Advertisement of Segment Routing Policies using BGP Link-State
draft-ietf-idr-bgp-ls-sr-policy-09
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| Authors | Stefano Previdi , Ketan Talaulikar , Jie Dong , Hannes Gredler , Jeff Tantsura | ||
| Last updated | 2024-12-06 (Latest revision 2024-11-28) | ||
| Replaces | draft-ietf-idr-te-lsp-distribution | ||
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draft-ietf-idr-bgp-ls-sr-policy-09
Inter-Domain Routing S. Previdi
Internet-Draft Individual
Intended status: Standards Track K. Talaulikar, Ed.
Expires: 1 June 2025 Cisco Systems
J. Dong
Huawei Technologies
H. Gredler
RtBrick Inc.
J. Tantsura
Nvidia
28 November 2024
Advertisement of Segment Routing Policies using BGP Link-State
draft-ietf-idr-bgp-ls-sr-policy-09
Abstract
This document describes a mechanism to collect the Segment Routing
Policy information that is locally available in a node and advertise
it into BGP Link-State (BGP-LS) updates. Such information can be
used by external components for path computation, re-optimization,
service placement, network visualization, etc.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 1 June 2025.
Copyright Notice
Copyright (c) 2024 IETF Trust and the persons identified as the
document authors. All rights reserved.
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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 Revised BSD License text as
described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 5
2. Carrying SR Policy Information in BGP . . . . . . . . . . . . 5
3. SR Policy Candidate Path NLRI Type . . . . . . . . . . . . . 6
4. SR Policy Candidate Path Descriptor . . . . . . . . . . . . . 7
5. SR Policy State TLVs . . . . . . . . . . . . . . . . . . . . 9
5.1. SR Binding SID TLV . . . . . . . . . . . . . . . . . . . 9
5.2. SRv6 Binding SID TLV . . . . . . . . . . . . . . . . . . 12
5.3. SR Candidate Path State TLV . . . . . . . . . . . . . . . 13
5.4. SR Policy Name TLV . . . . . . . . . . . . . . . . . . . 16
5.5. SR Candidate Path Name TLV . . . . . . . . . . . . . . . 16
5.6. SR Candidate Path Constraints TLV . . . . . . . . . . . . 17
5.6.1. SR Affinity Constraint Sub-TLV . . . . . . . . . . . 20
5.6.2. SR SRLG Constraint Sub-TLV . . . . . . . . . . . . . 21
5.6.3. SR Bandwidth Constraint Sub-TLV . . . . . . . . . . . 22
5.6.4. SR Disjoint Group Constraint Sub-TLV . . . . . . . . 22
5.6.5. SR Bidirectional Group Constraint Sub-TLV . . . . . . 25
5.6.6. SR Metric Constraint Sub-TLV . . . . . . . . . . . . 26
5.7. SR Segment List TLV . . . . . . . . . . . . . . . . . . . 29
5.8. SR Segment Sub-TLV . . . . . . . . . . . . . . . . . . . 31
5.8.1. Segment Descriptors . . . . . . . . . . . . . . . . . 33
5.9. SR Segment List Metric Sub-TLV . . . . . . . . . . . . . 40
5.10. SR Segment List Bandwidth Sub-TLV . . . . . . . . . . . . 42
5.11. SR Segment List Identifier Sub-TLV . . . . . . . . . . . 43
6. Procedures . . . . . . . . . . . . . . . . . . . . . . . . . 44
7. Manageability Considerations . . . . . . . . . . . . . . . . 44
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 45
8.1. BGP-LS NLRI-Types . . . . . . . . . . . . . . . . . . . . 45
8.2. BGP-LS Protocol-IDs . . . . . . . . . . . . . . . . . . . 45
8.3. BGP-LS TLVs . . . . . . . . . . . . . . . . . . . . . . . 45
8.4. SR Policy Protocol Origin . . . . . . . . . . . . . . . . 46
8.5. BGP-LS SR Segment Descriptors . . . . . . . . . . . . . . 47
8.6. BGP-LS SR Policy Metric Type . . . . . . . . . . . . . . 48
9. Security Considerations . . . . . . . . . . . . . . . . . . . 49
10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 50
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 50
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 50
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12.1. Normative References . . . . . . . . . . . . . . . . . . 50
12.2. Informative References . . . . . . . . . . . . . . . . . 51
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 54
1. Introduction
SR Policy architecture details are specified in [RFC9256]. An SR
Policy comprises one or more candidate paths (CP) of which at a given
time one and only one may be active (i.e., installed in forwarding
and usable for steering of traffic). Each CP in turn may have one or
more SID-List of which one or more SID-List may be active. When
multiple SID-Lists are active then traffic is load balanced over
them. This document covers the advertisement of state information at
the individual SR Policy CP level.
SR Policies are generally instantiated at the head-end and are based
on either local configuration or controller-based programming of the
node using various APIs and protocols (e.g., PCEP or BGP).
In many network environments, the configuration, and state of each SR
Policy that is available in the network is required by controllers.
Such controllers, that are aware of both topology and SR Policy state
information, allow the network operator to optimize several functions
and operations in their networks.
One example of a controller is the stateful Path Computation Element
(PCE) [RFC8231], which could provide benefits in path optimization.
While some extensions are proposed in the Path Computation Element
Communication Protocol (PCEP) for the Path Computation Clients (PCCs)
to report the LSP states to the PCE, this mechanism may not be
applicable in a management-based PCE architecture as specified in
section 5.5 of [RFC4655]. As illustrated in the figure below, the
PCC is not an LSR in the routing domain, thus the head-end nodes of
the SR Policies may not implement the PCEP protocol. In this case, a
general mechanism to collect the SR Policy states from the ingress
LERs is needed. This document proposes an SR Policy state collection
mechanism complementary to the mechanism defined in [RFC8231].
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-----------
| ----- |
Service | | TED |<-+----------->
Request | ----- | TED synchronization
| | | | mechanism (e.g.,
v | | | routing protocol)
------------- Request/ | v |
| | Response| ----- |
| NMS |<--------+> | PCE | |
| | | ----- |
------------- -----------
Service |
Request |
v
---------- Signaling ----------
| Head-End | