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Keywords: BGP-LS, Segment Routing, SID, MPLS, Label advertisement, IS-IS, OSPF, OSPFv3
Internet Engineering Task Force (IETF) S. Previdi
Request for Comments: 9085 Huawei Technologies
Category: Standards Track K. Talaulikar, Ed.
ISSN: 2070-1721 C. Filsfils
Cisco Systems, Inc.
H. Gredler
RtBrick Inc.
M. Chen
Huawei Technologies
August 2021
Border Gateway Protocol - Link State (BGP-LS) Extensions for Segment
Routing
Abstract
Segment Routing (SR) allows for a flexible definition of end-to-end
paths by encoding paths as sequences of topological subpaths, called
"segments". These segments are advertised by routing protocols,
e.g., by the link-state routing protocols (IS-IS, OSPFv2, and OSPFv3)
within IGP topologies.
This document defines extensions to the Border Gateway Protocol -
Link State (BGP-LS) address family in order to carry SR information
via BGP.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc9085.
Copyright Notice
Copyright (c) 2021 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
1.1. Requirements Language
2. BGP-LS Extensions for Segment Routing
2.1. Node Attribute TLVs
2.1.1. SID/Label TLV
2.1.2. SR Capabilities TLV
2.1.3. SR-Algorithm TLV
2.1.4. SR Local Block TLV
2.1.5. SRMS Preference TLV
2.2. Link Attribute TLVs
2.2.1. Adjacency SID TLV
2.2.2. LAN Adjacency SID TLV
2.2.3. L2 Bundle Member Attributes TLV
2.3. Prefix Attribute TLVs
2.3.1. Prefix-SID TLV
2.3.2. Prefix Attribute Flags TLV
2.3.3. Source Router Identifier TLV
2.3.4. Source OSPF Router-ID TLV
2.3.5. Range TLV
2.4. Equivalent IS-IS Segment Routing TLVs/Sub-TLVs
2.5. Equivalent OSPFv2/OSPFv3 Segment Routing TLVs/Sub-TLVs
3. IANA Considerations
3.1. TLV/Sub-TLV Code Points Summary
4. Manageability Considerations
5. Security Considerations
6. References
6.1. Normative References
6.2. Informative References
Acknowledgements
Contributors
Authors' Addresses
1. Introduction
Segment Routing (SR) allows for a flexible definition of end-to-end
paths by combining subpaths called "segments". A segment can
represent any instruction: topological or service based. A segment
can have a local semantic to an SR node or global semantic within a
domain. Within IGP topologies, an SR path is encoded as a sequence
of topological subpaths, called "IGP segments". These segments are
advertised by the link-state routing protocols (IS-IS, OSPFv2, and
OSPFv3).
[RFC8402] defines the link-state IGP segments -- prefix, node,
anycast, and adjacency segments. Prefix segments, by default,
represent an ECMP-aware shortest-path to a prefix, as per the state
of the IGP topology. Adjacency segments represent a hop over a
specific adjacency between two nodes in the IGP. A prefix segment is
typically a multi-hop path while an adjacency segment, in most of the
cases, is a one-hop path. Node and anycast segments are variations
of the prefix segment with their specific characteristics.
When SR is enabled in an IGP domain, segments are advertised in the
form of Segment Identifiers (SIDs). The IGP link-state routing
protocols have been extended to advertise SIDs and other SR-related
information. IGP extensions are described for: IS-IS [RFC8667],
OSPFv2 [RFC8665], and OSPFv3 [RFC8666]. Using these extensions, SR
can be enabled within an IGP domain.
SR allows advertisement of single or multi-hop paths. The flooding
scope for the IGP extensions for SR is IGP area-wide. Consequently,
the contents of a Link-State Database (LSDB) or a Traffic Engineering
Database (TED) has the scope of an IGP area; therefore, by using the
IGP alone, it is not enough to construct segments across multiple IGP
area or Autonomous System (AS) boundaries.
In order to address the need for applications that require
topological visibility across IGP areas, or even across ASes, the
BGP-LS address family / subaddress family have been defined to allow
BGP to carry link-state information. The BGP Network Layer
Reachability Information (NLRI) encoding format for BGP-LS and a new
BGP Path Attribute called the "BGP-LS Attribute" are defined in
[RFC7752]. The identifying key of each link-state object, namely a
node, link, or prefix, is encoded in the NLRI, and the properties of
the object are encoded in the BGP-LS Attribute.
+------------+
| Consumer |
+------------+
^
|
v
+-------------------+
| BGP Speaker | +-----------+
| (Route Reflector) | | Consumer |
+-------------------+ +-----------+
^ ^ ^ ^
| | | |
+---------------+ | +-------------------+ |
| | | |
v v v v
+-----------+ +-----------+ +-----------+
| BGP | | BGP | | BGP |
| Speaker | | Speaker | . . . | Speaker |
+-----------+ +-----------+ +-----------+
^ ^ ^
| | |
IGP IGP IGP
Figure 1: Link-State Information Collection
Figure 1 denotes a typical deployment scenario. In each IGP area,
one or more nodes are configured with BGP-LS. These BGP speakers
form an Internal BGP (IBGP) mesh by connecting to one or more route
reflectors. This way, all BGP speakers (specifically the route
reflectors) obtain link-state information from all IGP areas (and
from other ASes from External BGP (EBGP) peers). An external
component connects to the route reflector to obtain this information
(perhaps moderated by a policy regarding what information is or isn't
advertised to the external component) as described in [RFC7752].
This document describes extensions to BGP-LS to advertise the SR
information. An external component (e.g., a controller) can collect
SR information from across an SR domain (as described in [RFC8402])
and construct the end-to-end path (with its associated SIDs) that
needs to be applied to an incoming packet to achieve the desired end-
to-end forwarding. SR operates within a trusted domain consisting of
a single AS or multiple ASes managed by the same administrative
entity, e.g., within a single provider network.
