Inter-Domain RoutingInternet Engineering Task Force (IETF) H. Gredler, Ed.Internet-Draft PrivateRequest for Comments: 7752 Individual ContributorIntended status:Category: Standards Track J. MedvedExpires: April 18, 2016ISSN: 2070-1721 S. Previdi Cisco Systems, Inc. A. Farrel Juniper Networks, Inc. S. RayOctober 16, 2015February 2016 North-Bound Distribution of Link-State andTETraffic Engineering (TE) InformationusingUsing BGPdraft-ietf-idr-ls-distribution-13Abstract 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, includingtraffic engineeringTraffic Engineering (TE) information. This is information typically distributed by IGP routing protocols within the network. This document describes a mechanism by whichlinks statelinks-state andtraffic engineeringTE 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 includeApplication LayerApplication-Layer Traffic Optimization (ALTO)servers,servers and Path Computation Elements (PCEs).Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119].Status of This Memo ThisInternet-Draftissubmitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documentsan Internet Standards Track document. This document is a product of the Internet Engineering Task Force (IETF).Note that other groups may also distribute working documents as Internet-Drafts. The listIt represents the consensus ofcurrent Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents validthe IETF community. It has received public review and has been approved fora maximumpublication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 5741. Information about the current status ofsix monthsthis document, any errata, and how to provide feedback on it may beupdated, replaced, or obsoleted by other documentsobtained atany time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on April 18, 2016.http://www.rfc-editor.org/info/rfc7752. Copyright Notice Copyright (c)20152016 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 5 2. Motivation and Applicability . . . . . . . . . . . . . . . . 5 2.1. MPLS-TE with PCE . . . . . . . . . . . . . . . . . . . . 5 2.2. ALTO Server Network API . . . . . . . . . . . . . . . . . 6 3. CarryingLink StateLink-State Information in BGP . . . . . . . . . . . 7 3.1. TLV Format . . . . . . . . . . . . . . . . . . . . . . . 7 3.2. The Link-State NLRI . . . . . . . . . . . . . . . . . . . 8 3.2.1. Node Descriptors . . . . . . . . . . . . . . . . . . 12 3.2.2. Link Descriptors . . . . . . . . . . . . . . . . . . 16 3.2.3. Prefix Descriptors . . . . . . . . . . . . . . . . . 17 3.3. The BGP-LS Attribute . . . . . . . . . . . . . . . . . . 19 3.3.1. Node Attribute TLVs . . . . . . . . . . . . . . . . . 19 3.3.2. Link Attribute TLVs . . . . . . . . . . . . . . . . . 23 3.3.3. Prefix Attribute TLVs . . . . . . . . . . . . . . . . 28 3.4. BGPNext HopNext-Hop Information . . . . . . . . . . . . . . . . 31 3.5. Inter-AS Links . . . . . . . . . . . . . . . . . . . . . 32 3.6. Router-ID Anchoring Example: ISO Pseudonode . . . . . . . 32 3.7. Router-ID Anchoring Example: OSPF Pseudonode . . . . . . 33 3.8. Router-ID Anchoring Example: OSPFv2 to IS-IS Migration . 34 4. Link to Path Aggregation . . . . . . . . . . . . . . . . . . 34 4.1. Example: No Link Aggregation . . . . . . . . . . . . . . 35 4.2. Example: ASBR to ASBR Path Aggregation . . . . . . . . . 35 4.3. Example: Multi-AS Path Aggregation . . . . . . . . . . . 36 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 36 5.1. Guidance for Designated Experts . . . . . . . . . . . . . 37 6. Manageability Considerations . . . . . . . . . . . . . . . .3738 6.1. Operational Considerations . . . . . . . . . . . . . . .3738 6.1.1. Operations . . . . . . . . . . . . . . . . . . . . .3738 6.1.2. Installation and Initial Setup . . . . . . . . . . . 38 6.1.3. Migration Path . . . . . . . . . . . . . . . . . . . 38 6.1.4. Requirements on Other Protocols and Functional Components . . . . . . . . . . . . . . . . . . . . . 38 6.1.5. Impact on Network Operation . . . . . . . . . . . . . 38 6.1.6. Verifying Correct Operation . . . . . . . . . . . . .3839 6.2. Management Considerations . . . . . . . . . . . . . . . . 39 6.2.1. Management Information . . . . . . . . . . . . . . . 39 6.2.2. Fault Management . . . . . . . . . . . . . . . . . . 39 6.2.3. Configuration Management . . . . . . . . . . . . . .3940 6.2.4. Accounting Management . . . . . . . . . . . . . . . . 40 6.2.5. Performance Management . . . . . . . . . . . . . . . 40 6.2.6. Security Management . . . . . . . . . . . . . . . . .4041 7. TLV/Sub-TLV Code Points Summary . . . . . . . . . . . . . . .4041 8. Security Considerations . . . . . . . . . . . . . . . . . . . 42 9.ContributorsReferences . . . . . . . . . . . . . . . . . . . . . . . . . 4310. Acknowledgements9.1. Normative References . . . . . . . . . . . . . . . . . . 43 9.2. Informative References . . . .43 11. References. . . . . . . . . . . . . 46 Acknowledgements . . . . . . . . . . . .43 11.1. Normative References. . . . . . . . . . . . 47 Contributors . . . . . . .43 11.2. Informative References. . . . . . . . . . . . . . . . .45. . 47 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 47 1. Introduction The contents of aLink StateLink-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) in order to make better decisions. The IETF has defined the Path Computation Element (PCE) [RFC4655] as a mechanism for achieving the computation of end-to-end TE paths that cross the visibility of more than one TED orwhichthat require CPU- intensive or coordinated computations. The IETF has also defined the ALTOServerserver [RFC5693] as an entity that generates an abstracted network topology and provides it to network-aware applications. Both a PCE and an ALTOServerserver need to gather information about the topologies and capabilities of the network in order to be able to fulfill their function. This document describes a mechanism by whichLink Statelink-state and TE information can be collected from networks and shared with external components using the BGP routing protocol [RFC4271]. This is achieved using a new BGP Network Layer Reachability Information (NLRI) encoding format. The mechanism is applicable to physical and virtual 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 metric and TE metric, link bandwidth, reservable bandwidth, perCoSClass-of-Service (CoS) class reservation state,preemptionpreemption, and Shared Risk Link Groups(SRLG).(SRLGs). The router's BGP process can retrieve topology from these LSDBs and distribute it to a consumer, either directly or via a peer BGPSpeakerspeaker (typically a dedicated Route Reflector), using the encoding specified in this document. The collection ofLink Statelink-state and TElink stateinformation and its distribution to consumers is shown in the following figure. +-----------+ | Consumer | +-----------+ ^ | +-----------+ | BGP | +-----------+ | Speaker | | Consumer | +-----------+ +-----------+ ^ ^ ^ ^ | | | | +---------------+ | +-------------------+ | | | | | +-----------+ +-----------+ +-----------+ | BGP | | BGP | | BGP | | Speaker | | Speaker | . . . | Speaker | +-----------+ +-----------+ +-----------+ ^ ^ ^ | | | IGP IGP IGP Figure 1: Collection of Link-State and TELink State info collectionInformation A BGPSpeakerspeaker may apply 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 aPOP. AbstractedPoint of Presence (POP). Abstracted topology can also be a mix of physical and virtual nodes and physical and virtual links. Furthermore, the BGPSpeakerspeaker can apply policy to determine when information is updated to the consumer so that there is a reduction of information flow from the network to the consumers. Mechanisms through which topologies can be aggregated or virtualized are outside the scope of this document 1.1. Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119]. 2. Motivation and Applicability This section describes use cases from which the requirements can be derived. 2.1. MPLS-TE with PCE As described in[RFC4655][RFC4655], 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-areaAS,AS or multiple ASes). o 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. o If a router wants to compute a 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-endpath,path and cannot even select the right exit router (Area Border Router- ABR)(ABR)) for an optimal path. This is an issue for large-scale networks that need to segment their core networks into distinctareas,areas but still want to take advantage of MPLS-TE. Previous solutions used per-domain path computation [RFC5152]. 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 uses a technique called "loose-hop-expansion"[RFC3209],[RFC3209] and selects the exit ABR and other ABRs or AS Border Routers (ASBRs) using theIGP computedIGP-computed shortest path topology for the remainder of the path. This may lead to sub-optimal paths, makes alternate/back- up path computation hard, and might result in no TE path being found when one really 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 obviously needs access to the TED for the area(s) it serves, but [RFC4655] 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 sub-optimal when the network is subject to a high degree ofchurn,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. +----------+ +---------+ | ----- | | BGP | | | TED |<-+-------------------------->| Speaker | | ----- | TED synchronization | | | | | mechanism: +---------+ | | | BGP with Link-State NLRI | v | | ----- | | | PCE | | | ----- | +----------+ ^ | Request/ | Response v Service +----------+ Signaling +----------+ Request | Head-End | Protocol | Adjacent | -------->| Node |<------------>| Node | +----------+ +----------+ Figure 2: External PCEnode usingNode Using a TEDsynchronization mechanismSynchronization Mechanism 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. 