple domains (such as a multi-area AS or multiple ASes).
  • Within a single area, the PCE offers enhanced computational power that may not be available on individual routers, sophisticated policy control and algorithms, and coordination of computation across the whole area.
  • If a router wants to compute an MPLS-TE path across IGP areas, then its own TED lacks visibility of the complete topology. That means that the router cannot determine the end-to-end path and cannot even select the right exit router (Area Border Router (ABR)) for an optimal path. This is an issue for large-scale networks that need to segment their core networks into distinct areas but still want to take advantage of MPLS-TE.
Previous solutions used per-domain path computation . The source router could only compute the path for the first area because the router only has full topological visibility for the first area along the path but not for subsequent areas. Per-domain path computation selects the exit ABR and other ABRs or AS Border Routers (ASBRs) as loose-hops and using the IGP-computed shortest path topology for the remainder of the path. This may lead to suboptimal paths, makes alternate/back-up path computation hard, and might result in no TE path being found when one does exist. The PCE presents a computation server that may have visibility into more than one IGP area or AS or may cooperate with other PCEs to perform distributed path computation. The PCE needs access to the TED for the area(s) it serves, but does not describe how this is achieved. Many implementations make the PCE a passive participant in the IGP so that it can learn the latest state of the network, but this may be suboptimal when the network is subject to a high degree of churn or when the PCE is responsible for multiple areas. The following figure shows how a PCE can get its TED information using the mechanism described in this document.
External PCE Node Using a TED Synchronization Mechanism +----------+ +---------+ | ----- | | BGP | | | TED |<-+-------------------------->| Speaker | | ----- | TED synchronization | | | | | mechanism +---------+ | | | | v | | ----- | | | PCE | | | ----- | +----------+ ^ | Request/ | Response v Service +----------+ Signaling +----------+ Request | Head-End | Protocol | Adjacent | -------->| Node |<------------>| Node | +----------+ +----------+
The mechanism in this document allows the necessary TED information to be collected from the IGP within the network, filtered according to configurable policy, and distributed to the PCE as necessary.
ALTO Server Network API An ALTO server is an entity that generates an abstracted network topology and provides it to network-aware applications over a web-service-based API. Example applications are peer-to-peer (P2P) clients or trackers, or Content Distribution Networks (CDNs). The abstracted network topology comes in the form of two maps: a Network Map that specifies the allocation of prefixes to Partition Identifiers (PIDs) and a Cost Map that specifies the cost between PIDs listed in the Network Map. For more details, see . ALTO abstract network topologies can be auto-generated from the physical topology of the underlying network. The generation would typically be based on policies and rules set by the operator. Both prefix and TE data are required: prefix data is required to generate ALTO Network Maps and TE (topology) data is required to generate ALTO Cost Maps. Prefix data is carried and originated in BGP, and TE data is originated and carried in an IGP. The mechanism defined in this document provides a single interface through which an ALTO server can retrieve all the necessary prefixes and network topology data from the underlying network. Note that an ALTO server can use other mechanisms to get network data, for example, peering with multiple IGP and BGP Speakers. The following figure shows how an ALTO server can get network topology information from the underlying network using the mechanism described in this document.
ALTO Server Using Network Topology Information +--------+ | Client |<--+ +--------+ | | ALTO +--------+ Topology +---------+ +--------+ | Protocol | ALTO | Sync Mechanism | BGP | | Client |<--+------------| Server |<----------------| Speaker | +--------+ | | | | | | +--------+ +---------+ +--------+ | | Client |<--+ +--------+
BGP Speaker Roles for BGP-LS In , the BGP Speakers can be seen playing different roles in the distribution of information using BGP-LS. This section introduces terms that explain the different roles of the BGP Speakers that are then used throughout the rest of this document.
BGP-LS Producer:
The term BGP-LS Producer refers to a BGP Speaker that is originating link-state information into BGP. BGP Speakers R1, R2, ... Rn originate link-state information from their underlying link-state IGP protocols into BGP-LS. If R1 and R2 are in the same IGP flooding domain, then they would ordinarily originate the same link-state information into BGP-LS. R1 may also originate information from sources other than IGP, e.g., its local node information.
BGP-LS Consumer:
The term BGP-LS Consumer refers to a consumer application/process and not a BGP Speaker. BGP Speakers RR1 and Rn are handing off the BGP-LS information that they have collected to a consumer application. The BGP protocol implementation and the consumer application may be on the same or different nodes. This document only covers the BGP implementation. The consumer application and the design of the interface between BGP and the consumer application may be implementation specific and are outside the scope of this document. The communication of information MUST be unidirectional (i.e., from a BGP Speaker to the BGP-LS Consumer application), and a BGP-LS Consumer MUST NOT be able to send information to a BGP Speaker for origination into BGP-LS.
BGP-LS Propagator:
The term BGP-LS Propagator refers to a BGP Speaker that is performing BGP protocol processing on the link-state information. BGP Speaker RRm propagates the BGP-LS information between BGP Speaker Rn and BGP Speaker RR1. The BGP implementation on RRm is propagating BGP-LS information. It performs handling of BGP-LS UPDATE messages and performs the BGP Decision Process as part of deciding what information is to be propagated. Similarly, BGP Speaker RR1 is receiving BGP-LS information from R1, R2, and RRm and propagating the information to the BGP-LS Consumer after performing BGP Decision Process.
The above roles are not mutually exclusive. The same BGP Speaker may be the BGP-LS Producer for some link-state information and BGP-LS Propagator for some other link-state information while also providing this information to a BGP-LS Consumer. The rest of this document refers to the role when describing procedures that are specific to that role. When the role is not specified, then the said procedure applies to all BGP Speakers.
Advertising IGP Information into BGP-LS The origination and propagation of IGP link-state information via BGP needs to provide a consistent and accurate view of the topology of the IGP domain. BGP-LS provides an abstraction of the IGP specifics, and BGP-LS Consumers may be varied types of applications. The link-state information advertised in BGP-LS from the IGPs is derived from the IGP LSDB built using the OSPF Link-State Advertisements (LSAs) or the IS-IS Link-State Packets (LSPs). However, it does not serve as a verbatim reflection of the originating router's LSDB. It does not include the LSA/LSP sequence number information since a single link-state object may be put together with information that is coming from multiple LSAs/LSPs. Also, not all of the information carried in LSAs/LSPs may be required or suitable for advertisement via BGP-LS (e.g., ASBR reachability in OSPF, OSPF virtual links, link-local-scoped information, etc.). The LSAs/LSPs that are purged or aged out are not included in the BGP-LS advertisement even though they may be present in the LSDB (e.g., for the IGP flooding purposes). The information from the LSAs/LSPs that is invalid or malformed or that which needs to be ignored per the respective IGP protocol specifications are also not included in the BGP-LS advertisement. The details of the interface between IGPs and BGP for the advertisement of link-state information are outside the scope of this document. In some cases, the information derived from IGP processing (e.g., combination of link-state object from across multiple LSAs/LSPs, leveraging reachability and two-way connectivity checks, etc.) is required for the advertisement of link-state information into BGP-LS.
Carrying Link-State Information in BGP The link-state information is carried in BGP UPDATE messages as: (1) BGP NLRI information carried within MP_REACH_NLRI and MP_UNREACH_NLRI attributes that describes link, node, or prefix objects and (2) a BGP path attribute (BGP-LS Attribute) that carries properties of the link, node, or prefix objects such as the link and prefix metric, auxiliary Router-IDs of nodes, etc. It is desirable to keep the dependencies on the protocol source of this attribute to a minimum and represent any content in an IGP-neutral way, such that applications that want to learn about a link-state topology do not need to know about any OSPF or IS-IS protocol specifics. This section mainly describes the procedures for a BGP-LS Producer to originate link-state information into BGP-LS.
TLV Format Information in the Link-State NLRIs and the BGP-LS Attribute is encoded in Type/Length/Value triplets. The TLV format is shown in and applies to both the NLRI and the BGP-LS Attribute encodings.
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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ // Value (variable) // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Length field defines the length of the value portion in octets (thus, a TLV with no value portion would have a length of zero). The TLV is not padded to 4-octet alignment. Unknown and unsupported types MUST be preserved and propagated within both the NLRI and the BGP-LS Attribute. The presence of unknown or unexpected TLVs MUST NOT result in the NLRI or the BGP-LS Attribute being considered malformed. An example of an unexpected TLV is when a TLV is received along with an update for a link-state object other than the one that the TLV is specified as associated with. To compare NLRIs with unknown TLVs, all TLVs within the NLRI MUST be ordered in ascending order by TLV Type. If there are multiple TLVs of the same type within a single NLRI, then the TLVs sharing the same type MUST be first in ascending order based on the Length field followed by ascending order based on the Value field. Comparison of the Value fields is performed by treating the entire field as opaque binary data and ordered lexicographically (i.e., treating each byte of binary data as a symbol to compare, with the symbols ordered by their numerical value). NLRIs having TLVs that do not follow the above ordering rules MUST be considered as malformed by a BGP-LS Propagator. This insistence on canonical ordering ensures that multiple variant copies of the same NLRI from multiple BGP-LS Producers and the ambiguity arising therefrom is prevented. For both the NLRI and BGP-LS Attribute parts, all TLVs are considered as optional except where explicitly specified as mandatory or required in specific conditions. The TLVs within the BGP-LS Attribute SHOULD be ordered in ascending order by TLV type. The BGP-LS Attribute with unordered TLVs MUST NOT be considered malformed. The origination of the same link-state information by multiple BGP-LS Producers may result in differences and inconsistencies due to the inclusion or exclusion of optional TLVs. Different optional TLVs in the NLRI results in multiple NLRIs being generated for the same link-state object. Different optional TLVs in the BGP-LS Attribute may result in the propagation of partial information. To address these inconsistencies, the BGP-LS Consumer will need to recognize and merge the duplicate information or deal with missing information. The deployment of BGP-LS Producers that consistently originate the same set of optional TLVs is recommended to mitigate such situations.
The Link-State NLRI The MP_REACH_NLRI and MP_UNREACH_NLRI attributes are BGP's containers for carrying opaque information. This specification defines three Link-State NLRI types that describe either a node, a link, or a prefix. All non-VPN link, node, and prefix information SHALL be encoded using AFI 16388 / SAFI 71. VPN link, node, and prefix information SHALL be encoded using AFI 16388 / SAFI 72. For two BGP Speakers to exchange Link-State NLRI, they MUST use BGP Capabilities Advertisement to ensure that they are both capable of properly processing such NLRI. This is done as specified in by using capability code 1 (multiprotocol BGP), with AFI 16388 / SAFI 71 for BGP-LS and AFI 16388 / SAFI 72 for BGP-LS-VPN. New Link-State NLRI types may be introduced in the future. Since supported NLRI type values within the address family are not expressed in the Multiprotocol BGP (MP-BGP) capability , it is possible that a BGP Speaker has advertised support for BGP-LS but does not support a particular Link-State NLRI type. To allow the introduction of new Link-State NLRI types seamlessly in the future without the need for upgrading all BGP Speakers in the propagation path (e.g., a route reflector), this document deviates from the default handling behavior specified by Section (paragraph 2) of for Link-State address family. An implementation MUST handle unknown Link-State NLRI types as opaque objects and MUST preserve and propagate them. The format of the Link-State NLRI is shown in the following figures.
Link-State AFI 16388 / SAFI 71 NLRI 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | NLRI Type | Total NLRI Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | // Link-State NLRI (variable) // | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Link-State VPN AFI 16388 / SAFI 72 NLRI 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | NLRI Type | Total NLRI Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + Route Distinguisher (8 octets) + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | // Link-State NLRI (variable) // | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Total NLRI Length field contains the cumulative length, in octets, of the rest of the NLRI, not including the NLRI Type field or itself. For VPN applications, it also includes the length of the Route Distinguisher. NLRI Types
Type NLRI Type
1 Node NLRI
2 Link NLRI
3 IPv4 Topology Prefix NLRI
4 IPv6 Topology Prefix NLRI
Route Distinguishers are defined and discussed in . The Node NLRI (NLRI Type = 1) is shown in the following figure.
The Node NLRI 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 +-+-+-+-+-+-+-+-+ | Protocol-ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Identifier | + (8 octets) + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ // Local Node Descriptors TLV (variable) // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Link NLRI (NLRI Type = 2) is shown in the following figure.
The Link NLRI 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 +-+-+-+-+-+-+-+-+ | Protocol-ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Identifier | + (8 octets) + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ // Local Node Descriptors TLV (variable) // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ // Remote Node Descriptors TLV (variable) // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ // Link Descriptors TLVs (variable) // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The IPv4 and IPv6 Prefix NLRIs (NLRI Type = 3 and Type = 4) use the same format as shown in the following figure.