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
2. BGP-LS Extensions for Segment Routing
This document defines SR extensions to BGP-LS and specifies the TLVs
and sub-TLVs for advertising SR information within the BGP-LS
Attribute. Sections 2.4 and 2.5 list the equivalent TLVs and sub-
TLVs in the IS-IS, OSPFv2, and OSPFv3 protocols.
BGP-LS [RFC7752] defines the BGP-LS NLRI that can be a Node NLRI, a
Link NLRI, or a Prefix NLRI, and it defines the TLVs that map link-
state information to BGP-LS NLRI within the BGP-LS Attribute. This
document adds additional BGP-LS Attribute TLVs in order to encode SR
information. It does not introduce any changes to the encoding of
the BGP-LS NLRIs.
2.1. Node Attribute TLVs
The following Node Attribute TLVs are defined:
+======+=================+===============+
| Type | Description | Section |
+======+=================+===============+
| 1161 | SID/Label | Section 2.1.1 |
+------+-----------------+---------------+
| 1034 | SR Capabilities | Section 2.1.2 |
+------+-----------------+---------------+
| 1035 | SR Algorithm | Section 2.1.3 |
+------+-----------------+---------------+
| 1036 | SR Local Block | Section 2.1.4 |
+------+-----------------+---------------+
| 1037 | SRMS Preference | Section 2.1.5 |
+------+-----------------+---------------+
Table 1: Node Attribute TLVs
These TLVs should only be added to the BGP-LS Attribute associated
with the Node NLRI that describes the IGP node that is originating
the corresponding IGP TLV/sub-TLV described below.
2.1.1. SID/Label TLV
The SID/Label TLV is used as a sub-TLV by the SR Capabilities
(Section 2.1.2) and Segment Routing Local Block (SRLB)
(Section 2.1.4) TLVs. This information is derived from the protocol-
specific advertisements.
* IS-IS, as defined by the SID/Label Sub-TLV in Section 2.3 of
[RFC8667].
* OSPFv2/OSPFv3, as defined by the SID/Label Sub-TLV in Section 2.1
of [RFC8665] and Section 3.1 of [RFC8666].
The TLV has the following format:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SID/Label (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: SID/Label TLV Format
Where:
Type: 1161
Length: Variable. Either 3 or 4 octets depending on whether the
value is encoded as a label or as an index/SID.
SID/Label: If the length is set to 3, then the 20 rightmost bits
represent a label (the total TLV size is 7), and the 4 leftmost
bits are set to 0. If the length is set to 4, then the value
represents a 32-bit SID (the total TLV size is 8).
2.1.2. SR Capabilities TLV
The SR Capabilities TLV is used in order to advertise the node's SR
capabilities including its Segment Routing Global Base (SRGB)
range(s). In the case of IS-IS, the capabilities also include the
IPv4 and IPv6 support for the SR-MPLS forwarding plane. This
information is derived from the protocol-specific advertisements.
* IS-IS, as defined by the SR-Capabilities Sub-TLV in Section 3.1 of
[RFC8667].
* OSPFv2/OSPFv3, as defined by the SID/Label Range TLV in
Section 3.2 of [RFC8665]. OSPFv3 leverages the same TLV as
defined for OSPFv2.
The SR Capabilities TLV has the following format:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Range Size 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SID/Label Sub-TLV 1 //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Range Size N |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SID/Label Sub-TLV N //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: SR Capabilities TLV Format
Where:
Type: 1034
Length: Variable. The minimum length is 12 octets.
Flags: 1 octet of flags as defined in Section 3.1 of [RFC8667] for
IS-IS. The flags are not currently defined for OSPFv2 and OSPFv3
and MUST be set to 0 and ignored on receipt.
Reserved: 1 octet that MUST be set to 0 and ignored on receipt.
One or more entries, each of which have the following format:
Range Size: 3 octets with a non-zero value indicating the number
of labels in the range.
SID/Label TLV: (as defined in Section 2.1.1) used as a sub-TLV,
which encodes the first label in the range. Since the SID/
Label TLV is used to indicate the first label of the SRGB
range, only label encoding is valid under the SR Capabilities
TLV.
2.1.3. SR-Algorithm TLV
The SR-Algorithm TLV is used in order to advertise the SR algorithms
supported by the node. This information is derived from the
protocol-specific advertisements.
* IS-IS, as defined by the SR-Algorithm Sub-TLV in Section 3.2 of
[RFC8667].
* OSPFv2/OSPFv3, as defined by the SR-Algorithm TLV in Section 3.1
of [RFC8665]. OSPFv3 leverages the same TLV as defined for
OSPFv2.
The SR-Algorithm TLV has the following format:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Algorithm 1 | Algorithm... | Algorithm N |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: SR-Algorithm TLV Format
Where:
Type: 1035
Length: Variable. The minimum length is 1 octet and the maximum can
be 256.
Algorithm: One or more fields of 1 octet each that identifies the
algorithm.
2.1.4. SR Local Block TLV
The SRLB TLV contains the range(s) of labels the node has reserved
for local SIDs. Local SIDs are used, e.g., in IGP (IS-IS, OSPF) for
Adjacency SIDs and may also be allocated by components other than IGP
protocols. As an example, an application or a controller may
instruct a node to allocate a specific local SID. Therefore, in
order for such applications or controllers to know the range of local
SIDs available, the node is required to advertise its SRLB.
This information is derived from the protocol-specific
advertisements.
* IS-IS, as defined by the SRLB Sub-TLV in Section 3.3 of [RFC8667].
* OSPFv2/OSPFv3, as defined by the SR Local Block TLV in Section 3.3
of [RFC8665]. OSPFv3 leverages the same TLV as defined for
OSPFv2.
The SRLB TLV has the following format:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-Range Size 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SID/Label Sub-TLV 1 //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-Range Size N |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SID/Label Sub-TLV N //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: SRLB TLV Format
Where:
Type: 1036
Length: Variable. The minimum length is 12 octets.
Flags: 1 octet of flags. The flags are as defined in Section 3.3 of
[RFC8667] for IS-IS. The flags are not currently defined for
OSPFv2 and OSPFv3 and MUST be set to 0 and ignored on receipt.
