Internet DRAFT - draft-ietf-idr-rfc7752bis
draft-ietf-idr-rfc7752bis
Inter-Domain Routing K. Talaulikar, Ed.
Internet-Draft Cisco Systems
Obsoletes: 7752, 9029 (if approved) 25 August 2023
Intended status: Standards Track
Expires: 26 February 2024
Distribution of Link-State and Traffic Engineering Information Using BGP
draft-ietf-idr-rfc7752bis-17
Abstract
In many environments, a component external to a network is called
upon to perform computations based on the network topology and the
current state of the connections within the network, including
Traffic Engineering (TE) information. This is information typically
distributed by IGP routing protocols within the network.
This document describes a mechanism by which link-state and TE
information can be collected from networks and shared with external
components using the BGP routing protocol. This is achieved using a
BGP Network Layer Reachability Information (NLRI) encoding format.
The mechanism applies to physical and virtual (e.g., tunnel) IGP
links. The mechanism described is subject to policy control.
Applications of this technique include Application-Layer Traffic
Optimization (ALTO) servers and Path Computation Elements (PCEs).
This document obsoletes RFC7752 by completely replacing that
document. It makes some small changes and clarifications to the
previous specification. This document also obsoletes RFC9029 by
incorporating the updates that it made to RFC7752.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
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This Internet-Draft will expire on 26 February 2024.
Copyright Notice
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document authors. All rights reserved.
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Please review these documents carefully, as they describe your rights
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provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 6
2. Motivation and Applicability . . . . . . . . . . . . . . . . 6
2.1. MPLS-TE with PCE . . . . . . . . . . . . . . . . . . . . 6
2.2. ALTO Server Network API . . . . . . . . . . . . . . . . . 7
3. BGP Speaker Roles for BGP-LS . . . . . . . . . . . . . . . . 8
4. Advertising IGP Information into BGP-LS . . . . . . . . . . . 10
5. Carrying Link-State Information in BGP . . . . . . . . . . . 10
5.1. TLV Format . . . . . . . . . . . . . . . . . . . . . . . 11
5.2. The Link-State NLRI . . . . . . . . . . . . . . . . . . . 12
5.2.1. Node Descriptors . . . . . . . . . . . . . . . . . . 16
5.2.2. Link Descriptors . . . . . . . . . . . . . . . . . . 20
5.2.3. Prefix Descriptors . . . . . . . . . . . . . . . . . 24
5.3. The BGP-LS Attribute . . . . . . . . . . . . . . . . . . 26
5.3.1. Node Attribute TLVs . . . . . . . . . . . . . . . . . 27
5.3.2. Link Attribute TLVs . . . . . . . . . . . . . . . . . 31
5.3.3. Prefix Attribute TLVs . . . . . . . . . . . . . . . . 36
5.4. Private Use . . . . . . . . . . . . . . . . . . . . . . . 41
5.5. BGP Next-Hop Information . . . . . . . . . . . . . . . . 41
5.6. Inter-AS Links . . . . . . . . . . . . . . . . . . . . . 42
5.7. OSPF Virtual Links and Sham Links . . . . . . . . . . . . 42
5.8. OSPFv2 Type 4 Summary LSA & OSPFv3 Inter-Area Router
LSA . . . . . . . . . . . . . . . . . . . . . . . . . . 42
5.9. Handling of Unreachable IGP Nodes . . . . . . . . . . . . 43
5.10. Router-ID Anchoring Example: ISO Pseudonode . . . . . . . 44
5.11. Router-ID Anchoring Example: OSPF Pseudonode . . . . . . 45
5.12. Router-ID Anchoring Example: OSPFv2 to IS-IS Migration . 46
6. Link to Path Aggregation . . . . . . . . . . . . . . . . . . 47
6.1. Example: No Link Aggregation . . . . . . . . . . . . . . 47
6.2. Example: ASBR to ASBR Path Aggregation . . . . . . . . . 48
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6.3. Example: Multi-AS Path Aggregation . . . . . . . . . . . 48
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 49
7.1. BGP-LS Registries . . . . . . . . . . . . . . . . . . . . 49
7.1.1. BGP-LS NLRI Types Registry . . . . . . . . . . . . . 49
7.1.2. BGP-LS Protocol-IDs Registry . . . . . . . . . . . . 50
7.1.3. BGP-LS Well-Known Instance-IDs Registry . . . . . . . 51
7.1.4. BGP-LS Node Flags Registry . . . . . . . . . . . . . 51
7.1.5. BGP-LS MPLS Protocol Mask Registry . . . . . . . . . 52
7.1.6. BGP-LS IGP Prefix Flags Registry . . . . . . . . . . 53
7.1.7. BGP-LS TLVs Registry . . . . . . . . . . . . . . . . 53
7.2. Guidance for Designated Experts . . . . . . . . . . . . . 54
8. Manageability Considerations . . . . . . . . . . . . . . . . 55
8.1. Operational Considerations . . . . . . . . . . . . . . . 55
8.1.1. Operations . . . . . . . . . . . . . . . . . . . . . 55
8.1.2. Installation and Initial Setup . . . . . . . . . . . 56
8.1.3. Migration Path . . . . . . . . . . . . . . . . . . . 56
8.1.4. Requirements for Other Protocols and Functional
Components . . . . . . . . . . . . . . . . . . . . . 56
8.1.5. Impact on Network Operation . . . . . . . . . . . . . 56
8.1.6. Verifying Correct Operation . . . . . . . . . . . . . 57
8.2. Management Considerations . . . . . . . . . . . . . . . . 57
8.2.1. Management Information . . . . . . . . . . . . . . . 57
8.2.2. Fault Management . . . . . . . . . . . . . . . . . . 57
8.2.3. Configuration Management . . . . . . . . . . . . . . 59
8.2.4. Accounting Management . . . . . . . . . . . . . . . . 60
8.2.5. Performance Management . . . . . . . . . . . . . . . 60
8.2.6. Security Management . . . . . . . . . . . . . . . . . 60
9. TLV/Sub-TLV Code Points Summary . . . . . . . . . . . . . . . 61
10. Security Considerations . . . . . . . . . . . . . . . . . . . 63
11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 64
12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 64
13. References . . . . . . . . . . . . . . . . . . . . . . . . . 65
13.1. Normative References . . . . . . . . . . . . . . . . . . 65
13.2. Informative References . . . . . . . . . . . . . . . . . 68
Appendix A. Changes from RFC 7752 . . . . . . . . . . . . . . . 70
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 72
1. Introduction
The contents of a Link-State Database (LSDB) or of an IGP's Traffic
Engineering Database (TED) describe only the links and nodes within
an IGP area. Some applications, such as end-to-end Traffic
Engineering (TE), would benefit from visibility outside one area or
Autonomous System (AS) to make better decisions.
The IETF has defined the Path Computation Element (PCE) [RFC4655] as
a mechanism for achieving the computation of end-to-end TE paths that
cross the visibility of more than one TED or that requires CPU-
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intensive or coordinated computations. The IETF has also defined the
ALTO server [RFC5693] as an entity that generates an abstracted
network topology and provides it to network-aware applications.
Both a PCE and an ALTO server need to gather information about the
topologies and capabilities of the network to be able to fulfill
their function.
This document describes a mechanism by which link-state and TE
information can be collected from networks and shared with external
components using the BGP routing protocol [RFC4271]. This is
achieved using a BGP Network Layer Reachability Information (NLRI)
encoding format. The mechanism applies to physical and virtual
(e.g., tunnel) links. The mechanism described is subject to policy
control.
A router maintains one or more databases for storing link-state
information about nodes and links in any given area. Link attributes
stored in these databases include: local/remote IP addresses, local/
remote interface identifiers, link IGP metric, link TE metric, link
bandwidth, reservable bandwidth, per Class-of-Service (CoS) class
reservation state, preemption, and Shared Risk Link Groups (SRLGs).
The router's BGP Link-State (BGP-LS) process can retrieve topology
from these LSDBs and distribute it to a consumer, either directly or
via a peer BGP speaker (typically a dedicated Route Reflector), using
the encoding specified in this document.
An illustration of the collection of link-state and TE information
and its distribution to consumers is shown in Figure 1 below.
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+-----------+
| Consumer |
+-----------+
^
|
+-----------+ +-----------+
| BGP | | BGP |
| Speaker |<----------->| Speaker | +-----------+
| RR1 | | RRm | | Consumer |
+-----------+ +-----------+ +-----------+
^ ^ ^ ^
| | | |
+-----+ +---------+ +---------+ |
| | | |
+-----------+ +-----------+ +-----------+
| BGP | | BGP | | BGP |
| Speaker | | Speaker | . . . | Speaker |
| R1 | | R2 | | Rn |
+-----------+ +-----------+ +-----------+
^ ^ ^
| | |
IGP IGP IGP
Figure 1: Collection of Link-State and TE Information
A BGP speaker may apply a configurable policy to the information that
it distributes. Thus, it may distribute the real physical topology
from the LSDB or the TED. Alternatively, it may create an abstracted
topology, where virtual, aggregated nodes are connected by virtual
paths. Aggregated nodes can be created, for example, out of multiple
routers in a Point of Presence (POP). Abstracted topology can also
be a mix of physical and virtual nodes and physical and virtual
links. Furthermore, the BGP speaker can apply policy to determine
when information is updated to the consumer so that there is a
reduction in information flow from the network to the consumers.
Mechanisms through which topologies can be aggregated or virtualized
are outside the scope of this document.
This document focuses on the specifications related to the
origination of IGP-derived information and their propagation via BGP-
LS. It also describes the advertisement into BGP-LS of information,
either configured or derived, that is local to a node. In general,
the procedures in this document form part of the base BGP-LS protocol
specification and apply to information from other sources that are
introduced into BGP-LS.
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This document obsoletes [RFC7752] by completely replacing that
document. It makes some small changes and clarifications to the
previous specification as documented in Appendix A.
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
2. 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], a PCE can be used to compute MPLS-TE paths
within a "domain" (such as an IGP area) or across multiple domains
(such as a multi-area AS or multiple ASes).
* Within a single area, the PCE offers enhanced computational power
that may not be available on individual routers, sophisticated
policy control and algorithms, and coordination of computation
across the whole area.
* If a router wants to compute an MPLS-TE path across IGP areas,
then its own TED lacks visibility of the complete topology. That
means that the router cannot determine the end-to-end path and
cannot even select the right exit router (Area Border Router
(ABR)) for an optimal path. This is an issue for large-scale
networks that need to segment their core networks into distinct
areas but still want to take advantage of MPLS-TE.
Previous solutions used per-domain path computation [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]
and selects the exit ABR and other ABRs or AS Border Routers (ASBRs)
using the IGP-computed shortest path topology for the remainder of
the path. This may lead to suboptimal paths, makes alternate/back-up
path computation hard, and might result in no TE path being found
when one does exist.
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The PCE presents a computation server that may have visibility into
more than one IGP area or AS, or may cooperate with other PCEs to
perform distributed path computation. The PCE needs access to the
TED for the area(s) it serves, but [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 of churn or when the PCE is responsible for multiple
areas.
The following figure shows how a PCE can get its TED information
using the mechanism described in this document.
+----------+ +---------+
| ----- | | BGP |
| | TED |<-+-------------------------->| Speaker |
| ----- | TED synchronization | |
| | | mechanism +---------+
| | |
| v |
| ----- |
| | PCE | |
| ----- |
+----------+
^
| Request/
| Response
v
Service +----------+ Signaling +----------+
Request | Head-End | Protocol | Adjacent |
-------->| Node |<------------>| Node |
+----------+ +----------+
Figure 2: External PCE Node Using a TED Synchronization 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 ALTO server [RFC5693] is an entity that generates an abstracted
network topology and provides it to network-aware applications over a
web-service-based API. Example applications are peer-to-peer (P2P)
clients or trackers, or Content Distribution Networks (CDNs). The
abstracted network topology comes in the form of two maps: a Network
Map that specifies the allocation of prefixes to Partition
Identifiers (PIDs), and a Cost Map that specifies the cost between
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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 ALTO server can
retrieve all the necessary prefixes and network topology data from
the underlying network. Note that an ALTO server can use other
mechanisms to get network data, for example, peering with multiple
IGP and BGP speakers.
The following figure shows how an ALTO server can get network
topology information from the underlying network using the mechanism
described in this document.
+--------+
| Client |<--+
+--------+ |
| ALTO +--------+ Topology +---------+
+--------+ | Protocol | ALTO | Sync Mechanism | BGP |
| Client |<--+------------| Server |<----------------| Speaker |
+--------+ | | | | |
| +--------+ +---------+
+--------+ |
| Client |<--+
+--------+
Figure 3: ALTO Server Using Network Topology Information
3. BGP Speaker Roles for BGP-LS
In the illustration shown in Figure 1, the BGP Speakers can be seen
playing different roles in the distribution of information using BGP-
LS. This section introduces terms that explain the different roles
of the BGP Speakers which are then used through the rest of this
document.
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* BGP-LS Producer: The term BGP-LS Producer refers to a BGP Speaker
that is originating link-state information into BGP. The BGP
Speakers R1, R2, ... Rn, originate link-state information from
their underlying link-state IGP protocols into BGP-LS. If R1 and
R2 are in the same IGP flooding domain, then they would ordinarily
originate the same link-state information into BGP-LS. R1 may
also originate information from sources other than IGP, e.g. its
local node information.
* BGP-LS Consumer: The term BGP-LS Consumer refers to a consumer
application/process and not a BGP Speaker. The BGP Speakers RR1
and Rn are handing off the BGP-LS information that they have
collected to a consumer application. The BGP protocol
implementation and the consumer application may be on the same or
different nodes. This document only covers the BGP
implementation. The consumer application and the design of the
interface between BGP and the consumer application may be
implementation specific and are outside the scope of this
document. The communication of information MUST be unidirectional
(i.e., from a BGP Speaker to the BGP-LS Consumer application) and
a BGP-LS Consumer MUST NOT be able to send information to a BGP
Speaker for origination into BGP-LS.
* BGP-LS Propagator: The term BGP-LS Propagator refers to a BGP
Speaker that is performing BGP protocol processing on the link-
state information. The BGP Speaker RRm propagates the BGP-LS
information between the BGP Speaker Rn and the BGP Speaker RR1.
The BGP implementation on RRm is propagating BGP-LS information.
It performs handling of BGP-LS UPDATE messages and performs the
BGP Decision Process as part of deciding what information is to be
propagated. Similarly, the BGP Speaker RR1 is receiving BGP-LS
information from R1, R2, and RRm and propagating the information
to the BGP-LS Consumer after performing BGP Decision Process.
The above roles are not mutually exclusive. The same BGP Speaker may
be the BGP-LS Producer for some link-state information and BGP-LS
Propagator for some other link-state information while also providing
this information to a BGP-LS Consumer.
The rest of this document refers to the role when describing
procedures that are specific to that role. When the role is not
specified, then the said procedure applies to all BGP Speakers.
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4. Advertising IGP Information into BGP-LS
The origination and propagation of IGP link-state information via BGP
needs to provide a consistent and accurate view of the topology of
the IGP domain. BGP-LS provides an abstraction of the IGP specifics
and BGP-LS Consumers may be varied types of applications.
The link-state information advertised in BGP-LS from the IGPs is
derived from the IGP LSDB built using the OSPF Link State
Advertisements (LSAs) or the IS-IS Link State Packets (LSPs).
However, it does not serve as a verbatim reflection of the
originating router's LSDB. It does not include the LSA/LSP sequence
number information since a single link-state object may be put
together with information that is coming from multiple LSAs/LSPs.
Also, not all of the information carried in LSAs/LSPs may be required
or suitable for advertisement via BGP-LS (e.g., ASBR reachability in
OSPF, OSPF virtual links, link-local scoped information, etc.). The
LSAs/LSPs that are purged or max-aged are not included in the BGP-LS
advertisement even though they may be present in the LSDB (e.g., for
the IGP flooding purposes). The information from the LSAs/LSPs that
is invalid or malformed or that which needs to be ignored per the
respective IGP protocol specifications are also not included in the
BGP-LS advertisement.
The details of the interface between IGPs and BGP for the
advertisement of link-state information are outside the scope of this
document. In some cases, the information derived from IGP processing
(e.g., combination of link-state object from across multiple LSAs/
LSPs, leveraging reachability and two-way connectivity checks, etc.)
is required for advertisement of link-state information into BGP-LS.
5. Carrying Link-State Information in BGP
The link-state information is carried in BGP UPDATE messages as: (1)
BGP NLRI information carried within MP_REACH_NLRI and MP_UNREACH_NLRI
attributes that describes link, node, or prefix object, and (2) a BGP
path attribute (BGP-LS Attribute) that carries properties of the
link, node, or prefix objects such as the link and prefix metric or
auxiliary Router-IDs of nodes, etc.
It is desirable to keep the dependencies on the protocol source of
this attribute to a minimum and represent any content in an IGP-
neutral way, such that applications that want to learn about a link-
state topology do not need to know about any OSPF or IS-IS protocol
specifics.
This section mainly describes the procedures for a BGP-LS Producer to
originate link-state information into BGP-LS.
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5.1. TLV Format
Information in the Link-State NLRIs and the BGP-LS Attribute is
encoded in Type/Length/Value triplets. The TLV format is shown in
Figure 4 and applies to both the NLRI and the BGP-LS Attribute
encodings.
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: TLV Format
The Length field defines the length of the value portion in octets
(thus, a TLV with no value portion would have a length of zero). The
TLV is not padded to 4-octet alignment. Unknown and unsupported
types MUST be preserved and propagated within both the NLRI and the
BGP-LS Attribute. The presence of unknown or unexpected TLVs MUST
NOT result in the NLRI or the BGP-LS Attribute being considered
malformed. An example of an unexpected TLV is when a TLV is received
along with an update for a link state object other than the one that
the TLV is specified as associated with.
To compare NLRIs with unknown TLVs, all TLVs within the NLRI MUST be
ordered in ascending order by TLV Type. If there are multiple TLVs
of the same type within a single NLRI, then the TLVs sharing the same
type MUST be first in ascending order based on the length field
followed by ascending order based on the value field. Comparison of
the value fields is performed by treating the entire field as opaque
binary data and ordered lexicographically (i.e., treating each byte
of binary data as a symbol to compare, with the symbols ordered by
their numerical value). NLRIs having TLVs which do not follow the
above ordering rules MUST be considered as malformed by a BGP-LS
Propagator. This insistence on canonical ordering ensures that
multiple variant copies of the same NLRI from multiple BGP-LS
Producers and the ambiguity arising therefrom is prevented.
For both the NLRI and BGP-LS Attribute parts, all TLVs are considered
as optional except where explicitly specified as mandatory or
required in specific conditions.
The TLVs within the BGP-LS Attribute SHOULD be ordered in ascending
order by TLV type. BGP-LS Attribute with unordered TLVs MUST NOT be
considered malformed.
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The origination of the same link-state information by multiple BGP-LS
Producers may result in differences and inconsistencies due to the
inclusion or exclusion of optional TLVs. Different optional TLVs in
the NLRI results in multiple NLRIs being generated for the same link-
state object. Different optional TLVs in the BGP-LS Attribute may
result in the propagation of partial information. To address these
inconsistencies, the BGP-LS Consumer will need to recognize and merge
the duplicate information, or to deal with missing information. The
deployment of BGP-LS Producers that consistently originate the same
set of optional TLVs is recommended to mitigate such situations.
5.2. The Link-State NLRI
The MP_REACH_NLRI and MP_UNREACH_NLRI attributes are BGP's containers
for carrying opaque information. This specification defines three
Link-State NLRI types that describe either a node, a link, or a
prefix.
All non-VPN link, node, and prefix information SHALL be encoded using
AFI 16388 / SAFI 71. VPN link, node, and prefix information SHALL be
encoded using AFI 16388 / SAFI 72.
For two BGP speakers to exchange Link-State NLRI, they MUST use BGP
Capabilities Advertisement to ensure that they are both capable of
properly processing such NLRI. This is done as specified in
[RFC4760], by using capability code 1 (multiprotocol BGP), with AFI
16388 / SAFI 71 for BGP-LS, and AFI 16388 / SAFI 72 for BGP-LS-VPN.
New Link-State NLRI Types may be introduced in the future. Since
supported NLRI type values within the address family are not
expressed in the Multiprotocol BGP (MP-BGP) capability [RFC4760], it
is possible that a BGP speaker has advertised support for BGP-LS but
does not support a particular Link-State NLRI type. To allow the
introduction of new Link-State NLRI types seamlessly in the future,
without the need for upgrading all BGP speakers in the propagation
path (e.g., a route reflector), this document deviates from the
default handling behavior specified by section 5.4 (paragraph 2) of
[RFC7606] for Link-State address-family. An implementation MUST
handle unknown Link-State NLRI types as opaque objects and MUST
preserve and propagate them.
The format of the Link-State NLRI is shown in the following figures.
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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 (8 octets) +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// Link-State NLRI (variable) //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: Link-State VPN AFI 16388 / SAFI 72 NLRI Format
The Total NLRI Length field contains the cumulative length, in
octets, of the rest of the NLRI, not including the NLRI Type field or
itself. For VPN applications, it also includes the length of the
Route Distinguisher.
+======+===========================+
| 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].
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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 |
+ (8 octets) +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Local Node Descriptors TLV (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7: The Node NLRI Format
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 |
+ (8 octets) +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Local Node Descriptors TLV (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Remote Node Descriptors TLV (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Link Descriptors TLVs (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 8: The Link NLRI Format
The IPv4 and IPv6 Prefix NLRIs (NLRI Type = 3 and Type = 4) use the
same format, as shown in the following figure.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+
| Protocol-ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identifier |
+ (8 octets) +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Local Node Descriptors TLV (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Prefix Descriptors TLVs (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 9: The IPv4/IPv6 Topology Prefix NLRI Format
The 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 all information
derived from other protocols, the corresponding Protocol-ID MUST be
used. If BGP-LS has direct access to interface information and wants
to advertise a local link, then the Protocol-ID 'Direct' SHOULD be
used. For modeling virtual links, such as described in Section 6,
the Protocol-ID 'Static configuration' SHOULD be used.
A router may run multiple protocol instances of OSPF or IS-IS whereby
it becomes a border router between multiple IGP domains. Both OSPF
and IS-IS may also run multiple routing protocol instances over the
same link. See [RFC8202] and [RFC6549]. These instances define
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independent IGP routing domains. The Identifier field carries an
8-octet BGP-LS Instance Identifier (Instance-ID) number that is used
to identify the IGP routing domain where the NLRI belongs. The NLRIs
representing link-state objects (nodes, links, or prefixes) from the
same IGP routing instance should have the same BGP-LS Instance-ID.
NLRIs with different BGP-LS Instance-IDs are considered to be from
different IGP routing instances.
To support multiple IGP instances, an implementation needs to support
the configuration of unique BGP-LS Instance-IDs at the routing
protocol instance level. The BGP-LS Instance-ID 0 is RECOMMENDED to
be used when there is only a single protocol instance in the network
where BGP-LS is operational. The network operator MUST assign the
same BGP-LS Instance-IDs on all BGP-LS Producers within a given IGP
domain. Unique BGP-LS Instance-ID MUST be assigned to routing
protocol instances operating in different IGP domains. This can
allow the BGP-LS Consumer to build an accurate segregated multi-
domain topology based on the BGP-LS Instance-ID.
When the above-described semantics and recommendations are not
followed, a BGP-LS Consumer may see more than one link-state objects
for the same node, link, or prefix (each with a different BGP-LS
Instance-ID) when there are multiple BGP-LS Producers deployed. This
may also result in the BGP-LS Consumers getting an inaccurate
network-wide topology.
Each Node Descriptor, Link Descriptor, and Prefix Descriptor consists
of one or more TLVs, as described in the following sections. These
Descriptor TLVs are applicable for the Node, Link, and Prefix NLRI
Types for the protocols that are listed in Table 2. Documents
extending BGP-LS specifications with new NLRI Types and/or protocols
MUST specify the NLRI Descriptors for them.
When adding, removing, or modifying a TLV/sub-TLV from a Link-State
NLRI, the BGP-LS Producer MUST withdraw the old NLRI by including it
in the MP_UNREACH_NLRI. Not doing so can result in duplicate and in-
consistent link-state objects hanging around in the BGP-LS table.
5.2.1. Node Descriptors
Each link is anchored by a pair of Router-IDs that are used by the
underlying IGP, namely, a 48-bit ISO System-ID for IS-IS and a 32-bit
Router-ID for OSPFv2 and OSPFv3. An IGP may use one or more
additional auxiliary Router-IDs, mainly for Traffic Engineering
purposes. For example, IS-IS may have one or more IPv4 and IPv6 TE
Router-IDs [RFC5305] [RFC6119]. When configured, these auxiliary TE
Router-IDs (TLV 1028/1029) MUST be included in the node attribute
described in Section 5.3.1 and MAY be included in the link attribute
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described in Section 5.3.2. The advertisement of the TE Router-IDs
can help a BGP-LS Consumer to correlate multiple link-state objects
(e.g. in different IGP instances or areas/levels) to the same node in
the network.
It is desirable that the Router-ID assignments inside the Node
Descriptors are globally unique. However, there may be Router-ID
spaces (e.g., ISO) where no global registry exists, or worse, Router-
IDs have been allocated following the private-IP allocation described
in [RFC1918]. BGP-LS uses the Autonomous System (AS) Number to
disambiguate the Router-IDs, as described in Section 5.2.1.1.
5.2.1.1. Globally Unique Node/Link/Prefix Identifiers
One problem that needs to be addressed is the ability to identify an
IGP node globally (by "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,
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 and prefixes) within which each node has a unique IGP
representation by using the combination of OSPF Area-ID, Router-ID,
Protocol-ID, Multi-Topology ID, and BGP-LS Instance-ID. The problem
is that BGP may receive node/link/prefix information from multiple
independent "IGP domains", and we need to distinguish between them.
Moreover, we can't assume there is always one and only one IGP domain
per AS. During IGP transitions, it may happen that two redundant
IGPs are in place.
Furthermore, in deployments where BGP-LS is used to advertise
topology from multiple-ASes, the AS Number is used to distinguish
topology information reported from different ASes.
The BGP-LS Instance-ID carried in the Identifier field as described
earlier along with a set of sub-TLVs described in Section 5.2.1.4,
allows specification of a flexible key for any given node/link
information such that the global uniqueness of the NLRI is ensured.
Since the BGP-LS Instance-ID is operator assigned, its allocation
scheme can ensure that each IGP domain is uniquely identified even
across a multi-AS network.
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5.2.1.2. 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 Type is 256. The
length of this TLV is variable. The value contains one or more Node
Descriptor Sub-TLVs defined in Section 5.2.1.4.
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 TLV Format
5.2.1.3. 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
for Link NLRIs. The type is 257. The length of this TLV is
variable. The value contains one or more Node Descriptor Sub-TLVs
defined in Section 5.2.1.4.
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 TLV Format
5.2.1.4. Node Descriptor Sub-TLVs
The Node Descriptor Sub-TLV type code points and lengths are listed
in the following table:
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+====================+================================+==========+
| Sub-TLV Code Point | Description | Length |
+====================+================================+==========+
| 512 | Autonomous System | 4 |
+--------------------+--------------------------------+----------+
| 513 | BGP-LS Identifier (deprecated) | 4 |
+--------------------+--------------------------------+----------+
| 514 | OSPF Area-ID | 4 |
+--------------------+--------------------------------+----------+
| 515 | IGP Router-ID | Variable |
+--------------------+--------------------------------+----------+
Table 3: Node Descriptor Sub-TLVs
The sub-TLV values in Node Descriptor TLVs are defined as follows:
Autonomous System: Opaque value (32-bit AS Number). This is an
optional TLV. The value SHOULD be set to the AS Number associated
with the BGP process originating the link-state information. An
implementation MAY provide a configuration option on the BGP-LS
Producer to use a different value; e.g., to avoid collisions when
using private AS numbers.
