Inter-Domain Routing K. Talaulikar, Ed.
Internet-Draft Cisco Systems
Intended status: Standards Track H. Gredler
Expires: January 9, 2020 Rtbrick
J. Medved
Cisco Systems, Inc.
S. Previdi
Individual Contributor
A. Farrel
Old Dog Consulting
S. Ray
Individual Contributor
July 8, 2019
Distribution of Link-State and Traffic Engineering Information Using BGP
draft-ketant-idr-rfc7752bis-01
Abstract
In a number of environments, a component external to a network is
called upon to perform computations based on the network topology and
current state of the connections within the network, including
Traffic Engineering (TE) information. This is information typically
distributed by IGP routing protocols within the network.
This document describes a mechanism by which link-state and TE
information can be collected from networks and shared with external
components using the BGP routing protocol. This is achieved using a
new BGP Network Layer Reachability Information (NLRI) encoding
format. The mechanism is applicable to physical and virtual IGP
links. The mechanism described is subject to policy control.
Applications of this technique include Application-Layer Traffic
Optimization (ALTO) servers and Path Computation Elements (PCEs).
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.
Talaulikar, et al. Expires January 9, 2020 [Page 1]
Internet-Draft Link-State Info Distribution Using BGP July 2019
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
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
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."
This Internet-Draft will expire on January 9, 2020.
Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Motivation and Applicability . . . . . . . . . . . . . . . . 5
2.1. MPLS-TE with PCE . . . . . . . . . . . . . . . . . . . . 5
2.2. ALTO Server Network API . . . . . . . . . . . . . . . . . 7
3. BGP Speaker Roles for BGP-LS . . . . . . . . . . . . . . . . 8
4. Carrying Link-State Information in BGP . . . . . . . . . . . 9
4.1. TLV Format . . . . . . . . . . . . . . . . . . . . . . . 9
4.2. The Link-State NLRI . . . . . . . . . . . . . . . . . . . 10
4.2.1. Node Descriptors . . . . . . . . . . . . . . . . . . 15
4.2.2. Link Descriptors . . . . . . . . . . . . . . . . . . 19
4.2.3. Prefix Descriptors . . . . . . . . . . . . . . . . . 21
4.3. The BGP-LS Attribute . . . . . . . . . . . . . . . . . . 23
4.3.1. Node Attribute TLVs . . . . . . . . . . . . . . . . . 24
4.3.2. Link Attribute TLVs . . . . . . . . . . . . . . . . . 27
Talaulikar, et al. Expires January 9, 2020 [Page 2]
Internet-Draft Link-State Info Distribution Using BGP July 2019
4.3.3. Prefix Attribute TLVs . . . . . . . . . . . . . . . . 32
4.4. Private Use . . . . . . . . . . . . . . . . . . . . . . . 35
4.5. BGP Next-Hop Information . . . . . . . . . . . . . . . . 36
4.6. Inter-AS Links . . . . . . . . . . . . . . . . . . . . . 36
4.7. Handling of Unreachable IGP Nodes . . . . . . . . . . . . 36
4.8. Router-ID Anchoring Example: ISO Pseudonode . . . . . . . 38
4.9. Router-ID Anchoring Example: OSPF Pseudonode . . . . . . 39
4.10. Router-ID Anchoring Example: OSPFv2 to IS-IS Migration . 40
5. Link to Path Aggregation . . . . . . . . . . . . . . . . . . 40
5.1. Example: No Link Aggregation . . . . . . . . . . . . . . 41
5.2. Example: ASBR to ASBR Path Aggregation . . . . . . . . . 41
5.3. Example: Multi-AS Path Aggregation . . . . . . . . . . . 42
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 42
6.1. Guidance for Designated Experts . . . . . . . . . . . . . 43
7. Manageability Considerations . . . . . . . . . . . . . . . . 44
7.1. Operational Considerations . . . . . . . . . . . . . . . 44
7.1.1. Operations . . . . . . . . . . . . . . . . . . . . . 44
7.1.2. Installation and Initial Setup . . . . . . . . . . . 44
7.1.3. Migration Path . . . . . . . . . . . . . . . . . . . 44
7.1.4. Requirements on Other Protocols and Functional
Components . . . . . . . . . . . . . . . . . . . . . 44
7.1.5. Impact on Network Operation . . . . . . . . . . . . . 45
7.1.6. Verifying Correct Operation . . . . . . . . . . . . . 45
7.2. Management Considerations . . . . . . . . . . . . . . . . 45
7.2.1. Management Information . . . . . . . . . . . . . . . 45
7.2.2. Fault Management . . . . . . . . . . . . . . . . . . 45
7.2.3. Configuration Management . . . . . . . . . . . . . . 48
7.2.4. Accounting Management . . . . . . . . . . . . . . . . 48
7.2.5. Performance Management . . . . . . . . . . . . . . . 48
7.2.6. Security Management . . . . . . . . . . . . . . . . . 49
8. TLV/Sub-TLV Code Points Summary . . . . . . . . . . . . . . . 49
9. Security Considerations . . . . . . . . . . . . . . . . . . . 50
10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 51
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 51
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 52
12.1. Normative References . . . . . . . . . . . . . . . . . . 52
12.2. Informative References . . . . . . . . . . . . . . . . . 54
Appendix A. Changes from RFC 7752 . . . . . . . . . . . . . . . 56
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 57
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) in order to make better decisions.
Talaulikar, et al. Expires January 9, 2020 [Page 3]
Internet-Draft Link-State Info Distribution Using BGP July 2019
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 require CPU-
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 in order 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 new BGP Network Layer Reachability Information
(NLRI) encoding format. The mechanism is applicable to physical and
virtual links. The mechanism described is subject to policy control.
A router maintains one or more databases for storing link-state
information about nodes and links in any given area. Link attributes
stored in these databases include: local/remote IP addresses, local/
remote interface identifiers, link metric and TE metric, link
bandwidth, reservable bandwidth, per Class-of-Service (CoS) class
reservation state, preemption, and Shared Risk Link Groups (SRLGs).
The router's BGP 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 the Figure 1 below.
Talaulikar, et al. Expires January 9, 2020 [Page 4]
Internet-Draft Link-State Info Distribution Using BGP July 2019
+-----------+
| 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 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 of information flow from the network to the consumers.
Mechanisms through which topologies can be aggregated or virtualized
are outside the scope of this document
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).
Talaulikar, et al. Expires January 9, 2020 [Page 5]
Internet-Draft Link-State Info Distribution Using BGP July 2019
o Within a single area, the PCE offers enhanced computational power
that may not be available on individual routers, sophisticated
policy control and algorithms, and coordination of computation
across the whole area.
o If a router wants to compute a MPLS-TE path across IGP areas, then
its own TED lacks visibility of the complete topology. That means
that the router cannot determine the end-to-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 sub-optimal paths, makes alternate/back-
up path computation hard, and might result in no TE path being found
when one really does exist.
The PCE presents a computation server that may have visibility into
more than one IGP area or AS, or may cooperate with other PCEs to
perform distributed path computation. The PCE obviously needs access
to the TED for the area(s) it serves, but [RFC4655] does not describe
how this is achieved. Many implementations make the PCE a passive
participant in the IGP so that it can learn the latest state of the
network, but this may be sub-optimal when the network is subject to a
high degree 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.