Reserved: 1 octet that MUST be set to 0 and ignored on receipt.
One or more entries corresponding to a sub-range(s), each of which
have the following format:
Range Size: 3-octet value indicating the number of labels in the
range.
SID/Label TLV: (as defined in Section 2.1.1) used as a sub-TLV,
which encodes the first label in the sub-range. Since the SID/
Label TLV is used to indicate the first label of the SRLB sub-
range, only label encoding is valid under the SR Local Block
TLV.
2.1.5. SRMS Preference TLV
The Segment Routing Mapping Server (SRMS) Preference TLV is used in
order to associate a preference with SRMS advertisements from a
particular source. [RFC8661] specifies the SRMS functionality along
with the SRMS preference of the node advertising the SRMS Prefix-to-
SID mapping ranges.
This information is derived from the protocol-specific
advertisements.
* IS-IS, as defined by the SRMS Preference Sub-TLV in Section 3.4 of
[RFC8667].
* OSPFv2/OSPFv3, as defined by the SRMS Preference TLV in
Section 3.4 of [RFC8665]. OSPFv3 leverages the same TLV as
defined for OSPFv2.
The SRMS Preference TLV has the following format:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Preference |
+-+-+-+-+-+-+-+-+
Figure 6: SRMS Preference TLV Format
Where:
Type: 1037
Length: 1 octet
Preference: 1 octet carrying an unsigned 8-bit SRMS preference.
2.2. Link Attribute TLVs
The following Link Attribute TLVs are defined:
+======+=================================+===============+
| Type | Description | Section |
+======+=================================+===============+
| 1099 | Adjacency SID TLV | Section 2.2.1 |
+------+---------------------------------+---------------+
| 1100 | LAN Adjacency SID TLV | Section 2.2.2 |
+------+---------------------------------+---------------+
| 1172 | L2 Bundle Member Attributes TLV | Section 2.2.3 |
+------+---------------------------------+---------------+
Table 2: Link Attribute TLVs
These TLVs should only be added to the BGP-LS Attribute associated
with the Link NLRI that describes the link of the IGP node that is
originating the corresponding IGP TLV/sub-TLV described below.
2.2.1. Adjacency SID TLV
The Adjacency SID TLV is used in order to advertise information
related to an Adjacency SID. This information is derived from the
Adj-SID Sub-TLV of IS-IS (Section 2.2.1 of [RFC8667]), OSPFv2
(Section 6.1 of [RFC8665]), and OSPFv3 (Section 7.1 of [RFC8666]).
The Adjacency SID TLV has the following format:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags | Weight | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SID/Label/Index (variable) //
+---------------------------------------------------------------+
Figure 7: Adjacency SID TLV Format
Where:
Type: 1099
Length: Variable. Either 7 or 8 octets depending on the label or
index encoding of the SID.
Flags: 1-octet value that should be set as:
* IS-IS Adj-SID flags as defined in Section 2.2.1 of [RFC8667].
* OSPFv2 Adj-SID flags as defined in Section 6.1 of [RFC8665].
* OSPFv3 Adj-SID flags as defined in Section 7.1 of [RFC8666].
Weight: 1 octet carrying the weight used for load-balancing
purposes. The use of weight is described in Section 3.4 of
[RFC8402].
Reserved: 2 octets that MUST be set to 0 and ignored on receipt.
SID/Index/Label:
IS-IS: Label or index value as defined in Section 2.2.1 of
[RFC8667].
OSPFv2: Label or index value as defined in Section 6.1 of
[RFC8665].
OSPFv3: Label or index value as defined in Section 7.1 of
[RFC8666].
The Flags and, as an extension, the SID/Index/Label fields of this
TLV are interpreted according to the respective underlying IS-IS,
OSPFv2, or OSPFv3 protocol. The Protocol-ID of the BGP-LS Link NLRI
is used to determine the underlying protocol specification for
parsing these fields.
2.2.2. LAN Adjacency SID TLV
For a LAN, normally a node only announces its adjacency to the IS-IS
pseudonode (or the equivalent OSPF Designated and Backup Designated
Routers). The LAN Adjacency SID TLV allows a node to announce
adjacencies to all other nodes attached to the LAN in a single
instance of the BGP-LS Link NLRI. Without this TLV, the
corresponding BGP-LS Link NLRI would need to be originated for each
additional adjacency in order to advertise the SR TLVs for these
neighbor adjacencies.
This information is derived from the LAN-Adj-SID Sub-TLV of IS-IS
(Section 2.2.2 of [RFC8667]), the LAN Adj-SID Sub-TLV of OSPFv2
(Section 6.2 of [RFC8665]), and the LAN Adj-SID Sub-TLV of OSPFv3
(Section 7.2 of [RFC8666]).
The LAN Adjacency SID TLV has the following format:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags | Weight | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OSPF Neighbor ID / IS-IS System ID |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SID/Label/Index (variable) //
+---------------------------------------------------------------+
Figure 8: LAN Adjacency SID TLV Format
Where:
Type: 1100
Length: Variable. For IS-IS, it would be 13 or 14 octets depending
on the label or index encoding of the SID. For OSPF, it would be
11 or 12 octets depending on the label or index encoding of the
SID.
Flags: 1-octet value that should be set as:
* IS-IS LAN Adj-SID flags as defined in Section 2.2.2 of
[RFC8667].
* OSPFv2 LAN Adj-SID flags as defined in Section 6.2 of
[RFC8665].
* OSPFv3 LAN Adj-SID flags as defined in Section 7.2 of
[RFC8666].
Weight: 1 octet carrying the weight used for load-balancing
purposes. The use of weight is described in Section 3.4 of
[RFC8402].
Reserved: 2 octets that MUST be set to 0 and ignored on receipt.
Neighbor ID: 6 octets for IS-IS for the System ID, and 4 octets for
OSPF for the OSPF Router-ID of the neighbor.
SID/Index/Label:
IS-IS: Label or index value as defined in Section 2.2.2 of
[RFC8667].