2.2. ALTO Server Network API An ALTOServerserver [RFC5693] is an entity that generates an abstracted network topology and provides it to network-aware applications over aweb service basedweb-service-based API. Example applications arep2ppeer-to-peer (P2P) clients or trackers, orCDNs.Content Distribution Networks (CDNs). The abstracted network topology comes in the form of two maps: a Network Map that specifies 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 [RFC7285]. 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 ALTOServerserver can retrieve all the necessary prefix and network topology data from the underlying network. Note that an ALTOServerserver can use other mechanisms to get network data, for example, peering with multiple IGP and BGPSpeakers.speakers. The following figure shows how an ALTOServerserver can get network topology information from the underlying network using the mechanism described in this document. +--------+ | Client |<--+ +--------+ | | ALTO +--------+ BGP with +---------+ +--------+ | Protocol | ALTO | Link-State NLRI | BGP | | Client |<--+------------| Server |<----------------| Speaker | +--------+ | | | | | | +--------+ +---------+ +--------+ | | Client |<--+ +--------+ Figure 3: ALTO Serverusing network topology informationUsing Network Topology Information 3. CarryingLink StateLink-State Information in BGP This specification contains two parts: definition of a new BGP NLRI that describes links,nodesnodes, and prefixes comprising IGPlink state information,link-state information and definition of a new BGP path attribute (BGP-LS attribute) that carries link,nodenode, and prefix properties and attributes, such as the link and prefix metric or auxiliary Router- IDs of nodes, etc. It isdesireddesirable to keep the dependencies on the protocol source of thisattributesattribute to a minimum and represent any content in anIGPIGP- neutral way, such that applicationswhich dothat want to learn about aLink-statelink- state topology do not need to know about any OSPF or IS-IS protocol specifics. 3.1. TLV Format Information in the new Link-State NLRIs and attributes is encoded in Type/Length/Value triplets. The TLV format is shown in Figure 4. 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) // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 4: TLVformatFormat The Length field defines the length of the value portion in octets(thus(thus, a TLV with no value portion would have a length of zero). The TLV is not padded tofour-octet4-octet alignment. Unrecognized types MUST be preserved and propagated. In order to compare NLRIs with unknownTLVsTLVs, all TLVs MUST be ordered in ascending order by TLV Type. If there are more TLVs of the same type, then the TLVs MUST be ordered in ascending order of the TLV value within the TLVs with the same type by treating the entirevalueValue field as an opaque hexadecimal string and comparing leftmost octetsfirstfirst, regardless of the length of the string..All TLVs that are not specified as mandatory are considered optional. 3.2. The Link-State NLRI The MP_REACH_NLRI and MP_UNREACH_NLRI attributes are BGP's containers for carrying opaque information. Each Link-State NLRI describes either a node, alinklink, or a prefix. All non-VPN link,nodenode, and prefix information SHALL be encoded using AFI 16388 / SAFI 71. VPN link,nodenode, and prefix information SHALL be encoded using AFI 16388 / SAFITBD.72. In order for two BGP speakers to exchange Link-State NLRI, they MUST use BGP Capabilities Advertisement to ensure that theybothare both capable of properly processing such NLRI. This is done as specified in [RFC4760], by using capability code 1 (multi-protocol BGP), with AFI 16388 / SAFI 71 for BGP-LS, and AFI 16388 / SAFITBD72 forBGP-LS- VPN.BGP-LS-VPN. The format of the Link-State NLRI is shown in the followingfigure.figures. 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) // | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 5: 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + Route Distinguisher + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | // Link-State NLRI (variable) // | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 6: Link-State VPN AFI 16388 / SAFITBD72 NLRI Format The'TotalTotal NLRILength'Length field contains the cumulative length, in octets, of the rest of theNLRINLRI, not including the NLRI Type field or itself. For VPN applications, it also includes the length of the Route Distinguisher. +------+---------------------------+ | Type | NLRI Type | +------+---------------------------+ | 1 | Node NLRI | | 2 | Link NLRI | | 3 | IPv4 Topology Prefix NLRI | | 4 | IPv6 Topology Prefix NLRI | +------+---------------------------+ Table 1: NLRI Types Route Distinguishers are defined and discussed in [RFC4364]. The Node NLRI (NLRI Type = 1) is shown in the following figure. 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 | | (64 bits) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ // Local Node Descriptors (variable) // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 7: The Node NLRIformatFormat The Link NLRI (NLRI Type = 2) is shown in the following figure. 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 | | (64 bits) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ // Local Node Descriptors (variable) // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ // Remote Node Descriptors (variable) // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ // Link Descriptors (variable) // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 8: The Link NLRIformatFormat The IPv4 and IPv6 Prefix NLRIs (NLRI Type = 3 and Type = 4) use the sameformatformat, as shown in the following figure. 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 | | (64 bits) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ // Local NodeDescriptorDescriptors (variable) // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ // Prefix Descriptors (variable) // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 9: The IPv4/IPv6 Topology Prefix NLRIformatFormat The'Protocol-ID'Protocol-ID field can contain one of the following values: +-------------+----------------------------------+ | 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 | +-------------+----------------------------------+ Table 2: Protocol Identifiers The 'Direct' and 'Static configuration' protocol types SHOULD be used when BGP-LS is sourcing local information. For allinformation,information derived from otherprotocolsprotocols, the correspondingprotocol-IDProtocol-ID MUST be used. If BGP-LS hasgotdirect access to interface information and wants to advertise a locallinklink, then theprotocol-IDProtocol-ID 'Direct' SHOULD be used. For modeling virtual links,likesuch as described in Section44, theprotocol-IDProtocol-ID 'Static configuration' SHOULD be used. Both OSPF and IS-IS MAY run multiple routing protocol instances over the same link. See [RFC6822] and [RFC6549]. These instances define independent "routing universes". The64-Bit 'Identifier'64-bit Identifier field is used to identify the"routing universe"routing universe where the NLRI belongs. The NLRIs representingLink-statelink-state objects (nodes,linkslinks, or prefixes) from the same routing universe MUST have the same 'Identifier' value. NLRIs with different 'Identifier' values MUST be considered to be from different routing universes. Table 3 lists the 'Identifier' values that are defined as well-known in thisdraft.document. +------------+----------------------------------+ | Identifier | Routing Universe | +------------+----------------------------------+ | 0 | Default Layer 3 Routing topology | | 1-31 | Reserved | +------------+----------------------------------+ Table 3:Well-knownWell-Known Instance Identifiers If a givenProtocolprotocol does not support multiple routinguniversesuniverses, then it SHOULD set the'Identifier'Identifier field according to Table 3.HoweverHowever, an implementation MAY make the 'Identifier'configurable,configurable for a given protocol. Each Node Descriptor and Link Descriptor consists of one or moreTLVsTLVs, as described in the following sections. 3.2.1. Node Descriptors Each link is anchored by a pair of Router-IDs that are used by the underlying IGP, namely,48 Bita 48-bit ISO System-ID for IS-IS and32 bita 32-bit Router-ID for OSPFv2 and OSPFv3. An IGP may use one or more additional auxiliary Router-IDs, mainly fortraffic engineeringTraffic Engineering purposes. For example, IS-IS may have one or more IPv4 and IPv6 TE Router-IDs[RFC5305],[RFC5305] [RFC6119]. These auxiliary Router-IDs MUST be included in the link attribute described in Section 3.3.2. It is desirable that the Router-ID assignments inside the Node Descriptor are globally unique.HoweverHowever, there may be Router-ID spaces(e.g.(e.g., ISO) where no global registry exists, or worse, Router- IDs have been allocated following the private-IP allocation described in RFC 1918[RFC1918] allocation.[RFC1918]. BGP-LS uses the Autonomous System (AS) Number and BGP-LS Identifier (see Section 3.2.1.4) to disambiguate the Router-IDs, as described in Section 3.2.1.1. 3.2.1.1. Globally Unique Node/Link/Prefix Identifiers One problem that needs to be addressed is the ability to identify an IGP node globally (by"global","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: (A) The same node MUST NOT be represented by two keys(otherwise(otherwise, one node will look like two nodes). (B) 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 andprefixes),prefixes) withinwhich,which each node has a unique IGP representation by using the combination of Area-ID, Router-ID,Protocol, Topology-ID,Protocol-ID, Multi-Topology ID, andInstance ID.Instance-ID. The problem is that BGP may receive node/link/prefix information from multiple independent "IGPdomains"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 IGPtransitionstransitions, it may happen that two redundant IGPs are in place. In Section3.2.1.43.2.1.4, a set of sub-TLVs is described, which allows specification of a flexible key for any givenNode/Linknode/link information such that global uniqueness of the NLRI is ensured. 3.2.1.2. 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 length of this TLV is variable. The value contains one or more Node Descriptor Sub- TLVs defined in Section 3.2.1.4. 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) // | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 10: Local Node Descriptors TLVformatFormat 3.2.1.3. 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 forlinkLink NLRIs. The length of this TLV is variable. The value contains one or more Node Descriptor Sub-TLVs defined in Section 3.2.1.4. 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) // | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 11: Remote Node Descriptors TLVformatFormat 3.2.1.4. Node Descriptor Sub-TLVs The Node Descriptor Sub-TLV typecodepointscode points and lengths are listed in the following table: +--------------------+-------------------+----------+ | Sub-TLV Code Point | Description | Length | +--------------------+-------------------+----------+ | 512 | Autonomous System | 4 | | 513 | BGP-LS Identifier | 4 | | 514 | OSPF Area-ID | 4 | | 515 | IGP Router-ID | Variable | +--------------------+-------------------+----------+ Table 4: Node Descriptor Sub-TLVs The sub-TLV values in Node Descriptor TLVs are defined as follows: Autonomous System:opaqueOpaque value(32 Bit(32-bit AS Number) BGP-LS Identifier:opaqueOpaque value(32 Bit(32-bit ID). In conjunction withASN,Autonomous System Number (ASN), uniquely identifies the BGP-LS domain. The combination of ASN and BGP-LS ID MUST be globally unique. All BGP-LS speakers within an IGP flooding-set (set of IGP nodes within which anLSP/ LSALSP/LSA is flooded) MUST use the same ASN, BGP-LS ID tuple. If an IGP domain consists of multiple flooding-sets, then all BGP-LS speakers within the IGP domain SHOULD use the same ASN, BGP-LS ID tuple.The ASN, BGP Router-ID tuple (which is globally unique [RFC6286] ) of one of the BGP-LS speakers within the flooding-set (or IGP domain) may be used for all BGP-LS speakers in that flooding-set (or IGP domain). Area ID: It is usedArea-ID: Used to identify the32 Bit32-bit area to which the NLRI belongs. The Area Identifier allowsthedifferent NLRIs of the same router to be discriminated. IGPRouter ID: opaqueRouter-ID: Opaque value. This is a mandatory TLV. For an IS-ISnon-Pseudonode,non-pseudonode, this contains6 octeta 6-octet ISOnode-IDNode-ID (ISOsystem-ID).system- ID). For an IS-ISPseudonodepseudonode corresponding to a LAN, this contains6 octetthe 6-octet ISOnode-IDNode-ID of the"DesignatedDesignated IntermediateSystem"System (DIS) followed byone octeta 1-octet, nonzero PSN identifier (7 octets in total). For an OSPFv2 or OSPFv3non-"Pseudonode",non-pseudonode, this contains the4 octet4-octet Router-ID. For an OSPFv2"Pseudonode"pseudonode representing a LAN, this contains the4 octet4-octet Router-ID of thedesignated routerDesignated Router (DR) followed by the4 octet4-octet IPv4 address of the DR's interface to the LAN (8 octets in total). Similarly, for an OSPFv3"Pseudonode",pseudonode, this contains the4 octet4-octet Router-ID of the DR followed by the4 octet4-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. There can be at most one instance of each sub-TLV type present in any Node Descriptor. The sub-TLVs within a NodedescriptorDescriptor MUST be arranged in ascending order by sub-TLV type. This needs to be done in order to compare NLRIs, even when an implementation encounters an unknown sub-TLV. Using stablesortingsorting, an implementation can do binary comparison of NLRIs and hence allow incremental deployment of new key sub-TLVs. 3.2.1.5. Multi-Topology ID The Multi-Topology ID (MT-ID) TLV carries one or more IS-IS or OSPF Multi-Topology IDs for a link,nodenode, or prefix. Semantics of the IS-IS MT-ID are defined inRFC5120,Section 7.2 of RFC 5120 [RFC5120]. Semantics of the OSPF MT-ID are defined inRFC4915,Section 3.7 of RFC 4915 [RFC4915]. If the value in the MT-ID TLV is derived from OSPF, then the upper 9 bits MUST be set to 0. Bits R arereserved,reserved and SHOULD be set to 0 when originated and ignored on receipt. The format of the MT-ID TLV is shown in the following figure. 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 12: Multi-Topology ID TLVformatFormat where Type is 263, Length is2*n2*n, and n is the number of MT-IDs carried in the TLV. The MT-ID TLV MAY be present in a Link Descriptor, a Prefix Descriptor, orinthe BGP-LS attribute of anodeNode NLRI. In 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 Descriptor or Prefix Descriptor, multiple NLRIs need to be generated where each NLRI contains an unique MT-ID. In the BGP-LS attribute of anodeNode NLRI, one MT-ID TLV containing the array of MT-IDs of all topologies where the node is reachable is allowed. 3.2.2. Link Descriptors The'Link Descriptor'Link Descriptor field is a set of Type/Length/Value (TLV) triplets. The format of each TLV is shown in Section 3.1. The'Link descriptor'Link Descriptor TLVs uniquely identify a link among multiple parallel links between a pair of anchor routers. A link described by the LinkdescriptorDescriptor TLVs actually is a "half-link", a unidirectional representation of a logical link. In order to fully describe a single logical link, two originating routers advertise a half-link each, i.e., twolinkLink NLRIs are advertised for a given point-to-point link. The format and semantics of the'value'Value fields in most'Link Descriptor'Link Descriptor TLVs correspond to the format and semantics ofvalueValue fields in IS-IS Extended IS Reachability sub-TLVs, defined in [RFC5305],[RFC5307][RFC5307], and [RFC6119]. Although the encodings for'Link Descriptor'Link Descriptor TLVs were originally defined for IS-IS, the TLVs can carry data sourcedeitherby either IS-IS or OSPF. The following TLVs are valid as Link Descriptors in the Link NLRI:+-----------+---------------------+---------------+-----------------++-----------+---------------------+--------------+------------------+ | TLV Code | Description | IS-IS TLV |Value definedReference | | Point | | /Sub-TLV |in:(RFC/Section) |+-----------+---------------------+---------------+-----------------++-----------+---------------------+--------------+------------------+ | 258 | Link Local/Remote | 22/4 | [RFC5307]/1.1 | | | Identifiers | | | | 259 | IPv4 interface | 22/6 | [RFC5305]/3.2 | | | address | | | | 260 | IPv4 neighbor | 22/8 | [RFC5305]/3.3 | | | address | | | | 261 | IPv6 interface | 22/12 | [RFC6119]/4.2 | | | address | | | | 262 | IPv6 neighbor | 22/13 | [RFC6119]/4.3 | | | address | | | | 263 | Multi-Topology | --- | Section 3.2.1.5 | | | Identifier | | |+-----------+---------------------+---------------+-----------------++-----------+---------------------+--------------+------------------+ Table 5: Link Descriptor TLVs 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 IP address TLVs are included in thelink descriptor,Link Descriptor but not the link local/remote Identifier TLV. The link local/remote identifiers MAY be included in the link attribute. If interface and neighbor addresses are not present and the link local/remote identifiers are present, then the link local/remote Identifier TLV is included in thelink descriptor.Link Descriptor. The Multi-Topology Identifier TLV is included inlink descriptorLink Descriptor if that information is present. 3.2.3. Prefix Descriptors The'Prefix Descriptor'Prefix Descriptor field is a set of Type/Length/Value (TLV) triplets.'Prefix Descriptor'Prefix Descriptor TLVs uniquely identify an IPv4 or IPv6Prefixprefix originated by aNode.node. The following TLVs are valid as Prefix Descriptors in the IPv4/IPv6 Prefix NLRI:+--------------+-----------------------+----------+-----------------++-------------+---------------------+----------+--------------------+ | TLV Code | Description | Length |Value definedReference | | Point | | |in:(RFC/Section) |+--------------+-----------------------+----------+-----------------++-------------+---------------------+----------+--------------------+ | 263 | Multi-Topology | variable | Section 3.2.1.5 | | | Identifier | | | | 264 | OSPF Route Type | 1 | Section 3.2.3.1 | | 265 | IP Reachability | variable | Section 3.2.3.2 | | | Information | | |+--------------+-----------------------+----------+-----------------++-------------+---------------------+----------+--------------------+ Table 6: Prefix Descriptor TLVs 3.2.3.1. OSPF Route Type The OSPF Route Type TLV is an optional TLV that MAY be present in Prefix NLRIs. It is used to identify the OSPFroute-typeroute type of the prefix. It is used when an OSPF prefix is advertised in the OSPF domain with multipleroute-types.route types. The Route Type TLV allows the discrimination of these advertisements. The format of the OSPF Route Type TLV is shown in the following figure. 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 | +-+-+-+-+-+-+-+-+ Figure 13: OSPF Route Type TLV Format where the Type and Length fields of the TLV are defined in Table 6. The OSPF Route Type field values are defined in the OSPFprotocol,protocol and can be one of the following: o Intra-Area (0x1) o Inter-Area (0x2) o External 1 (0x3) o External 2 (0x4) o NSSA 1 (0x5) o NSSA 2 (0x6) 3.2.3.2. IP Reachability Information The IP Reachability Information TLV is a mandatory TLV that contains one IP address prefix (IPv4 or IPv6) originally advertised in the IGP topology. Its purpose is to glue a particular BGP service NLRI by virtue of its BGPnext-hopnext hop to a givenNodenode in the LSDB. A router SHOULD advertise an IP Prefix NLRI for each of its BGPNext-hops.next hops. The format of the IP Reachability Information TLV is shown in the following figure: 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) // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 14: IP Reachability Information TLV Format The Type and Length fields of the TLV are defined in Table 6. The following two fields determine theaddress-familyreachabilityinformation.information of the address family. The'Prefix Length'Prefix Length field contains the length of the prefix in bits. The'IP Prefix'IP Prefix field contains the most significant octets of theprefix;prefix, i.e., 1 octet for prefix length 1 up to 8, 2 octets for prefix length 9 to 16, 3 octets for prefix length 17 up to24 and24, 4 octets for prefix length 25 up to 32, etc. 3.3. The BGP-LS AttributeThisThe BGP-LS attribute is an optional, non-transitive BGP attribute that is used to carry link,nodenode, and prefix parameters and attributes. It is defined as a set of Type/Length/Value (TLV) triplets, described in the following section. This attribute SHOULD only be included withLink- StateLink-State NLRIs. This attribute MUST be ignored for all otheraddress-address families. 3.3.1. Node Attribute TLVs Node attribute TLVs are the TLVs that may be encoded in the BGP-LS attribute with anodeNode NLRI. The followingnode attributeNode Attribute TLVs are defined:+--------------+-----------------------+----------+-----------------++-------------+----------------------+----------+-------------------+ | TLV Code | Description | Length |Value definedReference | | Point | | |in:(RFC/Section) |+--------------+-----------------------+----------+-----------------++-------------+----------------------+----------+-------------------+ | 263 | Multi-Topology | variable | Section 3.2.1.5 | | | Identifier | | | | 1024 | Node Flag Bits | 1 | Section 3.3.1.1 | | 1025 | Opaque Node | variable | Section 3.3.1.5 | | |PropertiesAttribute | | | | 1026 | Node Name | variable | Section 3.3.1.3 | | 1027 | IS-IS AreaIdentifier| variable | Section 3.3.1.2 | | | Identifier | | | | 1028 | IPv4 Router-ID of | 4 | [RFC5305]/4.3 | | | Local Node | | | | 1029 | IPv6 Router-ID of | 16 | [RFC6119]/4.1 | | | Local Node | | |+--------------+-----------------------+----------+-----------------++-------------+----------------------+----------+-------------------+ Table 7: Node Attribute TLVs 3.3.1.1. Node Flag Bits TLV The Node Flag Bits TLV carries a bit mask describing node attributes. The value is avariable lengthvariable-length bit array of flags, where each bit represents a node capability. 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| Rsvd| +-+-+-+-+-+-+-+-+-+ Figure 15: Node Flag Bits TLVformatFormat The bits are defined as follows:+-----------------+-------------------------+-----------++-----------------+-------------------------+------------+ | Bit | Description | Reference |+-----------------+-------------------------+-----------++-----------------+-------------------------+------------+ | 'O' | Overload Bit |[RFC1195][ISO10589] | | 'T' | Attached Bit |[RFC1195][ISO10589] | | 'E' | External Bit | [RFC2328] | | 'B' | ABR Bit | [RFC2328] | | 'R' | Router Bit | [RFC5340] | | 'V' | V6 Bit | [RFC5340] | | Reserved (Rsvd) | Reserved for future use | |+-----------------+-------------------------+-----------++-----------------+-------------------------+------------+ Table 8: Node Flag Bits Definitions 3.3.1.2. IS-IS Area Identifier TLV An IS-IS node can be part of one or more IS-IS areas. Each of these area addresses is carried in the IS-IS Area Identifier TLV. If multipleArea Addressesarea 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. 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ // Area Identifier (variable) // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 16: IS-IS Area Identifier TLV Format 3.3.1.3. Node Name TLV The Node Name TLV is optional. Its structure and encoding has been borrowed from [RFC5301]. ThevalueValue field identifies the symbolic name of the router node. This symbolic name can be theFQDNFully Qualified Domain Name (FQDN) for the router, it can be a subset of the FQDN(e.g.(e.g., a hostname), or it can be any string operators want to use for the router. The use of FQDN or a subset of it is strongly RECOMMENDED. The maximum length of the'NodeNode NameTLV'TLV is 255 octets. The Value field is encoded in 7-bit ASCII. If auser-interfaceuser interface for configuring or displaying this field permits Unicode characters, thatuser-interfaceuser interface is responsible for applying the ToASCII and/or ToUnicode algorithm as described in [RFC5890] to achieve the correct format for transmission or display. Although [RFC5301]isdescribes anIS-IS specificIS-IS-specific extension, usage of the Node Name TLV is possible for all protocols. How a router derives and injects nodenames for e.g.names, e.g., OSPF nodes, is outside of the scope of this document. 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) // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 17: Node NameformatFormat 3.3.1.4. 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 purposeslikesuch 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 in its own TLV. 3.3.1.5. Opaque Node Attribute TLV The Opaque Node Attribute TLV is an envelope that transparently carries optionalnode attributeNode 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 noprotocol neutralprotocol-neutral representation in the BGPlink-stateLink-State NLRI. The primary use of the Opaque Node Attribute TLV is to bridge the document lagbetween e.g.between, e.g., a new IGPLink-statelink-state attribute being defined and the'protocol- neutral'protocol- neutral BGP-LS extensions being published. Arouterrouter, forexampleexample, could use this extension in order to advertise the nativeprotocols node attributeprotocol's Node Attribute TLVs, such as the OSPF Router Informational Capabilities TLV defined in[RFC4970],[RFC7770] or the IGP TE Node Capability Descriptor TLV described in [RFC5073]. 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) // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 18: Opaque Nodeattribute formatAttribute Format 3.3.2. Link Attribute TLVs LinkattributeAttribute TLVs are TLVs that may be encoded in the BGP-LS attribute with alinkLink NLRI. Each 'Link Attribute' is a Type/Length/ Value (TLV) triplet formatted as defined in Section 3.1. The format and semantics of the'value'Value fields in some'Link Attribute'Link Attribute TLVs correspond to the format and semantics ofvaluethe Value fields in IS-IS Extended IS Reachability sub-TLVs, defined in [RFC5305] and [RFC5307]. Other'Link Attribute'Link Attribute TLVs are defined in this document. Although the encodings for'Link Attribute'Link Attribute TLVs were originally defined for IS-IS, the TLVs can carry data sourcedeitherby either IS-IS or OSPF. The following'Link Attribute'Link Attribute TLVs are valid in the BGP-LS attribute with alinkLink NLRI: +-----------+---------------------+--------------+------------------+ | TLV Code | Description | IS-IS TLV |Defined in:Reference | | Point | | /Sub-TLV | (RFC/Section) | +-----------+---------------------+--------------+------------------+ | 1028 | IPv4 Router-ID of | 134/--- | [RFC5305]/4.3 | | | Local Node | | | | 1029 | IPv6 Router-ID of | 140/--- | [RFC6119]/4.1 | | | Local Node | | | | 1030 | IPv4 Router-ID of | 134/--- | [RFC5305]/4.3 | | | Remote Node | | | | 1031 | IPv6 Router-ID of | 140/--- | [RFC6119]/4.1 | | | Remote Node | | | | 1088 | Administrative | 22/3 | [RFC5305]/3.1 | | | group (color) | | | | 1089 | Maximum link | 22/9 |[RFC5305]/3.3[RFC5305]/3.4 | | | bandwidth | | | | 1090 | Max. reservable | 22/10 | [RFC5305]/3.5 | | | link bandwidth | | | | 1091 | Unreserved | 22/11 | [RFC5305]/3.6 | | | bandwidth | | | | 1092 | TE Default Metric | 22/18 | Section3.3.2.3/3.3.2.3 | | 1093 | Link Protection | 22/20 | [RFC5307]/1.2 | | | Type | | | | 1094 | MPLS Protocol Mask | --- | Section 3.3.2.2 | | 1095 | IGP Metric | --- | Section 3.3.2.4 | | 1096 | Shared Risk Link | --- | Section 3.3.2.5 | | | Group | | | | 1097 | OpaquelinkLink | --- | Section 3.3.2.6 | | |attributeAttribute | | | | 1098 | Link Nameattribute| --- | Section 3.3.2.7 | +-----------+---------------------+--------------+------------------+ Table 9: Link Attribute TLVs 3.3.2.1. 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 eachlinkLink NLRI. If thereareis more than one auxiliary Router-ID of a given type, then multiple TLVs are used to encode them. 3.3.2.2. MPLS Protocol Mask TLV The MPLS Protocol Mask TLV carries a bit mask 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.>GenerationGeneration of the MPLS Protocol Mask TLV is only valid for and SHOULD only be used with originators that have local link insight,likeforexampleexample, the Protocol-IDs'Static''Static configuration' or 'Direct' as per Table 2. The'MPLSMPLS ProtocolMask'Mask TLV MUST NOT be included in NLRIs with the other Protocol-IDs listed in Table 2. 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 | +-+-+-+-+-+-+-+-+ Figure 19: MPLS Protocol Mask TLV The following bits are defined: +------------+------------------------------------------+-----------+ | Bit | Description | Reference | +------------+------------------------------------------+-----------+ | 'L' | Label Distribution Protocol (LDP) | [RFC5036] | | 'R' | Extension to RSVP for LSP Tunnels(RSVP-| [RFC3209] | | |TE)(RSVP-TE) | | | 'Reserved' | Reserved for future use | | +------------+------------------------------------------+-----------+ Table 10: MPLS Protocol Mask TLV Codes 3.3.2.3. 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 aMetricmetric width of less than 32bitsbits, then thehighhigh- order bits of this field MUST be padded with zero. 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 20: TE Default Metric TLVformatFormat 3.3.2.4. 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 have a length of 1 octet (the two most significant bits are ignored). OSPF link metrics have a length oftwo2 octets. IS-ISwide-metricswide metrics have a length ofthree3 octets. 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) // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 21: IGP Metric TLVformatFormat 3.3.2.5. Shared Risk Link Group TLV The Shared Risk Link Group (SRLG) TLV carries the Shared Risk Link Group information (see Section2.3, "Shared2.3 ("Shared Risk Link GroupInformation",Information") of [RFC4202]). 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 Figure 22. The length of this TLV is 4 * (number of SRLG values). 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 22: Shared Risk Link Group TLVformatFormat The SRLG TLV for OSPF-TE is defined in [RFC4203]. InIS-ISIS-IS, the SRLG information is carried in two different TLVs: the IPv4 (SRLG) TLV (Type 138) defined in[RFC5307],[RFC5307] and the IPv6 SRLG TLV (Type 139) defined in [RFC6119]. In Link-StateNLRINLRI, both IPv4 and IPv6 SRLG information are carried in a single TLV. 3.3.2.6. Opaque Link Attribute TLV The OpaquelinkLink Attribute TLV is an envelope that transparently carries optionallink attributeLink 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 noprotocol neutralprotocol-neutral representation in the BGPlink-stateLink-State NLRI. The primary use of the Opaque Link Attribute TLV is to bridge the document lagbetween e.g.between, e.g., a new IGPLink-statelink-state attribute being defined and the 'protocol- neutral' BGP-LS extensions being published. 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) // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 23: Opaquelink attribute formatLink Attribute TLV Format 3.3.2.7. Link Name TLV The Link Name TLV is optional. ThevalueValue field identifies the symbolic name of the router link. This symbolic name can be the FQDN for the link, it can be a subset of the FQDN, or it can be any string operators want to use for the link. The use of FQDN or a subset of it is strongly RECOMMENDED. The maximum length of the'LinkLink NameTLV'TLV is 255 octets. The Value field is encoded in 7-bit ASCII. If auser-interfaceuser interface for configuring or displaying this field permits Unicode characters, thatuser-interfaceuser interface is responsible for applying the ToASCII and/or ToUnicode algorithm as described in [RFC5890] 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. 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) // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 24: Link NameformatTLV Format 3.3.3. 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 MUST be reflected into the BGP-LS attribute with alinkprefix NLRI. This section describes the different attributes related to the IPv4/IPv6 prefixes. PrefixAttributesAttribute TLVs SHOULD be used when advertising NLRI types 3 and 4 only. The followingattributesPrefix Attribute TLVs are defined: +---------------+----------------------+----------+-----------------+ | TLV Code | Description | Length | Reference | | Point | | | | +---------------+----------------------+----------+-----------------+ | 1152 | IGP Flags | 1 | Section 3.3.3.1 | | 1153 | IGP Route Tag | 4*n |Section 3.3.3.2[RFC5130] | | 1154 | IGP ExtendedTagRoute | 8*n |Section 3.3.3.3[RFC5130] | | | Tag | | | | 1155 | Prefix Metric | 4 |Section 3.3.3.4[RFC5305] | | 1156 | OSPF Forwarding | 4 |Section 3.3.3.5[RFC2328] | | | Address | | | | 1157 | Opaque Prefix | variable | Section 3.3.3.6 | | | Attribute | | | +---------------+----------------------+----------+-----------------+ Table 11: Prefix Attribute TLVs 3.3.3.1. IGP Flags TLV The IGP Flags TLV contains IS-IS and OSPF flags and bits originally assigned to the prefix. The IGP Flags TLV is encoded as follows: 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| Resvd.| +-+-+-+-+-+-+-+-+ Figure 25: IGP Flag TLVformatFormat ThevalueValue field contains bits defined according to the table below: +----------+---------------------------+-----------+ | Bit | Description | Reference | +----------+---------------------------+-----------+ | 'D' | IS-IS Up/Down Bit | [RFC5305] | | 'N' | OSPF "no unicast" Bit | [RFC5340] | | 'L' | OSPF "local address" Bit | [RFC5340] | | 'P' | OSPF "propagate NSSA" Bit | [RFC5340] | | Reserved | Reserved for future use. | | +----------+---------------------------+-----------+ Table 12: IGP Flag Bits Definitions 3.3.3.2. IGP Route Tag TLV The IGP Route Tag TLV carries original IGPTAGsTags (IS-IS [RFC5130] or OSPF) of the prefix and is encoded as follows: 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) // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 26: IGP RouteTAGTag TLVformatFormat Length is a multiple of 4. ThevalueValue field contains one or more Route Tags as learned in the IGP topology. 3.3.3.3. Extended IGP Route Tag TLV The Extended IGP Route Tag TLV carries IS-IS Extended RouteTAGsTags of the prefix [RFC5130] and is encoded as follows: 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) // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 27: Extended IGP RouteTAGTag TLVformatFormat Length is a multiple of 8. The'ExtendedExtended RouteTag'Tag field contains one or more Extended Route Tags as learned in the IGP topology. 3.3.3.4. 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 Section 4 of [RFC5305] (and therefore represents the reachability cost to the prefix). If not present, it means that the prefix is advertised without any reachability. 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 28: Prefix Metric TLV Format Length is 4. 3.3.3.5. OSPF Forwarding Address TLV The OSPF Forwarding Address TLV [RFC2328]and[RFC5340] carries the OSPF forwarding address as known in the original OSPF advertisement. Forwarding address can be either IPv4 or IPv6. 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) // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 29: OSPF Forwarding Address TLV Format Length is 4 for an IPv4 forwardingaddress anaddress, and 16 for an IPv6 forwarding address. 3.3.3.6. Opaque Prefix Attribute TLV The Opaque Prefix Attribute TLV is an envelope that transparently carries optionalprefix attributePrefix 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 noprotocol neutralprotocol-neutral representation in the BGPlink-stateLink-State NLRI. The primary use of the Opaque Prefix Attribute TLV is to bridge the document lagbetween e.g.between, e.g., a new IGPLink-statelink-state attribute being defined and the'protocol- neutral'protocol- neutral BGP-LS extensions being published. The format of the TLV is as follows: 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) // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 30: Opaque Prefix Attribute TLV Format Type is as specified in Table11 and11. Length is variable. 3.4. BGPNext HopNext-Hop Information BGP link-state information for both IPv4 and IPv6 networks can be carried over either an IPv4 BGPsession,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.UsuallyUsually, the next hop will be set to the localend-pointendpoint address of the BGP session. Thenext hopnext-hop address MUST be encoded as described in [RFC4760]. ThelengthLength field of thenext hopnext-hop address will specify thenext hop address-family.next-hop address family. If thenext hopnext-hop length is 4, then the next hop is an IPv4 address; if thenext hopnext-hop length is 16, then it is a global IPv6addressaddress; and if thenext hopnext-hop length is 32, then there is one global IPv6 address followed by a link-local IPv6 address. The link-local IPv6 address should be used as described in [RFC2545]. For VPNSAFI,Subsequent Address Family Identifier (SAFI), as per custom, an8 byte route-distinguisher8-byte Route Distinguisher set to all zero is prepended to the next hop. The BGP Next Hop attribute is used by each BGP-LS speaker to validate the NLRI it receives. In case identical NLRIs are sourced by multipleoriginatorsoriginators, the BGPnext hopNext Hop attribute is used totie-breaktiebreak as per the standard BGP path decision process. This specification doesn't mandate any rule regarding there-writerewrite of the BGP Next Hop attribute. 3.5. 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([RFC5392], [RFC5316]).[RFC5392] [RFC5316]. In other cases, an implementation SHOULD provide a means to inject inter-AS links into BGP-LS. The exact mechanism used to provision the inter-AS links is outside the scope of this document 3.6. Router-ID Anchoring Example: ISO Pseudonode Encoding of a broadcast LAN in IS-IS provides a good example of how Router-IDs are encoded. Consider Figure 31. This represents a Broadcast LAN between a pair of routers. The "real"(=non pseudonode)(non-pseudonode) routers have both an IPv4 Router-ID and IS-IS Node-ID. The pseudonode does not have an IPv4 Router-ID. Node1 is the DIS for the LAN. Two unidirectional links (Node1,Pseudonode 1)Pseudonode1) and (Pseudonode1, Node2) are being generated. ThelinkLink NLRI of (Node1, Pseudonode1) is encoded asfollows: thefollows. The IGP Router-ID TLV of the localnode descriptorNode Descriptor is 6 octets longcontainingand contains the ISO-ID of Node1,1920.0000.2001; the1920.0000.2001. The IGP Router-ID TLV of the remotenode descriptorNode Descriptor is 7 octets longcontainingand contains theISO-IDISO- 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. ThelinkLink NLRI of(Pseudonode1.(Pseudonode1, Node2) is encoded asfollows: thefollows. The IGP Router-ID TLV of the localnode descriptorNode Descriptor is 7 octets longcontainingand contains the ISO-ID of Pseudonode1,1920.0000.2001.02; the1920.0000.2001.02. The IGP Router-ID TLV of the remotenode descriptorNode Descriptor is 6 octets longcontainingand 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. +-----------------+ +-----------------+ +-----------------+ | Node1 | | Pseudonode1 | | Node2 | |1920.0000.2001.00|--->|1920.0000.2001.02|--->|1920.0000.2002.00| | 192.0.2.1 | | | | 192.0.2.2 | +-----------------+ +-----------------+ +-----------------+ Figure 31: IS-IS Pseudonodes 3.7. Router-ID Anchoring Example: OSPF Pseudonode Encoding of a broadcast LAN in OSPF provides a good example of how Router-IDs and local Interface IPs are encoded. Consider Figure 32. This represents a Broadcast LAN between a pair of routers. The "real"(=non pseudonode)(non-pseudonode) routers have both an IPv4 Router-ID and an Area Identifier. The pseudonode does have an IPv4 Router-ID, an IPv4interfaceInterface Address (fordisambiguation)disambiguation), and an OSPF Area. Node1 is the DR for theLAN, henceLAN; hence, its local IP address 10.1.1.1 is usedbothas both the Router-ID and Interface IP for thePseudonodepseudonode keys. Two unidirectionallinkslinks, (Node1,Pseudonode 1)Pseudonode1) and (Pseudonode1,Node2)Node2), are being generated. ThelinkLink NLRI of (Node1, Pseudonode1) is encoded as follows: o Local Node Descriptor TLV #515: IGPRouter ID:Router-ID: 11.11.11.11 TLV #514: OSPF Area-ID: ID:0.0.0.0 o Remote Node Descriptor TLV #515: IGPRouter ID:Router-ID: 11.11.11.11:10.1.1.1 TLV #514: OSPF Area-ID: ID:0.0.0.0 ThelinkLink NLRI of (Pseudonode1, Node2) is encoded as follows: o Local Node Descriptor TLV #515: IGPRouter ID:Router-ID: 11.11.11.11:10.1.1.1 TLV #514: OSPF Area-ID: ID:0.0.0.0 o Remote Node Descriptor TLV #515: IGPRouter ID:Router-ID: 33.33.33.34 TLV #514: OSPF Area-ID: ID:0.0.0.0 +-----------------+ +-----------------+ +-----------------+ | Node1 | | Pseudonode1 | | Node2 | | 11.11.11.11 |--->| 11.11.11.11 |--->| 33.33.33.34 | | | | 10.1.1.1 | | | | Area 0 | | Area 0 | | Area 0 | +-----------------+ +-----------------+ +-----------------+ Figure 32: OSPF Pseudonodes 3.8. 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 a coordination requires identifying a given physical link in both IGPs. The IPv4 Router-ID provides that"glue""glue", which is present in thenode descriptorsNode Descriptors of the OSPFlinkLink NLRI and in the link attribute of the IS-ISlinkLink NLRI. Consider a point-to-point link between two routers, A and B, that initially were OSPFv2-only routers and then IS-IS is enabled on them. Node A has IPv4 Router-ID and ISO-ID; node B has IPv4 Router-ID, IPv6Router-IDRouter-ID, and ISO-ID. Each protocol generates onelinkLink NLRI for the link (A, B), both of which are carried by BGP-LS. The OSPFv2linkLink NLRI for the link is encoded with the IPv4 Router-ID of nodes A and B in the local and remotenode descriptors,Node Descriptors, respectively. The IS-ISlinkLink NLRI for the link is encoded with the ISO-ID of nodes A and B in the local and remotenode descriptors,Node Descriptors, respectively. In addition, the BGP-LS attribute of the IS-ISlinkLink NLRI contains the TLV type 1028 containing the IPv4 Router-ID of nodeA;A, TLV type 1030 containing the IPv4 Router-ID of nodeBB, 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 protocol. 4. Link to Path Aggregation Distribution of all links available in the global Internet is certainlypossible, howeverpossible; however, it not desirable from a scaling and privacy point of view.ThereforeTherefore, 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 anon-adjacentnon- 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)metric, etc.) are outside the scope of this document. The decision 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. 4.1. Example: No Link Aggregation Consider Figure 33. Both AS1 and AS2 operators want to protect their inter-AS{R1,R3},{R1, R3}, {R2, R4} links using RSVP-FRR LSPs. If R1 wants to compute its link-protection LSP toR3R3, it needs to "see" an alternate path to R3.ThereforeTherefore, the AS2 operator exposes its topology. AllBGP TE enabledBGP-TE-enabled routers in AS1 "see" the full topology of AS2 and therefore can compute a backup path. Note that thedecisioncomputing router decides if the direct link between {R3, R4} or the {R4, R5,R3)R3} path isused is made by the computing router.used. AS1 : AS2 : R1-------R3 | : | \ | : | R5 | : | / R2-------R4 : : Figure 33: Nolink aggregationLink Aggregation 4.2. 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 Figure 34. The only linkwhichthat gets advertised by AS2 is an "aggregate" link between R3 and R4. This is enough to tell AS1 that there is a backup path.HoweverHowever, the actual links being used are hidden from the topology. AS1 : AS2 : R1-------R3 | : | | : | | : | R2-------R4 : : Figure 34: ASBRlink aggregationLink Aggregation 4.3. Example: Multi-AS Path Aggregation Service providers in control of multiple ASes may even decide to not expose their internal inter-AS links. Consider Figure 35. AS3 is modeled as a single nodewhichthat connects to the border routers of the aggregated domain. AS1 : AS2 : AS3 : : R1-------R3----- | : : \ | : : vR0 | : : / R2-------R4----- : : : : Figure 35: Multi-ASaggregationAggregation 5. IANA ConsiderationsThis document isIANA has assigned address family number 16388 (BGP-LS) in thereference for Address"Address FamilyNumber 16388, 'BGP- LS'. This document requests code point 71 from theNumbers" registryof Subsequent Address Family Numbers named 'BGP-LS'. Thiswith this documentrequestsas acode point from the registry of Subsequent Address Family Numbers named 'BGP-LS-VPN'. Thereference. IANA has assigned SAFIassignment does not need to be out of the range 1-63values 71 (BGP-LS) andmay come out of72 (BGP-LS-VPN) in the"First Come First Served" range 128-240. This document requests a code point from"SAFI Values" sub-registry under theBGP Path Attributes"Subsequent Address Family Identifiers (SAFI) Parameters" registry.As per early allocation procedure this is Path Attribute 29. AllIANA has assigned value 29 (BGP-LS Attribute) in thefollowing Registries are BGP-LS specific and shall be accessible"BGP Path Attributes" sub-registry under thefollowing URL: "http://www.iana.org/assignments/ bgp-ls-parameters" Title"Border Gateway Protocol (BGP) Parameters" registry. IANA has created a new "Border Gateway Protocol - Link State(BGP- LS)(BGP-LS) Parameters"This document requests creation of a newregistryforat <http://www.iana.org/assignments/bgp-ls- parameters>. All of the following registries are BGP-LSNLRI- Types.specific and are accessible under this registry: o "BGP-LS NLRI-Types" registry Value 0 is reserved. The maximum value is 65535. The registrywill be initialized ashas been populated with the values shown in Table 1. Allocations within the registrywillrequire documentation of the proposed use of the allocated value(=Specification required)(Specification Required) and approval by the Designated Expert assigned by the IESG (see [RFC5226]).This document requests creation of a newo "BGP-LS Protocol-IDs" registryfor BGP-LS Protocol-IDs.Value 0 is reserved. The maximum value is 255. The registrywill be initialized ashas been populated with the values shown in Table 2. Allocations within the registrywillrequire documentation of the proposed use of the allocated value(=Specification required)(Specification Required) and approval by the Designated Expert assigned by the IESG (see [RFC5226]).This document requests creation of a newo "BGP-LS Well-Known Instance-IDs" registryfor BGP-LS Well- known Instance-IDs.The registrywill be initialized ashas been populated with the values shown in Table 3. Allocations within the registrywillrequire documentation of the proposed use of the allocated value(=Specification required)(Specification Required) and approval by the Designated Expert assigned by the IESG (see [RFC5226]).This document requests creation of a new registry for node anchor, link descriptoro "BGP-LS Node Descriptor, Link Descriptor, Prefix Descriptor, andlink attribute TLVs.Attribute TLVs" registry Values 0-255 are reserved. Values 256-65535 will be used for code points. The registrywill be initialized ashas been populated with the values shown in Table 13. Allocations within the registrywillrequire documentation of the proposed use of the allocated value(=Specification required)(Specification Required) and approval by the Designated Expert assigned by the IESG (see [RFC5226]). 5.1. Guidance for Designated Experts In all cases of review by the Designated Expert (DE) described here, the DE is expected to ascertain the existence of suitable documentation (a specification) as described in[RFC5226],[RFC5226] and to verify that thepermanentdocument is permanently andpublically ready availability of the document.publicly available. The DE is also expected to check the clarity of purpose and use of the requested code points.Lastly,Last, the DE must verify that any specification produced in the IETF that requests one of these code points has been made available for review by the IDR workinggroup,group and that any specification produced outside the IETF does not conflict with work that is active or already published within the IETF. 6. Manageability Considerations This section is structured as recommended in [RFC5706]. 6.1. Operational Considerations 6.1.1. 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 documentpurelycarriesapplication levelpurely application-level data that has no immediate corresponding forwarding state impact. As such, any churn in reachability information has a different impact than regular BGPupdatesupdates, which need to change the forwarding state for an entire router.FurthermoreFurthermore, it is anticipated that distribution of this NLRI will be handled by dedicatedroute-reflectorsroute reflectors providing a level of isolation andfault-containmentfault containment between different NLRI types. 6.1.2. Installation and Initial Setup Configuration parameters defined in Section 6.2.3 SHOULD be initialized to the following default values: o The Link-State NLRI capability is turned off for all neighbors. o The maximum rate at which Link-State NLRIs will be advertised/ withdrawn from neighbors is set to 200 updates per second. 6.1.3. 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 Section 6.2.3), so the extension can be gradually rolled out in the network. 6.1.4. Requirements on Other Protocols and Functional Components The protocol extension defined in this document does not put new requirements on other protocols or functional components. 6.1.5. Impact on Network Operation Frequency of Link-State NLRI updates could interfere with regular BGP prefix distribution. A network operator MAY use a dedicated Route- Reflector infrastructure to distribute Link-State NLRIs. 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. 6.1.6. Verifying Correct Operation Existing BGP procedures apply. In addition, an implementation SHOULD allow an operator to: o List neighbors with whom theSpeakerspeaker is exchanging Link-StateNLRIsNLRIs. 6.2. Management Considerations 6.2.1. 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. 6.2.2. Fault Management If an implementation of BGP-LS detects a malformed attribute, then it MUST use the 'Attribute Discard' action as per[RFC7606][RFC7606], Section 2. An implementation of BGP-LS MUST perform the following syntactic checks for determining if a message is malformed. o Does the sum of all TLVs found in theBGP LSBGP-LS attribute correspond to theBGP LSBGP-LS path attribute length? o Does the sum of all TLVs found in the BGP MP_REACH_NLRI attribute correspond to the BGP MP_REACH_NLRI length? o Does the sum of all TLVs found in the BGP MP_UNREACH_NLRI attribute correspond to the BGP MP_UNREACH_NLRI length? o Does the sum of all TLVs found in aNode-,Node, Link or Prefix Descriptor NLRI attribute correspond to theNode-, Link-Total NLRI Length field of the Node, Link, or PrefixDescriptors 'Total NLRI Length' field?Descriptors? o Does anyfixed lengthfixed-length TLV correspond to the TLV Length field in this document? 6.2.3. 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'sRIB.Routing Information Base (RIB). An implementation SHOULD allow the operator to create abstracted topologies that are advertised toneighbors; Createneighbors and create different abstractions for different neighbors. An implementation SHOULD allow the operator to configure a 64-bitinstance ID.Instance-ID. An implementation SHOULD allow the operator to configure a pair of ASN and BGP-LSidentifieridentifiers (Section 3.2.1.4) per flooding set in which the node participates. 6.2.4. Accounting Management Not Applicable. 6.2.5. Performance Management An implementation SHOULD provide the following statistics: o Total number of Link-State NLRI updates sent/received o Number of Link-State NLRI updates sent/received, per neighbor o Number of errored received Link-State NLRI updates, per neighbor o Total number of locally originated Link-State NLRIs These statistics should be recorded as absolute counts since system or session start time. An implementation MAY also enhance this information byalsorecording peak per-second counts in each case. 6.2.6. Security Management An operator SHOULD define an import policy to limit inbound updates as follows: o Drop all updates fromConsumer peersconsumer peers. An implementation MUST have the means to limit inbound updates. 7. TLV/Sub-TLV Code Points Summary This section contains the global table of allTLVs/Sub-TLVsTLVs/sub-TLVs defined in this document.+-----------+---------------------+---------------+-----------------++-----------+---------------------+--------------+------------------+ | TLV Code | Description | IS-IS TLV/ |Value definedReference | | Point | | Sub-TLV |in:(RFC/Section) |+-----------+---------------------+---------------+-----------------++-----------+---------------------+--------------+------------------+ | 256 | Local Node | --- | Section 3.2.1.2 | | | Descriptors | | | | 257 | Remote Node | --- | Section 3.2.1.3 | | | Descriptors | | | | 258 | Link Local/Remote | 22/4 | [RFC5307]/1.1 | | | Identifiers | | | | 259 | IPv4 interface | 22/6 | [RFC5305]/3.2 | | | address | | | | 260 | IPv4 neighbor | 22/8 | [RFC5305]/3.3 | | | address | | | | 261 | IPv6 interface | 22/12 | [RFC6119]/4.2 | | | address | | | | 262 | IPv6 neighbor | 22/13 | [RFC6119]/4.3 | | | address | | | | 263 | Multi-Topology ID | --- | Section 3.2.1.5 | | 264 | OSPF Route Type | --- | Section 3.2.3 | | 265 | IP Reachability | --- | Section 3.2.3 | | | Information | | | | 512 | Autonomous System | --- | Section 3.2.1.4 | | 513 | BGP-LS Identifier | --- | Section 3.2.1.4 | | 514 | OSPFArea IDArea-ID | --- | Section 3.2.1.4 | | 515 | IGP Router-ID | --- | Section 3.2.1.4 | | 1024 | Node Flag Bits | --- | Section 3.3.1.1 | | 1025 | Opaque Node | --- | Section 3.3.1.5 | | |PropertiesAttribute | | | | 1026 | Node Name | variable | Section 3.3.1.3 | | 1027 | IS-IS Area | variable | Section 3.3.1.2 | | | Identifier | | | | 1028 | IPv4 Router-ID of | 134/--- | [RFC5305]/4.3 | | | Local Node | | | | 1029 | IPv6 Router-ID of | 140/--- | [RFC6119]/4.1 | | | Local Node | | | | 1030 | IPv4 Router-ID of | 134/--- | [RFC5305]/4.3 | | | Remote Node | | | | 1031 | IPv6 Router-ID of | 140/--- | [RFC6119]/4.1 | | | Remote Node | | | | 1088 | Administrative | 22/3 | [RFC5305]/3.1 | | | group (color) | | | | 1089 | Maximum link | 22/9 |[RFC5305]/3.3[RFC5305]/3.4 | | | bandwidth | | | | 1090 | Max. reservable | 22/10 | [RFC5305]/3.5 | | | link bandwidth | | | | 1091 | Unreserved | 22/11 | [RFC5305]/3.6 | | | bandwidth | | | | 1092 | TE Default Metric | 22/18 | Section 3.3.2.3 | | 1093 | Link Protection | 22/20 | [RFC5307]/1.2 | | | Type | | | | 1094 | MPLS Protocol Mask | --- | Section 3.3.2.2 | | 1095 | IGP Metric | --- | Section 3.3.2.4 | | 1096 | Shared Risk Link | --- | Section 3.3.2.5 | | | Group | | | | 1097 | OpaquelinkLink | --- | Section 3.3.2.6 | | |attributeAttribute | | | | 1098 | Link Nameattribute| --- | Section 3.3.2.7 | | 1152 | IGP Flags | --- | Section 3.3.3.1 | | 1153 | IGP Route Tag | --- | [RFC5130] | | 1154 | IGP ExtendedTagRoute | --- | [RFC5130] | | | Tag | | | | 1155 | Prefix Metric | --- | [RFC5305] | | 1156 | OSPF Forwarding | --- | [RFC2328] | | | Address | | | | 1157 | Opaque Prefix | --- | Section 3.3.3.6 | | | Attribute | | |+-----------+---------------------+---------------+-----------------++-----------+---------------------+--------------+------------------+ Table 13: Summary Table of TLV/Sub-TLVcode pointsCode Points 8. Security Considerations Procedures and protocol extensions defined in this document do not affect the BGP security model. See the'Security Considerations'Security Considerations section of [RFC4271] for a discussion of BGP security. Also refer to [RFC4272] and [RFC6952] for analysis of security issues for BGP. In the context of the BGP peerings associated with this document, a BGPSpeakerspeaker MUST NOT accept updates from aConsumerconsumer peer. That is, a participating BGPSpeaker,speaker should be aware of the nature of its relationships forlink statelink-state relationships and should protect itself from peers sending updates that either represent erroneous information feedbackloops,loops or are false input. Such protection can be achieved by manual configuration ofConsumerconsumer peers at the BGPSpeaker.speaker. An operator SHOULD employ a mechanism to protect a BGPSpeakerspeaker against DDoS attacks fromConsumers.consumers. The principal attack a consumer may apply is to attempt to start multiple sessions either sequentially or simultaneously. Protection can be applied by imposing rate limits. Additionally, it may be considered that the export oflink statelink-state and TE information as described in this document constitutes a risk to confidentiality of mission-critical orcommercially-sensitivecommercially sensitive information about the network. BGP peerings are not automatic and requireconfiguration, thusconfiguration; thus, it is the responsibility of the network operator to ensure that only trustedConsumersconsumers are configured to receive such information. 9.Contributors We would like to thank Robert Varga for the significant contribution he gave to this document. 10. Acknowledgements We would like to thank Nischal Sheth, Alia Atlas, David Ward, Derek Yeung, Murtuza Lightwala, John Scudder, Kaliraj Vairavakkalai, Les Ginsberg, Liem Nguyen, Manish Bhardwaj, Matt Miller, Mike Shand, Peter Psenak, Rex Fernando, Richard Woundy, Steven Luong, Tamas Mondal, Waqas Alam, Vipin Kumar, Naiming Shen, Carlos Pignataro, Balaji Rajagopalan, Yakov Rekhter, Alvaro Retana, Barry Leiba, and Ben Campbell for their comments. 11.References11.1.9.1. Normative References[RFC1195] Callon, R., "Use of OSI IS-IS[ISO10589] International Organization forroutingStandardization, "Intermediate System to Intermediate System intra-domain routeing information exchange protocol for use inTCP/IP and dual environments", RFC 1195, DOI 10.17487/RFC1195, December 1990, <http://www.rfc-editor.org/info/rfc1195>.conjunction with the protocol for providing the connectionless-mode network service (ISO 8473)", ISO/ IEC 10589, November 2002. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, <http://www.rfc-editor.org/info/rfc2119>. [RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, DOI 10.17487/RFC2328, April 1998, <http://www.rfc-editor.org/info/rfc2328>. [RFC2545] Marques, P. and F. Dupont, "Use of BGP-4 Multiprotocol Extensions for IPv6 Inter-Domain Routing", RFC 2545, DOI 10.17487/RFC2545, March 1999, <http://www.rfc-editor.org/info/rfc2545>. [RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V., and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001, <http://www.rfc-editor.org/info/rfc3209>. [RFC4202] Kompella, K., Ed. and Y. Rekhter, Ed., "Routing Extensions in Support of Generalized Multi-Protocol Label Switching (GMPLS)", RFC 4202, DOI 10.17487/RFC4202, October 2005, <http://www.rfc-editor.org/info/rfc4202>. [RFC4203] Kompella, K., Ed. and Y. Rekhter, Ed., "OSPF Extensions in Support of Generalized Multi-Protocol Label Switching (GMPLS)", RFC 4203, DOI 10.17487/RFC4203, October 2005, <http://www.rfc-editor.org/info/rfc4203>. [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A Border Gateway Protocol 4 (BGP-4)", RFC 4271, DOI 10.17487/RFC4271, January 2006, <http://www.rfc-editor.org/info/rfc4271>. [RFC4760] Bates, T., Chandra, R., Katz, D., and Y. Rekhter, "Multiprotocol Extensions for BGP-4", RFC 4760, DOI 10.17487/RFC4760, January 2007, <http://www.rfc-editor.org/info/rfc4760>. [RFC4915] Psenak, P., Mirtorabi, S., Roy, A., Nguyen, L., and P. Pillay-Esnault, "Multi-Topology (MT) Routing in OSPF", RFC 4915, DOI 10.17487/RFC4915, June 2007, <http://www.rfc-editor.org/info/rfc4915>. [RFC5036] Andersson, L., Ed., Minei, I., Ed., and B. Thomas, Ed., "LDP Specification", RFC 5036, DOI 10.17487/RFC5036, October 2007, <http://www.rfc-editor.org/info/rfc5036>. [RFC5120] Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi Topology (MT) Routing in Intermediate System to Intermediate Systems (IS-ISs)", RFC 5120, DOI 10.17487/RFC5120, February 2008, <http://www.rfc-editor.org/info/rfc5120>. [RFC5130] Previdi, S., Shand, M., Ed., and C. Martin, "A Policy Control Mechanism in IS-IS Using Administrative Tags", RFC 5130, DOI 10.17487/RFC5130, February 2008, <http://www.rfc-editor.org/info/rfc5130>. [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 5226, DOI 10.17487/RFC5226, May 2008, <http://www.rfc-editor.org/info/rfc5226>. [RFC5301] McPherson, D. and N. Shen, "Dynamic Hostname Exchange Mechanism for IS-IS", RFC 5301, DOI 10.17487/RFC5301, October 2008, <http://www.rfc-editor.org/info/rfc5301>. [RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic Engineering", RFC 5305, DOI 10.17487/RFC5305, October 2008, <http://www.rfc-editor.org/info/rfc5305>. [RFC5307] Kompella, K., Ed. and Y. Rekhter, Ed., "IS-IS Extensions in Support of Generalized Multi-Protocol Label Switching (GMPLS)", RFC 5307, DOI 10.17487/RFC5307, October 2008, <http://www.rfc-editor.org/info/rfc5307>. [RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008, <http://www.rfc-editor.org/info/rfc5340>. [RFC5890] Klensin, J., "Internationalized Domain Names for Applications (IDNA): Definitions and Document Framework", RFC 5890, DOI 10.17487/RFC5890, August 2010, <http://www.rfc-editor.org/info/rfc5890>. [RFC6119] Harrison, J., Berger, J., and M. Bartlett, "IPv6 Traffic Engineering in IS-IS", RFC 6119, DOI 10.17487/RFC6119, February 2011, <http://www.rfc-editor.org/info/rfc6119>.[RFC6286] Chen, E. and J. Yuan, "Autonomous-System-Wide Unique BGP Identifier for BGP-4", RFC 6286, DOI 10.17487/RFC6286, June 2011, <http://www.rfc-editor.org/info/rfc6286>.[RFC6549] Lindem, A., Roy, A., and S. Mirtorabi, "OSPFv2 Multi- Instance Extensions", RFC 6549, DOI 10.17487/RFC6549, March 2012, <http://www.rfc-editor.org/info/rfc6549>. [RFC6822] Previdi, S., Ed., Ginsberg, L., Shand, M., Roy, A., and D. Ward, "IS-IS Multi-Instance", RFC 6822, DOI 10.17487/RFC6822, December 2012, <http://www.rfc-editor.org/info/rfc6822>. [RFC7606] Chen, E., Ed., Scudder, J., Ed., Mohapatra, P., and K. Patel, "Revised Error Handling for BGP UPDATE Messages", RFC 7606, DOI 10.17487/RFC7606, August 2015, <http://www.rfc-editor.org/info/rfc7606>.11.2.9.2. Informative References [RFC1918] Rekhter, Y., Moskowitz, B., Karrenberg, D., de Groot, G., and E. Lear, "Address Allocation for Private Internets", BCP 5, RFC 1918, DOI 10.17487/RFC1918, February 1996, <http://www.rfc-editor.org/info/rfc1918>. [RFC4272] Murphy, S., "BGP Security Vulnerabilities Analysis", RFC 4272, DOI 10.17487/RFC4272, January 2006, <http://www.rfc-editor.org/info/rfc4272>. [RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private Networks (VPNs)", RFC 4364, DOI 10.17487/RFC4364, February 2006, <http://www.rfc-editor.org/info/rfc4364>. [RFC4655] Farrel, A., Vasseur, J., and J. Ash, "A Path Computation Element (PCE)-Based Architecture", RFC 4655, DOI 10.17487/RFC4655, August 2006, <http://www.rfc-editor.org/info/rfc4655>.[RFC4970] Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R., and S. Shaffer, "Extensions to OSPF for Advertising Optional Router Capabilities", RFC 4970, DOI 10.17487/RFC4970, July 2007, <http://www.rfc-editor.org/info/rfc4970>.[RFC5073] Vasseur, J., Ed. and J. Le Roux, Ed., "IGP Routing Protocol Extensions for Discovery of Traffic Engineering Node Capabilities", RFC 5073, DOI 10.17487/RFC5073, December 2007, <http://www.rfc-editor.org/info/rfc5073>. [RFC5152] Vasseur, JP., Ed., Ayyangar, A., Ed., and R. Zhang, "A Per-Domain Path Computation Method for Establishing Inter- Domain Traffic Engineering (TE) Label Switched Paths (LSPs)", RFC 5152, DOI 10.17487/RFC5152, February 2008, <http://www.rfc-editor.org/info/rfc5152>. [RFC5316] Chen, M., Zhang, R., and X. Duan, "ISIS Extensions in Support of Inter-Autonomous System (AS) MPLS and GMPLS Traffic Engineering", RFC 5316, DOI 10.17487/RFC5316, December 2008, <http://www.rfc-editor.org/info/rfc5316>. [RFC5392] Chen, M., Zhang, R., and X. Duan, "OSPF Extensions in Support of Inter-Autonomous System (AS) MPLS and GMPLS Traffic Engineering", RFC 5392, DOI 10.17487/RFC5392, January 2009, <http://www.rfc-editor.org/info/rfc5392>. [RFC5693] Seedorf, J. and E. Burger, "Application-Layer Traffic Optimization (ALTO) Problem Statement", RFC 5693, DOI 10.17487/RFC5693, October 2009, <http://www.rfc-editor.org/info/rfc5693>. [RFC5706] Harrington, D., "Guidelines for Considering Operations and Management of New Protocols and Protocol Extensions", RFC 5706, DOI 10.17487/RFC5706, November 2009, <http://www.rfc-editor.org/info/rfc5706>. [RFC6952] Jethanandani, M., Patel, K., and L. Zheng, "Analysis of BGP, LDP, PCEP, and MSDP Issues According to the Keying and Authentication for Routing Protocols (KARP) Design Guide", RFC 6952, DOI 10.17487/RFC6952, May 2013, <http://www.rfc-editor.org/info/rfc6952>. [RFC7285] Alimi, R., Ed., Penno, R., Ed., Yang, Y., Ed., Kiesel, S., Previdi, S., Roome, W., Shalunov, S., and R. Woundy, "Application-Layer Traffic Optimization (ALTO) Protocol", RFC 7285, DOI 10.17487/RFC7285, September 2014, <http://www.rfc-editor.org/info/rfc7285>. [RFC7770] Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R., and S. Shaffer, "Extensions to OSPF for Advertising Optional Router Capabilities", RFC 7770, DOI 10.17487/RFC7770, February 2016, <http://www.rfc-editor.org/info/rfc7770>. Acknowledgements We would like to thank Nischal Sheth, Alia Atlas, David Ward, Derek Yeung, Murtuza Lightwala, John Scudder, Kaliraj Vairavakkalai, Les Ginsberg, Liem Nguyen, Manish Bhardwaj, Matt Miller, Mike Shand, Peter Psenak, Rex Fernando, Richard Woundy, Steven Luong, Tamas Mondal, Waqas Alam, Vipin Kumar, Naiming Shen, Carlos Pignataro, Balaji Rajagopalan, Yakov Rekhter, Alvaro Retana, Barry Leiba, and Ben Campbell for their comments. Contributors We would like to thank Robert Varga for the significant contribution he gave to this document. Authors' Addresses Hannes Gredler (editor)PrivateIndividual Contributor Email: hannes@gredler.at Jan Medved Cisco Systems, Inc.170,170 West Tasman Drive San Jose, CA 95134USUnited States Email: jmedved@cisco.com Stefano Previdi Cisco Systems, Inc. Via Del Serafico, 200 Rome 00142 Italy Email: sprevidi@cisco.com Adrian Farrel Juniper Networks, Inc. Email: adrian@olddog.co.uk Saikat Ray Email: raysaikat@gmail.com