The IPv4/IPv6 Topology Prefix NLRI 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 +-+-+-+-+-+-+-+-+ | Protocol-ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Identifier | + (8 octets) + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ // Local Node Descriptors TLV (variable) // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ // Prefix Descriptors TLVs (variable) // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Protocol-ID field can contain one of the following values: Protocol Identifiers
Protocol-ID NLRI information source protocol
1 IS-IS Level 1
2 IS-IS Level 2
3 OSPFv2
4 Direct
5 Static configuration
6 OSPFv3
The 'Direct' and 'Static configuration' protocol types SHOULD be used when BGP-LS is sourcing local information. For all information derived from other protocols, the corresponding Protocol-ID MUST be used. If BGP-LS has direct access to interface information and wants to advertise a local link, then the Protocol-ID 'Direct' SHOULD be used. For modeling virtual links, such as described in , the Protocol-ID 'Static configuration' SHOULD be used. A router may run multiple protocol instances of OSPF or IS-IS whereby it becomes a border router between multiple IGP domains. Both OSPF and IS-IS may also run multiple routing protocol instances over the same link. See and . These instances define independent IGP routing domains. The Identifier field carries an 8-octet BGP-LS Instance Identifier (Instance-ID) number that is used to identify the IGP routing domain where the NLRI belongs. The NLRIs representing link-state objects (nodes, links, or prefixes) from the same IGP routing instance should have the same BGP-LS Instance-ID. NLRIs with different BGP-LS Instance-IDs are considered to be from different IGP routing instances. To support multiple IGP instances, an implementation needs to support the configuration of unique BGP-LS Instance-IDs at the routing protocol instance level. The BGP-LS Instance-ID 0 is RECOMMENDED to be used when there is only a single protocol instance in the network where BGP-LS is operational. The network operator MUST assign the same BGP-LS Instance-IDs on all BGP-LS Producers within a given IGP domain. Unique BGP-LS Instance-IDs MUST be assigned to routing protocol instances operating in different IGP domains. This can allow the BGP-LS Consumer to build an accurate segregated multi-domain topology based on the BGP-LS Instance-ID. When the above-described semantics and recommendations are not followed, a BGP-LS Consumer may see more than one link-state object for the same node, link, or prefix (each with a different BGP-LS Instance-ID) when there are multiple BGP-LS Producers deployed. This may also result in the BGP-LS Consumers getting an inaccurate network-wide topology. Each Node Descriptor, Link Descriptor, and Prefix Descriptor consists of one or more TLVs, as described in the following sections. These Descriptor TLVs are applicable for the Node, Link, and Prefix NLRI Types for the protocols that are listed in . Documents extending BGP-LS specifications with new NLRI Types and/or protocols MUST specify the NLRI descriptors for them. When adding, removing, or modifying a TLV/sub-TLV from a Link-State NLRI, the BGP-LS Producer MUST withdraw the old NLRI by including it in the MP_UNREACH_NLRI. Not doing so can result in duplicate and inconsistent link-state objects hanging around in the BGP-LS table.
Node Descriptors Each link is anchored by a pair of Router-IDs that are used by the underlying IGP, namely a 48-bit ISO System-ID for IS-IS and a 32-bit Router-ID for OSPFv2 and OSPFv3. An IGP may use one or more additional auxiliary Router-IDs, mainly for Traffic Engineering purposes. For example, IS-IS may have one or more IPv4 and IPv6 TE Router-IDs . When configured, these auxiliary TE Router-IDs (TLV 1028/1029) MUST be included in the node attribute described in and MAY be included in the link attribute described in . The advertisement of the TE Router-IDs can help a BGP-LS Consumer to correlate multiple link-state objects (e.g., in different IGP instances or areas/levels) to the same node in the network. It is desirable that the Router-ID assignments inside the Node Descriptors are globally unique. However, there may be Router-ID spaces (e.g., ISO) where no global registry exists, or worse, Router-IDs have been allocated following the private-IP allocation described in . BGP-LS uses the Autonomous System Number to disambiguate the Router-IDs, as described in .
Globally Unique Node/Link/Prefix Identifiers One problem that needs to be addressed is the ability to identify an IGP node globally (by "globally", we mean within the BGP-LS database collected by all BGP-LS Speakers that talk to each other). This can be expressed through the following two requirements:
  1. The same node MUST NOT be represented by two keys (otherwise, one node will look like two nodes).
  2. Two different nodes MUST NOT be represented by the same key (otherwise, two nodes will look like one node).
We define an "IGP domain" to be the set of nodes (hence, by extension, links and prefixes) within which each node has a unique IGP representation by using the combination of OSPF Area-ID, Router-ID, Protocol-ID, Multi-Topology Identifier (MT-ID), and BGP-LS Instance-ID. The problem is that BGP may receive node/link/prefix information from multiple independent "IGP domains", and we need to distinguish between them. Moreover, we can't assume there is always one and only one IGP domain per AS. During IGP transitions, it may happen that two redundant IGPs are in place. Furthermore, in deployments where BGP-LS is used to advertise topology from multiple ASes, the Autonomous System Number (ASN) is used to distinguish topology information reported from different ASes. The BGP-LS Instance-ID carried in the Identifier field, as described earlier along with a set of sub-TLVs described in , allows specification of a flexible key for any given node/link information such that the global uniqueness of the NLRI is ensured. Since the BGP-LS Instance-ID is operator assigned, its allocation scheme can ensure that each IGP domain is uniquely identified even across a multi-AS network.
Local Node Descriptors The Local Node Descriptors TLV contains Node Descriptors for the node anchoring the local end of the link. This is a mandatory TLV in all three types of NLRIs (node, link, and prefix). The Type is 256. The length of this TLV is variable. The value contains one or more Node Descriptor sub-TLVs defined in .
Local Node Descriptors 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | // Node Descriptor Sub-TLVs (variable) // | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Remote Node Descriptors The Remote Node Descriptors TLV contains Node Descriptors for the node anchoring the remote end of the link. This is a mandatory TLV for Link NLRIs. The Type is 257. The length of this TLV is variable. The value contains one or more Node Descriptor sub-TLVs defined in .
Remote Node Descriptors 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | // Node Descriptor Sub-TLVs (variable) // | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Node Descriptor Sub-TLVs The Node Descriptor sub-TLV type code points and lengths are listed in the following table: Node Descriptor Sub-TLVs
Sub-TLV Code Point Description Length
512 Autonomous System 4
513 BGP-LS Identifier (deprecated) 4
514 OSPF Area-ID 4
515 IGP Router-ID Variable
The sub-TLV values in Node Descriptor TLVs are defined as follows:
Autonomous System:
Opaque value (32-bit AS Number). This is an optional TLV. The value SHOULD be set to the AS Number associated with the BGP process originating the link-state information. An implementation MAY provide a configuration option on the BGP-LS Producer to use a different value, e.g., to avoid collisions when using private AS Numbers.
BGP-LS Identifier:
Opaque value (32-bit ID). This is an optional TLV that has been deprecated by this document (refer to for more details). It MAY be advertised for compatibility with implementations. See the final paragraph of this section for further considerations and a recommended default value.
OSPF Area-ID:
Used to identify the 32-bit area to which the information advertised in the NLRI belongs. This is a mandatory TLV when originating information from OSPF that is derived from area-scope LSAs. The OSPF Area Identifier allows different NLRIs of the same router to be differentiated on a per-area basis. It is not used for NLRIs when carrying information that is derived from AS-scope LSAs as that information is not associated with a specific area.
IGP Router-ID:
Opaque value. This is a mandatory TLV when originating information from IS-IS, OSPF, 'Direct', or 'Static configuration'. For an IS-IS non-pseudonode, this contains a 6-octet ISO Node-ID (ISO System-ID). For an IS-IS pseudonode corresponding to a LAN, this contains the 6-octet ISO Node-ID of the Designated Intermediate System (DIS) followed by a 1-octet, nonzero PSN identifier (7 octets in total). For an OSPFv2 or OSPFv3 non-pseudonode, this contains the 4-octet Router-ID. For an OSPFv2 pseudonode representing a LAN, this contains the 4-octet Router-ID of the Designated Router (DR) followed by the 4-octet IPv4 address of the DR's interface to the LAN (8 octets in total). Similarly, for an OSPFv3 pseudonode, this contains the 4-octet Router-ID of the DR followed by the 4-octet interface identifier of the DR's interface to the LAN (8 octets in total). The TLV size in combination with the protocol identifier enables the decoder to determine the type of the node. For 'Direct' or 'Static configuration', the value SHOULD be taken from an IPv4 or IPv6 address (e.g., loopback interface) configured on the node. When the node is running an IGP protocol, an implementation MAY choose to use the IGP Router-ID for 'Direct' or 'Static configuration'.
At most, there MUST be one instance of each sub-TLV type present in any Node Descriptor. The sub-TLVs within a Node Descriptor MUST be arranged in ascending order by sub-TLV type. This needs to be done to compare NLRIs, even when an implementation encounters an unknown sub-TLV. Using stable sorting, an implementation can do a binary comparison of NLRIs and hence allow incremental deployment of new key sub-TLVs. The BGP-LS Identifier was introduced by , and its use is being deprecated by this document. Implementations SHOULD support the advertisement of this sub-TLV for backward compatibility in deployments where there are BGP-LS Producer implementations that conform to to ensure consistency of NLRI encoding for link-state objects. The default value of 0 is RECOMMENDED to be used when a BGP-LS Producer includes this sub-TLV when originating information into BGP-LS. Implementations SHOULD provide an option to configure this value for backward compatibility reasons. As a reminder, the use of the BGP-LS Instance-ID that is carried in the Identifier field is the way of segregation of link-state objects of different IGP domains in BGP-LS.
Link Descriptors The Link Descriptor field is a set of Type/Length/Value (TLV) triplets. The format of each TLV is shown in . The Link Descriptor TLVs uniquely identify a link among multiple parallel links between a pair of anchor routers. A link described by the Link Descriptor TLVs actually is a "half-link", a unidirectional representation of a logical link. To fully describe a single logical link, two anchor routers advertise a half-link each, i.e., two Link NLRIs are advertised for a given point-to-point link. A link between two nodes is not considered as complete (or available) unless it is described by the two Link NLRIs corresponding to the half-link representation from the pair of anchor nodes. This check is similar to the 'two-way connectivity check' that is performed by link-state IGPs. An implementation MAY suppress the advertisement of a Link NLRI, corresponding to a half-link, from a link-state IGP unless the IGP has verified that the link is being reported in the IS-IS LSP or OSPF Router LSA by both the nodes connected by that link. This 'two-way connectivity check' is performed by link-state IGPs during their computation and can be leveraged before passing information for any half-link that is reported from these IGPs into BGP-LS. This ensures that only those link-state IGP adjacencies that are established get reported via Link NLRIs. Such a 'two-way connectivity check' could also be required in certain cases (e.g., with OSPF) to obtain the proper link identifiers of the remote node. The format and semantics of the Value fields in most Link Descriptor TLVs correspond to the format and semantics of Value fields in IS-IS Extended IS Reachability sub-TLVs, which are defined in , , and . Although the encodings for Link Descriptor TLVs were originally defined for IS-IS, the TLVs can carry data sourced by either IS-IS or OSPF. The following TLVs are defined as Link Descriptors in the Link NLRI: Link Descriptor TLVs
TLV Code Point Description IS-IS TLV/Sub-TLV Reference
258 Link Local/Remote Identifiers 22/4
259 IPv4 interface address 22/6
260 IPv4 neighbor address 22/8
261 IPv6 interface address 22/12
262 IPv6 neighbor address 22/13
263 Multi-Topology Identifier ---
The information about a link present in the LSA/LSP originated by the local node of the link determines the set of TLVs in the Link Descriptor of the link. If interface and neighbor addresses, either IPv4 or IPv6, are present, then the interface/neighbor address TLVs MUST be included, and the Link Local/Remote Identifiers TLV MUST NOT be included in the Link Descriptor. The Link Local/Remote Identifiers TLV MAY be included in the link attribute when available. IPv4/IPv6 link-local addresses MUST NOT be carried in the IPv4/IPv6 interface/neighbor address TLVs (259/260/261/262) as descriptors of a link since they are not considered unique. If interface and neighbor addresses are not present and the link local/remote identifiers are present, then the Link Local/Remote Identifiers TLV MUST be included in the Link Descriptor. The Link Local/Remote identifiers MUST be included in the Link Descriptor and in the case of links having only IPv6 link-local addressing on them. The Multi-Topology Identifier TLV MUST be included as a Link Descriptor if the underlying IGP link object is associated with a non-default topology. The TLVs/sub-TLVs corresponding to the interface addresses and/or the local/remote identifiers may not always be signaled in the IGPs unless their advertisement is enabled specifically. In such cases, it is valid to advertise a BGP-LS Link NLRI without any of these identifiers.
Multi-Topology Identifier The Multi-Topology Identifier (MT-ID) TLV carries one or more IS-IS or OSPF Multi-Topology Identifiers for a link, node, or prefix. The semantics of the IS-IS MT-ID are defined in Sections and of . The semantics of the OSPF MT-ID are defined in . If the value in the MT-ID TLV is derived from OSPF, then the upper R bits of the MT-ID field MUST be set to 0 and only the values from 0 to 127 are valid for the MT-ID. The format of the MT-ID TLV is shown in the following figure.
Multi-Topology 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=2*n | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |R R R R| Multi-Topology ID 1 | .... // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ // .... |R R R R| Multi-Topology ID n | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Type is 263, the length is 2*n, and n is the number of MT-IDs carried in the TLV. The MT-ID TLV MAY be included as a Link Descriptor, as a Prefix Descriptor, or in the BGP-LS Attribute of a Node NLRI. When included as a Link or Prefix Descriptor, only a single MT-ID TLV containing the MT-ID of the topology where the link or the prefix is reachable is allowed. In case one wants to advertise multiple topologies for a given Link or Prefix Descriptor, multiple NLRIs MUST be generated where each NLRI contains a single unique MT-ID. When used as a Link or Prefix Descriptor for IS-IS, the Bits R are reserved and MUST be set to 0 (as per ) when originated and ignored on receipt. In the BGP-LS Attribute of a Node NLRI, one MT-ID TLV containing the array of MT-IDs of all topologies where the node is reachable is allowed. When used in the Node Attribute TLV for IS-IS, the Bits R are set as per .
Prefix Descriptors The Prefix Descriptor field is a set of Type/Length/Value (TLV) triplets. Prefix Descriptor TLVs uniquely identify an IPv4 or IPv6 prefix originated by a node. The following TLVs are defined as Prefix Descriptors in the IPv4/IPv6 Prefix NLRI: Prefix Descriptor TLVs
TLV Code Point Description Length Reference
263 Multi-Topology Identifier variable
264 OSPF Route Type 1
265 IP Reachability Information variable
The Multi-Topology Identifier TLV MUST be included in the Prefix Descriptor if the underlying IGP prefix object is associated with a non-default topology.
OSPF Route Type The OSPF Route Type TLV is an optional TLV corresponding to Prefix NLRIs originated from OSPF. It is used to identify the OSPF route type of the prefix. An OSPF prefix MAY be advertised in the OSPF domain with multiple route types. The Route Type TLV allows the discrimination of these advertisements. The OSPF Route Type TLV MUST be included in the advertisement when the type is either being signaled explicitly in the underlying LSA or can be determined via another LSA for the same prefix when it is not signaled explicitly (e.g., in the case of OSPFv2 Extended Prefix Opaque LSA ). The route type advertised in the OSPFv2 Extended Prefix TLV () does not make a distinction between Type 1 and 2 for AS external and Not-So-Stubby Area (NSSA) external routes. In this case, the route type to be used in the BGP-LS advertisement can be determined by checking the OSPFv2 External or NSSA External LSA for the prefix. A similar check for the base OSPFv2 LSAs can be done to determine the route type to be used when the route type value 0 is carried in the OSPFv2 Extended Prefix TLV. The format of the OSPF Route Type TLV is shown in the following figure.
OSPF Route Type 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Route Type | +-+-+-+-+-+-+-+-+
The Type and Length fields of the TLV are defined in . The Route Type field follows the route types defined in the OSPF protocol and can be one of the following:
  • Intra-Area (0x1)
  • Inter-Area (0x2)
  • External 1 (0x3)
  • External 2 (0x4)
  • NSSA 1 (0x5)
  • NSSA 2 (0x6)
IP Reachability Information The IP Reachability Information TLV is a mandatory TLV for IPv4 & IPv6 Prefix NLRI types. The TLV contains one IP address prefix (IPv4 or IPv6) originally advertised in the IGP topology. A router SHOULD advertise an IP Prefix NLRI for each of its BGP next hops. The format of the IP Reachability Information TLV is shown in the following figure:
IP Reachability Information 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Prefix Length | IP Prefix (variable) // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Type and Length fields of the TLV are defined in . The following two fields determine the reachability information of the address family. The Prefix Length field contains the length of the prefix in bits. The IP Prefix field contains an IP address prefix followed by the minimum number of trailing bits needed to make the end of the field fall on an octet boundary. Any trailing bits MUST be set to 0. Thus, the IP Prefix field contains the most significant octets of the prefix, i.e., 1 octet for prefix length 1 up to 8, 2 octets for prefix length 9 up to 16, 3 octets for prefix length 17 up to 24, 4 octets for prefix length 25 up to 32, etc.
The BGP-LS Attribute The BGP-LS Attribute (assigned value 29 by IANA) is an optional, non-transitive BGP Attribute that is used to carry link, node, and prefix parameters and attributes. It is defined as a set of Type/Length/Value (TLV) triplets, as described in the following section. This attribute SHOULD only be included with Link-State NLRIs. The use of this attribute for other address families is outside the scope of this document. The Node Attribute TLVs, Link Attribute TLVs, and Prefix Attribute TLVs are sets of TLVs that may be encoded in the BGP-LS Attribute associated with a Node NLRI, Link NLRI, and Prefix NLRI respectively. The size of the BGP-LS Attribute may potentially grow large, depending on the amount of link-state information associated with a single Link-State NLRI. The BGP specification mandates a maximum BGP message size of 4096 octets. It is RECOMMENDED that implementations support the extended message size for BGP to accommodate a larger size of information within the BGP-LS Attribute. BGP-LS Producers MUST ensure that the TLVs included in the BGP-LS Attribute does not result in a BGP UPDATE message for a single Link-State NLRI that crosses the maximum limit for a BGP message. An implementation MAY adopt mechanisms to avoid this problem that may be based on the BGP-LS Consumer applications' requirement; these mechanisms are beyond the scope of this specification. However, if an implementation chooses to mitigate the problem by excluding some TLVs from the BGP-LS Attribute, this exclusion SHOULD be done consistently by all BGP-LS Producers within a given BGP-LS domain. In the event of inconsistent exclusion of TLVs from the BGP-LS Attribute, the result would be a differing set of attributes of the link-state object being propagated to BGP-LS Consumers based on the BGP Decision Process at BGP-LS Propagators. When a BGP-LS Propagator finds that it is exceeding the maximum BGP message size due to the addition or update of some other BGP Attribute (e.g., AS_PATH), it MUST consider the BGP-LS Attribute to be malformed, apply the 'Attribute Discard' error-handling approach , and handle the propagation as described in . When a BGP-LS Propagator needs to perform 'Attribute Discard' for reducing the BGP UPDATE message size as specified in , it MUST first discard the BGP-LS Attribute to enable the detection and diagnosis of this error condition as discussed in . This brings the deployment consideration that the consistent propagation of BGP-LS information with a BGP UPDATE message size larger than 4096 octets can only happen along a set of BGP Speakers that all support the contents of .
Node Attribute TLVs The following Node Attribute TLVs are defined for the BGP-LS Attribute associated with a Node NLRI: Node Attribute TLVs
TLV Code Point Description Length Reference
263 Multi-Topology Identifier variable
1024 Node Flag Bits 1
1025 Opaque Node Attribute variable
1026 Node Name variable
1027 IS-IS Area Identifier variable
1028 IPv4 Router-ID of Local Node 4
1029 IPv6 Router-ID of Local Node 16
Node Flag Bits TLV The Node Flag Bits TLV carries a bitmask describing node attributes. The value is a 1-octet-length bit array of flags, where each bit represents a node-operational state or attribute.
Node Flag Bits 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |O|T|E|B|R|V| | +-+-+-+-+-+-+-+-+
The bits are defined as follows: Node Flag Bits Definitions
Bit Description Reference
'O' Overload Bit
'A' Attached Bit
'E' External Bit
'B' ABR Bit
'R' Router Bit
'V' V6 Bit
The bits that are not defined MUST be set to 0 by the originator and MUST be ignored by the receiver.
IS-IS Area Identifier TLV An IS-IS node can be part of only a single IS-IS area. However, a node can have multiple synonymous area addresses. Each of these area addresses is carried in the IS-IS Area Identifier TLV. If multiple area addresses are present, multiple TLVs are used to encode them. The IS-IS Area Identifier TLV may be present in the BGP-LS Attribute only when advertised in the Link-State Node NLRI.
IS-IS Area 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ // IS-IS Area Identifier (variable) // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Node Name TLV The Node Name TLV is optional. The encoding semantics for the node name has been borrowed from . The Value field identifies the symbolic name of the router node. This symbolic name can be the Fully Qualified Domain Name (FQDN) for the router, a substring of the FQDN (e.g., a hostname), or any string that an operator wants to use for the router. The use of the FQDN or a substring of it is strongly RECOMMENDED. The maximum length of the Node Name TLV is 255 octets. The Value field is encoded in 7-bit ASCII. If a user interface for configuring or displaying this field permits Unicode characters, then the user interface is responsible for applying the ToASCII and/or ToUnicode algorithm as described in to achieve the correct format for transmission or display. describes an IS-IS-specific extension, and describes an OSPF extension for the advertisement of the node name, which may be encoded in the Node Name TLV.
Node Name 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ // Node Name (variable) // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Local IPv4/IPv6 Router-ID TLVs The local IPv4/IPv6 Router-ID TLVs are used to describe auxiliary Router-IDs that the IGP might be using, e.g., for TE and migration purposes such as correlating a Node-ID between different protocols. If there is more than one auxiliary Router-ID of a given type, then each one is encoded as a separate TLV.
Opaque Node Attribute TLV The Opaque Node Attribute TLV is an envelope that transparently carries optional Node Attribute TLVs advertised by a router. An originating router shall use this TLV for encoding information specific to the protocol advertised in the NLRI header Protocol-ID field or new protocol extensions to the protocol as advertised in the NLRI header Protocol-ID field for which there is no protocol-neutral representation in the BGP Link-State NLRI. The primary use of the Opaque Node Attribute TLV is to bridge the document lag between a new IGP link-state attribute and its protocol-neutral BGP-LS extension being defined. Once the protocol-neutral BGP-LS extensions are defined, the BGP-LS implementations may still need to advertise the information both within the Opaque Attribute TLV and the new TLV definition for incremental deployment and transition. In the case of OSPF, this TLV MUST NOT be used to advertise TLVs other than those in the OSPF Router Information (RI) LSA .
Opaque Node Attribute 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ // Opaque Node Attributes (variable) // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Type is as specified in . The length is variable.
Link Attribute TLVs Link Attribute TLVs are TLVs that may be encoded in the BGP-LS Attribute with a Link NLRI. Each 'Link Attribute' is a Type/Length/Value (TLV) triplet formatted as defined in . The format and semantics of the Value fields in some Link Attribute TLVs correspond to the format and semantics of the Value fields in IS-IS Extended IS Reachability sub-TLVs, which are defined in and . Other Link Attribute TLVs are defined in this document. Although the encodings for Link Attribute TLVs were originally defined for IS-IS, the TLVs can carry data sourced by either IS-IS or OSPF. The following Link Attribute TLVs are defined for the BGP-LS Attribute associated with a Link NLRI: Link Attribute TLVs
TLV Code Point Description IS-IS TLV/Sub-TLV Reference
1028 IPv4 Router-ID of Local Node 134/---
1029 IPv6 Router-ID of Local Node 140/---
1030 IPv4 Router-ID of Remote Node 134/---
1031 IPv6 Router-ID of Remote Node 140/---
1088 Administrative group (color) 22/3
1089 Maximum link bandwidth 22/9
1090 Max. reservable link bandwidth 22/10
1091 Unreserved bandwidth 22/11
1092 TE Default Metric 22/18
1093 Link Protection Type 22/20
1094 MPLS Protocol Mask ---
1095 IGP Metric ---
1096 Shared Risk Link Group ---
1097 Opaque Link Attribute ---
1098 Link Name ---
IPv4/IPv6 Router-ID TLVs The local/remote IPv4/IPv6 Router-ID TLVs are used to describe auxiliary Router-IDs that the IGP might be using, e.g., for TE purposes. All auxiliary Router-IDs of both the local and the remote node MUST be included in the link attribute of each Link NLRI. If there is more than one auxiliary Router-ID of a given type, then multiple TLVs are used to encode them.
MPLS Protocol Mask TLV The MPLS Protocol Mask TLV carries a bitmask describing which MPLS signaling protocols are enabled. The length of this TLV is 1. The value is a bit array of 8 flags, where each bit represents an MPLS Protocol capability. Generation of the MPLS Protocol Mask TLV is only valid for and SHOULD only be used with originators that have local link insight, for example, the Protocol-IDs 'Static configuration' or 'Direct' as per . The MPLS Protocol Mask TLV MUST NOT be included in NLRIs with the other Protocol-IDs listed in .
MPLS Protocol Mask TLV 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |L|R| Reserved | +-+-+-+-+-+-+-+-+
The following bits are defined, and the reserved bits MUST be set to zero and SHOULD be ignored on receipt: MPLS Protocol Mask TLV Codes
Bit Description Reference
'L' Label Distribution Protocol (LDP)
'R' Extension to RSVP for LSP Tunnels (RSVP-TE)
The bits that are not defined MUST be set to 0 by the originator and MUST be ignored by the receiver.
TE Default Metric TLV The TE Default Metric TLV carries the Traffic Engineering metric for this link. The length of this TLV is fixed at 4 octets. If a source protocol uses a metric width of fewer than 32 bits, then the high-order bits of this field MUST be padded with zero.
TE Default Metric 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | TE Default Link Metric | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
IGP Metric TLV The IGP Metric TLV carries the metric for this link. The length of this TLV is variable, depending on the metric width of the underlying protocol. IS-IS small metrics are 6 bits in size but are encoded in a 1-octet field; therefore, the two most significant bits of the field MUST be set to 0 by the originator and MUST be ignored by the receiver. OSPF link metrics have a length of 2 octets. IS-IS wide metrics have a length of 3 octets.
IGP Metric 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ // IGP Link Metric (variable length) // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Shared Risk Link Group TLV The Shared Risk Link Group (SRLG) TLV carries the Shared Risk Link Group information (see Section "Shared Risk Link Group Information" of ). It contains a data structure consisting of a (variable) list of SRLG values, where each element in the list has 4 octets, as shown in . The length of this TLV is 4 * (number of SRLG values).
Shared Risk Link Group 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Shared Risk Link Group Value | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ // ............ // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Shared Risk Link Group Value | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The SRLG TLV for OSPF-TE is defined in . In IS-IS, the SRLG information is carried in two different TLVs: the GMPLS-SRLG TLV (for IPv4) (Type 138) defined in and the IPv6 SRLG TLV (Type 139) defined in . Both IPv4 and IPv6 SRLG information is carried in a single TLV.
Opaque Link Attribute TLV The Opaque Link Attribute TLV is an envelope that transparently carries optional Link Attribute TLVs advertised by a router. An originating router shall use this TLV for encoding information specific to the protocol advertised in the NLRI header Protocol-ID field or new protocol extensions to the protocol as advertised in the NLRI header Protocol-ID field for which there is no protocol-neutral representation in the BGP Link-State NLRI. The primary use of the Opaque Link Attribute TLV is to bridge the document lag between a new IGP link-state attribute and its 'protocol-neutral' BGP-LS extension being defined. Once the protocol-neutral BGP-LS extensions are defined, the BGP-LS implementations may still need to advertise the information both within the Opaque Attribute TLV and the new TLV definition for incremental deployment and transition. In the case of OSPFv2, this TLV MUST NOT be used to advertise information carried using TLVs other than those in the OSPFv2 Extended Link Opaque LSA . In the case of OSPFv3, this TLV MUST NOT be used to advertise TLVs other than those in the OSPFv3 E-Router-LSA or E-Link-LSA .
Opaque Link Attribute 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ // Opaque Link Attributes (variable) // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Link Name TLV The Link Name TLV is optional. The Value field identifies the symbolic name of the router link. This symbolic name can be the FQDN for the link, a substring of the FQDN, or any string that an operator wants to use for the link. The use of the FQDN or a substring of it is strongly RECOMMENDED. The maximum length of the Link Name TLV is 255 octets. The Value field is encoded in 7-bit ASCII. If a user interface for configuring or displaying this field permits Unicode characters, then the user interface is responsible for applying the ToASCII and/or ToUnicode algorithm as described in to achieve the correct format for transmission or display. How a router derives and injects link names is outside of the scope of this document.
Link Name 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ // Link Name (variable) // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Prefix Attribute TLVs Prefixes are learned from the IGP topology (IS-IS or OSPF) with a set of IGP attributes (such as metric, route tags, etc.) that are advertised in the BGP-LS Attribute with Prefix NLRI types 3 and 4. The following Prefix Attribute TLVs are defined for the BGP-LS Attribute associated with a Prefix NLRI: Prefix Attribute TLVs
TLV Code Point Description Length Reference
1152 IGP Flags 1
1153 IGP Route Tag 4*n
1154 IGP Extended Route Tag 8*n
1155 Prefix Metric 4
1156 OSPF Forwarding Address 4
1157 Opaque Prefix Attribute variable
IGP Flags TLV The IGP Flags TLV contains one octet of IS-IS and OSPF flags and bits originally assigned to the prefix. The IGP Flags TLV is encoded as follows:
IGP Flag 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |D|N|L|P| | +-+-+-+-+-+-+-+-+
The Value field contains bits defined according to the table below: IGP Flag Bits Definitions
Bit Description Reference
'D' IS-IS Up/Down Bit
'N' OSPF "no unicast" Bit
'L' OSPF "local address" Bit
'P' OSPF "propagate NSSA" Bit
The bits that are not defined MUST be set to 0 by the originator and MUST be ignored by the receiver.
IGP Route Tag TLV The IGP Route Tag TLV carries original IGP Tags (IS-IS or OSPF) of the prefix and is encoded as follows:
IGP Route Tag 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ // Route Tags (one or more) // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The length is a multiple of 4. The Value field contains one or more Route Tags as learned in the IGP topology.
IGP Extended Route Tag TLV The IGP Extended Route Tag TLV carries IS-IS Extended Route Tags of the prefix and is encoded as follows:
IGP Extended Route Tag 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ // Extended Route Tag (one or more) // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The length is a multiple of 8. The Extended Route Tag field contains one or more Extended Route Tags as learned in the IGP topology.
Prefix Metric TLV The Prefix Metric TLV is an optional attribute and may only appear once. If present, it carries the metric of the prefix as known in the IGP topology, as described in (and therefore represents the reachability cost to the prefix). If not present, it means that the prefix is advertised without any reachability.
Prefix Metric 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Metric | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The length is 4.
OSPF Forwarding Address TLV The OSPF Forwarding Address TLV carries the OSPF forwarding address as known in the original OSPF advertisement. The forwarding address can be either IPv4 or IPv6.
OSPF Forwarding Address 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ // Forwarding Address (variable) // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The length is 4 for an IPv4 forwarding address and 16 for an IPv6 forwarding address.
Opaque Prefix Attribute TLV The Opaque Prefix Attribute TLV is an envelope that transparently carries optional Prefix Attribute TLVs advertised by a router. An originating router shall use this TLV for encoding information specific to the protocol advertised in the NLRI header Protocol-ID field or it shall use new protocol extensions for the protocol as advertised in the NLRI header Protocol-ID field for which there is no protocol-neutral representation in the BGP Link-State NLRI. The primary use of the Opaque Prefix Attribute TLV is to bridge the document lag between a new IGP link-state attribute and its protocol-neutral BGP-LS extension being defined. Once the protocol-neutral BGP-LS extensions are defined, the BGP-LS implementations may still need to advertise the information both within the Opaque Attribute TLV and the new TLV definition for incremental deployment and transition. In the case of OSPFv2, this TLV MUST NOT be used to advertise information carried using TLVs other than those in the OSPFv2 Extended Prefix Opaque LSA . In the case of OSPFv3, this TLV MUST NOT be used to advertise TLVs other than those in the OSPFv3 E-Inter-Area-Prefix-LSA, E-Intra-Area-Prefix-LSA, E-AS-External-LSA, and E-NSSA-LSA . The format of the TLV is as follows:
Opaque Prefix Attribute 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ // Opaque Prefix Attributes (variable) // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Type is as specified in . The length is variable.
Private Use TLVs for Vendor Private Use are supported using the code point range reserved as indicated in . For such TLV use in the NLRI or BGP-LS Attribute, the format described in is to be used and a 4-octet field MUST be included as the first field in the value to carry the Enterprise Code. For a private use NLRI type, a 4-octet field MUST be included as the first field in the NLRI immediately following the Total NLRI Length field of the Link-State NLRI format as described in to carry the Enterprise Code . This enables the use of vendor-specific extensions without conflicts. Multiple instances of private-use TLVs MAY appear in the BGP-LS Attribute.
BGP Next-Hop Information BGP link-state information for both IPv4 and IPv6 networks can be carried over either an IPv4 BGP session or an IPv6 BGP session. If an IPv4 BGP session is used, then the next hop in the MP_REACH_NLRI SHOULD be an IPv4 address. Similarly, if an IPv6 BGP session is used, then the next hop in the MP_REACH_NLRI SHOULD be an IPv6 address. Usually, the next hop will be set to the local endpoint address of the BGP session. The next-hop address MUST be encoded as described in . The Length field of the next-hop address will specify the next-hop address family. If the next-hop length is 4, then the next hop is an IPv4 address; if the next-hop length is 16, then it is a global IPv6 address; and if the next-hop length is 32, then there is one global IPv6 address followed by an IPv6 link-local address. The IPv6 link-local address should be used as described in . For VPN Subsequent Address Family Identifier (SAFI), as per custom, an 8-byte Route Distinguisher set to all zero is prepended to the next hop. The BGP Next-Hop is used by each BGP-LS Speaker to validate the NLRI it receives. In case identical NLRIs are sourced by multiple BGP-LS Producers, the BGP Next-Hop is used to tiebreak as per the standard BGP path decision process. This specification doesn't mandate any rule regarding the rewrite of the BGP Next-Hop.
Inter-AS Links The main source of TE information is the IGP, which is not active on inter-AS links. In some cases, the IGP may have information of inter-AS links . In other cases, an implementation SHOULD provide a means to inject inter-AS links into BGP-LS. The exact mechanism used to advertise the inter-AS links is outside the scope of this document.
OSPF Virtual Links and Sham Links In an OSPF network, OSPF virtual links serve to connect physically separate components of the backbone to establish/maintain continuity of the backbone area. While OSPF virtual links are modeled as point-to-point, unnumbered links in the OSPF topology, their characteristics and purpose are different from other types of links in the OSPF topology. They are advertised using a distinct "virtual link" type in OSPF LSAs. The mechanism for the advertisement of OSPF virtual links via BGP-LS is outside the scope of this document. In an OSPF network, sham links are used to provide intra-area connectivity between VPN Routing and Forwarding (VRF) instances on Provider Edge (PE) routers over the VPN provider's network. These links are advertised in OSPF as point-to-point, unnumbered links and represent connectivity over a service provider network using encapsulation mechanisms like MPLS. As such, the mechanism for the advertisement of OSPF sham links follows the same procedures as other point-to-point, unnumbered links as described previously in this document.
OSPFv2 Type 4 Summary-LSA & OSPFv3 Inter-Area-Router-LSA OSPFv2 defines the type 4 summary-LSA and OSPFv3 defines the inter-area-router-LSA for an Area Border Router (ABR) to advertise reachability to an AS Border Router (ASBR) that is external to the area yet internal to the AS. The nature of information advertised by OSPF using this type of LSA does not map to either a node, a link, or a prefix as discussed in this document. Therefore, the mechanism for the advertisement of the information carried by these LSAs is outside the scope of this document.
Handling of Unreachable IGP Nodes Consider an OSPF network as shown in , where R2 and R3 are the BGP-LS Producers and also the OSPF Area Border Routers (ABRs). The link between R2 and R3 is in area 0, while the other links are in area 1 as indicated by the a0 and a1 references respectively against the links. A BGP-LS Consumer talks to BGP route reflector RR0, which is a BGP-LS Propagator that is aggregating the BGP-LS feed from BGP-LS Producers R2 and R3. Here, R2 and R3 provide a redundant topology feed via BGP-LS to RR0. Normally, RR0 would receive two identical copies of all the Link-State NLRIs from both R2 and R3 and it would pick one of them (say R2) based on the standard BGP Decision Process.
Incorrect Reporting Due to BGP Path Selection BGP-LS Consumer ^ | RR0 (BGP Route Reflector) / \ / \ a1 / a0 \ a1 R1 ------ R2 -------- R3 ------ R4 a1 | | a1 | | R5 ---------------------------- R6 a1
Consider a scenario where the link between R5 and R6 is lost (thereby partitioning the area 1), and consider its impact on the OSPF LSDB at R2 and R3. Now, R5 will remove the link R5-R6 from its Router LSA, and this updated LSA is available at R2. R2 also has a stale copy of R6's Router LSA that still has the link R6-R5 in it. Based on this view in its LSDB, R2 will advertise only the half-link R6-R5 that it derives from R6's stale Router LSA. At the same time, R6 has removed the link R6-R5 from its Router LSA, and this updated LSA is available at R3. Similarly, R3 also has a stale copy of R5's Router LSA having the link R5-R6 in it. Based on its LSDB, R3 will advertise only the half-link R5-R6 that it derives from R5's stale Router LSA. Now, the BGP-LS Consumer receives both the Link NLRIs corresponding to the half-links from R2 and R3 via RR0. When viewed together, it would not detect or realize that area 1 is partitioned. Also, if R2 continues to report Node and Prefix NLRIs corresponding to the stale copy of R4's and R6's Router LSAs, then RR0 could prefer them over the valid Node and Prefix NLRIs for R4 and R6 that it is receiving from R3 depending on RR0's BGP Decision Process. This would result in the BGP-LS Consumer getting stale and inaccurate topology information. This problem scenario is avoided if R2 were to not advertise the link-state information corresponding to R4 and R6 and if R3 were to not advertise similarly for R1 and R5. A BGP-LS Producer SHOULD withdraw all link-state objects advertised by it in BGP when the node that originated its corresponding LSPs/LSAs is determined to have become unreachable in the IGP. An implementation MAY continue to advertise link-state objects corresponding to unreachable nodes in a deployment use case where the BGP-LS Consumer is interested in receiving a topology feed corresponding to a complete IGP LSDB view. In such deployments, it is expected that the problem described above is mitigated by the BGP-LS Consumer via appropriate handling of such a topology feed in addition to the use of either a direct BGP peering with the BGP-LS Producer nodes or mechanisms such as those described in when using RRs. Details of these mechanisms are outside the scope of this document. If the BGP-LS Producer does withdraw link-state objects associated with an IGP node based on the failure of reachability check for that node, then it MUST re-advertise those link-state objects after that node becomes reachable again in the IGP domain.
Router-ID Anchoring Example: ISO Pseudonode The encoding of a broadcast LAN in IS-IS provides a good example of how Router-IDs are encoded. Consider . This represents a broadcast LAN between a pair of routers. The "real" (non-pseudonode) routers have both an IPv4 Router-ID and an IS-IS Node-ID. The pseudonode does not have an IPv4 Router-ID. Node1 is the DIS for the LAN. Two unidirectional links, (Node1, Pseudonode1) and (Pseudonode1, Node2), are being generated. The Link NLRI of (Node1, Pseudonode1) is encoded as follows. The IGP Router-ID TLV of the local Node Descriptor is 6 octets long and contains the ISO-ID of Node1, 1920.0000.2001. The IGP Router-ID TLV of the remote Node Descriptor is 7 octets long and contains the ISO-ID of Pseudonode1, 1920.0000.2001.02. The BGP-LS Attribute of this link contains one local IPv4 Router-ID TLV (TLV type 1028) containing 192.0.2.1, the IPv4 Router-ID of Node1. The Link NLRI of (Pseudonode1, Node2) is encoded as follows. The IGP Router-ID TLV of the local Node Descriptor is 7 octets long and contains the ISO-ID of Pseudonode1, 1920.0000.2001.02. The IGP Router-ID TLV of the remote Node Descriptor is 6 octets long and contains the ISO-ID of Node2, 1920.0000.2002. The BGP-LS Attribute of this link contains one remote IPv4 Router-ID TLV (TLV type 1030) containing 192.0.2.2, the IPv4 Router-ID of Node2.
IS-IS Pseudonodes +-----------------+ +-----------------+ +-----------------+ | Node1 | | Pseudonode1 | | Node2 | |1920.0000.2001.00|--->|1920.0000.2001.02|--->|1920.0000.2002.00| | 192.0.2.1 | | | | 192.0.2.2 | +-----------------+ +-----------------+ +-----------------+
Router-ID Anchoring Example: OSPF Pseudonode The encoding of a broadcast LAN in OSPF provides a good example of how Router-IDs and local Interface IPs are encoded. Consider . This represents a broadcast LAN between a pair of routers. The "real" (non-pseudonode) routers have both an IPv4 Router-ID and an Area Identifier. The pseudonode does have an IPv4 Router-ID, an IPv4 Interface Address (for disambiguation), and an OSPF Area. Node1 is the DR for the LAN; hence, its local IP address 198.51.100.1 is used as both the Router-ID and Interface IP for the pseudonode keys. Two unidirectional links, (Node1, Pseudonode1) and (Pseudonode1, Node2), are being generated. The Link NLRI of (Node1, Pseudonode1) is encoded as follows:
  • Local Node Descriptor
    TLV #515:
    IGP Router-ID: 192.0.2.1
    TLV #514:
    OSPF Area-ID: ID:0.0.0.0
  • Remote Node Descriptor
    TLV #515:
    IGP Router-ID: 192.0.2.1:198.51.100.1
    TLV #514:
    OSPF Area-ID: ID:0.0.0.0
The Link NLRI of (Pseudonode1, Node2) is encoded as follows:
  • Local Node Descriptor
    TLV #515:
    IGP Router-ID: 192.0.2.1:198.51.100.1
    TLV #514:
    OSPF Area-ID: ID:0.0.0.0
  • Remote Node Descriptor
    TLV #515:
    IGP Router-ID: 192.0.2.2
    TLV #514:
    OSPF Area-ID: ID:0.0.0.0
OSPF Pseudonodes 198.51.100.1/24 198.51.100.2/24 +-------------+ +-------------+ +-------------+ | Node1 | | Pseudonode1 | | Node2 | | 192.0.2.1 |--->| 192.0.2.1 |--->| 192.0.2.2 | | | |198.51.100.1 | | | | Area 0 | | Area 0 | | Area 0 | +-------------+ +-------------+ +-------------+
The LAN subnet 198.51.100.0/24 is not included in the Router LSA of Node1 or Node2. The Network LSA for this LAN advertised by the DR Node1 contains the subnet mask for the LAN along with the DR address. A Prefix NLRI corresponding to the LAN subnet is advertised with the Pseudonode1 used as the local node using the DR address and the subnet mask from the Network LSA.
Router-ID Anchoring Example: OSPFv2 to IS-IS Migration Graceful migration from one IGP to another requires coordinated operation of both protocols during the migration period. Such coordination requires identifying a given physical link in both IGPs. The IPv4 Router-ID provides that "glue", which is present in the Node Descriptors of the OSPF Link NLRI and in the link attribute of the IS-IS Link NLRI. Consider a point-to-point link between two routers, A and B, which initially were OSPFv2-only routers and then had IS-IS enabled on them. Node A has IPv4 Router-ID and ISO-ID; node B has IPv4 Router-ID, IPv6 Router-ID, and ISO-ID. Each protocol generates one Link NLRI for the link (A, B), both of which are carried by BGP-LS. The OSPFv2 Link NLRI for the link is encoded with the IPv4 Router-ID of nodes A and B in the local and remote Node Descriptors, respectively. The IS-IS Link NLRI for the link is encoded with the ISO-ID of nodes A and B in the local and remote Node Descriptors, respectively. In addition, the BGP-LS Attribute of the IS-IS Link NLRI contains the TLV type 1028 containing the IPv4 Router-ID of node A, TLV type 1030 containing the IPv4 Router-ID of node B, and TLV type 1031 containing the IPv6 Router-ID of node B. In this case, by using IPv4 Router-ID, the link (A, B) can be identified in both the IS-IS and OSPF protocols.
Link to Path Aggregation Distribution of all links available on the global Internet is certainly possible; however, it is not desirable from a scaling and privacy point of view. Therefore, an implementation may support a link to path aggregation. Rather than advertising all specific links of a domain, an ASBR may advertise an "aggregate link" between a non-adjacent pair of nodes. The "aggregate link" represents the aggregated set of link properties between a pair of non-adjacent nodes. The actual methods to compute the path properties (of bandwidth, metric, etc.) are outside the scope of this document. The decision of whether to advertise all specific links or aggregated links is an operator's policy choice. To highlight the varying levels of exposure, the following deployment examples are discussed.
Example: No Link Aggregation Consider . Both AS1 and AS2 operators want to protect their inter-AS {R1, R3}, {R2, R4} links using RSVP - Fast Reroute (RSVP-FRR) LSPs. If R1 wants to compute its link-protection LSP to R3, it needs to "see" an alternate path to R3. Therefore, the AS2 operator exposes its topology. All BGP-TE-enabled routers in AS1 "see" the full topology of AS2 and therefore can compute a backup path. Note that the computing router decides if the direct link between {R3, R4} or the {R4, R5, R3} path is used.
No Link Aggregation AS1 : AS2 : R1-------R3 | : | \ | : | R5 | : | / R2-------R4 : :
Example: ASBR to ASBR Path Aggregation The brief difference between the "no-link aggregation" example and this example is that no specific link gets exposed. Consider . The only link that gets advertised by AS2 is an "aggregate" link between R3 and R4. This is enough to tell AS1 that there is a backup path. However, the actual links being used are hidden from the topology.
ASBR Link Aggregation AS1 : AS2 : R1-------R3 | : | | : | | : | R2-------R4 : :
Example: Multi-AS Path Aggregation Service providers in control of multiple ASes may even decide to not expose their internal inter-AS links. Consider . AS3 is modeled as a single node that connects to the border routers of the aggregated domain.
Multi-AS Aggregation AS1 : AS2 : AS3 : : R1-------R3----- | : : \ | : : vR0 | : : / R2-------R4----- : : : :
IANA Considerations As this document obsoletes and , IANA has updated all registration information that references those documents to instead reference this document. IANA has assigned address family number 16388 (BGP-LS) in the "Address Family Numbers" registry. IANA has assigned SAFI values 71 (BGP-LS) and 72 (BGP-LS-VPN) in the "SAFI Values" registry under the "Subsequent Address Family Identifiers (SAFI) Parameters" registry group. IANA has assigned value 29 (BGP-LS Attribute) in the "BGP Path Attributes" registry under the "Border Gateway Protocol (BGP) Parameters" registry group. IANA has created a "Border Gateway Protocol - Link-State (BGP-LS) Parameters" registry group at . This section also incorporates all the changes to the allocation procedures for the BGP-LS IANA registry group as well as the guidelines for designated experts introduced by .
BGP-LS Registries All of the registries listed in the following subsections are specific to BGP-LS and are accessible under this registry.
BGP-LS NLRI Types Registry The "BGP-LS NLRI Types" registry has been set up for assignment for the two-octet-sized code points for BGP-LS NLRI types and populated with the values shown below: BGP-LS NLRI Types
Type NLRI Type Reference
0 Reserved RFC 9552
1 Node NLRI RFC 9552
2 Link NLRI RFC 9552
3 IPv4 Topology Prefix NLRI RFC 9552
4 IPv6 Topology Prefix NLRI RFC 9552
65000-65535 Private Use RFC 9552
A range is reserved for Private Use . All other allocations within the registry are to be made using the "Expert Review" policy , which requires documentation of the proposed use of the allocated value and approval by the designated expert assigned by the IESG.
BGP-LS Protocol-IDs Registry The "BGP-LS Protocol-IDs" registry has been set up for assignment for the one-octet-sized code points for BGP-LS Protocol-IDs and populated with the values shown below: BGP-LS Protocol-IDs
Protocol-ID NLRI information source protocol Reference
0 Reserved RFC 9552
1 IS-IS Level 1 RFC 9552
2 IS-IS Level 2 RFC 9552
3 OSPFv2 RFC 9552
4 Direct RFC 9552
5 Static configuration RFC 9552
6 OSPFv3 RFC 9552
200-255 Private Use RFC 9552
A range is reserved for Private Use . All other allocations within the registry are to be made using the "Expert Review" policy , which requires documentation of the proposed use of the allocated value and approval by the designated expert assigned by the IESG.
BGP-LS Well-Known Instance-IDs Registry The "BGP-LS Well-Known Instance-IDs" registry that was set up via is no longer required. IANA has marked this registry obsolete and changed its registration procedure to "registry closed".
BGP-LS Node Flags Registry The "BGP-LS Node Flags" registry has been created for the one-octet-sized flags field of the Node Flag Bits TLV (1024) and populated with the initial values shown below: BGP-LS Node Flags
Bit Description Reference
0 Overload Bit (O-bit) RFC 9552
1 Attached Bit (A-bit) RFC 9552
2 External Bit (E-bit) RFC 9552
3 ABR Bit (B-bit) RFC 9552
4 Router Bit (R-bit) RFC 9552
5 V6 Bit (V-bit) RFC 9552
6-7 Unassigned
Allocations within the registry are to be made using the "Expert Review" policy , which requires documentation of the proposed use of the allocated value and approval by the designated expert assigned by the IESG.
BGP-LS MPLS Protocol Mask Registry The "BGP-LS MPLS Protocol Mask" registry has been created for the one-octet-sized flags field of the MPLS Protocol Mask TLV (1094) and populated with the initial values shown below: BGP-LS MPLS Protocol Mask
Bit Description Reference
0 Label Distribution Protocol (L-bit) RFC 9552
1 Extension to RSVP for LSP Tunnels (R-bit) RFC 9552
2-7 Unassigned
Allocations within the registry are to be made using the "Expert Review" policy , which requires documentation of the proposed use of the allocated value and approval by the designated expert assigned by the IESG.
BGP-LS IGP Prefix Flags Registry The "BGP-LS IGP Prefix Flags" registry has been created for the one-octet-sized flags field of the IGP Flags TLV (1152) and populated with the initial values shown below: BGP-LS IGP Prefix Flags
Bit Description Reference
0 IS-IS Up/Down Bit (D-bit) RFC 9552
1 OSPF "no unicast" Bit (N-bit) RFC 9552
2 OSPF "local address" Bit (L-bit) RFC 9552
3 OSPF "propagate NSSA" Bit (P-bit) RFC 9552
4-7 Unassigned
Allocations within the registry are to be made using the "Expert Review" policy , which requires documentation of the proposed use of the allocated value and approval by the designated expert assigned by the IESG.
BGP-LS TLVs Registry The "BGP-LS Node Descriptor, Link Descriptor, Prefix Descriptor, and Attribute TLVs" registry was created via . Per this document, IANA has renamed that registry to "BGP-LS NLRI and Attribute TLVs" and removed the column for "IS-IS TLV/Sub-TLV". The registration procedures are as follows: BGP-LS TLVs Registration Process
TLV Code Point Registration Process
0-255 Reserved (not to be allocated)
256-64999 Expert Review
65000-65535 Private Use
A range is reserved for Private Use . All other allocations except for the reserved range within the registry are to be made using the "Expert Review" policy , which requires documentation of the proposed use of the allocated value and approval by the designated expert assigned by the IESG. The registry was pre-populated with the values shown in , and the reference for each allocation has been changed to this document and the respective section where those TLVs are specified.
Guidance for Designated Experts In all cases of review by the designated expert described here, the designated expert is expected to check the clarity of purpose and use of the requested code points. The following points apply to the registries discussed in this document:
  1. Application for a code point allocation may be made to the designated experts at any time and MUST be accompanied by technical documentation explaining the use of the code point. Such documentation SHOULD be presented in the form of an Internet-Draft but MAY arrive in any form that can be reviewed and exchanged among reviewers.
  2. The designated experts SHOULD only consider requests that arise from Internet-Drafts that have already been accepted as working group documents or that are planned for progression as AD-Sponsored documents in the absence of a suitably chartered working group.
  3. In the case of working group documents, the designated experts MUST check with the working group chairs that there is a consensus within the working group to allocate at this time. In the case of AD-Sponsored documents, the designated experts MUST check with the AD for approval to allocate at this time.
  4. If the document is not adopted by the IDR Working Group (or its successor), the designated expert MUST notify the IDR mailing list (or its successor) of the request and MUST provide access to the document. The designated expert MUST allow two weeks for any response. Any comments received MUST be considered by the designated expert as part of the subsequent step.
  5. The designated experts MUST then review the assignment requests on their technical merit. The designated experts MAY raise issues related to the allocation request with the authors and on the IDR (or successor) mailing list for further consideration before the assignments are made.
  6. The designated expert MUST ensure that any request for a code point does not conflict with work that is active or already published within the IETF.
  7. Once the designated experts have approved, IANA will update the registry by marking the allocated code points with a reference to the associated document.
  8. In the event that the document is a working group document or is AD-Sponsored and fails to progress to publication as an RFC, the working group chairs or AD SHOULD contact IANA to coordinate about marking the code points as deprecated. A deprecated code point is not marked as allocated for use and is not available for allocation in a future document. The WG chairs may inform IANA that a deprecated code point can be completely deallocated (i.e., made available for new allocations) at any time after it has been deprecated if there is a shortage of unallocated code points in the registry.
Manageability Considerations This section is structured as recommended in .
Operational Considerations
Operations Existing BGP operational procedures apply. No new operation procedures are defined in this document. It is noted that the NLRI information present in this document carries purely application-level data that has no immediate impact on the corresponding forwarding state computed by BGP. As such, any churn in reachability information has a different impact than regular BGP updates, which need to change the forwarding state for an entire router. Distribution of the BGP-LS NLRIs SHOULD be handled by dedicated route reflectors in most deployments providing a level of isolation and fault containment between different BGP address families. In the event of dedicated route reflectors not being available, other alternate mechanisms like separation of BGP instances or separate BGP sessions (e.g., using different addresses for peering) for Link-State information distribution SHOULD be used. It is RECOMMENDED that operators deploying BGP-LS enable two or more BGP-LS Producers in each IGP flooding domain to achieve redundancy in the origination of link-state information into BGP-LS. It is also RECOMMENDED that operators ensure BGP peering designs that ensure redundancy in the BGP update propagation paths (e.g., using at least a pair of route reflectors) and ensure that BGP-LS Consumers are receiving the topology information from at least two BGP-LS Speakers. In a multi-domain IGP network, the correct provisioning of the BGP-LS Instance-IDs on the BGP-LS Producers is required for consistent reporting of the multi-domain link-state topology. Refer to for more details.
Installation and Initial Setup Configuration parameters defined in SHOULD be initialized to the following default values:
  • The Link-State NLRI capability is turned off for all neighbors.
  • The maximum rate at which Link-State NLRIs will be advertised/withdrawn from neighbors is set to 200 updates per second.
Migration Path The proposed extension is only activated between BGP peers after capability negotiation. Moreover, the extensions can be turned on/off on an individual peer basis (see ), so the extension can be gradually rolled out in the network.
Requirements for Other Protocols and Functional Components The protocol extension defined in this document does not put new requirements on other protocols or functional components.
Impact on Network Operation The frequency of Link-State NLRI updates could interfere with regular BGP prefix distribution. A network operator should use a dedicated route reflector infrastructure to distribute Link-State NLRIs as discussed in . Distribution of Link-State NLRIs SHOULD be limited to a single admin domain, which can consist of multiple areas within an AS or multiple ASes.
Verifying Correct Operation Existing BGP procedures apply. In addition, an implementation SHOULD allow an operator to:
  • List neighbors with whom the speaker is exchanging Link-State NLRIs.
Management Considerations
Management Information The IDR Working Group has documented and continues to document parts of the Management Information Base and YANG models for managing and monitoring BGP Speakers and the sessions between them. It is currently believed that the BGP session running BGP-LS is not substantially different from any other BGP session and can be managed using the same data models.
Fault Management This section describes the fault management actions, as described in , that are to be performed for the handling of BGP UPDATE messages for BGP-LS. A Link-State NLRI MUST NOT be considered malformed or invalid based on the inclusion/exclusion of TLVs or contents of the TLV fields (i.e., semantic errors), as described in Sections and . A BGP-LS Speaker MUST perform the following syntactic validation of the Link-State NLRI to determine if it is malformed.
  • The sum of all TLV lengths found in the BGP MP_REACH_NLRI attribute corresponds to the BGP MP_REACH_NLRI length.
  • The sum of all TLV lengths found in the BGP MP_UNREACH_NLRI attribute corresponds to the BGP MP_UNREACH_NLRI length.
  • The sum of all TLV lengths found in a Link-State NLRI corresponds to the Total NLRI Length field of all its descriptors.
  • The length of the TLVs and, when the TLV is recognized then, the length of its sub-TLVs in the NLRI are valid.
  • The syntactic correctness of the NLRI fields has been verified as per .
  • The rule regarding the ordering of TLVs has been followed as described in .
  • For NLRIs carrying either a Local or Remote Node Descriptor TLV, there is not more than one instance of a sub-TLV present.
When the error that is determined allows for the router to skip the malformed NLRI(s) and continue the processing of the rest of the BGP UPDATE message (e.g., when the TLV ordering rule is violated), then it MUST handle such malformed NLRIs as 'NLRI discard' (i.e., processing similar to what is described in ). In other cases, where the error in the NLRI encoding results in the inability to process the BGP UPDATE message (e.g., length-related encoding errors), then the router SHOULD handle such malformed NLRIs as 'AFI/SAFI disable' when other AFI/SAFI besides BGP-LS are being advertised over the same session. Alternately, the router MUST perform a 'session reset' when the session is only being used for BGP-LS or if 'AFI/SAFI disable' action is not possible. A BGP-LS Attribute MUST NOT be considered malformed or invalid based on the inclusion/exclusion of TLVs or contents of the TLV fields (i.e., semantic errors), as described in Sections and . A BGP-LS Speaker MUST perform the following syntactic validation of the BGP-LS Attribute to determine if it is malformed.
  • The sum of all TLV lengths found in the BGP-LS Attribute corresponds to the BGP-LS Attribute length.
  • The syntactic correctness of the Attributes (including the BGP-LS Attribute) have been verified as per .
  • The length of each TLV and, when the TLV is recognized then, the length of its sub-TLVs in the BGP-LS Attribute are valid.
When the error that is determined allows for the router to skip the malformed BGP-LS Attribute and continue the processing of the rest of the BGP UPDATE message (e.g., when the BGP-LS Attribute length and the total Path Attribute Length are correct but some TLV/sub-TLV length within the BGP-LS Attribute is invalid), then it MUST handle such malformed BGP-LS Attribute as 'Attribute Discard'. In other cases, where the error in the BGP-LS Attribute encoding results in the inability to process the BGP UPDATE message, the handling is the same as described above for the malformed NLRI. Note that the 'Attribute Discard' action results in the loss of all TLVs in the BGP-LS Attribute and not the removal of a specific malformed TLV. The removal of specific malformed TLVs may give a wrong indication to a BGP-LS Consumer of that specific information being deleted or not available. When a BGP Speaker receives an UPDATE message with Link-State NLRI(s) in the MP_REACH_NLRI but without the BGP-LS Attribute, it is most likely an indication that a BGP Speaker preceding it has performed the 'Attribute Discard' fault handling. An implementation SHOULD preserve and propagate the Link-State NLRIs, unless denied by local policy, in such an UPDATE message so that the BGP-LS Consumers can detect the loss of link-state information for that object and not assume its deletion/withdrawal. This also makes it possible for a network operator to trace back to the BGP-LS Propagator that detected the fault with the BGP-LS Attribute. An implementation SHOULD log a message for any errors found during syntax validation for further analysis. A BGP-LS Propagator, even when it has a coexisting BGP-LS Consumer on the same node, should not perform semantic validation of the Link-State NLRI or the BGP-LS Attribute to determine if it is malformed or invalid. Some types of semantic validation that are not to be performed by a BGP-LS Propagator are as follows (and this is not to be considered as an exhaustive list):
  • presence of a mandatory TLV
  • the length of a fixed-length TLV is correct or the length of a variable length TLV is valid or permissible
  • the values of TLV fields are valid or permissible
  • the inclusion and use of TLVs/sub-TLVs with specific Link-State NLRI types is valid
Each TLV may indicate the valid and permissible values and their semantics that can be used only by a BGP-LS Consumer for its semantic validation. However, the handling of any errors may be specific to the particular application and outside the scope of this document.
Configuration Management An implementation SHOULD allow the operator to specify neighbors to which Link-State NLRIs will be advertised and from which Link-State NLRIs will be accepted. An implementation SHOULD allow the operator to specify the maximum rate at which Link-State NLRIs will be advertised/withdrawn from neighbors. An implementation SHOULD allow the operator to specify the maximum number of Link-State NLRIs stored in a router's Routing Information Base (RIB). An implementation SHOULD allow the operator to create abstracted topologies that are advertised to neighbors and create different abstractions for different neighbors. An implementation MUST allow the operator to configure an 8-octet BGP-LS Instance-ID. Refer to for guidance to the operator for the configuration of BGP-LS Instance-ID. An implementation SHOULD allow the operator to configure Autonomous System Number (ASN) and BGP-LS identifiers (refer to ). An implementation SHOULD allow the operator to configure a 4096-byte size limit for a BGP-LS UPDATE message on a BGP-LS Producer or allow larger values when they know that all BGP-LS Speakers support the extended message size .
Accounting Management Not Applicable.
Performance Management An implementation SHOULD provide the following statistics:
  • Total number of Link-State NLRI updates sent/received
  • Number of Link-State NLRI updates sent/received, per neighbor
  • Number of errored received Link-State NLRI updates, per neighbor
  • Total number of locally originated Link-State NLRIs
These statistics should be recorded as absolute counts since the system or session start time. An implementation MAY also enhance this information by recording peak per-second counts in each case.
Security Management An operator MUST define an import policy to limit inbound updates as follows:
  • Drop all updates from peers that are only serving BGP-LS Consumers.
An implementation MUST have the means to limit inbound updates.
TLV/Sub-TLV Code Points Summary This section contains the global table of all TLVs/sub-TLVs defined in this document. Summary Table of TLV/Sub-TLV Code Points
TLV Code Point Description Reference Section
256 Local Node Descriptors
257 Remote Node Descriptors
258 Link Local/Remote Identifiers
259 IPv4 interface address
260 IPv4 neighbor address
261 IPv6 interface address
262 IPv6 neighbor address
263 Multi-Topology Identifier
264 OSPF Route Type
265 IP Reachability Information
512 Autonomous System
513 BGP-LS Identifier (deprecated)
514 OSPF Area-ID
515 IGP Router-ID
1024 Node Flag Bits
1025 Opaque Node Attribute
1026 Node Name
1027 IS-IS Area Identifier
1028 IPv4 Router-ID of Local Node Sections and
1029 IPv6 Router-ID of Local Node Sections and
1030 IPv4 Router-ID of Remote Node
1031 IPv6 Router-ID of Remote Node
1088 Administrative group (color)
1089 Maximum link bandwidth
1090 Max. reservable link bandwidth
1091 Unreserved bandwidth
1092 TE Default Metric
1093 Link Protection Type
1094 MPLS Protocol Mask
1095 IGP Metric
1096 Shared Risk Link Group
1097 Opaque Link Attribute
1098 Link Name
1152 IGP Flags
1153 IGP Route Tag
1154 IGP Extended Route Tag
1155 Prefix Metric
1156 OSPF Forwarding Address
1157 Opaque Prefix Attribute
Security Considerations Procedures and protocol extensions defined in this document do not affect the BGP security model. See the Security Considerations section of for a discussion of BGP security. Also, refer to and for analysis of security issues for BGP. The operator should ensure that a BGP-LS Speaker does not accept UPDATE messages from a peer that only provides information to a BGP-LS Consumer by using the policy configuration options discussed in Sections and . Generally, an operator is aware of the BGP-LS Speaker's role and link-state peerings. Therefore, the operator can protect the BGP-LS Speaker from peers sending updates that may represent erroneous information, feedback loops, or false input. An error or tampering of the link-state information that is originated into BGP-LS and propagated through the network for use by BGP-LS Consumers applications can result in the malfunction of those applications. Some examples of such risks are the origination of incorrect information that is not present or consistent with the IGP LSDB at the BGP-LS Producer, incorrect ordering of TLVs in the NLRI, or inconsistent origination from multiple BGP-LS Producers and updates to either the NLRI or BGP-LS Attribute during propagation (including discarding due to errors). These are not new risks from a BGP protocol perspective; however, in the case of BGP-LS, impact reflects on the consumer applications instead of BGP routing functionalities. Additionally, it may be considered that the export of link-state and TE information as described in this document constitutes a risk to confidentiality of mission-critical or commercially sensitive information about the network. BGP peerings are not automatic and require configuration; thus, it is the responsibility of the network operator to ensure that only trusted BGP Speakers are configured to receive such information. Similar security considerations also arise on the interface between BGP Speakers and BGP-LS Consumers, but their discussion is outside the scope of this document.
References Normative References Private Enterprise Numbers (PENs) IANA Information technology - Telecommunications and information exchange between systems - Intermediate System to Intermediate System intra-domain routeing information exchange protocol for use in conjunction with the protocol for providing the connectionless-mode network service (ISO 8473) ISO 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. OSPF Version 2 This memo documents version 2 of the OSPF protocol. OSPF is a link- state routing protocol. [STANDARDS-TRACK] Use of BGP-4 Multiprotocol Extensions for IPv6 Inter-Domain Routing BGP-4 Multiprotocol Extensions (BGP-MP) defines the format of two BGP attributes (MP_REACH_NLRI and MP_UNREACH_NLRI) that can be used to announce and withdraw the announcement of reachability information. This document defines how compliant systems should make use of those attributes for the purpose of conveying IPv6 routing information. [STANDARDS-TRACK] RSVP-TE: Extensions to RSVP for LSP Tunnels This document describes the use of RSVP (Resource Reservation Protocol), including all the necessary extensions, to establish label-switched paths (LSPs) in MPLS (Multi-Protocol Label Switching). Since the flow along an LSP is completely identified by the label applied at the ingress node of the path, these paths may be treated as tunnels. A key application of LSP tunnels is traffic engineering with MPLS as specified in RFC 2702. [STANDARDS-TRACK] 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] OSPF Extensions in Support of Generalized Multi-Protocol Label Switching (GMPLS) This document specifies encoding of extensions to the OSPF routing protocol in support of Generalized Multi-Protocol Label Switching (GMPLS). [STANDARDS-TRACK] A Border Gateway Protocol 4 (BGP-4) This document discusses the Border Gateway Protocol (BGP), which is an inter-Autonomous System routing protocol. The primary function of a BGP speaking system is to exchange network reachability information with other BGP systems. This network reachability information includes information on the list of Autonomous Systems (ASes) that reachability information traverses. This information is sufficient for constructing a graph of AS connectivity for this reachability from which routing loops may be pruned, and, at the AS level, some policy decisions may be enforced. BGP-4 provides a set of mechanisms for supporting Classless Inter-Domain Routing (CIDR). These mechanisms include support for advertising a set of destinations as an IP prefix, and eliminating the concept of network "class" within BGP. BGP-4 also introduces mechanisms that allow aggregation of routes, including aggregation of AS paths. This document obsoletes RFC 1771. [STANDARDS-TRACK] OSPF as the Provider/Customer Edge Protocol for BGP/MPLS IP Virtual Private Networks (VPNs) Many Service Providers offer Virtual Private Network (VPN) services to their customers, using a technique in which customer edge routers (CE routers) are routing peers of provider edge routers (PE routers). The Border Gateway Protocol (BGP) is used to distribute the customer's routes across the provider's IP backbone network, and Multiprotocol Label Switching (MPLS) is used to tunnel customer packets across the provider's backbone. This is known as a "BGP/MPLS IP VPN". The base specification for BGP/MPLS IP VPNs presumes that the routing protocol on the interface between a PE router and a CE router is BGP. This document extends that specification by allowing the routing protocol on the PE/CE interface to be the Open Shortest Path First (OSPF) protocol. This document updates RFC 4364. [STANDARDS-TRACK] Multiprotocol Extensions for BGP-4 This document defines extensions to BGP-4 to enable it to carry routing information for multiple Network Layer protocols (e.g., IPv6, IPX, L3VPN, etc.). The extensions are backward compatible - a router that supports the extensions can interoperate with a router that doesn't support the extensions. [STANDARDS-TRACK] Multi-Topology (MT) Routing in OSPF This document describes an extension to Open Shortest Path First (OSPF) in order to define independent IP topologies called Multi- Topologies (MTs). The Multi-Topologies extension can be used for computing different paths for unicast traffic, multicast traffic, different classes of service based on flexible criteria, or an in- band network management topology. An optional extension to exclude selected links from the default topology is also described. [STANDARDS-TRACK] LDP Specification The architecture for Multiprotocol Label Switching (MPLS) is described in RFC 3031. A fundamental concept in MPLS is that two Label Switching Routers (LSRs) must agree on the meaning of the labels used to forward traffic between and through them. This common understanding is achieved by using a set of procedures, called a label distribution protocol, by which one LSR informs another of label bindings it has made. This document defines a set of such procedures called LDP (for Label Distribution Protocol) by which LSRs distribute labels to support MPLS forwarding along normally routed paths. [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] A Policy Control Mechanism in IS-IS Using Administrative Tags This document describes an extension to the IS-IS protocol to add operational capabilities that allow for ease of management and control over IP prefix distribution within an IS-IS domain. This document enhances the IS-IS protocol by extending the information that an Intermediate System (IS) router can place in Link State Protocol (LSP) Data Units for policy use. This extension will provide operators with a mechanism to control IP prefix distribution throughout multi-level IS-IS domains. [STANDARDS-TRACK] Dynamic Hostname Exchange Mechanism for IS-IS RFC 2763 defined a simple and dynamic mechanism for routers running IS-IS to learn about symbolic hostnames. RFC 2763 defined a new TLV that allows the IS-IS routers to flood their name-to-systemID mapping information across the IS-IS network. This document obsoletes RFC 2763. This document moves the capability provided by RFC 2763 to the Standards Track. [STANDARDS-TRACK] IS-IS Extensions for Traffic Engineering This document describes extensions to the Intermediate System to Intermediate System (IS-IS) protocol to support Traffic Engineering (TE). This document extends the IS-IS protocol by specifying new information that an Intermediate System (router) can place in Link State Protocol Data Units (LSP). This information describes additional details regarding the state of the network that are useful for traffic engineering computations. [STANDARDS-TRACK] IS-IS Extensions in Support of Generalized Multi-Protocol Label Switching (GMPLS) This document specifies encoding of extensions to the IS-IS routing protocol in support of Generalized Multi-Protocol Label Switching (GMPLS). [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] Dynamic Hostname Exchange Mechanism for OSPF This document defines a new OSPF Router Information (RI) TLV that allows OSPF routers to flood their hostname-to-Router-ID mapping information across an OSPF network to provide a simple and dynamic mechanism for routers running OSPF to learn about symbolic hostnames, just like for routers running IS-IS. This mechanism is applicable to both OSPFv2 and OSPFv3. [STANDARDS-TRACK] Internationalized Domain Names for Applications (IDNA): Definitions and Document Framework This document is one of a collection that, together, describe the protocol and usage context for a revision of Internationalized Domain Names for Applications (IDNA), superseding the earlier version. It describes the document collection and provides definitions and other material that are common to the set. [STANDARDS-TRACK] IPv6 Traffic Engineering in IS-IS This document specifies a method for exchanging IPv6 traffic engineering information using the IS-IS routing protocol. This information enables routers in an IS-IS network to calculate traffic-engineered routes using IPv6 addresses. [STANDARDS-TRACK] OSPFv3 as a Provider Edge to Customer Edge (PE-CE) Routing Protocol Many Service Providers (SPs) offer Virtual Private Network (VPN) services to their customers using a technique in which Customer Edge (CE) routers are routing peers of Provider Edge (PE) routers. The Border Gateway Protocol (BGP) is used to distribute the customer's routes across the provider's IP backbone network, and Multiprotocol Label Switching (MPLS) is used to tunnel customer packets across the provider's backbone. Support currently exists for both IPv4 and IPv6 VPNs; however, only Open Shortest Path First version 2 (OSPFv2) as PE-CE protocol is specified. This document extends those specifications to support OSPF version 3 (OSPFv3) as a PE-CE routing protocol. The OSPFv3 PE-CE functionality is identical to that of OSPFv2 except for the differences described in this document. [STANDARDS-TRACK] Revised Error Handling for BGP UPDATE Messages According to the base BGP specification, a BGP speaker that receives an UPDATE message containing a malformed attribute is required to reset the session over which the offending attribute was received. This behavior is undesirable because a session reset would impact not only routes with the offending attribute but also other valid routes exchanged over the session. This document partially revises the error handling for UPDATE messages and provides guidelines for the authors of documents defining new attributes. Finally, it revises the error handling procedures for a number of existing attributes. This document updates error handling for RFCs 1997, 4271, 4360, 4456, 4760, 5543, 5701, and 6368. 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. Extensions to OSPF for Advertising Optional Router Capabilities It is useful for routers in an OSPFv2 or OSPFv3 routing domain to know the capabilities of their neighbors and other routers in the routing domain. This document proposes extensions to OSPFv2 and OSPFv3 for advertising optional router capabilities. The Router Information (RI) Link State Advertisement (LSA) is defined for this purpose. In OSPFv2, the RI LSA will be implemented with an Opaque LSA type ID. In OSPFv3, the RI LSA will be implemented with a unique LSA type function code. In both protocols, the RI LSA can be advertised at any of the defined flooding scopes (link, area, or autonomous system (AS)). This document obsoletes RFC 4970 by providing a revised specification that includes support for advertisement of multiple instances of the RI LSA and a TLV for functional capabilities. Guidelines for Writing an IANA Considerations Section in RFCs Many protocols make use of points of extensibility that use constants to identify various protocol parameters. To ensure that the values in these fields do not have conflicting uses and to promote interoperability, their allocations are often coordinated by a central record keeper. For IETF protocols, that role is filled by the Internet Assigned Numbers Authority (IANA). To make assignments in a given registry prudently, guidance describing the conditions under which new values should be assigned, as well as when and how modifications to existing values can be made, is needed. This document defines a framework for the documentation of these guidelines by specification authors, in order to assure that the provided guidance for the IANA Considerations is clear and addresses the various issues that are likely in the operation of a registry. This is the third edition of this document; it obsoletes RFC 5226. 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. Extended Message Support for BGP The BGP specification (RFC 4271) mandates a maximum BGP message size of 4,096 octets. As BGP is extended to support new Address Family Identifiers (AFIs), Subsequent AFIs (SAFIs), and other features, there is a need to extend the maximum message size beyond 4,096 octets. This document updates the BGP specification by extending the maximum message size from 4,096 octets to 65,535 octets for all messages except for OPEN and KEEPALIVE messages. Informative References Address Allocation for Private Internets This document describes address allocation for private internets. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. BGP Security Vulnerabilities Analysis Border Gateway Protocol 4 (BGP-4), along with a host of other infrastructure protocols designed before the Internet environment became perilous, was originally designed with little consideration for protection of the information it carries. There are no mechanisms internal to BGP that protect against attacks that modify, delete, forge, or replay data, any of which has the potential to disrupt overall network routing behavior. This document discusses some of the security issues with BGP routing data dissemination. This document does not discuss security issues with forwarding of packets. This memo provides information for the Internet community. BGP/MPLS IP Virtual Private Networks (VPNs) This document describes a method by which a Service Provider may use an IP backbone to provide IP Virtual Private Networks (VPNs) for its customers. This method uses a "peer model", in which the customers' edge routers (CE routers) send their routes to the Service Provider's edge routers (PE routers); there is no "overlay" visible to the customer's routing algorithm, and CE routers at different sites do not peer with each other. Data packets are tunneled through the backbone, so that the core routers do not need to know the VPN routes. [STANDARDS-TRACK] A Path Computation Element (PCE)-Based Architecture Constraint-based path computation is a fundamental building block for traffic engineering systems such as Multiprotocol Label Switching (MPLS) and Generalized Multiprotocol Label Switching (GMPLS) networks. Path computation in large, multi-domain, multi-region, or multi-layer networks is complex and may require special computational components and cooperation between the different network domains. This document specifies the architecture for a Path Computation Element (PCE)-based model to address this problem space. This document does not attempt to provide a detailed description of all the architectural components, but rather it describes a set of building blocks for the PCE architecture from which solutions may be constructed. This memo provides information for the Internet community. A Per-Domain Path Computation Method for Establishing Inter-Domain Traffic Engineering (TE) Label Switched Paths (LSPs) This document specifies a per-domain path computation technique for establishing inter-domain Traffic Engineering (TE) Multiprotocol Label Switching (MPLS) and Generalized MPLS (GMPLS) Label Switched Paths (LSPs). In this document, a domain refers to a collection of network elements within a common sphere of address management or path computational responsibility such as Interior Gateway Protocol (IGP) areas and Autonomous Systems. Per-domain computation applies where the full path of an inter-domain TE LSP cannot be or is not determined at the ingress node of the TE LSP, and is not signaled across domain boundaries. This is most likely to arise owing to TE visibility limitations. The signaling message indicates the destination and nodes up to the next domain boundary. It may also indicate further domain boundaries or domain identifiers. The path through each domain, possibly including the choice of exit point from the domain, must be determined within the domain. [STANDARDS-TRACK] OSPF Extensions in Support of Inter-Autonomous System (AS) MPLS and GMPLS Traffic Engineering This document describes extensions to the OSPF version 2 and 3 protocols to support Multiprotocol Label Switching (MPLS) and Generalized MPLS (GMPLS) Traffic Engineering (TE) for multiple Autonomous Systems (ASes). OSPF-TE v2 and v3 extensions are defined for the flooding of TE information about inter-AS links that can be used to perform inter-AS TE path computation. No support for flooding information from within one AS to another AS is proposed or defined in this document. [STANDARDS-TRACK] Application-Layer Traffic Optimization (ALTO) Problem Statement Distributed applications -- such as file sharing, real-time communication, and live and on-demand media streaming -- prevalent on the Internet use a significant amount of network resources. Such applications often transfer large amounts of data through connections established between nodes distributed across the Internet with little knowledge of the underlying network topology. Some applications are so designed that they choose a random subset of peers from a larger set with which to exchange data. Absent any topology information guiding such choices, or acting on suboptimal or local information obtained from measurements and statistics, these applications often make less than desirable choices. This document discusses issues related to an information-sharing service that enables applications to perform better-than-random peer selection. This memo provides information for the Internet community. 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. OSPFv2 Multi-Instance Extensions OSPFv3 includes a mechanism to support multiple instances of the protocol running on the same interface. OSPFv2 can utilize such a mechanism in order to support multiple routing domains on the same subnet. This document defines the OSPFv2 Instance ID to enable separate OSPFv2 protocol instances on the same interface. Unlike OSPFv3 where the Instance ID can be used for multiple purposes, such as putting the same interface in multiple areas, the OSPFv2 Instance ID is reserved for identifying protocol instances. This document updates RFC 2328. [STANDARDS-TRACK] Analysis of BGP, LDP, PCEP, and MSDP Issues According to the Keying and Authentication for Routing Protocols (KARP) Design Guide This document analyzes TCP-based routing protocols, the Border Gateway Protocol (BGP), the Label Distribution Protocol (LDP), the Path Computation Element Communication Protocol (PCEP), and the Multicast Source Distribution Protocol (MSDP), according to guidelines set forth in Section 4.2 of "Keying and Authentication for Routing Protocols Design Guidelines", RFC 6518. Application-Layer Traffic Optimization (ALTO) Protocol Applications using the Internet already have access to some topology information of Internet Service Provider (ISP) networks. For example, views to Internet routing tables at Looking Glass servers are available and can be practically downloaded to many network application clients. What is missing is knowledge of the underlying network topologies from the point of view of ISPs. In other words, what an ISP prefers in terms of traffic optimization -- and a way to distribute it. The Application-Layer Traffic Optimization (ALTO) services defined in this document provide network information (e.g., basic network location structure and preferences of network paths) with the goal of modifying network resource consumption patterns while maintaining or improving application performance. The basic information of ALTO is based on abstract maps of a network. These maps provide a simplified view, yet enough information about a network for applications to effectively utilize them. Additional services are built on top of the maps. This document describes a protocol implementing the ALTO services. Although the ALTO services would primarily be provided by ISPs, other entities, such as content service providers, could also provide ALTO services. Applications that could use the ALTO services are those that have a choice to which end points to connect. Examples of such applications are peer-to-peer (P2P) and content delivery networks. 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). Advertisement of Multiple Paths in BGP This document defines a BGP extension that allows the advertisement of multiple paths for the same address prefix without the new paths implicitly replacing any previous ones. The essence of the extension is that each path is identified by a Path Identifier in addition to the address prefix. IS-IS Multi-Instance This document describes a mechanism that allows a single router to share one or more circuits among multiple Intermediate System to Intermediate System (IS-IS) routing protocol instances. Multiple instances allow the isolation of resources associated with each instance. Routers will form instance-specific adjacencies. Each instance can support multiple topologies. Each topology has a unique Link State Database (LSDB). Each Protocol Data Unit (PDU) will contain a new Type-Length-Value (TLV) identifying the instance and the topology (or topologies) to which the PDU belongs. This document obsoletes RFC 6822. Updates to the Allocation Policy for the Border Gateway Protocol - Link State (BGP-LS) Parameters Registries RFC 7752 defines the Border Gateway Protocol - Link State (BGP-LS). IANA created a registry consistent with that document called "Border Gateway Protocol - Link State (BGP-LS) Parameters" with a number of subregistries. The allocation policy applied by IANA for those registries is "Specification Required", as defined in RFC 8126. This document updates RFC 7752 by changing the allocation policy for all of the registries to "Expert Review" and by updating the guidance to the designated experts. IS-IS Extensions in Support of Inter-Autonomous System (AS) MPLS and GMPLS Traffic Engineering This document describes extensions to the Intermediate System to Intermediate System (IS-IS) protocol to support Multiprotocol Label Switching (MPLS) and Generalized MPLS (GMPLS) Traffic Engineering (TE) for multiple Autonomous Systems (ASes). It defines IS-IS extensions for the flooding of TE information about inter-AS links, which can be used to perform inter-AS TE path computation. No support for flooding information from within one AS to another AS is proposed or defined in this document. This document builds on RFC 5316 by adding support for IPv6-only operation. This document obsoletes RFC 5316.
Changes from RFC 7752 This section lists the high-level changes from RFC 7752 and provides reference to the document sections wherein those have been introduced.
  1. Updated in and added to illustrate the different roles of a BGP implementation in conveying link-state information.
  2. Clarified aspects related to advertisement of link-state information from IGPs into BGP-LS in .
  3. In , clarified aspects about TLV handling that apply to both the NLRI and BGP-LS Attribute parts as well as those that are applicable only for the NLRI portion. An implementation may have missed the part about the handling of an unknown TLV and so, based on guidelines, might discard the unknown NLRI types. This aspect is now unambiguously clarified in . Also, the TLVs in the BGP-LS Attribute that are not ordered are not to be considered malformed.
  4. Clarified aspects of mandatory and optional TLVs in both NLRI and BGP-LS Attribute portions all through the document.
  5. In , the handling of a large-sized BGP-LS Attribute with growth in BGP-LS information is explained along with mitigation of errors arising out of it.
  6. Clarified that the document describes the NLRI descriptor TLVs for the protocols and NLRI types specified in this document as well as future BGP-LS extensions must describe the same for other protocols and NLRI types that they introduce.
  7. In , clarified the use of the Identifier field in the Link-State NLRI. It was defined ambiguously to refer to only multi-instance IGP on a single link while it can also be used for multiple IGP protocol instances on a router. The IANA registry is accordingly being removed.
  8. The BGP-LS Identifier TLV in the Node Descriptors has been deprecated. Its use was not well specified by , and there has been some amount of confusion between implementors on its usage for identification of IGP domains as against the use of the Identifier field carrying the BGP-LS Instance-ID when running multiple instances of IGP routing protocols. The original purpose of the BGP-LS Identifier was that, in conjunction with the ASN, it would uniquely identify the BGP-LS domain and that the combination of ASN and BGP-LS ID would be globally unique. However, the BGP-LS Instance-ID carried in the Identifier field in the fixed part of the NLRI also provides a similar functionality. Hence, the inclusion of the BGP-LS Identifier TLV is not necessary. If advertised, all BGP-LS Speakers within an IGP flooding-set (set of IGP nodes within which an LSP/LSA is flooded) had to use the same (ASN, BGP-LS ID) tuple, and if an IGP domain consists of multiple flooding-sets, then all BGP-LS Speakers within the IGP domain had to use the same (ASN, BGP-LS ID) tuple.
  9. Clarified that the Area-ID TLV is mandatory in the Node Descriptor for the origination of information from OSPF except for when sourcing information from AS-scope LSAs where this TLV is not applicable. Also clarified the IS-IS area and area addresses.
  10. Moved the MT-ID TLV from the Node Descriptor section to under the Link Descriptor section since it is not a Node Descriptor sub-TLV. Fixed the ambiguity in the encoding of OSPF MT-ID in this TLV. Updated the IS-IS specification reference section and described the differences in the applicability of the R flags when the MT-ID TLV is used as the Link Descriptor TLV and Prefix Attribute TLV. The MT-ID TLV use is now elevated to SHOULD when it is enabled in the underlying IGP.
  11. Clarified that IPv6 link-local addresses are not advertised in the Link Descriptor TLVs and the local/remote identifiers are to be used instead for links with IPv6 link-local addresses only.
  12. Updated the usage of OSPF Route Type TLV to mandate its use for OSPF prefixes in since this is required for segregation of intra-area prefixes that are used to reach a node (e.g., a loopback) from other types of inter-area and external prefixes.
  13. Clarified the specific OSPFv2 and OSPFv3 protocol TLV space to be used in the Node, Link, and Prefix Opaque Attribute TLVs.
  14. Clarified that the length of the Node Flag Bits and IGP Flags TLVs are to be one octet.
  15. Updated the Node Name TLV in with the OSPF specification.
  16. Clarified the size of the IS-IS Narrow Metric advertisement via the IGP Metric TLV and the handling of the unused bits.
  17. Clarified the advertisement of the prefix corresponding to the LAN segment in an OSPF network in .
  18. Clarified the advertisement and support for OSPF-specific concepts like virtual links, sham links, and Type 4 LSAs in Sections and .
  19. Introduced the Private Use TLV code point space and specified their encoding in .
  20. In , introduced where issues related to the consistency of reporting IGP link-state along with their solutions are covered.
  21. Added a recommendation for isolation of BGP-LS sessions from other BGP route exchanges to avoid errors and faults in BGP-LS affecting the normal BGP routing.
  22. Updated the Fault Management section with detailed rules based on the role of the BGP Speaker in the BGP-LS information propagation flow.
  23. Changed the management of BGP-LS IANA registries from "Specification Required" to "Expert Review" along with updated guidelines for designated experts, more specifically, the inclusion of changes introduced via that are obsoleted by this document.
  24. Added BGP-LS IANA registries with "Expert Review" policy for the flag fields of various TLVs that was missed out. Renamed the BGP-LS TLV registry and removed the "IS-IS TLV/Sub-TLV" column from it.
Acknowledgements This document update to the BGP-LS specification is a result of feedback and input from the discussions in the IDR Working Group. It also incorporates certain details and clarifications based on implementation and deployment experience with BGP-LS. and brought forward the need to clarify the advertisement of a LAN subnet for OSPF. We would like to thank , , , , , , , , , , , and for their review and feedback on this document. Thanks to for his review and comments on the IANA Considerations section. We would also like to thank for his detailed shepherd review and input for improving the document. The detailed AD review by and his suggestions have helped improve this document significantly. We would like to thank Robert Varga for his significant contribution to . We would like to thank , , , , , , , , , , , , , , , , , , , , , , , , , and for their comments on .
Contributors The following persons contributed significant text to and this document. They should be considered coauthors. Rtbrick
hannes@rtbrick.com
Cisco Systems Inc.
United States of America jmedved@cisco.com
Huawei Technologies
Italy stefano@previdi.net
Old Dog Consulting
adrian@olddog.co.uk
Individual
United States of America raysaikat@gmail.com
Author's Address Cisco Systems
India ketant.ietf@gmail.com