OSPFv2: Label or index value as defined in Section 6.2 of
[RFC8665].
OSPFv3: Label or index value as defined in Section 7.2 of
[RFC8666].
The Neighbor ID, Flags, and, as an extension, the SID/Index/Label
fields of this TLV are interpreted according to the respective
underlying IS-IS, OSPFv2, or OSPFv3 protocol. The Protocol-ID of the
BGP-LS Link NLRI is used to determine the underlying protocol
specification for parsing these fields.
2.2.3. L2 Bundle Member Attributes TLV
The L2 Bundle Member Attributes TLV identifies an L2 Bundle Member
link, which in turn is associated with a parent L3 link. The L3 link
is described by the Link NLRI defined in [RFC7752], and the L2 Bundle
Member Attributes TLV is associated with the Link NLRI. The TLV MAY
include sub-TLVs that describe attributes associated with the bundle
member. The identified bundle member represents a unidirectional
path from the originating router to the neighbor specified in the
parent L3 link. Multiple L2 Bundle Member Attributes TLVs MAY be
associated with a Link NLRI.
This information is derived from L2 Bundle Member Attributes TLV of
IS-IS (Section 2 of [RFC8668]). The equivalent functionality has not
been specified as yet for OSPF.
The L2 Bundle Member Attributes TLV has the following format:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| L2 Bundle Member Descriptor |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link Attribute Sub-TLVs(variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 9: L2 Bundle Member Attributes TLV Format
Where:
Type: 1172
Length: Variable.
L2 Bundle Member Descriptor: 4-octet field that carries a link-local
identifier as defined in [RFC4202].
Link attributes for L2 Bundle Member links are advertised as sub-TLVs
of the L2 Bundle Member Attributes TLV. The sub-TLVs are identical
to existing BGP-LS TLVs as identified in the table below.
+================+==========================+====================+
| TLV Code Point | Description | Reference Document |
+================+==========================+====================+
| 1088 | Administrative group | [RFC7752] |
| | (color) | |
+----------------+--------------------------+--------------------+
| 1089 | Maximum link bandwidth | [RFC7752] |
+----------------+--------------------------+--------------------+
| 1090 | Max. reservable link | [RFC7752] |
| | bandwidth | |
+----------------+--------------------------+--------------------+
| 1091 | Unreserved bandwidth | [RFC7752] |
+----------------+--------------------------+--------------------+
| 1092 | TE default metric | [RFC7752] |
+----------------+--------------------------+--------------------+
| 1093 | Link protection type | [RFC7752] |
+----------------+--------------------------+--------------------+
| 1099 | Adjacency Segment | Section 2.2.1 |
| | Identifier (Adj-SID) TLV | |
+----------------+--------------------------+--------------------+
| 1100 | LAN Adjacency Segment | Section 2.2.2 |
| | Identifier (Adj-SID) TLV | |
+----------------+--------------------------+--------------------+
| 1114 | Unidirectional link | [RFC8571] |
| | delay | |
+----------------+--------------------------+--------------------+
| 1115 | Min/Max Unidirectional | [RFC8571] |
| | link delay | |
+----------------+--------------------------+--------------------+
| 1116 | Unidirectional Delay | [RFC8571] |
| | Variation | |
+----------------+--------------------------+--------------------+
| 1117 | Unidirectional Link Loss | [RFC8571] |
+----------------+--------------------------+--------------------+
| 1118 | Unidirectional residual | [RFC8571] |
| | bandwidth | |
+----------------+--------------------------+--------------------+
| 1119 | Unidirectional available | [RFC8571] |
| | bandwidth | |
+----------------+--------------------------+--------------------+
| 1120 | Unidirectional Utilized | [RFC8571] |
| | Bandwidth | |
+----------------+--------------------------+--------------------+
Table 3: BGP-LS Attribute TLVs are also used as sub-TLVs of
the L2 Bundle Member Attributes TLV
2.3. Prefix Attribute TLVs
The following Prefix Attribute TLVs are defined:
+======+==========================+===============+
| Type | Description | Section |
+======+==========================+===============+
| 1158 | Prefix-SID | Section 2.3.1 |
+------+--------------------------+---------------+
| 1159 | Range | Section 2.3.5 |
+------+--------------------------+---------------+
| 1170 | Prefix Attribute Flags | Section 2.3.2 |
+------+--------------------------+---------------+
| 1171 | Source Router Identifier | Section 2.3.3 |
+------+--------------------------+---------------+
| 1174 | Source OSPF Router-ID | Section 2.3.4 |
+------+--------------------------+---------------+
Table 4: Prefix Attribute TLVs
These TLVs should only be added to the BGP-LS Attribute associated
with the Prefix NLRI that describes the prefix of the IGP node that
is originating the corresponding IGP TLV/sub-TLV described below.
2.3.1. Prefix-SID TLV
The Prefix-SID TLV is used in order to advertise information related
to a Prefix-SID. This information is derived from the Prefix-SID
Sub-TLV of IS-IS (Section 2.1 of [RFC8667]), the Prefix-SID Sub-TLV
of OSPFv2 (Section 5 of [RFC8665]), and the Prefix-SID Sub-TLV of
OSPFv3 (Section 6 of [RFC8666]).
The Prefix-SID TLV has the following format:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags | Algorithm | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SID/Index/Label (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 10: Prefix-SID TLV Format
Where:
Type: 1158
Length: Variable. 7 or 8 octets depending on the label or index
encoding of the SID.
Flags: 1-octet value that should be set as:
* IS-IS Prefix-SID flags as defined in Section 2.1.1 of
[RFC8667].
* OSPFv2 Prefix-SID flags as defined in Section 5 of [RFC8665].
* OSPFv3 Prefix-SID flags as defined in Section 6 of [RFC8665].
Algorithm: 1-octet value identifies the algorithm. The semantics of
the algorithm are described in Section 3.1.1 of [RFC8402].
Reserved: 2 octets that MUST be set to 0 and ignored on receipt.