BGP-LS Identifier: Opaque value (32-bit ID). This is an optional
TLV which has been deprecated by this document (refer to
Appendix A for more details). It MAY be advertised for
compatibility with [RFC7752] implementations. See the final
paragraph of this section for further considerations and
recommended default value.
OSPF Area-ID: Used to identify the 32-bit area to which the
information advertised in the NLRI belongs. This is a mandatory
TLV when originating information from OSPF that is derived from
area-scope LSAs. The OSPF Area Identifier allows different NLRIs
of the same router to be differentiated on a per-area basis. It
is not used for NLRIs when carrying information that is derived
from AS-scope LSAs as that information is not associated with a
specific area.
IGP Router-ID: Opaque value. This is a mandatory TLV when
originating information from IS-IS, OSPF, direct or static. For
an IS-IS non-pseudonode, this contains a 6-octet ISO Node-ID (ISO
system-ID). For an IS-IS pseudonode corresponding to a LAN, this
contains the 6-octet ISO Node-ID of the Designated Intermediate
System (DIS) followed by a 1-octet, nonzero PSN identifier (7
octets in total). For an OSPFv2 or OSPFv3 non-pseudonode, this
contains the 4-octet Router-ID. For an OSPFv2 pseudonode
representing a LAN, this contains the 4-octet Router-ID of the
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Designated Router (DR) followed by the 4-octet IPv4 address of the
DR's interface to the LAN (8 octets in total). Similarly, for an
OSPFv3 pseudonode, this contains the 4-octet Router-ID of the DR
followed by the 4-octet interface identifier of the DR's interface
to the LAN (8 octets in total). The TLV size in combination with
the protocol identifier enables the decoder to determine the type
of the node. For Direct or Static configuration, the value SHOULD
be taken from an IPv4 or IPv6 address (e.g. loopback interface)
configured on the node. When the node is running an IGP protocol,
an implementation MAY choose to use the IGP Router-ID for direct
or static.
There MUST be at most one instance of each sub-TLV type present in
any Node Descriptor. The sub-TLVs within a Node Descriptor MUST be
arranged in ascending order by sub-TLV type. This needs to be done
to compare NLRIs, even when an implementation encounters an unknown
sub-TLV. Using stable sorting, an implementation can do a binary
comparison of NLRIs and hence allow incremental deployment of new key
sub-TLVs.
The BGP-LS Identifier was introduced by [RFC7752] and its use is
being deprecated by this document. Implementations SHOULD support
the advertisement of this sub-TLV for backward compatibility in
deployments where there are BGP-LS Producer implementations that
conform to [RFC7752] to ensure consistency of NLRI encoding for link-
state objects. The default value of 0 is RECOMMENDED to be used when
a BGP-LS Producer includes this sub-TLV when originating information
into BGP-LS. Implementations SHOULD provide an option to configure
this value for backward compatibility reasons. As a reminder, the
use of the BGP-LS Instance-ID that is carried in the Identifier field
is the way of segregation of link-state objects of different IGP
domains in BGP-LS.
5.2.2. Link Descriptors
The Link Descriptor field is a set of Type/Length/Value (TLV)
triplets. The format of each TLV is shown in Section 5.1. The Link
Descriptor TLVs uniquely identify a link among multiple parallel
links between a pair of anchor routers. A link described by the Link
Descriptor TLVs actually is a "half-link", a unidirectional
representation of a logical link. To fully describe a single logical
link, two anchor routers advertise a half-link each, i.e., two Link
NLRIs are advertised for a given point-to-point link.
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A link between two nodes is not considered as complete (or available)
unless it is described by the two Link NLRIs corresponding to the
half-link representation from the pair of anchor nodes. This check
is similar to the 'two-way connectivity check' that is performed by
link-state IGPs.
An implementation MAY suppress the advertisement of a Link NLRI,
corresponding to a half-link, from a link-state IGP unless the IGP
has verified that the link is being reported in the IS-IS LSP or OSPF
Router LSA by both the nodes connected by that link. This 'two-way
connectivity check' is performed by link-state IGPs during their
computation and can be leveraged before passing information for any
half-link that is reported from these IGPs into BGP-LS. This ensures
that only those Link State IGP adjacencies which are established get
reported via Link NLRIs. Such a 'two-way connectivity check' could
be also required in certain cases (e.g., with OSPF) to obtain the
proper link identifiers of the remote node.
The format and semantics of the Value fields in most Link Descriptor
TLVs correspond to the format and semantics of value fields in IS-IS
Extended IS Reachability sub-TLVs, defined in [RFC5305], [RFC5307],
and [RFC6119]. Although the encodings for Link Descriptor TLVs were
originally defined for IS-IS, the TLVs can carry data sourced by
either IS-IS or OSPF.
The following TLVs are defined as Link Descriptors in the Link NLRI:
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+================+===================+============+===============+
| TLV Code Point | Description | IS-IS TLV/ | Reference |
| | | Sub-TLV | (RFC/Section) |
+================+===================+============+===============+
| 258 | Link Local/Remote | 22/4 | [RFC5307] / |
| | Identifiers | | 1.1 |
+----------------+-------------------+------------+---------------+
| 259 | IPv4 interface | 22/6 | [RFC5305] / |
| | address | | 3.2 |
+----------------+-------------------+------------+---------------+
| 260 | IPv4 neighbor | 22/8 | [RFC5305] / |
| | address | | 3.3 |
+----------------+-------------------+------------+---------------+
| 261 | IPv6 interface | 22/12 | [RFC6119] / |
| | address | | 4.2 |
+----------------+-------------------+------------+---------------+
| 262 | IPv6 neighbor | 22/13 | [RFC6119] / |
| | address | | 4.3 |
+----------------+-------------------+------------+---------------+
| 263 | Multi-Topology | --- | Section |
| | Identifier | | 5.2.2.1 |
+----------------+-------------------+------------+---------------+
Table 4: 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 interface/neighbor address TLVs MUST be
included, and the Link Local/Remote Identifiers TLV MUST NOT be
included in the Link Descriptor. The Link Local/Remote
Identifiers TLV MAY be included in the link attribute when
available. IPv4/IPv6 link-local addresses MUST NOT be carried in
the IPv4/IPv6 interface/neighbor address TLVs (259/260/261/262) as
descriptors of a link as they are not considered unique.
If interface and neighbor addresses are not present and the link
local/remote identifiers are present, then the Link Local/Remote
Identifiers TLV MUST be included in the Link Descriptor. The Link
Local/Remote Identifiers MUST be included in the Link Descriptor
also in the case of links having only IPv6 link-local addressing
on them.
The Multi-Topology Identifier TLV MUST be included as a Link
Descriptor if the underlying IGP link object is associated with a
non-default topology.
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The TLVs/sub-TLVs corresponding to the interface addresses and/or the
local/remote identifiers may not always be signaled in the IGPs
unless their advertisement is enabled specifically. In such cases,
it is valid to advertise a BGP-LS Link NLRI without any of these
identifiers.
5.2.2.1. Multi-Topology ID
The Multi-Topology ID (MT-ID) TLV carries one or more IS-IS or OSPF
Multi-Topology IDs for a link, node, or prefix.
The semantics of the IS-IS MT-ID are defined in sections 7.1 and 7.2
of [RFC5120]. The semantics of the OSPF MT-ID are defined in section
3.7 of [RFC4915]. If the value in the MT-ID TLV is derived from
OSPF, then the upper R bits of the MT-ID field MUST be set to 0 and
only the values from 0 to 127 are valid for the MT-ID.
The format of the MT-ID TLV is shown in the following figure.
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 TLV Format
where Type is 263, Length is 2*n, and n is the number of MT-IDs
carried in the TLV.
The MT-ID TLV MAY be included as a Link Descriptor, a Prefix
Descriptor, or in the BGP-LS Attribute of a Node NLRI. When included
as a Link or Prefix Descriptor, only a single MT-ID TLV containing
the MT-ID of the topology where the link or the prefix is reachable
is allowed. In case one wants to advertise multiple topologies for a
given Link Descriptor or Prefix Descriptor, multiple NLRIs MUST be
generated where each NLRI contains a single unique MT-ID. When used
as a Link or Prefix Descriptor for IS-IS, the Bits R are reserved and
MUST be set to 0 (as per section 7.2 of [RFC5120]) when originated
and ignored on receipt.
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In the BGP-LS Attribute of a Node NLRI, one MT-ID TLV containing the
array of MT-IDs of all topologies where the node is reachable is
allowed. When used in the Node Attribute TLV for IS-IS, the Bits R
are set as per section 7.1 of [RFC5120].
5.2.3. Prefix Descriptors
The Prefix Descriptor field is a set of Type/Length/Value (TLV)
triplets. Prefix Descriptor TLVs uniquely identify an IPv4 or IPv6
prefix originated by a node. The following TLVs are defined as
Prefix Descriptors in the IPv4/IPv6 Prefix NLRI:
+================+=================+==========+===============+
| TLV Code Point | Description | Length | Reference |
| | | | (RFC/Section) |
+================+=================+==========+===============+
| 263 | Multi-Topology | variable | Section |
| | Identifier | | 5.2.2.1 |
+----------------+-----------------+----------+---------------+
| 264 | OSPF Route Type | 1 | Section |
| | | | 5.2.3.1 |
+----------------+-----------------+----------+---------------+
| 265 | IP Reachability | variable | Section |
| | Information | | 5.2.3.2 |
+----------------+-----------------+----------+---------------+
Table 5: Prefix Descriptor TLVs
The Multi-Topology Identifier TLV MUST be included in the Prefix
Descriptor if the underlying IGP prefix object is associated with a
non-default topology.
5.2.3.1. OSPF Route Type
The OSPF Route Type TLV is an optional TLV corresponding to Prefix
NLRIs originated from OSPF. It is used to identify the OSPF route
type of the prefix. An OSPF prefix MAY be advertised in the OSPF
domain with multiple route types. The Route Type TLV allows the
discrimination of these advertisements. The OSPF Route Type TLV MUST
be included in the advertisement when the type is either being
signaled explicitly in the underlying LSA or can be determined via
another LSA for the same prefix when it is not signaled explicitly
(e.g., in the case of OSPFv2 Extended Prefix Opaque LSA [RFC7684]).
The route type advertised in the OSPFv2 Extended Prefix TLV (section
2.1 of [RFC7684]) does not make a distinction between Type 1 and 2
for AS external and NSSA external routes. In this case, the route
type to be used in the BGP-LS advertisement can be determined by
checking the OSPFv2 External or NSSA External LSA for the prefix. A
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similar check for the base OSPFv2 LSAs can be done to determine the
route type to be used when the route type value 0 is carried in the
OSPFv2 Extended Prefix TLV.
The format of the OSPF Route Type TLV is shown in the following
figure.
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 5.
The OSPF Route Type field follows the route types defined in the OSPF
protocol and can be one of the following:
* Intra-Area (0x1)
* Inter-Area (0x2)
* External 1 (0x3)
* External 2 (0x4)
* NSSA 1 (0x5)
* NSSA 2 (0x6)
5.2.3.2. IP Reachability Information
The IP Reachability Information TLV is a mandatory TLV for IPv4 &
IPv6 Prefix NLRI types. The TLV contains one IP address prefix (IPv4
or IPv6) originally advertised in the IGP topology. A router SHOULD
advertise an IP Prefix NLRI for each of its BGP next-hops. The
format of the IP Reachability Information TLV is shown in the
following figure:
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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 5. The
following two fields determine the reachability information of the
address family. The Prefix Length field contains the length of the
prefix in bits. The IP Prefix field contains an IP address prefix,
followed by the minimum number of trailing bits needed to make the
end of the field fall on an octet boundary. Any trailing bits MUST
be set to 0. Thus, the IP Prefix field contains the most significant
octets of the prefix, i.e., 1 octet for prefix length 1 up to 8, 2
octets for prefix length 9 to 16, 3 octets for prefix length 17 up to
24, 4 octets for prefix length 25 up to 32, etc.
5.3. The BGP-LS Attribute
The BGP-LS Attribute (assigned value 29 by IANA) is an optional, non-
transitive BGP attribute that is used to carry link, node, and prefix
parameters and attributes. It is defined as a set of Type/Length/
Value (TLV) triplets, described in the following section. This
attribute SHOULD only be included with Link-State NLRIs. The use of
this attribute for other address families is outside the scope of
this document.
The Node Attribute TLVs, Link Attribute TLVs, and Prefix Attribute
TLVs are sets of TLVs that may be encoded in the BGP-LS Attribute
associated with a Node NLRI, Link NLRI, and Prefix NLRI respectively.
The size of the BGP-LS Attribute may potentially grow large depending
on the amount of link-state information associated with a single
Link-State NLRI. The BGP specification [RFC4271] mandates a maximum
BGP message size of 4096 octets. It is RECOMMENDED that an
implementation supports [RFC8654] to accommodate a larger size of
information within the BGP-LS Attribute. BGP-LS Producers MUST
ensure that the TLVs included in the BGP-LS Attribute does not result
in a BGP UPDATE message for a single Link-State NLRI that crosses the
maximum limit for a BGP message.
An implementation MAY adopt mechanisms to avoid this problem that may
be based the BGP-LS Consumer applications' requirement; these
mechanisms are beyond the scope of this specification. However, if
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an implementation chooses to mitigate the problem by excluding some
TLVs from the BGP-LS Attribute, this exclusion SHOULD be done
consistently by all BGP-LS Producers within a given BGP-LS domain.
In the event of inconsistent exclusion of TLVs from the BGP-LS
Attribute, the result would be a differing set of attributes of the
link-state object being propagated to BGP-LS Consumers based on the
BGP decision process at BGP-LS Propagators.
When a BGP-LS Propagator finds that it is exceeding the maximum BGP
message size due to the addition or update of some other BGP
Attribute (e.g. AS_PATH), it MUST consider the BGP-LS Attribute to
be malformed, apply the "Attribute Discard" error-handling approach
[RFC7606], and handle the propagation as described in Section 8.2.2.
When a BGP-LS Propagator needs to perform "Attribute Discard" for
reducing the BGP UPDATE message size as specified in section 4 of
[RFC8654], it MUST first discard the BGP-LS Attribute to enable the
detection and diagnosis of this error condition as discussed in
Section 8.2.2. This brings the deployment consideration that the
consistent propagation of BGP-LS information with a BGP UPDATE
message size larger than 4096 octets can only happen along a set of
BGP Speakers that all support [RFC8654].
5.3.1. Node Attribute TLVs
The following Node Attribute TLVs are defined for the BGP-LS
Attribute associated with a Node NLRI:
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+================+================+==========+===============+
| TLV Code Point | Description | Length | Reference |
| | | | (RFC/Section) |
+================+================+==========+===============+
| 263 | Multi-Topology | variable | Section |
| | Identifier | | 5.2.2.1 |
+----------------+----------------+----------+---------------+
| 1024 | Node Flag Bits | 1 | Section |
| | | | 5.3.1.1 |
+----------------+----------------+----------+---------------+
| 1025 | Opaque Node | variable | Section |
| | Attribute | | 5.3.1.5 |
+----------------+----------------+----------+---------------+
| 1026 | Node Name | variable | Section |
| | | | 5.3.1.3 |
+----------------+----------------+----------+---------------+
| 1027 | IS-IS Area | variable | Section |
| | Identifier | | 5.3.1.2 |
+----------------+----------------+----------+---------------+
| 1028 | IPv4 Router-ID | 4 | [RFC5305] / |
| | of Local Node | | 4.3 |
+----------------+----------------+----------+---------------+
| 1029 | IPv6 Router-ID | 16 | [RFC6119] / |
| | of Local Node | | 4.1 |
+----------------+----------------+----------+---------------+
Table 6: Node Attribute TLVs
5.3.1.1. Node Flag Bits TLV
The Node Flag Bits TLV carries a bitmask describing node attributes.
The value is a 1 octet length bit array of flags, where each bit
represents a node operational state or attribute.
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| |
+-+-+-+-+-+-+-+-+
Figure 15: Node Flag Bits TLV Format
The bits are defined as follows:
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+=====+==============+============+
| Bit | Description | Reference |
+=====+==============+============+
| 'O' | Overload Bit | [ISO10589] |
+-----+--------------+------------+
| 'T' | Attached Bit | [ISO10589] |
+-----+--------------+------------+
| 'E' | External Bit | [RFC2328] |
+-----+--------------+------------+
| 'B' | ABR Bit | [RFC2328] |
+-----+--------------+------------+
| 'R' | Router Bit | [RFC5340] |
+-----+--------------+------------+
| 'V' | V6 Bit | [RFC5340] |
+-----+--------------+------------+
Table 7: Node Flag Bits Definitions
The bits that are not defined MUST be set to 0 by the originator and
MUST be ignored by the receiver.
5.3.1.2. IS-IS Area Identifier TLV
An IS-IS node can be part of only a single IS-IS area. However, a
node can have multiple synonymous area addresses. Each of these area
addresses is carried in the IS-IS Area Identifier TLV. If multiple
area addresses are present, multiple TLVs are used to encode them.
The IS-IS Area Identifier TLV may be present in the BGP-LS Attribute
only when advertised in the Link-State Node NLRI.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// IS-IS Area Identifier (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 16: IS-IS Area Identifier TLV Format
5.3.1.3. Node Name TLV
The Node Name TLV is optional. The encoding semantics for the node
name has been borrowed from [RFC5301]. The Value field identifies
the symbolic name of the router node. This symbolic name can either
be the Fully Qualified Domain Name (FQDN) for the router, or it can
be a substring of the FQDN (e.g., a hostname), or it can be any
string that an operator wants to use for the router. The use of FQDN
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or a substring of it is strongly RECOMMENDED. The maximum length of
the Node Name TLV is 255 octets.
The Value field is encoded in 7-bit ASCII. If a user interface for
configuring or displaying this field permits Unicode characters, that
the user interface is responsible for applying the ToASCII and/or
ToUnicode algorithm as described in [RFC5890] to achieve the correct
format for transmission or display.
[RFC5301] describes an IS-IS-specific extension and [RFC5642]
describes an OSPF extension for the advertisement of Node Name which
may be encoded in the Node Name TLV.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Node Name (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 17: Node Name Format
5.3.1.4. 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
purposes such as correlating a Node-ID between different protocols.
If there is more than one auxiliary Router-ID of a given type, then
each one is encoded as a separate TLV.
5.3.1.5. Opaque Node Attribute TLV
The Opaque Node Attribute TLV is an envelope that transparently
carries optional Node Attribute TLVs advertised by a router. An
originating router shall use this TLV for encoding information
specific to the protocol advertised in the NLRI header Protocol-ID
field or new protocol extensions to the protocol as advertised in the
NLRI header Protocol-ID field for which there is no protocol-neutral
representation in the BGP Link-State NLRI. The primary use of the
Opaque Node Attribute TLV is to bridge the document lag between a new
IGP link-state attribute and its protocol-neutral BGP-LS extension
being defined. Once the protocol-neutral BGP-LS extensions are
defined, the BGP-LS implementations may still need to advertise the
information both within the Opaque Attribute TLV and the new TLV
definition for incremental deployment and transition.
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In the case of OSPF, this TLV MUST NOT be used to advertise TLVs
other than those in the OSPF Router Information (RI) LSA [RFC7770].
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 Node Attribute Format
The type is as specified in Table 6. Length is variable.
5.3.2. Link Attribute TLVs
Link Attribute TLVs are TLVs that may be encoded in the BGP-LS
Attribute with a Link NLRI. Each 'Link Attribute' is a Type/Length/
Value (TLV) triplet formatted as defined in Section 5.1. The format
and semantics of the Value fields in some Link Attribute TLVs
correspond to the format and semantics of the Value fields in IS-IS
Extended IS Reachability sub-TLVs, defined in [RFC5305] and
[RFC5307]. Other Link Attribute TLVs are defined in this document.
Although the encodings for Link Attribute TLVs were originally
defined for IS-IS, the TLVs can carry data sourced by either IS-IS or
OSPF.
The following Link Attribute TLVs are defined for the BGP-LS
Attribute associated with a Link NLRI:
+================+=================+============+===============+
| TLV Code Point | Description | IS-IS TLV/ | Reference |
| | | Sub-TLV | (RFC/Section) |
+================+=================+============+===============+
| 1028 | IPv4 Router-ID | 134/--- | [RFC5305] / |
| | of Local Node | | 4.3 |
+----------------+-----------------+------------+---------------+
| 1029 | IPv6 Router-ID | 140/--- | [RFC6119] / |
| | of Local Node | | 4.1 |
+----------------+-----------------+------------+---------------+
| 1030 | IPv4 Router-ID | 134/--- | [RFC5305] / |
| | of Remote Node | | 4.3 |
+----------------+-----------------+------------+---------------+
| 1031 | IPv6 Router-ID | 140/--- | [RFC6119] / |
| | of Remote Node | | 4.1 |
+----------------+-----------------+------------+---------------+
| 1088 | Administrative | 22/3 | [RFC5305] / |
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| | group (color) | | 3.1 |
+----------------+-----------------+------------+---------------+
| 1089 | Maximum link | 22/9 | [RFC5305] / |
| | bandwidth | | 3.4 |
+----------------+-----------------+------------+---------------+
| 1090 | Max. reservable | 22/10 | [RFC5305] / |
| | link bandwidth | | 3.5 |
+----------------+-----------------+------------+---------------+
| 1091 | Unreserved | 22/11 | [RFC5305] / |
| | bandwidth | | 3.6 |
+----------------+-----------------+------------+---------------+
| 1092 | TE Default | 22/18 | Section |
| | Metric | | 5.3.2.3 |
+----------------+-----------------+------------+---------------+
| 1093 | Link Protection | 22/20 | [RFC5307] / |
| | Type | | 1.2 |
+----------------+-----------------+------------+---------------+
| 1094 | MPLS Protocol | --- | Section |
| | Mask | | 5.3.2.2 |
+----------------+-----------------+------------+---------------+
| 1095 | IGP Metric | --- | Section |
| | | | 5.3.2.4 |
+----------------+-----------------+------------+---------------+
| 1096 | Shared Risk | --- | Section |
| | Link Group | | 5.3.2.5 |
+----------------+-----------------+------------+---------------+
| 1097 | Opaque Link | --- | Section |
| | Attribute | | 5.3.2.6 |
+----------------+-----------------+------------+---------------+
| 1098 | Link Name | --- | Section |
| | | | 5.3.2.7 |
+----------------+-----------------+------------+---------------+
Table 8: Link Attribute TLVs
5.3.2.1. 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 each Link NLRI. If
there is more than one auxiliary Router-ID of a given type, then
multiple TLVs are used to encode them.
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5.3.2.2. MPLS Protocol Mask TLV
The MPLS Protocol Mask TLV carries a bitmask describing which MPLS
signaling protocols are enabled. The length of this TLV is 1. The
value is a bit array of 8 flags, where each bit represents an MPLS
Protocol capability.
Generation of the MPLS Protocol Mask TLV is only valid for and SHOULD
only be used with originators that have local link insight, for
example, the Protocol-IDs 'Static configuration' or 'Direct' as per
Table 2. The MPLS Protocol 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, and the reserved bits MUST be set to
zero and SHOULD be ignored on receipt:
+=====+=============================================+===========+
| Bit | Description | Reference |
+=====+=============================================+===========+
| 'L' | Label Distribution Protocol (LDP) | [RFC5036] |
+-----+---------------------------------------------+-----------+
| 'R' | Extension to RSVP for LSP Tunnels (RSVP-TE) | [RFC3209] |
+-----+---------------------------------------------+-----------+
Table 9: MPLS Protocol Mask TLV Codes
The bits that are not defined MUST be set to 0 by the originator and
MUST be ignored by the receiver.
5.3.2.3. 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 a metric width of fewer than 32 bits, then the high-
order bits of this field MUST be padded with zero.
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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 TLV Format
5.3.2.4. 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 are of 6-bit size, but are encoded in
a 1 octet field; therefore the two most significant bits of the field
MUST be set to 0 by the originator and MUST be ignored by the
receiver. OSPF link metrics have a length of 2 octets. IS-IS wide
metrics have a length of 3 octets.
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 TLV Format
5.3.2.5. Shared Risk Link Group TLV
The Shared Risk Link Group (SRLG) TLV carries the Shared Risk Link
Group information (see Section 2.3 ("Shared Risk Link Group
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).
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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 TLV Format
The SRLG TLV for OSPF-TE is defined in [RFC4203]. In IS-IS, the SRLG
information is carried in two different TLVs: the IPv4 (SRLG) TLV
(Type 138) defined in [RFC5307] and the IPv6 SRLG TLV (Type 139)
defined in [RFC6119]. Both IPv4 and IPv6 SRLG information is carried
in a single TLV.
5.3.2.6. Opaque Link Attribute TLV
The Opaque Link Attribute TLV is an envelope that transparently
carries optional Link Attribute TLVs advertised by a router. An
originating router shall use this TLV for encoding information
specific to the protocol advertised in the NLRI header Protocol-ID
field or new protocol extensions to the protocol as advertised in the
NLRI header Protocol-ID field for which there is no protocol-neutral
representation in the BGP Link-State NLRI. The primary use of the
Opaque Link Attribute TLV is to bridge the document lag between a new
IGP link-state attribute and its 'protocol-neutral' BGP-LS extension
being defined. Once the protocol-neutral BGP-LS extensions are
defined, the BGP-LS implementations may still need to advertise the
information both within the Opaque Attribute TLV and the new TLV
definition for incremental deployment and transition.
In the case of OSPFv2, this TLV MUST NOT be used to advertise
information carried using TLVs other than those in the OSPFv2
Extended Link Opaque LSA [RFC7684]. In the case of OSPFv3, this TLV
MUST NOT be used to advertise TLVs other than those in the OSPFv3 E-
Router-LSA or E-Link-LSA [RFC8362].
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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: Opaque Link Attribute TLV Format
5.3.2.7. Link Name TLV
The Link Name TLV is optional. The Value field identifies the
symbolic name of the router link. This symbolic name can either be
the FQDN for the link, or it can be a substring of the FQDN, or it
can be any string that an operator wants to use for the link. The
use of FQDN or a substring of it is strongly RECOMMENDED. The
maximum length of the Link Name TLV is 255 octets.
The Value field is encoded in 7-bit ASCII. If a user interface for
configuring or displaying this field permits Unicode characters, that
the user 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 Name TLV Format
5.3.3. 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 are
advertised in the BGP-LS Attribute with Prefix NLRI types 3 and 4.
The following Prefix Attribute TLVs are defined for the BGP-LS
Attribute associated with a Prefix NLRI:
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+================+=================+==========+=================+
| TLV Code Point | Description | Length | Reference |
+================+=================+==========+=================+
| 1152 | IGP Flags | 1 | Section 5.3.3.1 |
+----------------+-----------------+----------+-----------------+
| 1153 | IGP Route Tag | 4*n | [RFC5130] |
+----------------+-----------------+----------+-----------------+
| 1154 | IGP Extended | 8*n | [RFC5130] |
| | Route Tag | | |
+----------------+-----------------+----------+-----------------+
| 1155 | Prefix Metric | 4 | [RFC5305] |
+----------------+-----------------+----------+-----------------+
| 1156 | OSPF Forwarding | 4 | [RFC2328] |
| | Address | | |
+----------------+-----------------+----------+-----------------+
| 1157 | Opaque Prefix | variable | Section 5.3.3.6 |
| | Attribute | | |
+----------------+-----------------+----------+-----------------+
Table 10: Prefix Attribute TLVs
5.3.3.1. IGP Flags TLV
The IGP Flags TLV contains one octet of IS-IS and OSPF flags and bits
originally assigned to the prefix. The IGP Flags TLV is encoded as
follows:
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| |
+-+-+-+-+-+-+-+-+
Figure 25: IGP Flag TLV Format
The Value field contains bits defined according to the table below:
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+=====+===========================+===========+
| 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] |
+-----+---------------------------+-----------+
Table 11: IGP Flag Bits Definitions
The bits that are not defined MUST be set to 0 by the originator and
MUST be ignored by the receiver.
5.3.3.2. IGP Route Tag TLV
The IGP Route Tag TLV carries original IGP Tags (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 Route Tag TLV Format
Length is a multiple of 4.
The Value field contains one or more Route Tags as learned in the IGP
topology.
5.3.3.3. Extended IGP Route Tag TLV
The Extended IGP Route Tag TLV carries IS-IS Extended Route Tags of
the prefix [RFC5130] and is encoded as follows:
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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 Route Tag TLV Format
Length is a multiple of 8.
The Extended Route Tag field contains one or more Extended Route Tags
as learned in the IGP topology.
5.3.3.4. 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.
5.3.3.5. OSPF Forwarding Address TLV
The OSPF Forwarding Address TLV [RFC2328] [RFC5340] carries the OSPF
forwarding address as known in the original OSPF advertisement. The
forwarding address can be either IPv4 or IPv6.
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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 forwarding address, and 16 for an IPv6
forwarding address.
5.3.3.6. Opaque Prefix Attribute TLV
The Opaque Prefix Attribute TLV is an envelope that transparently
carries optional Prefix Attribute TLVs advertised by a router. An
originating router shall use this TLV for encoding information
specific to the protocol advertised in the NLRI header Protocol-ID
field or new protocol extensions to the protocol as advertised in the
NLRI header Protocol-ID field for which there is no protocol-neutral
representation in the BGP Link-State NLRI. The primary use of the
Opaque Prefix Attribute TLV is to bridge the document lag between a
new IGP link-state attribute and its protocol-neutral BGP-LS
extension being defined. Once the protocol-neutral BGP-LS extensions
are defined, the BGP-LS implementations may still need to advertise
the information both within the Opaque Attribute TLV and the new TLV
definition for incremental deployment and transition.
In the case of OSPFv2, this TLV MUST NOT be used to advertise
information carried using TLVs other than those in the OSPFv2
Extended Prefix Opaque LSA [RFC7684]. In the case of OSPFv3, this
TLV MUST NOT be used to advertise TLVs other than those in the OSPFv3
E-Inter-Area-Prefix-LSA, E-Intra-Area-Prefix-LSA, E-AS-External-
Prefix-LSA, and E-NSSA-LSA [RFC8362].
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
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The type is as specified in Table 10. Length is variable.
5.4. Private Use
TLVs for Vendor Private use are supported using the code point range
reserved as indicated in Section 7. For such TLV use in the NLRI or
BGP-LS Attribute, the format as described in Section 5.1 is to be
used and a 4-octet field MUST be included as the first field in the
value to carry the Enterprise Code. For a private use NLRI Type, a 4
octet field MUST be included as the first field in the NLRI
immediately following the Total NLRI Length field of the Link-State
NLRI format as described in Section 5.2 to carry the Enterprise Code
[ENTNUM]. This enables the use of vendor-specific extensions without
conflicts.
Multiple instances of private-use TLVs MAY appear in the BGP-LS
Attribute.
5.5. BGP Next-Hop Information
BGP link-state information for both IPv4 and IPv6 networks can be
carried over either an IPv4 BGP session or an IPv6 BGP session. If
an IPv4 BGP session is used, then the next-hop in the MP_REACH_NLRI
SHOULD be an IPv4 address. Similarly, if an IPv6 BGP session is
used, then the next-hop in the MP_REACH_NLRI SHOULD be an IPv6
address. Usually, the next-hop will be set to the local endpoint
address of the BGP session. The next-hop address MUST be encoded as
described in [RFC4760]. The Length field of the next-hop address
will specify the next-hop address family. If the next-hop length is
4, then the next-hop is an IPv4 address; if the next-hop length is
16, then it is a global IPv6 address; and if the next-hop length is
32, then there is one global IPv6 address followed by a link-local
IPv6 address. The link-local IPv6 address should be used as
described in [RFC2545]. For VPN Subsequent Address Family Identifier
(SAFI), as per custom, an 8-byte Route Distinguisher set to all zero
is prepended to the next-hop.
The BGP Next-Hop is used by each BGP-LS speaker to validate the NLRI
it receives. In case identical NLRIs are sourced by multiple BGP-LS
Producers, the BGP Next-Hop is used to tiebreak as per the standard
BGP path decision process. This specification doesn't mandate any
rule regarding the rewrite of the BGP Next-Hop.
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5.6. 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] [RFC9346]. In other cases, an
implementation SHOULD provide a means to inject inter-AS links into
BGP-LS. The exact mechanism used to advertise the inter-AS links is
outside the scope of this document.
5.7. OSPF Virtual Links and Sham Links
In an OSPF [RFC2328] [RFC5340] network, OSPF virtual links serve to
connect physically separate components of the backbone to establish/
maintain continuity of the backbone area. While OSPF virtual links
are modeled as point-to-point unnumbered links in the OSPF topology,
their characteristics and purpose are different from other types of
links in the OSPF topology. They are advertised using a distinct
"virtual link" type in OSPF LSAs. The mechanism for the
advertisement of OSPF virtual links via BGP-LS is outside the scope
of this document.
In an OSPF network, sham links [RFC4577] [RFC6565] are used to
provide intra-area connectivity between VPN Routing and Forwarding
(VRF) instances on PE routers over the VPN provider's network. These
links are advertised in OSPF as point-to-point unnumbered links and
represent connectivity over a service provider network using
encapsulation mechanisms like MPLS. As such, the mechanism for the
advertisement of OSPF sham links follows the same procedures as other
point-to-point unnumbered links as described previously in this
document.
5.8. OSPFv2 Type 4 Summary LSA & OSPFv3 Inter-Area Router LSA
OSPFv2 [RFC2328] defines the Type 4 Summary LSA and OSPFv3 [RFC5340]
the Inter-area-router-LSA for an Area Border Router (ABR) to
advertise reachability to an AS Border Router (ASBR) that is external
to the area yet internal to the AS. The nature of information
advertised by OSPF using this type of LSA does not map to either a
node or a link or a prefix as discussed in this document. Therefore,
the mechanism for the advertisement of the information carried by
these LSAs is outside the scope of this document.
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5.9. Handling of Unreachable IGP Nodes
Consider an OSPF network as shown in Figure 31, where R2 and R3 are
the BGP-LS Producers and also the OSPF Area Border Routers (ABRs).
The link between R2 and R3 is in area 0 while the other links are in
area 1 as indicated by the a0 and a1 references respectively against
the links.
A BGP-LS Consumer talks to a BGP route reflector RR0 which is a BGP-
LS Propagator that is aggregating the BGP-LS feed from the BGP-LS
Producers R2 and R3. Here R2 and R3 provide a redundant topology
feed via BGP-LS to RR0. Normally, RR0 would receive two identical
copies of all the Link-State NLRIs from both R2 and R3 and it would
pick one of them (say R2) based on the standard BGP Decision Process.
BGP-LS Consumer
^
|
RR0
(BGP Route Reflector)
/ \
/ \
a1 / a0 \ a1
R1 ------ R2 -------- R3 ------ R4
a1 | | a1
| |
R5 ---------------------------- R6
a1
Figure 31: Incorrect Reporting due to BGP Path Selection
Consider a scenario where the link between R5 and R6 is lost (thereby
partitioning the area 1) and its impact on the OSPF LSDB at R2 and
R3.
Now, R5 will remove the link R5-R6 from its Router LSA, and this
updated LSA is available at R2. R2 also has a stale copy of R6's
Router LSA that still has the link R6-R5 in it. Based on this view
in its LSDB, R2 will advertise only the half-link R6-R5 that it
derives from R6's stale Router LSA.
At the same time, R6 has removed the link R6-R5 from its Router LSA,
and this updated LSA is available at R3. Similarly, R3 also has a
stale copy of R5's Router LSA having the link R5-R6 in it. Based on
its LSDB, R3 will advertise only the half-link R5-R6 that it has
derived from R5's stale Router LSA.
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Now, the BGP-LS Consumer receives both the Link NLRIs corresponding
to the half-links from R2 and R3 via RR0. When viewed together, it
would not detect or realize that area 1 is partitioned. Also, if R2
continues to report Node and Prefix NLRIs corresponding to the stale
copy of R4 and R6's Router LSAs then RR0 could prefer them over the
valid Node and Prefix NLRIs for R4 and R6 that it is receiving from
R3 depending on RR0's BGP decision process. This would result in the
BGP-LS Consumer getting stale and inaccurate topology information.
This problem scenario is avoided if R2 were to not advertise the
link-state information corresponding to R4 and R6 and if R3 were to
not advertise similarly for R1 and R5.
A BGP-LS Producer SHOULD withdraw all link-state objects advertised
by it in BGP when the node that originated its corresponding LSP/LSAs
is determined to have become unreachable in the IGP. An
implementation MAY continue to advertise link-state objects
corresponding to unreachable nodes in a deployment use-case where the
BGP-LS Consumer is interested in receiving a topology feed
corresponding to a complete IGP LSDB view. In such deployments, it
is expected that the problem described above is mitigated by the BGP-
LS Consumer via appropriate handling of such a topology feed in
addition to the use of either a direct BGP peering with the BGP-LS
Producer nodes or mechanisms such as [RFC7911] when using RRs.
Details of these mechanisms are outside the scope of this document.
If the BGP-LS Producer does withdraw link-state objects associated
with an IGP node based on the failure of reachability check for that
node, then it MUST re-advertise those link-state objects after that
node becomes reachable again in the IGP domain.
5.10. Router-ID Anchoring Example: ISO Pseudonode
The encoding of a broadcast LAN in IS-IS provides a good example of
how Router-IDs are encoded. Consider Figure 32. This represents a
Broadcast LAN between a pair of routers. The "real" (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, Pseudonode1) and (Pseudonode1,
Node2) are being generated.
The Link NLRI of (Node1, Pseudonode1) is encoded as follows. The IGP
Router-ID TLV of the local Node Descriptor is 6 octets long and
contains the ISO-ID of Node1, 1920.0000.2001. The IGP Router-ID TLV
of the remote Node Descriptor is 7 octets long and contains the ISO-
ID of Pseudonode1, 1920.0000.2001.02. The BGP-LS Attribute of this
link contains one local IPv4 Router-ID TLV (TLV type 1028) containing
192.0.2.1, the IPv4 Router-ID of Node1.
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The Link NLRI of (Pseudonode1, Node2) is encoded as follows. The IGP
Router-ID TLV of the local Node Descriptor is 7 octets long and
contains the ISO-ID of Pseudonode1, 1920.0000.2001.02. The IGP
Router-ID TLV of the remote Node Descriptor is 6 octets long and
contains the ISO-ID of Node2, 1920.0000.2002. The BGP-LS Attribute
of this link contains one remote IPv4 Router-ID TLV (TLV type 1030)
containing 192.0.2.2, the IPv4 Router-ID of Node2.
+-----------------+ +-----------------+ +-----------------+
| Node1 | | Pseudonode1 | | Node2 |
|1920.0000.2001.00|--->|1920.0000.2001.02|--->|1920.0000.2002.00|
| 192.0.2.1 | | | | 192.0.2.2 |
+-----------------+ +-----------------+ +-----------------+
Figure 32: IS-IS Pseudonodes
5.11. Router-ID Anchoring Example: OSPF Pseudonode
The encoding of a broadcast LAN in OSPF provides a good example of
how Router-IDs and local Interface IPs are encoded. Consider
Figure 33. This represents a Broadcast LAN between a pair of
routers. The "real" (non-pseudonode) routers have both an IPv4
Router-ID and an Area Identifier. The pseudonode does have an IPv4
Router-ID, an IPv4 Interface Address (for disambiguation), and an
OSPF Area. Node1 is the DR for the LAN; hence, its local IP address
198.51.100.1 is used as both the Router-ID and Interface IP for the
pseudonode keys. Two unidirectional links, (Node1, Pseudonode1) and
(Pseudonode1, Node2), are being generated.
The Link NLRI of (Node1, Pseudonode1) is encoded as follows:
* Local Node Descriptor
TLV #515: IGP Router-ID: 192.0.2.1
TLV #514: OSPF Area-ID: ID:0.0.0.0
* Remote Node Descriptor
TLV #515: IGP Router-ID: 192.0.2.1:198.51.100.1
TLV #514: OSPF Area-ID: ID:0.0.0.0
The Link NLRI of (Pseudonode1, Node2) is encoded as follows:
* Local Node Descriptor
TLV #515: IGP Router-ID: 192.0.2.1:198.51.100.1
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TLV #514: OSPF Area-ID: ID:0.0.0.0
* Remote Node Descriptor
TLV #515: IGP Router-ID: 192.0.2.2
TLV #514: OSPF Area-ID: ID:0.0.0.0
198.51.100.1/24 198.51.100.2/24
+-------------+ +-------------+ +-------------+
| Node1 | | Pseudonode1 | | Node2 |
| 192.0.2.1 |--->| 192.0.2.1 |--->| 192.0.2.2 |
| | |198.51.100.1 | | |
| Area 0 | | Area 0 | | Area 0 |
+-------------+ +-------------+ +-------------+
Figure 33: OSPF Pseudonodes
The LAN subnet 198.51.100.0/24 is not included in the Router LSA of
Node1 or Node2. The Network LSA for this LAN advertised by the DR
Node1 contains the subnet mask for the LAN along with the DR address.
A Prefix NLRI corresponding to the LAN subnet is advertised with the
Pseudonode1 used as the Local node using the DR address and the
subnet mask from the Network LSA.
5.12. Router-ID Anchoring Example: OSPFv2 to IS-IS Migration
Graceful migration from one IGP to another requires coordinated
operation of both protocols during the migration period. Such
coordination requires identifying a given physical link in both IGPs.
