Internet DRAFT - draft-ietf-idr-bgp-ls-segment-routing-ext
draft-ietf-idr-bgp-ls-segment-routing-ext
Inter-Domain Routing S. Previdi
Internet-Draft Huawei Technologies
Intended status: Standards Track K. Talaulikar, Ed.
Expires: October 17, 2021 C. Filsfils
Cisco Systems, Inc.
H. Gredler
RtBrick Inc.
M. Chen
Huawei Technologies
April 15, 2021
BGP Link-State extensions for Segment Routing
draft-ietf-idr-bgp-ls-segment-routing-ext-18
Abstract
Segment Routing (SR) allows for a flexible definition of end-to-end
paths by encoding paths as sequences of topological sub-paths, 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 BGP Link-state address-family
in order to carry segment routing information via BGP.
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.
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."
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This Internet-Draft will expire on October 17, 2021.
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 . . . . . . . . . . . . . . . . . . . . . . . . 3
2. BGP-LS Extensions for Segment Routing . . . . . . . . . . . . 5
2.1. Node Attributes TLVs . . . . . . . . . . . . . . . . . . 5
2.1.1. SID/Label TLV . . . . . . . . . . . . . . . . . . . . 5
2.1.2. SR Capabilities TLV . . . . . . . . . . . . . . . . . 6
2.1.3. SR Algorithm TLV . . . . . . . . . . . . . . . . . . 8
2.1.4. SR Local Block TLV . . . . . . . . . . . . . . . . . 8
2.1.5. SRMS Preference TLV . . . . . . . . . . . . . . . . . 10
2.2. Link Attribute TLVs . . . . . . . . . . . . . . . . . . . 11
2.2.1. Adjacency SID TLV . . . . . . . . . . . . . . . . . . 11
2.2.2. LAN Adjacency SID TLV . . . . . . . . . . . . . . . . 12
2.2.3. L2 Bundle Member Attribute TLV . . . . . . . . . . . 14
2.3. Prefix Attribute TLVs . . . . . . . . . . . . . . . . . . 15
2.3.1. Prefix SID TLV . . . . . . . . . . . . . . . . . . . 16
2.3.2. Prefix Attribute Flags TLV . . . . . . . . . . . . . 17
2.3.3. Source Router Identifier TLV . . . . . . . . . . . . 18
2.3.4. Source OSPF Router-ID TLV . . . . . . . . . . . . . . 19
2.3.5. Range TLV . . . . . . . . . . . . . . . . . . . . . . 20
2.4. Equivalent IS-IS Segment Routing TLVs/Sub-TLVs . . . . . 21
2.5. Equivalent OSPFv2/OSPFv3 Segment Routing TLVs/Sub-TLVs . 22
3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 25
3.1. TLV/Sub-TLV Code Points Summary . . . . . . . . . . . . . 25
4. Manageability Considerations . . . . . . . . . . . . . . . . 25
5. Security Considerations . . . . . . . . . . . . . . . . . . . 26
6. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 27
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 28
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 28
8.1. Normative References . . . . . . . . . . . . . . . . . . 28
8.2. Informative References . . . . . . . . . . . . . . . . . 30
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Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 30
1. Introduction
Segment Routing (SR) allows for a flexible definition of end-to-end
paths by combining sub-paths 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 sub-paths, 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 Segment Routing 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, Segment Routing can be enabled within an IGP domain.
Segment Routing (SR) allows advertisement of single or multi-hop
paths. The flooding scope for the IGP extensions for Segment routing
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 and therefore, by using the IGP alone it is not enough
to construct segments across multiple IGP Area or AS boundaries.
In order to address the need for applications that require
topological visibility across IGP areas, or even across Autonomous
Systems (AS), the BGP-LS address-family/sub-address-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.
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+------------+
| Consumer |
+------------+
^
|
v
+-------------------+
| BGP Speaker | +-----------+
| (Route-Reflector) | | Consumer |
+-------------------+ +-----------+
^ ^ ^ ^
| | | |
+---------------+ | +-------------------+ |
| | | |
v v v v
+-----------+ +-----------+ +-----------+
| BGP | | BGP | | BGP |
| Speaker | | Speaker | . . . | Speaker |
+-----------+ +-----------+ +-----------+
^ ^ ^
| | |
IGP IGP IGP
Figure 1: Link State info 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 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
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
need 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 or multiple ASes managed by the same administrative entity
e.g. within a single provider network.
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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. Section 2.4 and Section 2.5 lists the equivalent TLVs and
sub-TLVs in 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. BGP-LS [RFC7752] 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 Attributes 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 describing 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.
o IS-IS, as defined by the SID/Label sub-TLV in section 2.3 of
[RFC8667].
o 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:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SID/Label (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: SID/Label TLV Format
Where:
Type: 1161
Length: Variable. Either 3 or 4 depending whether the value is
encoded as a label or as an index/SID.
SID/Label: If 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 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.
o IS-IS, as defined by the SR Capabilities sub-TLV in section 3.1 of
[RFC8667].
o 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:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 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. Minimum length is 12.
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 octet 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 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.
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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.
o IS-IS, as defined by the SR-Algorithm sub-TLV in section 3.2 of
[RFC8667].
o 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. Minimum length is 1 and maximum can be 256.
Algorithm: One or more fields of 1 octet each identifying the
algorithm.
2.1.4. SR Local Block TLV
The SR Local Block (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, it is required that the node
advertises its SRLB.
This information is derived from the protocol specific
advertisements.
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o IS-IS, as defined by the SR Local Block sub-TLV in section 3.3 of
[RFC8667].
o 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. Minimum length is 12.
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 sub-range(s), each of which
have the following format:
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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 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 SRMS preference of the node advertising the SRMS Prefix-to-SID
Mapping ranges.
This information is derived from the protocol specific
advertisements.
o IS-IS, as defined by the SRMS Preference sub-TLV in section 3.4 of
[RFC8667].
o 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.
Preference: 1 octet carrying an unsigned 8 bit SRMS preference.
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2.2. Link Attribute TLVs
The following Link Attribute TLVs are 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 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 describing 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 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 depending on Label or Index
encoding of the SID
Flags. 1 octet value which should be set as:
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* IS-IS Adj-SID flags are defined in section 2.2.1 of [RFC8667].
* OSPFv2 Adj-SID flags are defined in section 6.1 of [RFC8665].
* OSPFv3 Adj-SID flags are 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
pseudo-node (or the equivalent OSPF Designated and Backup Designated
Routers). The LAN Adjacency Segment 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 LAN-Adj-SID sub-TLV of IS-IS
(section 2.2.2 of [RFC8667]) and LAN Adj-SID sub-TLV of OSPFv2
(section 6.2 of [RFC8665]) and OSPFv3 (section 7.2 of [RFC8666]).
The LAN Adjacency SID TLV has the following format:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 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 depending on
Label or Index encoding of the SID. For OSPF it would be 11 or 12
depending on Label or Index encoding of the SID.
Flags. 1 octet value which should be set as:
* IS-IS LAN Adj-SID flags are defined in section 2.2.2 of
[RFC8667].
* OSPFv2 LAN Adj-SID flags are defined in section 6.2 of
[RFC8665].
* OSPFv3 LAN Adj-SID flags are 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.
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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 Attribute TLV
The L2 Bundle Member Attribute 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 Attribute TLV is associated with the Link NLRI. The TLV MAY
include sub-TLVs which 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 Attribute 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 Attribute 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
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Where:
Type: 1172
Length: Variable.
L2 Bundle Member Descriptor: 4 octets 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 Attribute TLV. The sub-TLVs are identical to
existing BGP-LS TLVs as identified in the table below.
+-------------+------------------------------------+----------------+
| TLV Code | Description | Reference |
| Point | | Document |
+-------------+------------------------------------+----------------+
| 1088 | Administrative group (color) | [RFC7752] |
| 1089 | Maximum link bandwidth | [RFC7752] |
| 1090 | Max. reservable link bandwidth | [RFC7752] |
| 1091 | Unreserved bandwidth | [RFC7752] |
| 1092 | TE default metric | [RFC7752] |
| 1093 | Link protection type | [RFC7752] |
| 1099 | Adjacency Segment Identifier (Adj- | Section 2.2.1 |
| | SID) TLV | |
| 1100 | LAN Adjacency Segment Identifier | Section 2.2.2 |
| | (Adj-SID) TLV | |
| 1114 | Unidirectional link delay | [RFC8571] |
| 1115 | Min/Max Unidirectional link delay | [RFC8571] |
| 1116 | Unidirectional Delay Variation | [RFC8571] |
| 1117 | Unidirectional packet loss | [RFC8571] |
| 1118 | Unidirectional residual bandwidth | [RFC8571] |
| 1119 | Unidirectional available bandwidth | [RFC8571] |
| 1120 | Unidirectional bandwidth | [RFC8571] |
| | utilization | |
+-------------+------------------------------------+----------------+
Table 3: BGP-LS Attribute TLVs also used as sub-TLVs of L2 Bundle
Member Attribute TLV
2.3. Prefix Attribute TLVs
The following Prefix Attribute TLVs are defined:
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+------------------+--------------------------+---------------+
| 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 (suggested) | 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 describing 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 Prefix-SID sub-TLV
of IS-IS (section 2.1 of [RFC8667]) and the Prefix SID sub-TLV of
OSPFv2 (section 5 of [RFC8665]) and 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 depending on Label or Index encoding of
the SID
Flags: 1 octet value which should be set as:
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* IS-IS Prefix SID flags are defined in section 2.1.1 of
[RFC8667].
* OSPFv2 Prefix SID flags are defined in section 5 of [RFC8665].
* OSPFv3 Prefix SID flags are defined in section 6 of [RFC8666].
Algorithm: 1 octet value identify the algorithm. The semantics of
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], for OSPFv3 in section A.4.1.1 of [RFC5340] and for 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
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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 section
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 [I-D.ietf-lsr-ospf-prefix-originator].
The Source Router Identifier TLV has the following format:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 4 or 16 octet Router Identifier //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 12: Source Router Identifier TLV Format
Where:
Type: 1171
Length: Variable. 4 or 16 for IPv4 and IPv6 prefix respectively.
Router-ID: the IPv4 or IPv6 Router-ID in 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 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 [I-D.ietf-lsr-ospf-prefix-originator].
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 (suggested)
Length: 4
OSPF Router-ID: the OSPF Router-ID of the node originating the
prefix.
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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 Segment Routing Mapping Server (SRMS)
functionality [RFC8661], as defined in the respective underlying IGP
SR extensions [RFC8665] (section 4), [RFC8666] (section 5) and
[RFC8667] (section 2.4). 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 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 depending on Label or Index encoding of
the SID
Flags: 1 octet value which should be set as:
* IS-IS SID/Label Binding TLV flags are defined in section 2.4.1
of [RFC8667].
* OSPFv2 OSPF Extended Prefix Range TLV flags are defined in
section 4 of [RFC8665].
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* OSPFv3 Extended Prefix Range TLV flags are 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 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 illustrate the IS-IS Segment Routing Extensions TLVs and
sub-TLVs mapped to the ones defined in this document.
The following table, illustrates for each BGP-LS TLV, its equivalence
in IS-IS.
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+----------------------+--------------------------------+-----------+
| 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 Attributes 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 illustrate the OSPFv2 and OSPFv3 Segment Routing
Extensions TLVs and sub-TLVs mapped to the ones defined in this
document.
The following table, illustrates for each BGP-LS TLV, its equivalence
in OSPFv2 and OSPFv3.
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+-------------+--------------+--------------------------------------+
| Description | OSPFv2 | Reference |
| | TLV/sub-TLV | |
+-------------+--------------+--------------------------------------+
| SR Capabili | SID/Label | [RFC8665] |
| ties | Range TLV | |
| | (9) | |
| SR | SR-Algorithm | [RFC8665] |
| Algorithm | TLV (8) | |
| SR Local | SR Local | [RFC8665] |
| Block | Block TLV | |
| | (14) | |
| SRMS | SRMS | [RFC8665] |
| Preference | Preference | |
| | TLV (15) | |
| Adjacency | Adj-SID sub- | [RFC8665] |
| SID | TLV (2) | |
| LAN | LAN Adj-SID | [RFC8665] |
| Adjacency | sub-TLV (3) | |
| SID | | |
| Prefix SID | Prefix SID | [RFC8665] |
| | sub-TLV (2) | |
| Range | OSPF | [RFC8665] |
| | Extended | |
| | Prefix Range | |
| | TLV (2) | |
| SID/Label | SID/Label | [RFC8665] |
| | sub-TLV (1) | |
| Prefix | Flags of | [RFC7684] |
| Attribute | OSPFv2 | |
| Flags | Extended | |
| | Prefix TLV | |
| | (1) | |
| Source | Prefix | [I-D.ietf-lsr-ospf-prefix-originator |
| Router | Source | ] |
| Identifier | Router-ID | |
| | sub-TLV (4) | |
| Source OSPF | Prefix | [I-D.ietf-lsr-ospf-prefix-originator |
| Router-ID | Source OSPF | ] |
| | Router-ID | |
| | sub-TLV (5) | |
+-------------+--------------+--------------------------------------+
Table 6: OSPFv2 Segment Routing Extensions TLVs/Sub-TLVs
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+-------------+--------------+--------------------------------------+
| Description | OSPFv3 | Reference |
| | TLV/sub-TLV | |
+-------------+--------------+--------------------------------------+
| SR Capabili | SID/Label | [RFC8665] |
| ties | Range TLV | |
| | (9) | |
| SR | SR-Algorithm | [RFC8665] |
| Algorithm | TLV (8) | |
| SR Local | SR Local | [RFC8665] |
| Block | Block TLV | |
| | (14) | |
| SRMS | SRMS | [RFC8665] |
| Preference | Preference | |
| | TLV (15) | |
| Adjacency | Adj-SID sub- | [RFC8666] |
| SID | TLV (5) | |
| LAN | LAN Adj-SID | [RFC8666] |
| Adjacency | sub-TLV (6) | |
| SID | | |
| Prefix SID | Prefix SID | [RFC8666] |
| | sub-TLV (4) | |
| Range | OSPFv3 | [RFC8666] |
| | Extended | |
| | Prefix Range | |
| | TLV (9) | |
| SID/Label | SID/Label | [RFC8666] |
| | sub-TLV (7) | |
| Prefix | Prefix | [RFC8362] |
| Attribute | Option | |
| Flags | Fields of | |
| | Prefix TLV | |
| | types 3,5,6 | |
| Source OSPF | Prefix | [I-D.ietf-lsr-ospf-prefix-originator |
| Router | Source | ] |
| Identifier | Router-ID | |
| | sub-TLV (27) | |
| Source OSPF | Prefix | [I-D.ietf-lsr-ospf-prefix-originator |
| Router-ID | Source OSPF | ] |
| | Router-ID | |
| | sub-TLV (28) | |
+-------------+--------------+--------------------------------------+
Table 7: OSPFv3 Segment Routing Extensions TLVs/Sub-TLVs
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3. IANA Considerations
Early allocation of codepoints has been done by IANA for this
document from the registry "BGP-LS Node Descriptor, Link Descriptor,
Prefix Descriptor, and Attribute TLVs" under the "BGP-LS Parameters"
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 (suggested) | Source OSPF Router-ID | Section 2.3.4 |
+------------------+-----------------------------+---------------+
Table 8: Summary Table of TLV/Sub-TLV Codepoints
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
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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 Section 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 a 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 [I-D.ietf-spring-sr-yang],
[I-D.ietf-isis-sr-yang] and [I-D.ietf-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 ([RFC8667], [RFC8665] and [RFC8666]). These TLVs
represent the SR information associated with the IGP node, link and
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prefix. The IGP instances originating these TLVs are assumed to
support all the required security and authentication mechanisms (as
described in [RFC8667], [RFC8665] and [RFC8666]) 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
Segment Routing 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 AS/
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 setup 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. 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
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7. 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.
8. References
8.1. Normative References
[I-D.ietf-lsr-ospf-prefix-originator]
Wang, A., Lindem, A., Dong, J., Psenak, P., and K.
Talaulikar, "OSPF Prefix Originator Extensions", draft-
ietf-lsr-ospf-prefix-originator-07 (work in progress),
October 2020.
[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>.
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[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>.
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[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>.
8.2. Informative References
[I-D.ietf-isis-sr-yang]
Litkowski, S., Qu, Y., Sarkar, P., Chen, I., and J.
Tantsura, "YANG Data Model for IS-IS Segment Routing",
draft-ietf-isis-sr-yang-09 (work in progress), January
2021.
[I-D.ietf-ospf-sr-yang]
Yeung, D., Qu, Y., Zhang, Z., Chen, I., and A. Lindem,
"YANG Data Model for OSPF SR (Segment Routing) Protocol",
draft-ietf-ospf-sr-yang-13 (work in progress), January
2021.
[I-D.ietf-spring-sr-yang]
Litkowski, S., Qu, Y., Lindem, A., Sarkar, P., and J.
Tantsura, "YANG Data Model for Segment Routing", draft-
ietf-spring-sr-yang-30 (work in progress), January 2021.
[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>.
Authors' Addresses
Stefano Previdi
Huawei Technologies
Rome
Italy
Email: stefano@previdi.net
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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
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