SID/Index/Label:
IS-IS: Label or index value as defined in Section 2.1 of
[RFC8667].
OSPFv2: Label or index value as defined in Section 5 of
[RFC8665].
OSPFv3: Label or index value as defined in Section 6 of
[RFC8666].
The Flags and, as an extension, the SID/Index/Label fields of this
TLV are interpreted according to the respective underlying IS-IS,
OSPFv2, or OSPFv3 protocol. The Protocol-ID of the BGP-LS Prefix
NLRI is used to determine the underlying protocol specification for
parsing these fields.
2.3.2. Prefix Attribute Flags TLV
The Prefix Attribute Flags TLV carries IPv4/IPv6 prefix attribute
flags information. These flags are defined for OSPFv2 in Section 2.1
of [RFC7684], OSPFv3 in Appendix A.4.1.1 of [RFC5340], and IS-IS in
Section 2.1 of [RFC7794].
The Prefix Attribute Flags TLV has the following format:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 11: Prefix Attribute Flags TLV Format
Where:
Type: 1170
Length: Variable.
Flags: a variable-length Flag field (according to the Length field).
Flags are routing protocol specific and are to be set as below:
* IS-IS flags correspond to the IPv4/IPv6 Extended Reachability
Attribute Flags defined in Section 2.1 of [RFC7794]. In the
case of the X-flag when associated with IPv6 prefix
reachability, the setting corresponds to the setting of the
X-flag in the fixed format of IS-IS TLVs 236 [RFC5308] and 237
[RFC5120].
* OSPFv2 flags correspond to the Flags field of the OSPFv2
Extended Prefix TLV defined in Section 2.1 of [RFC7684].
* OSPFv3 flags map to the Prefix Options field defined in
Appendix A.4.1.1 of [RFC5340] and extended in Section 3.1 of
[RFC8362].
The Flags field of this TLV is interpreted according to the
respective underlying IS-IS, OSPFv2, or OSPFv3 protocol. The
Protocol-ID of the BGP-LS Prefix NLRI is used to determine the
underlying protocol specification for parsing this field.
2.3.3. Source Router Identifier TLV
The Source Router Identifier TLV contains the IPv4 or IPv6 Router
Identifier of the originator of the prefix. For the IS-IS protocol,
this is derived from the IPv4/IPv6 Source Router ID Sub-TLV as
defined in Section 2.2 of [RFC7794]. For the OSPF protocol, this is
derived from the Prefix Source Router Address Sub-TLV as defined in
Section 2.2 of [RFC9084].
The Source Router Identifier TLV has the following format:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 4- or 16-octet Router Identifier //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 12: Source Router Identifier TLV Format
Where:
Type: 1171
Length: Variable. 4 or 16 octets for the IPv4 or IPv6 prefix,
respectively.
Router-ID: the IPv4 or IPv6 Router-ID in the case of IS-IS, and the
IPv4 or IPv6 Router Address in the case of OSPF.
2.3.4. Source OSPF Router-ID TLV
The Source OSPF Router-ID TLV is applicable only for the OSPF
protocol and contains the OSPF Router-ID of the originator of the
prefix. It is derived from the Prefix Source OSPF Router-ID Sub-TLV
as defined in Section 2.1 of [RFC9084].
The Source OSPF Router-ID TLV has the following format:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 4-octet OSPF Router-ID //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 13: Source OSPF Router-ID TLV Format
Where:
Type: 1174
Length: 4 octets
OSPF Router-ID: the OSPF Router-ID of the node originating the
prefix.
2.3.5. Range TLV
The Range TLV is used in order to advertise a range of prefix-to-SID
mappings as part of the SRMS functionality [RFC8661], as defined in
the respective underlying IGP SR extensions: Section 4 of [RFC8665],
Section 5 of [RFC8666], and Section 2.4 of [RFC8667]. The
information advertised in the Range TLV is derived from the SID/Label
Binding TLV in the case of IS-IS and the OSPFv2/OSPFv3 Extended
Prefix Range TLV in the case of OSPFv2/OSPFv3.
A Prefix NLRI, that has been advertised with a Range TLV, is
considered a normal routing prefix (i.e., prefix reachability) only
when there is also an IGP metric TLV (TLV 1095) associated it.
Otherwise, it is considered only as the first prefix in the range for
prefix-to-SID mapping advertisement.
The format of the Range TLV is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags | Reserved | Range Size |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| sub-TLVs //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 14: Range TLV Format
Where:
Type: 1159
Length: Variable. 11 or 12 octets depending on the label or index
encoding of the SID.
Flags: 1-octet value that should be set as:
* IS-IS SID/Label Binding TLV flags as defined in Section 2.4.1
of [RFC8667].
* OSPFv2 OSPF Extended Prefix Range TLV flags as defined in
Section 4 of [RFC8665].
* OSPFv3 Extended Prefix Range TLV flags as defined in Section 5
of [RFC8666].
Reserved: 1 octet that MUST be set to 0 and ignored on receipt.
Range Size: 2 octets that carry the number of prefixes that are
covered by the advertisement.
The Flags field of this TLV is interpreted according to the
respective underlying IS-IS, OSPFv2, or OSPFv3 protocol. The
Protocol-ID of the BGP-LS Prefix NLRI is used to determine the
underlying protocol specification for parsing this field.
The prefix-to-SID mappings are advertised using sub-TLVs as below:
IS-IS:
SID/Label Range TLV
Prefix-SID Sub-TLV
OSPFv2/OSPFv3:
OSPFv2/OSPFv3 Extended Prefix Range TLV
Prefix-SID Sub-TLV
BGP-LS:
Range TLV
Prefix-SID TLV (used as a sub-TLV in this context)
The prefix-to-SID mapping information for the BGP-LS Prefix-SID TLV
(used as a sub-TLV in this context) is encoded as described in
Section 2.3.1.
2.4. Equivalent IS-IS Segment Routing TLVs/Sub-TLVs
This section illustrates the IS-IS Segment Routing Extensions TLVs
and sub-TLVs mapped to the ones defined in this document.