The IPv4 Router-ID provides that "glue", which is present in the Node
Descriptors of the OSPF Link NLRI and in the link attribute of the
IS-IS Link NLRI.
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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, IPv6
Router-ID, and ISO-ID. Each protocol generates one Link NLRI for the
link (A, B), both of which are carried by BGP-LS. The OSPFv2 Link
NLRI for the link is encoded with the IPv4 Router-ID of nodes A and B
in the local and remote Node Descriptors, respectively. The IS-IS
Link NLRI for the link is encoded with the ISO-ID of nodes A and B in
the local and remote Node Descriptors, respectively. In addition,
the BGP-LS Attribute of the IS-IS Link NLRI contains the TLV type
1028 containing the IPv4 Router-ID of node A, TLV type 1030
containing the IPv4 Router-ID of node B, and TLV type 1031 containing
the IPv6 Router-ID of node B. In this case, by using IPv4 Router-ID,
the link (A, B) can be identified in both the IS-IS and OSPF
protocols.
6. Link to Path Aggregation
Distribution of all links available on the global Internet is
certainly possible; however, it is not desirable from a scaling and
privacy point of view. Therefore, an implementation may support a
link to path aggregation. Rather than advertising all specific links
of a domain, an ASBR may advertise an "aggregate link" between a non-
adjacent pair of nodes. The "aggregate link" represents the
aggregated set of link properties between a pair of non-adjacent
nodes. The actual methods to compute the path properties (of
bandwidth, metric, etc.) are outside the scope of this document. The
decision of whether to advertise all specific links or aggregated
links is an operator's policy choice. To highlight the varying
levels of exposure, the following deployment examples are discussed.
6.1. Example: No Link Aggregation
Consider Figure 34. Both AS1 and AS2 operators want to protect their
inter-AS {R1, R3}, {R2, R4} links using RSVP-FRR LSPs. If R1 wants
to compute its link-protection LSP to R3, it needs to "see" an
alternate path to R3. Therefore, the AS2 operator exposes its
topology. All BGP-TE-enabled routers in AS1 "see" the full topology
of AS2 and therefore can compute a backup path. Note that the
computing router decides if the direct link between {R3, R4} or the
{R4, R5, R3} path is used.
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AS1 : AS2
:
R1-------R3
| : | \
| : | R5
| : | /
R2-------R4
:
:
Figure 34: No Link Aggregation
6.2. 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 35. The only link that gets advertised by AS2 is an
"aggregate" link between R3 and R4. This is enough to tell AS1 that
there is a backup path. However, the actual links being used are
hidden from the topology.
AS1 : AS2
:
R1-------R3
| : |
| : |
| : |
R2-------R4
:
:
Figure 35: ASBR Link Aggregation
6.3. 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 36. AS3 is
modeled as a single node that connects to the border routers of the
aggregated domain.
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AS1 : AS2 : AS3
: :
R1-------R3-----
| : : \
| : : vR0
| : : /
R2-------R4-----
: :
: :
Figure 36: Multi-AS Aggregation
7. IANA Considerations
As this document obsoletes [RFC7752] and [RFC9029], IANA is requested
to change all registration information that references those
documents to instead reference this document.
IANA has assigned address family number 16388 (BGP-LS) in the
"Address Family Numbers" registry.
IANA has assigned SAFI values 71 (BGP-LS) and 72 (BGP-LS-VPN) in the
"SAFI Values" registry under the "Subsequent Address Family
Identifiers (SAFI) Parameters" registry group.
IANA has assigned value 29 (BGP-LS Attribute) in the "BGP Path
Attributes" registry under the "Border Gateway Protocol (BGP)
Parameters" registry group.
IANA has created a "Border Gateway Protocol - Link-State (BGP-LS)
Parameters" registry group at <https://www.iana.org/assignments/bgp-
ls-parameters>.
This section also incorporates all the changes to the allocation
procedures for the BGP-LS IANA registry group as well as the
guidelines for designated experts introduced by [RFC9029].
7.1. BGP-LS Registries
All of the registries listed in the following subsections are BGP-LS
specific and are accessible under this registry.
7.1.1. BGP-LS NLRI Types Registry
The "BGP-LS NLRI Types" registry has been set up for assignment for
the two-octet sized code-points for BGP-LS NLRI types and populated
with the values shown below:
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+=============+===========================+=================+
| Type | NLRI Type | Reference |
+=============+===========================+=================+
| 0 | Reserved | [This document] |
+-------------+---------------------------+-----------------+
| 1 | Node NLRI | [This document] |
+-------------+---------------------------+-----------------+
| 2 | Link NLRI | [This document] |
+-------------+---------------------------+-----------------+
| 3 | IPv4 Topology Prefix NLRI | [This document] |
+-------------+---------------------------+-----------------+
| 4 | IPv6 Topology Prefix NLRI | [This document] |
+-------------+---------------------------+-----------------+
| 65000-65535 | Private Use | [This document] |
+-------------+---------------------------+-----------------+
Table 12: BGP-LS NLRI Types
A range is reserved for Private Use [RFC8126]. All other allocations
within the registry are to be made using the "Expert Review" policy
[RFC8126] that requires documentation of the proposed use of the
allocated value and approval by the Designated Expert assigned by the
IESG.
7.1.2. BGP-LS Protocol-IDs Registry
The "BGP-LS Protocol-IDs" registry has been set up for assignment for
the one-octet sized code-points for BGP-LS Protocol-IDs and populated
with the values shown below:
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+=============+==================================+=================+
| Protocol-ID | NLRI information source protocol | Reference |
+=============+==================================+=================+
| 0 | Reserved | [This document] |
+-------------+----------------------------------+-----------------+
| 1 | IS-IS Level 1 | [This document] |
+-------------+----------------------------------+-----------------+
| 2 | IS-IS Level 2 | [This document] |
+-------------+----------------------------------+-----------------+
| 3 | OSPFv2 | [This document] |
+-------------+----------------------------------+-----------------+
| 4 | Direct | [This document] |
+-------------+----------------------------------+-----------------+
| 5 | Static configuration | [This document] |
+-------------+----------------------------------+-----------------+
| 6 | OSPFv3 | [This document] |
+-------------+----------------------------------+-----------------+
| 200-255 | Private Use | [This document] |
+-------------+----------------------------------+-----------------+
Table 13: BGP-LS Protocol-IDs
A range is reserved for Private Use [RFC8126]. All other allocations
within the registry are to be made using the "Expert Review" policy
[RFC8126] that requires documentation of the proposed use of the
allocated value and approval by the Designated Expert assigned by the
IESG.
7.1.3. BGP-LS Well-Known Instance-IDs Registry
The "BGP-LS Well-Known Instance-IDs" registry that was set up via
[RFC7752] is no longer required. IANA is requested to mark this
registry as obsolete and to change its registration procedure to
"registry closed".
7.1.4. BGP-LS Node Flags Registry
The "BGP-LS Node Flags" registry is requested to be created for the
one octet-sized flags field of the Node Flag Bits TLV (1024) and
populated with the initial values shown below:
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+=====+======================+=================+
| Bit | Description | Reference |
+=====+======================+=================+
| 0 | Overload Bit (O-bit) | [This document] |
+-----+----------------------+-----------------+
| 1 | Attached Bit (A-bit) | [This document] |
+-----+----------------------+-----------------+
| 2 | External Bit (E-bit) | [This document] |
+-----+----------------------+-----------------+
| 3 | ABR Bit (B-bit) | [This document] |
+-----+----------------------+-----------------+
| 4 | Router Bit (R-bit) | [This document] |
+-----+----------------------+-----------------+
| 5 | V6 Bit (V-bit) | [This document] |
+-----+----------------------+-----------------+
| 6-7 | Unassigned | [This document] |
+-----+----------------------+-----------------+
Table 14: BGP-LS Node Flags
Allocations within the registry are to be made using the "Expert
Review" policy [RFC8126] that requires documentation of the proposed
use of the allocated value and approval by the Designated Expert
assigned by the IESG.
7.1.5. BGP-LS MPLS Protocol Mask Registry
The "BGP-LS MPLS Protocol Mask" registry is requested to be created
for the one octet-sized flags field of the MPLS Protocol Mask TLV
(1094) and populated with the initial values shown below:
+=====+===========================================+=================+
| Bit | Description | Reference |
+=====+===========================================+=================+
| 0 | Label Distribution Protocol (L-bit) | [This document] |
+-----+-------------------------------------------+-----------------+
| 1 | Extension to RSVP for LSP Tunnels | [This document] |
| | (R-bit) | |
+-----+-------------------------------------------+-----------------+
| 2-7 | Unassigned | [This document] |
+-----+-------------------------------------------+-----------------+
Table 15: BGP-LS MPLS Protocol Mask
Allocations within the registry are to be made using the "Expert
Review" policy [RFC8126] that requires documentation of the proposed
use of the allocated value and approval by the Designated Expert
assigned by the IESG.
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7.1.6. BGP-LS IGP Prefix Flags Registry
The "BGP-LS IGP Prefix Flags" registry is requested to be created for
the one octet-sized flags field of the IGP Flags TLV (1152) and
populated with the initial values shown below:
+=====+===================================+=================+
| Bit | Description | Reference |
+=====+===================================+=================+
| 0 | IS-IS Up/Down Bit (D-bit) | [This document] |
+-----+-----------------------------------+-----------------+
| 1 | OSPF "no unicast" Bit (N-bit) | [This document] |
+-----+-----------------------------------+-----------------+
| 2 | OSPF "local address" Bit (L-bit) | [This document] |
+-----+-----------------------------------+-----------------+
| 3 | OSPF "propagate NSSA" Bit (P-bit) | [This document] |
+-----+-----------------------------------+-----------------+
| 4-7 | Unassigned | [This document] |
+-----+-----------------------------------+-----------------+
Table 16: BGP-LS IGP Prefix Flags
Allocations within the registry are to be made using the "Expert
Review" policy [RFC8126] that requires documentation of the proposed
use of the allocated value and approval by the Designated Expert
assigned by the IESG.
7.1.7. BGP-LS TLVs Registry
The "BGP-LS Node Descriptor, Link Descriptor, Prefix Descriptor, and
Attribute TLVs" registry was created via [RFC7752]. This document
requests IANA to rename that registry to "BGP-LS NLRI and Attribute
TLVs" and to remove the column for "IS-IS TLV/Sub-TLV". The
registration procedures are as below:
+================+================================+
| TLV Code Point | Registration Process |
+================+================================+
| 0-255 | Reserved (not to be allocated) |
+----------------+--------------------------------+
| 256-64999 | Expert Review |
+----------------+--------------------------------+
| 65000-65535 | Private Use |
+----------------+--------------------------------+
Table 17: BGP-LS TLVs Registration Process
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A range is reserved for Private Use [RFC8126]. All other allocations
except for the reserved range within the registry are to be made
using the "Expert Review" policy [RFC8126] that requires
documentation of the proposed use of the allocated value and approval
by the Designated Expert assigned by the IESG.
The registry was pre-populated with the values shown in Table 18 and
the reference for all those allocations should be changed to this
document and the respective section where those TLVs are specified.
7.2. Guidance for Designated Experts
In all cases of review by the designated expert described here, the
designated expert is expected to check the clarity of purpose and use
of the requested code points. The following points apply to the
registries discussed in this document:
1. Application for a code point allocation may be made to the
designated experts at any time and MUST be accompanied by
technical documentation explaining the use of the code point.
Such documentation SHOULD be presented in the form of an
Internet-Draft, but MAY arrive in any form that can be reviewed
and exchanged among reviewers.
2. The designated experts SHOULD only consider requests that arise
from Internet-Drafts that have already been accepted as working
group documents or that are planned for progression as AD-
Sponsored documents in the absence of a suitably chartered
working group.
3. In the case of working group documents, the designated experts
MUST check with the working group chairs that there is a
consensus within the working group to allocate at this time. In
the case of AD-Sponsored documents, the designated experts MUST
check with the AD for approval to allocate at this time.
4. If the document is not adopted by the IDR Working Group (or its
successor), the designated expert MUST notify the IDR mailing
list (or its successor) of the request and MUST provide access to
the document. The designated expert MUST allow two weeks for any
response. Any comments received MUST be considered by the
designated expert as part of the subsequent step.
5. The designated experts MUST then review the assignment requests
on their technical merit. The designated experts MAY raise
issues related to the allocation request with the authors and on
the IDR (or successor) mailing list for further consideration
before the assignments are made.
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6. The designated expert MUST ensure that any request for a code
point does not conflict with work that is active or already
published within the IETF.
7. Once the designated experts have approved, IANA will update the
registry by marking the allocated code points with a reference to
the associated document.
8. In the event that the document is a working group document or is
AD-Sponsored, and that document fails to progress to publication
as an RFC, the working group chairs or AD SHOULD contact IANA to
coordinate about marking the code points as deprecated. A
deprecated code point is not marked as allocated for use and is
not available for allocation in a future document. The WG chairs
may inform IANA that a deprecated code point can be completely
deallocated (i.e., made available for new allocations) at any
time after it has been deprecated if there is a shortage of
unallocated code points in the registry.
8. Manageability Considerations
This section is structured as recommended in [RFC5706].
8.1. Operational Considerations
8.1.1. 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 document carries purely application-level
data that has no immediate impact on the corresponding forwarding
state computed by BGP. As such, any churn in reachability
information has a different impact than regular BGP updates, which
need to change the forwarding state for an entire router.
Distribution of the BGP-LS NLRIs SHOULD be handled by dedicated route
reflectors in most deployments providing a level of isolation and
fault containment between different BGP address families. In the
event of dedicated route reflectors not being available, other
alternate mechanisms like separation of BGP instances or separate BGP
sessions (e.g. using different addresses for peering) for Link-State
information distribution SHOULD be used.
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It is RECOMMENDED that operators deploying BGP-LS enable two or more
BGP-LS Producers in each IGP flooding domain to achieve redundancy in
the origination of link-state information into BGP-LS. It is also
RECOMMENDED that operators ensure BGP peering designs that ensure
redundancy in the BGP update propagation paths (e.g., using at least
a pair of route reflectors) and ensuring that BGP-LS Consumers are
receiving the topology information from at least two BGP-LS Speakers.
In a multi-domain IGP network, the correct provisioning of the BGP-LS
Instance-IDs on the BGP-LS Producers is required for consistent
reporting of the multi-domain link-state topology. Refer to
Section 5.2 for more details.
8.1.2. Installation and Initial Setup
Configuration parameters defined in Section 8.2.3 SHOULD be
initialized to the following default values:
* The Link-State NLRI capability is turned off for all neighbors.
* The maximum rate at which Link-State NLRIs will be advertised/
withdrawn from neighbors is set to 200 updates per second.
8.1.3. 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 8.2.3), so the extension
can be gradually rolled out in the network.
8.1.4. Requirements for Other Protocols and Functional Components
The protocol extension defined in this document does not put new
requirements on other protocols or functional components.
8.1.5. Impact on Network Operation
The frequency of Link-State NLRI updates could interfere with regular
BGP prefix distribution. A network operator should use a dedicated
route reflector infrastructure to distribute Link-State NLRIs as
discussed in Section 8.1.1.
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.
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8.1.6. Verifying Correct Operation
Existing BGP procedures apply. In addition, an implementation SHOULD
allow an operator to:
* List neighbors with whom the speaker is exchanging Link-State
NLRIs.
8.2. Management Considerations
8.2.1. 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.
8.2.2. Fault Management
This section describes the fault management actions, as described in
[RFC7606], that are to be performed for the handling of BGP UPDATE
messages for BGP-LS.
A Link-State NLRI MUST NOT be considered malformed or invalid based
on the inclusion/exclusion of TLVs or contents of the TLV fields
(i.e. semantic errors), as described in Section 5.1 and Section 5.2.
A BGP-LS Speaker MUST perform the following syntactic validation of
the Link-State NLRI to determine if it is malformed.
* The sum of all TLVs lengths found in the BGP MP_REACH_NLRI
attribute corresponds to the BGP MP_REACH_NLRI length.
* The sum of all TLVs lengths found in the BGP MP_UNREACH_NLRI
attribute corresponds to the BGP MP_UNREACH_NLRI length.
* The sum of all TLVs lengths found in a Link-State NLRI corresponds
to the Total NLRI Length field of all its Descriptors.
* The length of the TLVs and, when the TLV is recognized then, the
length of its sub-TLVs in the NLRI is valid.
* The syntactic correctness of the NLRI fields been verified as per
[RFC7606].
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* The rule regarding the ordering of TLVs been followed as described
in Section 5.1.
* For NLRIs carrying either a Local or Remote Node Descriptor TLV,
there is not more than one instance of a sub-TLV present.
When the error that is determined allows for the router to skip the
malformed NLRI(s) and continue the processing of the rest of the BGP
UPDATE message (e.g. when the TLV ordering rule is violated), then it
MUST handle such malformed NLRIs as 'NLRI discard' (i.e., processing
similar to what is described in section 5.4 of [RFC7606]). In other
cases, where the error in the NLRI encoding results in the inability
to process the BGP UPDATE message (e.g. length related encoding
errors), then the router SHOULD handle such malformed NLRIs as 'AFI/
SAFI disable' when other AFI/SAFI besides BGP-LS are being advertised
over the same session. Alternately, the router MUST perform a
'session reset' when the session is only being used for BGP-LS or if
'AFI/SAFI disable' action is not possible.
A BGP-LS Attribute MUST NOT be considered malformed or invalid based
on the inclusion/exclusion of TLVs or contents of the TLV fields
(i.e. semantic errors), as described in Section 5.1 and Section 5.3.
A BGP-LS Speaker MUST perform the following syntactic validation of
the BGP-LS Attribute to determine if it is malformed.
* The sum of all TLVs lengths found in the BGP-LS Attribute
corresponds to the BGP-LS Attribute length.
* The syntactic correctness of the Attributes (including BGP-LS
Attribute) been verified as per [RFC7606].
* The length of each TLV and, when the TLV is recognized then, the
length of its sub-TLVs in the BGP-LS Attribute is valid.
When the error that is determined allows for the router to skip the
malformed BGP-LS Attribute and continue the processing of the rest of
the BGP UPDATE message (e.g. when the BGP-LS Attribute length and the
total Path Attribute Length are correct but some TLV/sub-TLV length
within the BGP-LS Attribute is invalid), then it MUST handle such
malformed BGP-LS Attribute as 'Attribute Discard'. In other cases,
where the error in the BGP-LS Attribute encoding results in the
inability to process the BGP UPDATE message then the handling is the
same as described above for the malformed NLRI.
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Note that the 'Attribute Discard' action results in the loss of all
TLVs in the BGP-LS Attribute and not the removal of a specific
malformed TLV. The removal of specific malformed TLVs may give a
wrong indication to a BGP-LS Consumer of that specific information
being deleted or not available.
When a BGP Speaker receives an UPDATE message with Link-State NLRI(s)
in the MP_REACH_NLRI but without the BGP-LS Attribute, it is most
likely an indication that a BGP Speaker preceding it has performed
the 'Attribute Discard' fault handling. An implementation SHOULD
preserve and propagate the Link-State NLRIs, unless denied by local
policy, in such an UPDATE message so that the BGP-LS Consumers can
detect the loss of link-state information for that object and not
assume its deletion/withdrawal. This also makes it possible for a
network operator to trace back to the BGP-LS Propagator that detected
the fault with the BGP-LS Attribute.
An implementation SHOULD log a message for any errors found during
syntax validation for further analysis.
A BGP-LS Propagator, even when it has a coexisting BGP-LS Consumer on
the same node, should not perform semantic validation of the Link-
State NLRI or the BGP-LS Attribute to determine if it is malformed or
invalid. Some types of semantic validation that are not to be
performed by a BGP-LS Propagator are as follows (and this is not to
be considered as an exhaustive list):
* presence of mandatory TLV
* the length of a fixed-length TLV correct or the length of a
variable length TLV is valid or permissible
* the values of TLV fields are valid or permissible
* the inclusion and use of TLVs/sub-TLVs with specific Link-State
NLRI types is valid
Each TLV may indicate the valid and permissible values and their
semantics that can be used only by a BGP-LS Consumer for its semantic
validation. However, the handling of any errors may be specific to
the particular application and outside the scope of this document.
8.2.3. 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.
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An implementation SHOULD allow the operator to specify the maximum
rate at which Link-State NLRIs will be advertised/withdrawn from
neighbors.
An implementation SHOULD allow the operator to specify the maximum
number of Link-State NLRIs stored in a router's Routing Information
Base (RIB).
An implementation SHOULD allow the operator to create abstracted
topologies that are advertised to neighbors and create different
abstractions for different neighbors.
An implementation MUST allow the operator to configure an 8-octet
BGP-LS Instance-ID. Refer to Section 5.2 for guidance to the
operator for the configuration of BGP-LS Instance-ID.
An implementation SHOULD allow the operator to configure ASN and BGP-
LS identifiers (refer to Section 5.2.1.4).
An implementation SHOULD allow the operator to configure limiting of
maximum size of a BGP-LS UPDATE message to 4096 bytes on a BGP-LS
Producer or to allow larger values when they know that [RFC8654] is
supported on all BGP-LS Speakers.
8.2.4. Accounting Management
Not Applicable.
8.2.5. Performance Management
An implementation SHOULD provide the following statistics:
* Total number of Link-State NLRI updates sent/received
* Number of Link-State NLRI updates sent/received, per neighbor
* Number of errored received Link-State NLRI updates, per neighbor
* Total number of locally originated Link-State NLRIs
These statistics should be recorded as absolute counts since the
system or session start time. An implementation MAY also enhance
this information by recording peak per-second counts in each case.
8.2.6. Security Management
An operator MUST define an import policy to limit inbound updates as
follows:
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* Drop all updates from peers that are only serving BGP-LS
Consumers.
An implementation MUST have the means to limit inbound updates.
9. TLV/Sub-TLV Code Points Summary
This section contains the global table of all TLVs/sub-TLVs defined
in this document.
+================+=========================+===================+
| TLV Code Point | Description | Reference Section |
+================+=========================+===================+
| 256 | Local Node Descriptors | Section 5.2.1.2 |
+----------------+-------------------------+-------------------+
| 257 | Remote Node Descriptors | Section 5.2.1.3 |
+----------------+-------------------------+-------------------+
| 258 | Link Local/Remote | Section 5.2.2 |
| | Identifiers | |
+----------------+-------------------------+-------------------+
| 259 | IPv4 interface address | Section 5.2.2 |
+----------------+-------------------------+-------------------+
| 260 | IPv4 neighbor address | Section 5.2.2 |
+----------------+-------------------------+-------------------+
| 261 | IPv6 interface address | Section 5.2.2 |
+----------------+-------------------------+-------------------+
| 262 | IPv6 neighbor address | Section 5.2.2 |
+----------------+-------------------------+-------------------+
| 263 | Multi-Topology ID | Section 5.2.2.1 |
+----------------+-------------------------+-------------------+
| 264 | OSPF Route Type | Section 5.2.3 |
+----------------+-------------------------+-------------------+
| 265 | IP Reachability | Section 5.2.3 |
| | Information | |
+----------------+-------------------------+-------------------+
| 512 | Autonomous System | Section 5.2.1.4 |
+----------------+-------------------------+-------------------+
| 513 | BGP-LS Identifier | Section 5.2.1.4 |
| | (deprecated) | |
+----------------+-------------------------+-------------------+
| 514 | OSPF Area-ID | Section 5.2.1.4 |
+----------------+-------------------------+-------------------+
| 515 | IGP Router-ID | Section 5.2.1.4 |
+----------------+-------------------------+-------------------+
| 1024 | Node Flag Bits | Section 5.3.1.1 |
+----------------+-------------------------+-------------------+
| 1025 | Opaque Node Attribute | Section 5.3.1.5 |
+----------------+-------------------------+-------------------+
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| 1026 | Node Name | Section 5.3.1.3 |
+----------------+-------------------------+-------------------+
| 1027 | IS-IS Area Identifier | Section 5.3.1.2 |
+----------------+-------------------------+-------------------+
| 1028 | IPv4 Router-ID of Local | Section 5.3.1.4 / |
| | Node | Section 5.3.2.1 |
+----------------+-------------------------+-------------------+
| 1029 | IPv6 Router-ID of Local | Section 5.3.1.4 / |
| | Node | Section 5.3.2.1 |
+----------------+-------------------------+-------------------+
| 1030 | IPv4 Router-ID of | Section 5.3.2.1 |
| | Remote Node | |
+----------------+-------------------------+-------------------+
| 1031 | IPv6 Router-ID of | Section 5.3.2.1 |
| | Remote Node | |
+----------------+-------------------------+-------------------+
| 1088 | Administrative group | Section 5.3.2 |
| | (color) | |
+----------------+-------------------------+-------------------+
| 1089 | Maximum link bandwidth | Section 5.3.2 |
+----------------+-------------------------+-------------------+
| 1090 | Max. reservable link | Section 5.3.2 |
| | bandwidth | |
+----------------+-------------------------+-------------------+
| 1091 | Unreserved bandwidth | Section 5.3.2 |
+----------------+-------------------------+-------------------+
| 1092 | TE Default Metric | Section 5.3.2.3 |
+----------------+-------------------------+-------------------+
| 1093 | Link Protection Type | Section 5.3.2 |
+----------------+-------------------------+-------------------+
| 1094 | MPLS Protocol Mask | Section 5.3.2.2 |
+----------------+-------------------------+-------------------+
| 1095 | IGP Metric | Section 5.3.2.4 |
+----------------+-------------------------+-------------------+
| 1096 | Shared Risk Link Group | Section 5.3.2.5 |
+----------------+-------------------------+-------------------+
| 1097 | Opaque Link Attribute | Section 5.3.2.6 |
+----------------+-------------------------+-------------------+
| 1098 | Link Name | Section 5.3.2.7 |
+----------------+-------------------------+-------------------+
| 1152 | IGP Flags | Section 5.3.3.1 |
+----------------+-------------------------+-------------------+
| 1153 | IGP Route Tag | Section 5.3.3.2 |
+----------------+-------------------------+-------------------+
| 1154 | IGP Extended Route Tag | Section 5.3.3.3 |
+----------------+-------------------------+-------------------+
| 1155 | Prefix Metric | Section 5.3.3.4 |
+----------------+-------------------------+-------------------+
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| 1156 | OSPF Forwarding Address | Section 5.3.3.5 |
+----------------+-------------------------+-------------------+
| 1157 | Opaque Prefix Attribute | Section 5.3.3.6 |
+----------------+-------------------------+-------------------+
Table 18: Summary Table of TLV/Sub-TLV Code Points
10. Security Considerations
Procedures and protocol extensions defined in this document do not
affect the BGP security model. See the Security Considerations
section of [RFC4271] for a discussion of BGP security. Also, refer
to [RFC4272] and [RFC6952] for analysis of security issues for BGP.
The operator should ensure that a BGP-LS speaker does not accept
UPDATE messages from a peer that only provides information to a BGP-
LS Consumer by using the policy configuration options discussed in
Section 8.2.3 and Section 8.2.6. Generally, an operator is aware of
the BGP-LS speaker's role and link-state peerings. Therefore, the
operator can protect the BGP-LS speaker from peers sending updates
that may represent erroneous information, feedback loops, or false
input.
An error or tampering of the link-state information that is
originated into BGP-LS and propagated through the network for use by
BGP-LS Consumers applications can result in the malfunction of those
applications. Some examples of such risks are the origination of
incorrect information that is not present or consistent with the IGP
LSDB at the BGP-LS Producer, incorrect ordering of TLVs in the NLRI
or inconsistent origination from multiple BGP-LS Producers and
updates to either the NLRI or BGP-LS Attribute during propagation
(including discarding due to errors). These are not new risks from a
BGP protocol perspective, however, in the case of BGP-LS impact
reflects on the consumer applications instead of BGP routing
functionalities.