Talaulikar, et al. Expires January 9, 2020 [Page 6]
Internet-Draft Link-State Info Distribution Using BGP July 2019
+----------+ +---------+
| ----- | | BGP |
| | TED |<-+-------------------------->| Speaker |
| ----- | TED synchronization | |
| | | mechanism: +---------+
| | | BGP with Link-State NLRI
| v |
| ----- |
| | PCE | |
| ----- |
+----------+
^
| Request/
| Response
v
Service +----------+ Signaling +----------+
Request | Head-End | Protocol | Adjacent |
-------->| Node |<------------>| Node |
+----------+ +----------+
Figure 2: External 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 allocation of prefixes to Partition Identifiers
(PIDs), and a Cost Map that specifies the cost between PIDs listed in
the Network Map. For more details, see [RFC7285].
ALTO abstract network topologies can be auto-generated from the
physical topology of the underlying network. The generation would
typically be based on policies and rules set by the operator. Both
prefix and TE data are required: prefix data is required to generate
ALTO Network Maps, and TE (topology) data is required to generate
ALTO Cost Maps. Prefix data is carried and originated in BGP, and TE
data is originated and carried in an IGP. The mechanism defined in
this document provides a single interface through which an ALTO
server can retrieve all the necessary prefix and network topology
data from the underlying network. Note that an ALTO server can use
Talaulikar, et al. Expires January 9, 2020 [Page 7]
Internet-Draft Link-State Info Distribution Using BGP July 2019
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 +--------+ BGP with +---------+
+--------+ | Protocol | ALTO | Link-State NLRI | 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.
o BGP-LS Producer: 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 area, then likely
they are originating the same link-state information into BGP-LS.
R1 may also source information from sources other than IGP, e.g.
its local node information. The term BGP-LS Producer refers to
the BGP Speaker that is originating link-state information into
BGP.
o BGP-LS Consumer: 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. The term BGP-
LS Consumer refers to the consumer application/process and not the
BGP Speaker. This document only covers the BGP implementation.
The consumer application and the design of interface between BGP
and consumer application may be implementation specific and
outside the scope of this document.
Talaulikar, et al. Expires January 9, 2020 [Page 8]
Internet-Draft Link-State Info Distribution Using BGP July 2019
o BGP-LS Propagator: 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 doing the propagation of BGP-LS
updates and performing BGP best path calculations. 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 best path calculations. The term BGP-LS Propagator
refers to the BGP Speaker that is performing BGP protocol
processing on the link-state information.
The above roles are not mutually exclusive. The same BGP Speaker may
be the producer for some link-state information and propagator for
some other link-state information while also providing this
information to a consumer application. Nothing precludes a BGP
implementation performing some of the validation and processing on
behalf of the BGP-LS Consumer as long as it does not impact the
semantics of its role as BGP-LS Propagator as described in this
document.
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.
4. Carrying Link-State Information in BGP
This specification contains two parts: definition of a new BGP NLRI
that describes links, nodes, and prefixes comprising IGP link-state
information and definition of a new BGP path attribute (BGP-LS
Attribute) that carries link, node, and prefix properties and
attributes, 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 at a BGP-LS Producer
that originate link-state information into BGP-LS.
4.1. TLV Format
Information in the new 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.
Talaulikar, et al. Expires January 9, 2020 [Page 9]
Internet-Draft Link-State Info Distribution Using BGP July 2019
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 unrecognized or unexpected TLVs
MUST NOT result in the NLRI or the BGP-LS Attribute being considered
as malformed.
In order 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 in ascending order based on the value
field. Comparison of the value fields is performed by treating the
entire field as an opaque hexadecimal string. Standard string
comparison rules apply. NLRIs having TLVs which do not follow the
above ordering rules MUST be considered as malformed by a BGP-LS
Propagator. This ensures that multiple copies of the same NLRI from
multiple BGP-LS Producers and the ambiguity arising there from is
prevented.
All TLVs within the NLRI that are not specified as mandatory are
considered optional. All TLVs within the BGP-LS Attribute are
considered optional unless specified otherwise.
The TLVs within the BGP-LS Attribute need not be ordered in any
specific order.
4.2. 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 describes either a node, a link, and 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.
Talaulikar, et al. Expires January 9, 2020 [Page 10]
Internet-Draft Link-State Info Distribution Using BGP July 2019
In order 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 (multi-protocol 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 Link-State
but does not support a particular Link-State NLRI type. In order to
allow 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 [RFC7606] for Link-
State address-family. An implementation MUST handle unrecognized
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.
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
Talaulikar, et al. Expires January 9, 2020 [Page 11]
Internet-Draft Link-State Info Distribution Using BGP July 2019
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| NLRI Type | Total NLRI Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Route Distinguisher +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// Link-State NLRI (variable) //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: Link-State VPN AFI 16388 / 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 |
| 65000-65535 | Private Use |
+-------------+---------------------------+
Table 1: NLRI Types
Route Distinguishers are defined and discussed in [RFC4364].
The Node NLRI (NLRI Type = 1) is shown in the following figure.
Talaulikar, et al. Expires January 9, 2020 [Page 12]
Internet-Draft Link-State Info Distribution Using BGP July 2019
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+
| Protocol-ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identifier |
| (64 bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Local Node Descriptors (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7: The Node 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 |
| (64 bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Local Node Descriptors (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Remote Node Descriptors (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Link Descriptors (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.
Talaulikar, et al. Expires January 9, 2020 [Page 13]
Internet-Draft Link-State Info Distribution Using BGP July 2019
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+
| Protocol-ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identifier |
| (64 bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Local Node Descriptors (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Prefix Descriptors (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 |
| 200-255 | Private Use |
+-------------+----------------------------------+
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 5,
the Protocol-ID 'Static configuration' SHOULD be used.
A router MAY run multiple protocol instances of OSPF or ISIS where by
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
independent IGP routing domains. The 64-bit Identifier field carries
a BGP-LS Instance Identifier (Instance-ID) 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 MUST have the same Identifier field value.
Talaulikar, et al. Expires January 9, 2020 [Page 14]
Internet-Draft Link-State Info Distribution Using BGP July 2019
NLRIs with different Identifier field values MUST be considered to be
from different IGP routing instances. The Identifier field value 0
is RECOMMENDED to be used when there is only a single protocol
instance in the network where BGP-LS is operational.
An implementation which supports multiple IGP instances MUST support
the configuration of unique BGP-LS Instance-IDs at the routing
protocol instance level. The network operator MUST assign consistent
BGP-LS Instance-ID values on all BGP-LS Producers within a given IGP
domain. Unique BGP-LS Instance-ID values MUST be assigned to routing
protocol instances operating in different IGP domains. This allows
the BGP-LS Consumer to build an accurate segregated multi-domain
topology based on the Identifier field even when the topology is
advertised via BGP-LS by multiple BGP-LS Producers in the network.
When the above described semantics and recommendations are not
followed, a BGP-LS Consumer may see duplicate link-state objects for
the same node, link or prefix when there are multiple BGP-LS
Producers deployed. This may also result in the BGP-LS Consumers
getting an inaccurate network-wide topology.
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.
Each Node Descriptor and Link Descriptor consists of one or more
TLVs, as described in the following sections.
4.2.1. 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]. These auxiliary Router-IDs MUST be
included in the node attribute described in Section 4.3.1 and MAY be
included in link attribute described in Section 4.3.2. The
advertisement of the TE Router-IDs 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
Descriptor 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
Talaulikar, et al. Expires January 9, 2020 [Page 15]
Internet-Draft Link-State Info Distribution Using BGP July 2019
in RFC 1918 [RFC1918]. BGP-LS uses the Autonomous System (AS) Number
to disambiguate the Router-IDs, as described in Section 4.2.1.1.
4.2.1.1. 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 Area-ID, Router-ID,
Protocol-ID, Multi-Topology ID, and 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.