For each BGP-LS TLV, the following table illustrates its equivalence
in IS-IS.
+========================+==============================+===========+
| Description | IS-IS TLV/sub-TLV | Reference |
+========================+==============================+===========+
| SR Capabilities | SR-Capabilities Sub-TLV (2) | [RFC8667] |
+------------------------+------------------------------+-----------+
| SR Algorithm | SR-Algorithm Sub-TLV (19) | [RFC8667] |
+------------------------+------------------------------+-----------+
| SR Local Block | SR Local Block Sub-TLV (22) | [RFC8667] |
+------------------------+------------------------------+-----------+
| SRMS Preference | SRMS Preference Sub-TLV (19) | [RFC8667] |
+------------------------+------------------------------+-----------+
| Adjacency SID | Adj-SID Sub-TLV (31) | [RFC8667] |
+------------------------+------------------------------+-----------+
| LAN Adjacency SID | LAN-Adj-SID Sub-TLV (32) | [RFC8667] |
+------------------------+------------------------------+-----------+
| Prefix-SID | Prefix-SID Sub-TLV (3) | [RFC8667] |
+------------------------+------------------------------+-----------+
| Range | SID/Label Binding TLV (149) | [RFC8667] |
+------------------------+------------------------------+-----------+
| SID/Label | SID/Label Sub-TLV (1) | [RFC8667] |
+------------------------+------------------------------+-----------+
| Prefix Attribute | Prefix Attribute Flags Sub- | [RFC7794] |
| Flags | TLV (4) | |
+------------------------+------------------------------+-----------+
| Source Router | IPv4/IPv6 Source Router ID | [RFC7794] |
| Identifier | Sub-TLV (11/12) | |
+------------------------+------------------------------+-----------+
| L2 Bundle Member | L2 Bundle Member Attributes | [RFC8668] |
| Attributes | TLV (25) | |
+------------------------+------------------------------+-----------+
Table 5: IS-IS Segment Routing Extensions TLVs/Sub-TLVs
2.5. Equivalent OSPFv2/OSPFv3 Segment Routing TLVs/Sub-TLVs
This section illustrates the OSPFv2 and OSPFv3 Segment Routing
Extensions TLVs and sub-TLVs mapped to the ones defined in this
document.
For each BGP-LS TLV, the following tables illustrate its equivalence
in OSPFv2 and OSPFv3.
+===================+==========================+===========+
| Description | OSPFv2 TLV/sub-TLV | Reference |
+===================+==========================+===========+
| SR Capabilities | SID/Label Range TLV (9) | [RFC8665] |
+-------------------+--------------------------+-----------+
| SR Algorithm | SR-Algorithm TLV (8) | [RFC8665] |
+-------------------+--------------------------+-----------+
| SR Local Block | SR Local Block TLV (14) | [RFC8665] |
+-------------------+--------------------------+-----------+
| SRMS Preference | SRMS Preference TLV (15) | [RFC8665] |
+-------------------+--------------------------+-----------+
| Adjacency SID | Adj-SID Sub-TLV (2) | [RFC8665] |
+-------------------+--------------------------+-----------+
| LAN Adjacency SID | LAN Adj-SID Sub-TLV (3) | [RFC8665] |
+-------------------+--------------------------+-----------+
| Prefix-SID | Prefix-SID Sub-TLV (2) | [RFC8665] |
+-------------------+--------------------------+-----------+
| Range | OSPF Extended Prefix | [RFC8665] |
| | Range TLV (2) | |
+-------------------+--------------------------+-----------+
| SID/Label | SID/Label Sub-TLV (1) | [RFC8665] |
+-------------------+--------------------------+-----------+
| Prefix Attribute | Flags of OSPFv2 Extended | [RFC7684] |
| Flags | Prefix TLV (1) | |
+-------------------+--------------------------+-----------+
| Source Router | Prefix Source Router | [RFC9084] |
| Identifier | Address Sub-TLV (5) | |
+-------------------+--------------------------+-----------+
| Source OSPF | Prefix Source OSPF | [RFC9084] |
| Router-ID | Router-ID Sub-TLV (4) | |
+-------------------+--------------------------+-----------+
Table 6: OSPFv2 Segment Routing Extensions TLVs/Sub-TLVs
+===================+==========================+===========+
| Description | OSPFv3 TLV/sub-TLV | Reference |
+===================+==========================+===========+
| SR Capabilities | SID/Label Range TLV (9) | [RFC8665] |
+-------------------+--------------------------+-----------+
| SR Algorithm | SR-Algorithm TLV (8) | [RFC8665] |
+-------------------+--------------------------+-----------+
| SR Local Block | SR Local Block TLV (14) | [RFC8665] |
+-------------------+--------------------------+-----------+
| SRMS Preference | SRMS Preference TLV (15) | [RFC8665] |
+-------------------+--------------------------+-----------+
| Adjacency SID | Adj-SID Sub-TLV (5) | [RFC8666] |
+-------------------+--------------------------+-----------+
| LAN Adjacency SID | LAN Adj-SID Sub-TLV (6) | [RFC8666] |
+-------------------+--------------------------+-----------+
| Prefix-SID | Prefix-SID Sub-TLV (4) | [RFC8666] |
+-------------------+--------------------------+-----------+
| Range | OSPFv3 Extended Prefix | [RFC8666] |
| | Range TLV (9) | |
+-------------------+--------------------------+-----------+
| SID/Label | SID/Label Sub-TLV (7) | [RFC8666] |
+-------------------+--------------------------+-----------+
| Prefix Attribute | Prefix Option Fields of | [RFC8362] |
| Flags | Prefix TLV types 3,5,6 | |
+-------------------+--------------------------+-----------+
| Source OSPF | Prefix Source Router | [RFC9084] |
| Router Identifier | Address Sub-TLV (28) | |
+-------------------+--------------------------+-----------+
| Source OSPF | Prefix Source OSPF | [RFC9084] |
| Router-ID | Router-ID Sub-TLV (27) | |
+-------------------+--------------------------+-----------+
Table 7: OSPFv3 Segment Routing Extensions TLVs/Sub-TLVs
3. IANA Considerations
IANA has registered the following code points in the "BGP-LS Node
Descriptor, Link Descriptor, Prefix Descriptor, and Attribute TLVs"
registry under the "Border Gateway Protocol - Link State (BGP-LS)
Parameter" registry based on Table 8. The column "IS-IS TLV/Sub-TLV"
defined in the registry does not require any value and should be left
empty.
3.1. TLV/Sub-TLV Code Points Summary
This section contains the global table of all TLVs/sub-TLVs defined
in this document.
+================+=============================+===============+
| TLV Code Point | Description | Reference |
+================+=============================+===============+
| 1034 | SR Capabilities | Section 2.1.2 |
+----------------+-----------------------------+---------------+
| 1035 | SR Algorithm | Section 2.1.3 |
+----------------+-----------------------------+---------------+
| 1036 | SR Local Block | Section 2.1.4 |
+----------------+-----------------------------+---------------+
| 1037 | SRMS Preference | Section 2.1.5 |
+----------------+-----------------------------+---------------+
| 1099 | Adjacency SID | Section 2.2.1 |
+----------------+-----------------------------+---------------+
| 1100 | LAN Adjacency SID | Section 2.2.2 |
+----------------+-----------------------------+---------------+
| 1158 | Prefix-SID | Section 2.3.1 |
+----------------+-----------------------------+---------------+
| 1159 | Range | Section 2.3.5 |
+----------------+-----------------------------+---------------+
| 1161 | SID/Label | Section 2.1.1 |
+----------------+-----------------------------+---------------+
| 1170 | Prefix Attribute Flags | Section 2.3.2 |
+----------------+-----------------------------+---------------+
| 1171 | Source Router Identifier | Section 2.3.3 |
+----------------+-----------------------------+---------------+
| 1172 | L2 Bundle Member Attributes | Section 2.2.3 |
+----------------+-----------------------------+---------------+
| 1174 | Source OSPF Router-ID | Section 2.3.4 |
+----------------+-----------------------------+---------------+
Table 8: Summary of TLV/Sub-TLV Code Points
4. Manageability Considerations
This section is structured as recommended in [RFC5706].
The new protocol extensions introduced in this document augment the
existing IGP topology information that is distributed via [RFC7752].
Procedures and protocol extensions defined in this document do not
affect the BGP protocol operations and management other than as
discussed in the Manageability Considerations section of [RFC7752].
Specifically, the malformed attribute tests for syntactic checks in
the Fault Management section of [RFC7752] now encompass the new BGP-
LS Attribute TLVs defined in this document. The semantic or content
checking for the TLVs specified in this document and their
association with the BGP-LS NLRI types or their BGP-LS Attribute is
left to the consumer of the BGP-LS information (e.g., an application
or a controller) and not the BGP protocol.
A consumer of the BGP-LS information retrieves this information over
a BGP-LS session (refer to Sections 1 and 2 of [RFC7752]). The
handling of semantic or content errors by the consumer would be
dictated by the nature of its application usage and hence is beyond
the scope of this document.
This document only introduces new Attribute TLVs, and any syntactic
error in them would result in the BGP-LS Attribute being discarded
with an error log. The SR information introduced in BGP-LS by this
specification may be used by BGP-LS consumer applications like an SR
Path Computation Engine (PCE) to learn the SR capabilities of the
nodes in the topology and the mapping of SR segments to those nodes.
This can enable the SR PCE to perform path computations based on SR
for traffic engineering use cases and to steer traffic on paths
different from the underlying IGP-based distributed best-path
computation. Errors in the encoding or decoding of the SR
information may result in the unavailability of such information to
the SR PCE or incorrect information being made available to it. This
may result in the SR PCE not being able to perform the desired SR-
based optimization functionality or to perform it in an unexpected or
inconsistent manner. The handling of such errors by applications
like SR PCE may be implementation specific and out of scope of this
document.
The extensions, specified in this document, do not introduce any new
configuration or monitoring aspects in BGP or BGP-LS other than as
discussed in [RFC7752]. The manageability aspects of the underlying
SR features are covered by [RFC9020], [ISIS-SR-YANG], and
[OSPF-SR-YANG].
5. Security Considerations
The new protocol extensions introduced in this document augment the
existing IGP topology information that is distributed via [RFC7752].
The advertisement of the SR link attribute information defined in
this document presents similar risk as associated with the existing
set of link attribute information as described in [RFC7752]. The
Security Considerations section of [RFC7752] also applies to these
extensions. The procedures and new TLVs defined in this document, by
themselves, do not affect the BGP-LS security model discussed in
[RFC7752].
The TLVs introduced in this document are used to propagate IGP-
defined information (see [RFC8665], [RFC8666], and [RFC8667]). These
TLVs represent the SR information associated with the IGP node, link,
and prefix. The IGP instances originating these TLVs are assumed to
support all the required security and authentication mechanisms (as
described in [RFC8665], [RFC8666], and [RFC8667]) in order to prevent
any security issue when propagating the TLVs into BGP-LS.
BGP-LS SR extensions enable traffic engineering use cases within the
SR domain. SR operates within a trusted domain [RFC8402], and its
security considerations also apply to BGP-LS sessions when carrying
SR information. The SR traffic engineering policies using the SIDs
advertised via BGP-LS are expected to be used entirely within this
trusted SR domain (e.g., between multiple ASes/domains within a
single provider network). Therefore, precaution is necessary to
ensure that the link-state information (including SR information)
advertised via BGP-LS sessions is limited to consumers in a secure
manner within this trusted SR domain. BGP peering sessions for
address families other than link state may be set up to routers
outside the SR domain. The isolation of BGP-LS peering sessions is
recommended to ensure that BGP-LS topology information (including the
newly added SR information) is not advertised to an external BGP
peering session outside the SR domain.
6. References
6.1. Normative References
[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>.
[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>.
[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>.
[RFC5308] Hopps, C., "Routing IPv6 with IS-IS", RFC 5308,
DOI 10.17487/RFC5308, October 2008,
<https://www.rfc-editor.org/info/rfc5308>.
[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>.
[RFC7684] Psenak, P., Gredler, H., Shakir, R., Henderickx, W.,
Tantsura, J., and A. Lindem, "OSPFv2 Prefix/Link Attribute
Advertisement", RFC 7684, DOI 10.17487/RFC7684, November
2015, <https://www.rfc-editor.org/info/rfc7684>.
[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>.
[RFC7794] Ginsberg, L., Ed., Decraene, B., Previdi, S., Xu, X., and
U. Chunduri, "IS-IS Prefix Attributes for Extended IPv4
and IPv6 Reachability", RFC 7794, DOI 10.17487/RFC7794,
March 2016, <https://www.rfc-editor.org/info/rfc7794>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8362] Lindem, A., Roy, A., Goethals, D., Reddy Vallem, V., and
F. Baker, "OSPFv3 Link State Advertisement (LSA)
Extensibility", RFC 8362, DOI 10.17487/RFC8362, April
2018, <https://www.rfc-editor.org/info/rfc8362>.
[RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
Decraene, B., Litkowski, S., and R. Shakir, "Segment
Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
July 2018, <https://www.rfc-editor.org/info/rfc8402>.
[RFC8571] Ginsberg, L., Ed., Previdi, S., Wu, Q., Tantsura, J., and
C. Filsfils, "BGP - Link State (BGP-LS) Advertisement of
IGP Traffic Engineering Performance Metric Extensions",
RFC 8571, DOI 10.17487/RFC8571, March 2019,
<https://www.rfc-editor.org/info/rfc8571>.
[RFC8665] Psenak, P., Ed., Previdi, S., Ed., Filsfils, C., Gredler,
H., Shakir, R., Henderickx, W., and J. Tantsura, "OSPF
Extensions for Segment Routing", RFC 8665,
DOI 10.17487/RFC8665, December 2019,
<https://www.rfc-editor.org/info/rfc8665>.
[RFC8666] Psenak, P., Ed. and S. Previdi, Ed., "OSPFv3 Extensions
for Segment Routing", RFC 8666, DOI 10.17487/RFC8666,
December 2019, <https://www.rfc-editor.org/info/rfc8666>.
[RFC8667] Previdi, S., Ed., Ginsberg, L., Ed., Filsfils, C.,
Bashandy, A., Gredler, H., and B. Decraene, "IS-IS
Extensions for Segment Routing", RFC 8667,
DOI 10.17487/RFC8667, December 2019,
<https://www.rfc-editor.org/info/rfc8667>.
[RFC8668] Ginsberg, L., Ed., Bashandy, A., Filsfils, C., Nanduri,
M., and E. Aries, "Advertising Layer 2 Bundle Member Link
Attributes in IS-IS", RFC 8668, DOI 10.17487/RFC8668,
December 2019, <https://www.rfc-editor.org/info/rfc8668>.
[RFC9084] Wang, A., Lindem, A., Dong, J., Psenak, P., and K.
Talaulikar, Ed., "OSPF Prefix Originator Extensions",
RFC 9084, DOI 10.17487/RFC9084, August 2021,
<https://www.rfc-editor.org/info/rfc9084>.
6.2. Informative References
[ISIS-SR-YANG]
Litkowski, S., Qu, Y., Sarkar, P., Chen, I., and J.
Tantsura, "YANG Data Model for IS-IS Segment Routing",
Work in Progress, Internet-Draft, draft-ietf-isis-sr-yang-
10, 21 February 2021,
<https://datatracker.ietf.org/doc/html/draft-ietf-isis-sr-
yang-10>.
[OSPF-SR-YANG]
Yeung, D., Qu, Y., Zhang, J., Chen, I., and A. Lindem,
"YANG Data Model for OSPF SR (Segment Routing) Protocol",
Work in Progress, Internet-Draft, draft-ietf-ospf-sr-yang-
15, 2 July 2021, <https://datatracker.ietf.org/doc/html/
draft-ietf-ospf-sr-yang-15>.
[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>.
[RFC8661] Bashandy, A., Ed., Filsfils, C., Ed., Previdi, S.,
Decraene, B., and S. Litkowski, "Segment Routing MPLS
Interworking with LDP", RFC 8661, DOI 10.17487/RFC8661,
December 2019, <https://www.rfc-editor.org/info/rfc8661>.
[RFC9020] Litkowski, S., Qu, Y., Lindem, A., Sarkar, P., and J.
Tantsura, "YANG Data Model for Segment Routing", RFC 9020,
DOI 10.17487/RFC9020, May 2021,
<https://www.rfc-editor.org/info/rfc9020>.
Acknowledgements
The authors would like to thank Jeffrey Haas, Aijun Wang, Robert
Raszuk, and Susan Hares for their review of this document and their
comments. The authors would also like to thank Alvaro Retana for his
extensive review and comments, which helped correct issues and
improve the document.
Contributors
The following people have substantially contributed to the editing of
this document:
Peter Psenak
Cisco Systems
Email: ppsenak@cisco.com
Les Ginsberg
Cisco Systems
Email: ginsberg@cisco.com
Acee Lindem
Cisco Systems
Email: acee@cisco.com
Saikat Ray
Individual
Email: raysaikat@gmail.com
Jeff Tantsura
Apstra Inc.
Email: jefftant.ietf@gmail.com
Authors' Addresses
Stefano Previdi
Huawei Technologies
Rome
Italy
Email: stefano@previdi.net
Ketan Talaulikar (editor)
Cisco Systems, Inc.
India
Email: ketant@cisco.com
Clarence Filsfils
Cisco Systems, Inc.
Brussels
Belgium
Email: cfilsfil@cisco.com
Hannes Gredler
RtBrick Inc.
Email: hannes@rtbrick.com
Mach(Guoyi) Chen
Huawei Technologies
Huawei Building, No. 156 Beiqing Rd.
Beijing
100095
China
Email: mach.chen@huawei.com