Additionally, it may be considered that the export of link-state and
TE information as described in this document constitutes a risk to
confidentiality of mission-critical or commercially sensitive
information about the network. BGP peerings are not automatic and
require configuration; thus, it is the responsibility of the network
operator to ensure that only trusted BGP Speakers are configured to
receive such information. Similar security considerations also arise
on the interface between BGP Speaker and BGP-LS Consumers, but their
discussion is outside the scope of this document.
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11. Contributors
The following persons contributed significant text to RFC7752 and
this document. They should be considered co-authors.
Hannes Gredler
Rtbrick
Email: hannes@rtbrick.com
Jan Medved
Cisco Systems Inc.
USA
Email: jmedved@cisco.com
Stefano Previdi
Huawei Technologies
Italy
Email: stefano@previdi.net
Adrian Farrel
Old Dog Consulting
Email: adrian@olddog.co.uk
Saikat Ray
Individual
USA
Email: raysaikat@gmail.com
12. Acknowledgements
This document update to the BGP-LS specification [RFC7752] is a
result of feedback and inputs from the discussions in the IDR working
group. It also incorporates certain details and clarifications based
on implementation and deployment experience with BGP-LS.
Cengiz Alaettinoglu and Parag Amritkar brought forward the need to
clarify the advertisement of a LAN subnet for OSPF.
We would like to thank Balaji Rajagopalan, Srihari Sangli, Shraddha
Hegde, Andrew Stone, Jeff Tantsura, Acee Lindem, Les Ginsberg, Jie
Dong, Aijun Wang, Nandan Saha, Joel Halpern, and Gyan Mishra for
their review and feedback on this document. Thanks to Tom Petch for
his review and comments on the IANA Considerations section. Would
also like to thank Jeffrey Haas for his detailed shepherd review and
inputs for improving the document.
The detailed AD review by Alvaro Retana and his suggestions have
helped improve this document significantly.
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We would like to thank Robert Varga for his significant contribution
to RFC7752.
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 on RFC7752.
13. References
13.1. Normative References
[ENTNUM] IANA, "Private Enterprise Numbers",
<https://www.iana.org/assignments/enterprise-numbers/>.
[ISO10589] International Organization for Standardization,
"Intermediate System to Intermediate System intra-domain
routeing information exchange protocol for use in
conjunction with the protocol for providing the
connectionless-mode network service (ISO 8473)", ISO/
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,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328,
DOI 10.17487/RFC2328, April 1998,
<https://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,
<https://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,
<https://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,
<https://www.rfc-editor.org/info/rfc4202>.
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[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,
<https://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,
<https://www.rfc-editor.org/info/rfc4271>.
[RFC4577] Rosen, E., Psenak, P., and P. Pillay-Esnault, "OSPF as the
Provider/Customer Edge Protocol for BGP/MPLS IP Virtual
Private Networks (VPNs)", RFC 4577, DOI 10.17487/RFC4577,
June 2006, <https://www.rfc-editor.org/info/rfc4577>.
[RFC4760] Bates, T., Chandra, R., Katz, D., and Y. Rekhter,
"Multiprotocol Extensions for BGP-4", RFC 4760,
DOI 10.17487/RFC4760, January 2007,
<https://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,
<https://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, <https://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,
<https://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,
<https://www.rfc-editor.org/info/rfc5130>.
[RFC5301] McPherson, D. and N. Shen, "Dynamic Hostname Exchange
Mechanism for IS-IS", RFC 5301, DOI 10.17487/RFC5301,
October 2008, <https://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, <https://www.rfc-editor.org/info/rfc5305>.
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[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,
<https://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,
<https://www.rfc-editor.org/info/rfc5340>.
[RFC5642] Venkata, S., Harwani, S., Pignataro, C., and D. McPherson,
"Dynamic Hostname Exchange Mechanism for OSPF", RFC 5642,
DOI 10.17487/RFC5642, August 2009,
<https://www.rfc-editor.org/info/rfc5642>.
[RFC5890] Klensin, J., "Internationalized Domain Names for
Applications (IDNA): Definitions and Document Framework",
RFC 5890, DOI 10.17487/RFC5890, August 2010,
<https://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, <https://www.rfc-editor.org/info/rfc6119>.
[RFC6565] Pillay-Esnault, P., Moyer, P., Doyle, J., Ertekin, E., and
M. Lundberg, "OSPFv3 as a Provider Edge to Customer Edge
(PE-CE) Routing Protocol", RFC 6565, DOI 10.17487/RFC6565,
June 2012, <https://www.rfc-editor.org/info/rfc6565>.
[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,
<https://www.rfc-editor.org/info/rfc7606>.
[RFC7684] Psenak, P., Gredler, H., Shakir, R., Henderickx, W.,
Tantsura, J., and A. Lindem, "OSPFv2 Prefix/Link Attribute
Advertisement", RFC 7684, DOI 10.17487/RFC7684, November
2015, <https://www.rfc-editor.org/info/rfc7684>.
[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, <https://www.rfc-editor.org/info/rfc7770>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
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[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8362] Lindem, A., Roy, A., Goethals, D., Reddy Vallem, V., and
F. Baker, "OSPFv3 Link State Advertisement (LSA)
Extensibility", RFC 8362, DOI 10.17487/RFC8362, April
2018, <https://www.rfc-editor.org/info/rfc8362>.
[RFC8654] Bush, R., Patel, K., and D. Ward, "Extended Message
Support for BGP", RFC 8654, DOI 10.17487/RFC8654, October
2019, <https://www.rfc-editor.org/info/rfc8654>.
13.2. Informative References
[RFC1918] Rekhter, Y., Moskowitz, B., Karrenberg, D., de Groot, G.
J., and E. Lear, "Address Allocation for Private
Internets", BCP 5, RFC 1918, DOI 10.17487/RFC1918,
February 1996, <https://www.rfc-editor.org/info/rfc1918>.
[RFC4272] Murphy, S., "BGP Security Vulnerabilities Analysis",
RFC 4272, DOI 10.17487/RFC4272, January 2006,
<https://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, <https://www.rfc-editor.org/info/rfc4364>.
[RFC4655] Farrel, A., Vasseur, J.-P., and J. Ash, "A Path
Computation Element (PCE)-Based Architecture", RFC 4655,
DOI 10.17487/RFC4655, August 2006,
<https://www.rfc-editor.org/info/rfc4655>.
[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,
<https://www.rfc-editor.org/info/rfc5152>.
[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, <https://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,
<https://www.rfc-editor.org/info/rfc5693>.
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[RFC5706] Harrington, D., "Guidelines for Considering Operations and
Management of New Protocols and Protocol Extensions",
RFC 5706, DOI 10.17487/RFC5706, November 2009,
<https://www.rfc-editor.org/info/rfc5706>.
[RFC6549] Lindem, A., Roy, A., and S. Mirtorabi, "OSPFv2 Multi-
Instance Extensions", RFC 6549, DOI 10.17487/RFC6549,
March 2012, <https://www.rfc-editor.org/info/rfc6549>.
[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,
<https://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,
<https://www.rfc-editor.org/info/rfc7285>.
[RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and
S. Ray, "North-Bound Distribution of Link-State and
Traffic Engineering (TE) Information Using BGP", RFC 7752,
DOI 10.17487/RFC7752, March 2016,
<https://www.rfc-editor.org/info/rfc7752>.
[RFC7911] Walton, D., Retana, A., Chen, E., and J. Scudder,
"Advertisement of Multiple Paths in BGP", RFC 7911,
DOI 10.17487/RFC7911, July 2016,
<https://www.rfc-editor.org/info/rfc7911>.
[RFC8202] Ginsberg, L., Previdi, S., and W. Henderickx, "IS-IS
Multi-Instance", RFC 8202, DOI 10.17487/RFC8202, June
2017, <https://www.rfc-editor.org/info/rfc8202>.
[RFC9029] Farrel, A., "Updates to the Allocation Policy for the
Border Gateway Protocol - Link State (BGP-LS) Parameters
Registries", RFC 9029, DOI 10.17487/RFC9029, June 2021,
<https://www.rfc-editor.org/info/rfc9029>.
[RFC9346] Chen, M., Ginsberg, L., Previdi, S., and D. Xiaodong, "IS-
IS Extensions in Support of Inter-Autonomous System (AS)
MPLS and GMPLS Traffic Engineering", RFC 9346,
DOI 10.17487/RFC9346, February 2023,
<https://www.rfc-editor.org/info/rfc9346>.
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Appendix A. Changes from RFC 7752
This section lists the high-level changes from RFC 7752 and provides
reference to the document sections wherein those have been
introduced.
1. Updated the Figure 1 in Section 1 and added Section 3 to
illustrate the different roles of a BGP implementation in
conveying link-state information.
2. Clarified aspects related to advertisement of link-state
information from IGPs into BGP-LS in Section 4.
3. In Section 5.1, clarification about the TLV handling aspects
that apply to both the NLRI and BGP-LS Attribute parts and those
that are applicable only for the NLRI portion. An
implementation may have missed the part about the handling of
unknown TLV and so, based on [RFC7606] guidelines, might discard
the unknown NLRI types. This aspect is now unambiguously
clarified in Section 5.2. Also, the TLVs in the BGP-LS
Attribute that are not ordered are not to be considered
malformed.
4. Clarification of mandatory and optional TLVs in both NLRI and
BGP-LS Attribute portions all through the document.
5. Handling of large size of BGP-LS Attribute with growth in BGP-LS
information is explained in Section 5.3 along with mitigation of
errors arising out of it.
6. Clarified that the document describes the NLRI descriptor TLVs
for the protocols and NLRI types specified in this document and
future BGP-LS extensions must describe the same for other
protocols and NLRI types that they introduce.
7. Clarification on the use of the Identifier field in the Link-
State NLRI in Section 5.2 is provided. It was defined
ambiguously to refer to only multi-instance IGP on a single link
while it can also be used for multiple IGP protocol instances on
a router. The IANA registry is accordingly being removed.
8. The BGP-LS Identifier TLV in the Node Descriptors has been
deprecated. Its use was not well specified by [RFC7752] and
there has been some amount of confusion between implementators
on its usage for identification of IGP domains as against the
use of the Identifier field carrying the BGP-LS Instance-ID when
running multiple instances of IGP routing protocols. The
original purpose of the BGP-LS Identifier was that, in
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conjunction with Autonomous System Number (ASN), it would
uniquely identify the BGP-LS domain and that the combination of
ASN and BGP-LS ID would be globally unique. However, the BGP-LS
Instance-ID carried in the Identifier field in the fixed part of
the NLRI also provides a similar functionality. Hence, the
inclusion of the BGP-LS Identifier TLV is not necessary. If
advertised, all BGP-LS speakers within an IGP flooding-set (set
of IGP nodes within which an LSP/LSA is flooded) had to use the
same (ASN, BGP-LS ID) tuple and if an IGP domain consists of
multiple flooding-sets, then all BGP-LS speakers within the IGP
domain had to use the same (ASN, BGP-LS ID) tuple.
9. Clarification that the Area-ID TLV is mandatory in the Node
Descriptor for the origination of information from OSPF except
for when sourcing information from AS-scope LSAs where this TLV
is not applicable. Also clarified on the IS-IS area and area
addresses.
10. Moved MT-ID TLV from the Node Descriptor section to under the
Link Descriptor section since it is not a Node Descriptor sub-
TLV. Fixed the ambiguity in the encoding of OSPF MT-ID in this
TLV. Updated the IS-IS specification reference section and
describe the differences in the applicability of the R flags
when MT-ID TLV is used as link descriptor TLV and Prefix
Attribute TLV. MT-ID TLV use is now elevated to SHOULD when it
is enabled in the underlying IGP.
11. Clarified that IPv6 Link-Local Addresses are not advertised in
the Link Descriptor TLVs and the local/remote identifiers are to
be used instead for links with IPv6 link-local addresses only.
12. Update the usage of OSPF Route Type TLV to mandate its use for
OSPF prefixes in Section 5.2.3.1 since this is required for
segregation of intra-area prefixes that are used to reach a node
(e.g. a loopback) from other types of inter-area and external
prefixes.
13. Clarification of the specific OSPFv2 and OSPFv3 protocol TLV
space to be used in the node, link, and prefix opaque attribute
TLVs.
14. Clarification on the length of the Node Flag Bits and IGP Flags
TLVs to be one octet.
15. Updated the Node Name TLV in Section 5.3.1.3 with the OSPF
specification.
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16. Clarification on the size of the IS-IS Narrow Metric
advertisement via the IGP Metric TLV and the handling of the
unused bits.
17. Clarified the advertisement of the prefix corresponding to the
LAN segment in an OSPF network in Section 5.11.
18. Clarified the advertisement and support for OSPF specific
concepts like Virtual links, Sham links, and Type 4 LSAs in
Section 5.7 and Section 5.8.
19. Introduced Private Use TLV code point space and specified their
encoding in Section 5.4.
20. Introduced Section 5.9 where issues related to the consistency
of reporting IGP link-state along with their solutions are
covered.
21. Added recommendation for isolation of BGP-LS sessions from other
BGP route exchange to avoid errors and faults in BGP-LS
affecting the normal BGP routing.
22. Updated the Fault Management section with detailed rules based
on the role of the BGP Speaker in the BGP-LS information
propagation flow.
23. Change to the management of BGP-LS IANA registries from
"Specification Required" to "Expert Review" along with updated
guidelines for Designated Experts. More specifically the
inclusion of changes introduced via [RFC9029] that is obsoleted
by this document.
24. Added BGP-LS IANA registries with "Expert Review" policy for the
flag fields of various TLVs that was missed out. Renamed the
BGP-LS TLV registry and removed the "IS-IS TLV/Sub-TLV" column
from it.
Author's Address
Ketan Talaulikar (editor)
Cisco Systems
India
Email: ketant.ietf@gmail.com
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