The mapping of the Instance-ID to the Identifier field as described
earlier along with a set of sub-TLVs described in Section 4.2.1.4,
allows specification of a flexible key for any given node/link
information such that global uniqueness of the NLRI is ensured.
4.2.1.2. 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 4.2.1.4.
Talaulikar, et al. Expires January 9, 2020 [Page 16]
Internet-Draft Link-State Info Distribution Using BGP July 2019
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
4.2.1.3. 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 4.2.1.4.
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
4.2.1.4. Node Descriptor Sub-TLVs
The Node Descriptor Sub-TLV type code points and lengths are listed
in the following table:
+--------------------+--------------------------------+----------+
| 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
Talaulikar, et al. Expires January 9, 2020 [Page 17]
Internet-Draft Link-State Info Distribution Using BGP July 2019
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 value different.
BGP-LS Identifier: Opaque value (32-bit ID). This is an optional
TLV. In conjunction with Autonomous System Number (ASN), uniquely
identifies the BGP-LS domain. The combination of ASN and BGP-LS
ID MUST be globally unique. All BGP-LS speakers within an IGP
flooding-set (set of IGP nodes within which an LSP/LSA is flooded)
MUST use the same ASN, BGP-LS ID tuple. If an IGP domain consists
of multiple flooding-sets, then all BGP-LS speakers within the IGP
domain SHOULD use the same ASN, BGP-LS ID tuple.
Area-ID: Used to identify the 32-bit area to which the NLRI belongs.
This is a mandatory TLV when originating information from OSPF.
The Area Identifier allows different NLRIs of the same router to
be discriminated.
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
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.
There can 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 in order to compare NLRIs, even when an implementation
encounters an unknown sub-TLV. Using stable sorting, an
implementation can do binary comparison of NLRIs and hence allow
incremental deployment of new key sub-TLVs.
Talaulikar, et al. Expires January 9, 2020 [Page 18]
Internet-Draft Link-State Info Distribution Using BGP July 2019
The BGP-LS Identifier was introduced by [RFC7752] and it's use is
being deprecated by this document. Implementations MUST continue to
support this sub-TLV for backward compatibility. The default value
of 0 is RECOMMENDED to be use when a BGP-LS Producer includes this
sub-TLV when originating information into BGP-LS. Implementations
MAY provide an option to configure this value for backward
compatibility reasons. The use of the Instance-ID in the Identifier
field is the RECOMMENDED way of segregation of different IGP domains
in BGP-LS.
4.2.2. Link Descriptors
The Link Descriptor field is a set of Type/Length/Value (TLV)
triplets. The format of each TLV is shown in Section 4.1. 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. In order to fully describe a
single logical link, two originating routers advertise a half-link
each, i.e., two Link NLRIs are advertised for a given point-to-point
link.
A BGP-LS Consumer should not consider a link between two nodes as
being available unless it has received the two Link NLRIs
corresponding to the half-link representation of that link from both
the nodes. This check is similar to the 'two way connectivity check'
that is performed by link-state IGPs and is also required to be done
by BGP-LS Consumers of link-state topology.
A BGP-LS Producer MAY supress the advertisement of a Link NLRI,
corresponding to a half link, from a link-state IGP unless it 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 may be leveraged before passing information for any
half-link that is reported from these IGPs in to 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' may 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.
Talaulikar, et al. Expires January 9, 2020 [Page 19]
Internet-Draft Link-State Info Distribution Using BGP July 2019
The following TLVs are defined as Link Descriptors in the Link NLRI:
+-----------+---------------------+--------------+------------------+
| TLV Code | Description | IS-IS TLV | Reference |
| Point | | /Sub-TLV | (RFC/Section) |
+-----------+---------------------+--------------+------------------+
| 258 | Link Local/Remote | 22/4 | [RFC5307]/1.1 |
| | Identifiers | | |
| 259 | IPv4 interface | 22/6 | [RFC5305]/3.2 |
| | address | | |
| 260 | IPv4 neighbor | 22/8 | [RFC5305]/3.3 |
| | address | | |
| 261 | IPv6 interface | 22/12 | [RFC6119]/4.2 |
| | address | | |
| 262 | IPv6 neighbor | 22/13 | [RFC6119]/4.3 |
| | address | | |
| 263 | Multi-Topology | --- | Section 4.2.2.1 |
| | Identifier | | |
+-----------+---------------------+--------------+------------------+
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 IP 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.
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 Multi-Topology Identifier TLV MUST be included in Link
Descriptor if the underlying IGP link object is associated with a
non-default topology.
4.2.2.1. 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.
Semantics of the IS-IS MT-ID are defined in Section 7.2 of RFC 5120
[RFC5120]. Semantics of the OSPF MT-ID are defined in Section 3.7 of
RFC 4915 [RFC4915]. Bits R are reserved and SHOULD be set to 0 when
Talaulikar, et al. Expires January 9, 2020 [Page 20]
Internet-Draft Link-State Info Distribution Using BGP July 2019
originated and ignored on receipt. If the value in the MT-ID TLV is
derived from OSPF, then the upper 5 bits of the MT-ID field MUST be
set to 0.
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 present in a Link Descriptor, a Prefix
Descriptor, or the BGP-LS attribute of a Node NLRI. In a Link or
Prefix Descriptor, only a single MT-ID TLV containing the MT-ID of
the topology where the link or the prefix is reachable is allowed.
In case one wants to advertise multiple topologies for a given Link
Descriptor or Prefix Descriptor, multiple NLRIs MUST be generated
where each NLRI contains a single unique MT-ID. 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.
4.2.3. 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:
Talaulikar, et al. Expires January 9, 2020 [Page 21]
Internet-Draft Link-State Info Distribution Using BGP July 2019
+-------------+---------------------+----------+--------------------+
| TLV Code | Description | Length | Reference |
| Point | | | (RFC/Section) |
+-------------+---------------------+----------+--------------------+
| 263 | Multi-Topology | variable | Section 4.2.2.1 |
| | Identifier | | |
| 264 | OSPF Route Type | 1 | Section 4.2.3.1 |
| 265 | IP Reachability | variable | Section 4.2.3.2 |
| | Information | | |
+-------------+---------------------+----------+--------------------+
Table 5: Prefix Descriptor TLVs
The Multi-Topology Identifier TLV MUST be included in Prefix
Descriptor if the underlying IGP prefix object is associated with a
non-default topology.
4.2.3.1. OSPF Route Type
The OSPF Route Type TLV is a mandatory 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 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 values are defined in the OSPF protocol and
can be one of the following:
o Intra-Area (0x1)
o Inter-Area (0x2)
o External 1 (0x3)
o External 2 (0x4)
Talaulikar, et al. Expires January 9, 2020 [Page 22]
Internet-Draft Link-State Info Distribution Using BGP July 2019
o NSSA 1 (0x5)
o NSSA 2 (0x6)
4.2.3.2. 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. Its purpose is
to glue a particular BGP service NLRI by virtue of its BGP next hop
to a given node in the LSDB. 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:
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 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.
4.3. The BGP-LS Attribute
The BGP-LS Attribute 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. This attribute MUST be
ignored for all other address families.
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 BGP-LS Attribute may potentially grow large in size depending on
the amount of link-state information associated with a single Link-
State NLRI. The BGP specification [RFC4271] mandates a maximum BGP
Talaulikar, et al. Expires January 9, 2020 [Page 23]
Internet-Draft Link-State Info Distribution Using BGP July 2019
message size of 4096 octets. It is RECOMMENDED that an
implementation support [I-D.ietf-idr-bgp-extended-messages] in order
to accommodate larger size of information within the BGP-LS
Attribute. BGP-LS Producers MUST ensure that they limit the TLVs
included in the BGP-LS Attribute to ensure that a BGP update message
for a single Link-State NLRI does not cross the maximum limit for a
BGP message. The determination of the types of TLVs to be included
MAY be made by the BGP-LS Producer based on the BGP-LS Consumer
applications requirement and is outside the scope of this document.
When a BGP-LS Propagator finds that it is exceeding the maximum BGP
message size due to addition or update of some other BGP Attribute
(e.g. AS_PATH), it MUST consider the BGP-LS Attribute to be
malformed and handle the propagation as described in Section 7.2.2.
4.3.1. Node Attribute TLVs
The following Node Attribute TLVs are defined for the BGP-LS
Attribute associated with a Node NLRI:
+-------------+----------------------+----------+-------------------+
| TLV Code | Description | Length | Reference |
| Point | | | (RFC/Section) |
+-------------+----------------------+----------+-------------------+
| 263 | Multi-Topology | variable | Section 4.2.2.1 |
| | Identifier | | |
| 1024 | Node Flag Bits | 1 | Section 4.3.1.1 |
| 1025 | Opaque Node | variable | Section 4.3.1.5 |
| | Attribute | | |
| 1026 | Node Name | variable | Section 4.3.1.3 |
| 1027 | IS-IS Area | variable | Section 4.3.1.2 |
| | Identifier | | |
| 1028 | IPv4 Router-ID of | 4 | [RFC5305]/4.3 |
| | Local Node | | |
| 1029 | IPv6 Router-ID of | 16 | [RFC6119]/4.1 |
| | Local Node | | |
+-------------+----------------------+----------+-------------------+
Table 6: Node Attribute TLVs
4.3.1.1. Node Flag Bits TLV
The Node Flag Bits TLV carries a bit mask describing node attributes.
The value is a variable-length bit array of flags, where each bit
represents a node capability.
Talaulikar, et al. Expires January 9, 2020 [Page 24]
Internet-Draft Link-State Info Distribution Using BGP July 2019
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|O|T|E|B|R|V| Rsvd|
+-+-+-+-+-+-+-+-+-+
Figure 15: Node Flag Bits TLV Format
The bits are defined as follows:
+-----------------+-------------------------+------------+
| 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] |
| Reserved (Rsvd) | Reserved for future use | |
+-----------------+-------------------------+------------+
Table 7: Node Flag Bits Definitions
4.3.1.2. IS-IS Area Identifier TLV
An IS-IS node can be part of one or more IS-IS areas. Each of these
area addresses is carried in the IS-IS Area Identifier TLV. If
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Area Identifier (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 16: IS-IS Area Identifier TLV Format
Talaulikar, et al. Expires January 9, 2020 [Page 25]
Internet-Draft Link-State Info Distribution Using BGP July 2019
4.3.1.3. Node Name TLV
The Node Name TLV is optional. Its structure and encoding has been
borrowed from [RFC5301]. The Value field identifies the symbolic
name of the router node. This symbolic name can be the Fully
Qualified Domain Name (FQDN) for the router, it can be a subset of
the FQDN (e.g., a hostname), or it can be any string operators want
to use for the router. The use of FQDN or a subset of it is strongly
RECOMMENDED. The maximum length of the 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
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 advertisement of Node Name which MAY
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
4.3.1.4. 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 in its own TLV.
4.3.1.5. 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,
Talaulikar, et al. Expires January 9, 2020 [Page 26]
Internet-Draft Link-State Info Distribution Using BGP July 2019
e.g., a new IGP link-state attribute being defined and the protocol-
neutral BGP-LS extensions being published. A router, for example,
could use this extension in order to advertise the native protocol's
Node Attribute TLVs, such as the OSPF Router Informational
Capabilities TLV defined in [RFC7770] or the IGP TE Node Capability
Descriptor TLV described in [RFC5073].
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Opaque node attributes (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 18: Opaque Node Attribute Format
4.3.2. 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 4.1. 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:
Talaulikar, et al. Expires January 9, 2020 [Page 27]
Internet-Draft Link-State Info Distribution Using BGP July 2019
+-----------+---------------------+--------------+------------------+
| TLV Code | Description | IS-IS TLV | Reference |
| Point | | /Sub-TLV | (RFC/Section) |
+-----------+---------------------+--------------+------------------+
| 1028 | IPv4 Router-ID of | 134/--- | [RFC5305]/4.3 |
| | Local Node | | |
| 1029 | IPv6 Router-ID of | 140/--- | [RFC6119]/4.1 |
| | Local Node | | |
| 1030 | IPv4 Router-ID of | 134/--- | [RFC5305]/4.3 |
| | Remote Node | | |
| 1031 | IPv6 Router-ID of | 140/--- | [RFC6119]/4.1 |
| | Remote Node | | |
| 1088 | Administrative | 22/3 | [RFC5305]/3.1 |
| | group (color) | | |
| 1089 | Maximum link | 22/9 | [RFC5305]/3.4 |
| | bandwidth | | |
| 1090 | Max. reservable | 22/10 | [RFC5305]/3.5 |
| | link bandwidth | | |
| 1091 | Unreserved | 22/11 | [RFC5305]/3.6 |
| | bandwidth | | |
| 1092 | TE Default Metric | 22/18 | Section 4.3.2.3 |
| 1093 | Link Protection | 22/20 | [RFC5307]/1.2 |
| | Type | | |
| 1094 | MPLS Protocol Mask | --- | Section 4.3.2.2 |
| 1095 | IGP Metric | --- | Section 4.3.2.4 |
| 1096 | Shared Risk Link | --- | Section 4.3.2.5 |
| | Group | | |
| 1097 | Opaque Link | --- | Section 4.3.2.6 |
| | Attribute | | |
| 1098 | Link Name | --- | Section 4.3.2.7 |
+-----------+---------------------+--------------+------------------+
Table 8: Link Attribute TLVs
4.3.2.1. 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.
4.3.2.2. MPLS Protocol Mask TLV
The MPLS Protocol Mask TLV carries a bit mask describing which MPLS
signaling protocols are enabled. The length of this TLV is 1. The
Talaulikar, et al. Expires January 9, 2020 [Page 28]
Internet-Draft Link-State Info Distribution Using BGP July 2019
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:
+------------+------------------------------------------+-----------+
| Bit | Description | Reference |
+------------+------------------------------------------+-----------+
| 'L' | Label Distribution Protocol (LDP) | [RFC5036] |
| 'R' | Extension to RSVP for LSP Tunnels | [RFC3209] |
| | (RSVP-TE) | |
| 'Reserved' | Reserved for future use | |
+------------+------------------------------------------+-----------+
Table 9: MPLS Protocol Mask TLV Codes
4.3.2.3. 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 less than 32 bits, then the high-
order bits of this field MUST be padded with zero.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TE Default Link Metric |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 20: TE Default Metric TLV Format
Talaulikar, et al. Expires January 9, 2020 [Page 29]
Internet-Draft Link-State Info Distribution Using BGP July 2019
4.3.2.4. IGP Metric TLV
The IGP Metric TLV carries the metric for this link. The length of
this TLV is variable, depending on the metric width of the underlying
protocol. IS-IS small metrics have a length of 1 octet (the two most
significant bits are ignored). OSPF link metrics have a length 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
4.3.2.5. 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).
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]. In Link-State NLRI, both IPv4 and IPv6 SRLG
information are carried in a single TLV.
Talaulikar, et al. Expires January 9, 2020 [Page 30]
Internet-Draft Link-State Info Distribution Using BGP July 2019
4.3.2.6. 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,
e.g., a new IGP link-state attribute being defined and the 'protocol-
neutral' BGP-LS extensions being published.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Opaque link attributes (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 23: Opaque Link Attribute TLV Format
4.3.2.7. Link Name TLV
The Link Name TLV is optional. The Value field identifies the
symbolic name of the router link. This symbolic name can be the FQDN
for the link, it can be a subset of the FQDN, or it can be any string
operators want to use for the link. The use of FQDN or a subset of
it is strongly RECOMMENDED. The maximum length of the 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
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.
Talaulikar, et al. Expires January 9, 2020 [Page 31]
Internet-Draft Link-State Info Distribution Using BGP July 2019
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
4.3.3. 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:
+---------------+-----------------------+----------+----------------+
| TLV Code | Description | Length | Reference |
| Point | | | |
+---------------+-----------------------+----------+----------------+
| 1152 | IGP Flags | 1 | Section |
| | | | 4.3.3.1 |
| 1153 | IGP Route Tag | 4*n | [RFC5130] |
| 1154 | IGP Extended Route | 8*n | [RFC5130] |
| | Tag | | |
| 1155 | Prefix Metric | 4 | [RFC5305] |
| 1156 | OSPF Forwarding | 4 | [RFC2328] |
| | Address | | |
| 1157 | Opaque Prefix | variable | Section |
| | Attribute | | 4.3.3.6 |
+---------------+-----------------------+----------+----------------+
Table 10: Prefix Attribute TLVs
4.3.3.1. IGP Flags TLV
The IGP Flags TLV contains IS-IS and OSPF flags and bits originally
assigned to the prefix. The IGP Flags TLV is encoded as follows:
Talaulikar, et al. Expires January 9, 2020 [Page 32]
Internet-Draft Link-State Info Distribution Using BGP July 2019
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|D|N|L|P| Resvd.|
+-+-+-+-+-+-+-+-+
Figure 25: IGP Flag TLV Format
The Value field contains bits defined according to the table below:
+----------+---------------------------+-----------+
| Bit | Description | Reference |
+----------+---------------------------+-----------+
| 'D' | IS-IS Up/Down Bit | [RFC5305] |
| 'N' | OSPF "no unicast" Bit | [RFC5340] |
| 'L' | OSPF "local address" Bit | [RFC5340] |
| 'P' | OSPF "propagate NSSA" Bit | [RFC5340] |
| Reserved | Reserved for future use. | |
+----------+---------------------------+-----------+
Table 11: IGP Flag Bits Definitions
4.3.3.2. 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.
Talaulikar, et al. Expires January 9, 2020 [Page 33]
Internet-Draft Link-State Info Distribution Using BGP July 2019
4.3.3.3. 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:
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.
4.3.3.4. 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.
4.3.3.5. OSPF Forwarding Address TLV
The OSPF Forwarding Address TLV [RFC2328] [RFC5340] carries the OSPF
forwarding address as known in the original OSPF advertisement.
Forwarding address can be either IPv4 or IPv6.
Talaulikar, et al. Expires January 9, 2020 [Page 34]
Internet-Draft Link-State Info Distribution Using BGP July 2019
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.
4.3.3.6. 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,
e.g., a new IGP link-state attribute being defined and the protocol-
neutral BGP-LS extensions being published.
The format of the TLV is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Opaque Prefix Attributes (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 30: Opaque Prefix Attribute TLV Format
Type is as specified in Table 10. Length is variable.
4.4. Private Use
TLVs for Vendor Private use are supported using the code point range
reserved as indicated in Section 6. For such TLV use in the NLRI or
BGP-LS Attribute, the format as described in Section 4.1 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
Talaulikar, et al. Expires January 9, 2020 [Page 35]
Internet-Draft Link-State Info Distribution Using BGP July 2019
immediately following the Total NLRI Length field of the Link-State
NLRI format as described in Section 4.2 to carry the Enterprise Code.
The Enterprise Codes are listed at <http://www.iana.org/assignments/
enterprise-numbers>. This enables use vendor specific extensions
without conflicts.
4.5. 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 attribute 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 attribute 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 attribute.
4.6. 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] [RFC5316]. In other cases, an
implementation SHOULD provide a means to inject inter-AS links into
BGP-LS. The exact mechanism used to provision the inter-AS links is
outside the scope of this document
4.7. Handling of Unreachable IGP Nodes
The origination and propagation of IGP link-state information via BGP
needs to provide a consistent and true view of the topology of the
IGP domain. BGP-LS provides an abstraction of the protocol specifics
and BGP-LS Consumers may be varied types of applications.
Talaulikar, et al. Expires January 9, 2020 [Page 36]
Internet-Draft Link-State Info Distribution Using BGP July 2019
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 shown
are in area 1.
A BGP-LS Consumer talks to a BGP route-reflector (RR) R0 which 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 R0.
Normally, R0 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 best path decision process.
Consumer
^
|
R0
(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 5-6 from its Router LSA and this updated
LSA is available at R2. R2 also has a stale copy of R6's Router LSA
which still has the link 6-5 in it. Based on this view in its LSDB,
R2 will advertise only the half-link 6-5 that it derives from R6's
stale Router LSA.
At the same time, R6 has removed the link 6-5 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 5-6 in it. Based on it's
LSDB, R3 will advertise only the half-link 5-6 that it has derived
from R5's stale Router LSA.
Now, the BGP-LS Consumer receives both the Link NLRIs corresponding
to the half-links from R2 and R3 via R0. When viewed together, it
would not detect or realize that the area 1 is actually partitioned.
Talaulikar, et al. Expires January 9, 2020 [Page 37]
Internet-Draft Link-State Info Distribution Using BGP July 2019
Also if R2 continues to report Link-State NLRIs corresponding to the
stale copy of Router LSA of R4 and R6 nodes then R0 would prefer them
over the valid Link-State NLRIs for R4 and R6 that it is receiving
from R3 based on its BGP decision process. This would result in the
BGP-LS Consumer getting stale and inaccurate topology information.
This problems 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 MUST 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 and it MUST re-
advertise those link-state objects only after that node becomes
reachable again in the IGP domain.
4.8. Router-ID Anchoring Example: ISO Pseudonode
Encoding of a broadcast LAN in IS-IS provides a good example of how
Router-IDs are encoded. Consider Figure 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.
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
Talaulikar, et al. Expires January 9, 2020 [Page 38]
Internet-Draft Link-State Info Distribution Using BGP July 2019
4.9. Router-ID Anchoring Example: OSPF Pseudonode
Encoding of a broadcast LAN in OSPF provides a good example of how
Router-IDs and local Interface IPs are encoded. Consider Figure 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 10.1.1.1 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:
o Local Node Descriptor
TLV #515: IGP Router-ID: 11.11.11.11
TLV #514: OSPF Area-ID: ID:0.0.0.0
o Remote Node Descriptor
TLV #515: IGP Router-ID: 11.11.11.11:10.1.1.1
TLV #514: OSPF Area-ID: ID:0.0.0.0
The Link NLRI of (Pseudonode1, Node2) is encoded as follows:
o Local Node Descriptor
TLV #515: IGP Router-ID: 11.11.11.11:10.1.1.1
TLV #514: OSPF Area-ID: ID:0.0.0.0
o Remote Node Descriptor
TLV #515: IGP Router-ID: 33.33.33.34
TLV #514: OSPF Area-ID: ID:0.0.0.0
Talaulikar, et al. Expires January 9, 2020 [Page 39]
Internet-Draft Link-State Info Distribution Using BGP July 2019
10.1.1.1/24 10.1.1.2/24
+-------------+ +-------------+ +-------------+
| Node1 | | Pseudonode1 | | Node2 |
| 11.11.11.11 |--->| 11.11.11.11 |--->| 33.33.33.34 |
| | | 10.1.1.1 | | |
| Area 0 | | Area 0 | | Area 0 |
+-------------+ +-------------+ +-------------+
Figure 33: OSPF Pseudonodes
The LAN subnet 10.1.1.0/24 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.
4.10. Router-ID Anchoring Example: OSPFv2 to IS-IS Migration
Graceful migration from one IGP to another requires coordinated
operation of both protocols during the migration period. Such a
coordination requires identifying a given physical link in both IGPs.
The IPv4 Router-ID provides that "glue", which is present in the Node
Descriptors of the OSPF Link NLRI and in the link attribute of the
IS-IS Link NLRI.
Consider a point-to-point link between two routers, A and B, 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
protocol.
5. Link to Path Aggregation
Distribution of all links available in the global Internet is
certainly possible; however, it 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
Talaulikar, et al. Expires January 9, 2020 [Page 40]
Internet-Draft Link-State Info Distribution Using BGP July 2019
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 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.
5.1. 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.
AS1 : AS2
:
R1-------R3
| : | \
| : | R5
| : | /
R2-------R4
:
:
Figure 34: No Link Aggregation
5.2. 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.
Talaulikar, et al. Expires January 9, 2020 [Page 41]
Internet-Draft Link-State Info Distribution Using BGP July 2019
AS1 : AS2
:
R1-------R3
| : |
| : |
| : |
R2-------R4
:
:
Figure 35: ASBR Link Aggregation
5.3. 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.
AS1 : AS2 : AS3
: :
R1-------R3-----
| : : \
| : : vR0
| : : /
R2-------R4-----
: :
: :
Figure 36: Multi-AS Aggregation
6. IANA Considerations
IANA has assigned address family number 16388 (BGP-LS) in the
"Address Family Numbers" registry with [RFC7752] as a reference.
IANA has assigned SAFI values 71 (BGP-LS) and 72 (BGP-LS-VPN) in the
"SAFI Values" sub-registry under the "Subsequent Address Family
Identifiers (SAFI) Parameters" registry.
IANA has assigned value 29 (BGP-LS Attribute) in the "BGP Path
Attributes" sub-registry under the "Border Gateway Protocol (BGP)
Parameters" registry.
IANA has created a new "Border Gateway Protocol - Link State (BGP-LS)
Parameters" registry at <http://www.iana.org/assignments/bgp-ls-
parameters>. All of the following registries are BGP-LS specific and
are accessible under this registry:
Talaulikar, et al. Expires January 9, 2020 [Page 42]
Internet-Draft Link-State Info Distribution Using BGP July 2019
o "BGP-LS NLRI-Types" registry
Value 0 is reserved. The maximum value is 65535. The range
65000-65535 is for Private Use. The registry has been populated
with the values shown in Table 1. Allocations within the registry
require documentation of the proposed use of the allocated value
(Specification Required) and approval by the Designated Expert
assigned by the IESG (see [RFC8126]).
o "BGP-LS Protocol-IDs" registry
Value 0 is reserved. The maximum value is 255. The range 200-255
is for Private Use. The registry has been populated with the
values shown in Table 2. Allocations within the registry require
documentation of the proposed use of the allocated value
(Specification Required) and approval by the Designated Expert
assigned by the IESG (see [RFC8126]).
o "BGP-LS Well-Known Instance-IDs" registry
This registry was setup via [RFC7752] and is no longer required.
It may be retained as deprecated.
o "BGP-LS Node Descriptor, Link Descriptor, Prefix Descriptor, and
Attribute TLVs" registry
Values 0-255 are reserved. Values 256-65535 will be used for code
points. The range 65000-65535 is for Private Use. The registry
has been populated with the values shown in Table 12. Allocations
within the registry require documentation of the proposed use of
the allocated value (Specification Required) and approval by the
Designated Expert assigned by the IESG (see [RFC8126]).
6.1. Guidance for Designated Experts
In all cases of review by the Designated Expert (DE) described here,
the DE is expected to ascertain the existence of suitable
documentation (a specification) as described in [RFC8126] and to
verify that the document is permanently and publicly available. The
DE is also expected to check the clarity of purpose and use of the
requested code points. Last, the DE must verify that any
specification produced in the IETF that requests one of these code
points has been made available for review by the IDR working group
and that any specification produced outside the IETF does not
conflict with work that is active or already published within the
IETF.
Talaulikar, et al. Expires January 9, 2020 [Page 43]
Internet-Draft Link-State Info Distribution Using BGP July 2019
7. Manageability Considerations
This section is structured as recommended in [RFC5706].
7.1. Operational Considerations
7.1.1. 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. It is
expected that the distribution of this NLRI SHOULD be handled by
dedicated route reflectors in most deployments providing a level of
isolation and fault containment between different NLRI types. 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.
7.1.2. Installation and Initial Setup
Configuration parameters defined in Section 7.2.3 SHOULD be
initialized to the following default values:
o The Link-State NLRI capability is turned off for all neighbors.
o The maximum rate at which Link-State NLRIs will be advertised/
withdrawn from neighbors is set to 200 updates per second.
7.1.3. 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 7.2.3), so the extension
can be gradually rolled out in the network.
7.1.4. Requirements on Other Protocols and Functional Components
The protocol extension defined in this document does not put new
requirements on other protocols or functional components.
Talaulikar, et al. Expires January 9, 2020 [Page 44]
Internet-Draft Link-State Info Distribution Using BGP July 2019
7.1.5. Impact on Network Operation
Frequency of Link-State NLRI updates could interfere with regular BGP
prefix distribution. A network operator MAY use a dedicated Route-
Reflector infrastructure to distribute Link-State NLRIs.
Distribution of Link-State NLRIs SHOULD be limited to a single admin
domain, which can consist of multiple areas within an AS or multiple
ASes.
7.1.6. Verifying Correct Operation
Existing BGP procedures apply. In addition, an implementation SHOULD
allow an operator to:
o List neighbors with whom the speaker is exchanging Link-State
NLRIs.
7.2. Management Considerations
7.2.1. 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.
7.2.2. Fault Management
This section describes the fault management actions, as described in
[RFC7606] , that are to be performed for handling of BGP update
messages for BGP-LS.
A Link-State NLRI MUST NOT be considered as malformed or invalid
based on the inclusion/exclusion of TLVs or contents of the TLV
fields (i.e. semantic errors), as described in Section 4.1 and
Section 4.2.
A BGP-LS Speaker MUST perform the following syntactic validation of
the Link-State NLRI to determine if it is malformed.
o Does the sum of all TLVs found in the BGP MP_REACH_NLRI attribute
correspond to the BGP MP_REACH_NLRI length?
o Does the sum of all TLVs found in the BGP MP_UNREACH_NLRI
attribute correspond to the BGP MP_UNREACH_NLRI length?
Talaulikar, et al. Expires January 9, 2020 [Page 45]
Internet-Draft Link-State Info Distribution Using BGP July 2019
o Does the sum of all TLVs found in a Link-State NLRI correspond to
the Total NLRI Length field of all its Descriptors?
o Is the length of the TLVs and, when the TLV is recognized then,
its sub-TLVs in the NLRI valid?
o Has the syntactic correctness of the NLRI fields been verified as
per [RFC7606]?
o Has the rule regarding ordering of TLVs been followed as described
in Section 4.1?
When the error determined allows for the router to skip the malformed
NLRI(s) and continue processing of the rest of the update message
(e.g. when the TLV ordering rule is violated), then it MUST handle
such malformed NLRIs as 'Treat-as-withdraw'. 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 'session reset' when
the session is only being used for BGP-LS or when it 'AFI/SAFI
disable' action is not possible.
A BGP-LS Attribute MUST NOT be considered as malformed or invalid
based on the inclusion/exclusion of TLVs or contents of the TLV
fields (i.e. semantic errors), as described in Section 4.1 and
Section 4.3.
A BGP-LS Speaker MUST perform the following syntactic validation of
the BGP-LS Attribute to determine if it is malformed.
o Does the sum of all TLVs found in the BGP-LS Attribute correspond
to the BGP-LS Attribute length?
o Has the syntactic correctness of the Attributes (including BGP-LS
Attribute) been verified as per [RFC7606]?
o Is the length of each TLV and, when the TLV is recognized then,
its sub-TLVs in the BGP-LS Attribute valid?
When the error determined allows for the router to skip the malformed
BGP-LS Attribute and continue processing of the rest of the 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
Talaulikar, et al. Expires January 9, 2020 [Page 46]
Internet-Draft Link-State Info Distribution Using BGP July 2019
the BGP update message then the handling is the same as described
above for the malformed NLRI.
Note that the 'Attribute Discard' action results in the loss of all
TLVs in the BGP-LS Attribute and not the removal of a specific
malformed TLV. The removal of specific malformed TLVs may give a
wrong indication to a BGP-LS Consumer of that specific information
being deleted or not available.
When a BGP Speaker receives an update message with Link-State NLRI(s)
in the MP_REACH_NLRI but without the BGP-LS Attribute, it is most
likely an indication that a BGP Speaker preceding it has performed
the 'Attribute Discard' fault handling. An implementation SHOULD
preserve and propagate the Link-State NLRIs 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/withdraw.
This also makes it possible for a network operator to trace back to
the BGP-LS Propagator which actually detected a fault with the BGP-LS
Attribute.
An implementation SHOULD log an error for any errors found during
syntax validation for further analysis.
A BGP-LS Propagator 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):
o is a mandatory TLV present or not?
o is the length of a fixed length TLV correct or the length of a
variable length TLV a valid/permissible?
o are the values of TLV fields valid or permissible?
o are the inclusion and use of TLVs/sub-TLVs with specific Link-
State NLRI types valid?
Each TLV MAY indicate the valid and permissible values and their
semantics that can to 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. A BGP-LS Consumer should ignore unrecognized and
unexpected TLV types in both the NLRI and BGP-LS Attribute portions
and not consider their presence as an error.
Talaulikar, et al. Expires January 9, 2020 [Page 47]
Internet-Draft Link-State Info Distribution Using BGP July 2019
7.2.3. Configuration Management
An implementation SHOULD allow the operator to specify neighbors to
which Link-State NLRIs will be advertised and from which Link-State
NLRIs will be accepted.
An implementation SHOULD allow the operator to specify the maximum
rate at which Link-State NLRIs will be advertised/withdrawn from
neighbors.
An implementation SHOULD allow the operator to specify the maximum
number of Link-State NLRIs stored in a router'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 SHOULD allow the operator to configure a 64-bit
Instance-ID.
An implementation SHOULD allow the operator to configure ASN and BGP-
LS identifiers (refer Section 4.2.1.4).
An implementation SHOULD allow the operator to configure the maximum
size of the BGP-LS Attribute that may be used on a BGP-LS Producer.
7.2.4. Accounting Management
Not Applicable.
7.2.5. Performance Management
An implementation SHOULD provide the following statistics:
o Total number of Link-State NLRI updates sent/received
o Number of Link-State NLRI updates sent/received, per neighbor
o Number of errored received Link-State NLRI updates, per neighbor
o Total number of locally originated Link-State NLRIs
These statistics should be recorded as absolute counts since system
or session start time. An implementation MAY also enhance this
information by recording peak per-second counts in each case.
Talaulikar, et al. Expires January 9, 2020 [Page 48]
Internet-Draft Link-State Info Distribution Using BGP July 2019
7.2.6. Security Management
An operator SHOULD define an import policy to limit inbound updates
as follows:
o Drop all updates from peers that are only serving BGP-LS
Consumers.
An implementation MUST have the means to limit inbound updates.
8. TLV/Sub-TLV Code Points Summary
This section contains the global table of all TLVs/sub-TLVs defined
in this document.
+-----------+---------------------+--------------+------------------+
| TLV Code | Description | IS-IS TLV/ | Reference |
| Point | | Sub-TLV | (RFC/Section) |
+-----------+---------------------+--------------+------------------+
| 256 | Local Node | --- | Section 4.2.1.2 |
| | Descriptors | | |
| 257 | Remote Node | --- | Section 4.2.1.3 |
| | Descriptors | | |
| 258 | Link Local/Remote | 22/4 | [RFC5307]/1.1 |
| | Identifiers | | |
| 259 | IPv4 interface | 22/6 | [RFC5305]/3.2 |
| | address | | |
| 260 | IPv4 neighbor | 22/8 | [RFC5305]/3.3 |
| | address | | |
| 261 | IPv6 interface | 22/12 | [RFC6119]/4.2 |
| | address | | |
| 262 | IPv6 neighbor | 22/13 | [RFC6119]/4.3 |
| | address | | |
| 263 | Multi-Topology ID | --- | Section 4.2.2.1 |
| 264 | OSPF Route Type | --- | Section 4.2.3 |
| 265 | IP Reachability | --- | Section 4.2.3 |
| | Information | | |
| 512 | Autonomous System | --- | Section 4.2.1.4 |
| 513 | BGP-LS Identifier | --- | Section 4.2.1.4 |
| | (deprecated) | | |
| 514 | OSPF Area-ID | --- | Section 4.2.1.4 |
| 515 | IGP Router-ID | --- | Section 4.2.1.4 |
| 1024 | Node Flag Bits | --- | Section 4.3.1.1 |
| 1025 | Opaque Node | --- | Section 4.3.1.5 |
| | Attribute | | |
| 1026 | Node Name | variable | Section 4.3.1.3 |
| 1027 | IS-IS Area | variable | Section 4.3.1.2 |
| | Identifier | | |
Talaulikar, et al. Expires January 9, 2020 [Page 49]
Internet-Draft Link-State Info Distribution Using BGP July 2019
| 1028 | IPv4 Router-ID of | 134/--- | [RFC5305]/4.3 |
| | Local Node | | |
| 1029 | IPv6 Router-ID of | 140/--- | [RFC6119]/4.1 |
| | Local Node | | |
| 1030 | IPv4 Router-ID of | 134/--- | [RFC5305]/4.3 |
| | Remote Node | | |
| 1031 | IPv6 Router-ID of | 140/--- | [RFC6119]/4.1 |
| | Remote Node | | |
| 1088 | Administrative | 22/3 | [RFC5305]/3.1 |
| | group (color) | | |
| 1089 | Maximum link | 22/9 | [RFC5305]/3.4 |
| | bandwidth | | |
| 1090 | Max. reservable | 22/10 | [RFC5305]/3.5 |
| | link bandwidth | | |
| 1091 | Unreserved | 22/11 | [RFC5305]/3.6 |
| | bandwidth | | |
| 1092 | TE Default Metric | 22/18 | Section 4.3.2.3 |
| 1093 | Link Protection | 22/20 | [RFC5307]/1.2 |
| | Type | | |
| 1094 | MPLS Protocol Mask | --- | Section 4.3.2.2 |
| 1095 | IGP Metric | --- | Section 4.3.2.4 |
| 1096 | Shared Risk Link | --- | Section 4.3.2.5 |
| | Group | | |
| 1097 | Opaque Link | --- | Section 4.3.2.6 |
| | Attribute | | |
| 1098 | Link Name | --- | Section 4.3.2.7 |
| 1152 | IGP Flags | --- | Section 4.3.3.1 |
| 1153 | IGP Route Tag | --- | [RFC5130] |
| 1154 | IGP Extended Route | --- | [RFC5130] |
| | Tag | | |
| 1155 | Prefix Metric | --- | [RFC5305] |
| 1156 | OSPF Forwarding | --- | [RFC2328] |
| | Address | | |
| 1157 | Opaque Prefix | --- | Section 4.3.3.6 |
| | Attribute | | |
+-----------+---------------------+--------------+------------------+
Table 12: Summary Table of TLV/Sub-TLV Code Points
9. 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.
In the context of the BGP peerings associated with this document, a
BGP speaker MUST NOT accept updates from a peer that is only
Talaulikar, et al. Expires January 9, 2020 [Page 50]
Internet-Draft Link-State Info Distribution Using BGP July 2019
providing information to a BGP-LS Consumer. That is, a participating
BGP speaker should be aware of the nature of its relationships for
link-state relationships and should protect itself from peers sending
updates that either represent erroneous information feedback loops or
are false input. Such protection can be achieved by manual
configuration of consumer peers at the BGP speaker.
An operator SHOULD employ a mechanism to protect a BGP speaker
against DDoS attacks from BGP-LS Consumers. The principal attack a
consumer may apply is to attempt to start multiple sessions either
sequentially or simultaneously. Protection can be applied by
imposing rate limits.
Additionally, it may be considered that the export 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 consumers are configured to
receive such information.
10. Contributors
We would like to thank Robert Varga for the significant contribution
he gave to RFC7752.
11. 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 LAN subnet for OSPF.
We would like to thank Balaji Rajagopalan, Srihari Sangli and
Shraddha Hegde for their review and feedback on this document.
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.
Talaulikar, et al. Expires January 9, 2020 [Page 51]
Internet-Draft Link-State Info Distribution Using BGP July 2019
12. References
12.1. Normative References
[I-D.ietf-idr-bgp-extended-messages]
Bush, R., Patel, K., and D. Ward, "Extended Message
support for BGP", draft-ietf-idr-bgp-extended-messages-33
(work in progress), July 2019.
[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>.
[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>.
Talaulikar, et al. Expires January 9, 2020 [Page 52]
Internet-Draft Link-State Info Distribution Using BGP July 2019
[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>.
[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>.
[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>.
Talaulikar, et al. Expires January 9, 2020 [Page 53]
Internet-Draft Link-State Info Distribution Using BGP July 2019
[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>.
[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>.
[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>.
[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>.
[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>.
[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>.
[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>.
12.2. Informative References
[RFC1918] Rekhter, Y., Moskowitz, B., Karrenberg, D., de Groot, G.,
and E. Lear, "Address Allocation for Private Internets",
BCP 5, RFC 1918, DOI 10.17487/RFC1918, February 1996,
<https://www.rfc-editor.org/info/rfc1918>.
Talaulikar, et al. Expires January 9, 2020 [Page 54]
Internet-Draft Link-State Info Distribution Using BGP July 2019
[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., 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>.
[RFC5073] Vasseur, J., Ed. and J. Le Roux, Ed., "IGP Routing
Protocol Extensions for Discovery of Traffic Engineering
Node Capabilities", RFC 5073, DOI 10.17487/RFC5073,
December 2007, <https://www.rfc-editor.org/info/rfc5073>.
[RFC5152] Vasseur, JP., Ed., Ayyangar, A., Ed., and R. Zhang, "A
Per-Domain Path Computation Method for Establishing Inter-
Domain Traffic Engineering (TE) Label Switched Paths
(LSPs)", RFC 5152, DOI 10.17487/RFC5152, February 2008,
<https://www.rfc-editor.org/info/rfc5152>.
[RFC5316] Chen, M., Zhang, R., and X. Duan, "ISIS Extensions in
Support of Inter-Autonomous System (AS) MPLS and GMPLS
Traffic Engineering", RFC 5316, DOI 10.17487/RFC5316,
December 2008, <https://www.rfc-editor.org/info/rfc5316>.
[RFC5392] Chen, M., Zhang, R., and X. Duan, "OSPF Extensions in
Support of Inter-Autonomous System (AS) MPLS and GMPLS
Traffic Engineering", RFC 5392, DOI 10.17487/RFC5392,
January 2009, <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>.
[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>.
Talaulikar, et al. Expires January 9, 2020 [Page 55]
Internet-Draft Link-State Info Distribution Using BGP July 2019
[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>.
[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>.
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. Update 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. In Section 4.1, clarification about the TLV handling aspects
that are applicable 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 handling of
unrecognized TLV and so, based on [RFC7606] guidelines, might
discard the unknown NLRI types. This aspect is now
unambiguously clarified in Section 4.2. Also, the ascending
order of TLVs in the BGP-LS Attribute is not necessary.
3. Clarification of mandatory and optional TLVs in both NLRI and
BGP-LS Attribute portions all through the document.
4. Handling of the growth of the BGP-LS Attribute is covered in
Section 4.3.
5. Clarification on the use of Identifier field in the Link-State
NLRI in Section 4.2 is provided. It was defined ambiguously to
refer to only mutli-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.
Talaulikar, et al. Expires January 9, 2020 [Page 56]
Internet-Draft Link-State Info Distribution Using BGP July 2019
6. 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 doing the same functionality as the
Instance-ID when running multiple instances of IGP routing
protocols.
7. Moved MT-ID TLV from the Node Descriptor section to under the
Link Descriptor section since it is not a Node Descriptor sub-
TLV. Also fixed the ambiguity in the encoding of OSPF MT-ID in
this TLV. MT-ID TLV use is now elevated to SHOULD when it is
enabled in the underlying IGP.
8. Update the usage of OSPF Route Type TLV to mandate its use for
OSPF prefixes in Section 4.2.3.1 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.
9. Updated the Node Name TLV in Section 4.3.1.3 with the OSPF
specification.
10. Clarified the advertisement of the prefix corresponding to the
LAN segment in an OSPF network in Section 4.9.
11. Introduced Private Use TLV code point space and specified their
encoding in Section 4.4.
12. Introduced Section 4.7 where issues related to consistency of
reporting IGP link-state along with their solutions are covered.
13. Handling of large size of BGP-LS Attribute with growth in BGP-LS
information is explained in Section 4.3 along with mitigation of
errors arising out of it.
14. 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.
15. Updated the Fault Management section with detailed rules based
on the role in the BGP-LS information propagation flow.
Authors' Addresses
Talaulikar, et al. Expires January 9, 2020 [Page 57]
Internet-Draft Link-State Info Distribution Using BGP July 2019
Ketan Talaulikar (editor)
Cisco Systems
India
Email: ketant@cisco.com
Hannes Gredler
Rtbrick
Email: hannes@rtbrick.com
Jan Medved
Cisco Systems, Inc.
170, West Tasman Drive
San Jose, CA 95134
US
Email: jmedved@cisco.com
Stefano Previdi
Individual Contributor
Rome
Italy
Email: stefano@previdi.net
Adrian Farrel
Old Dog Consulting
Email: adrian@olddog.co.uk
Saikat Ray
Individual Contributor
Email: raysaikat@gmail.com
Talaulikar, et al. Expires January 9, 2020 [Page 58]
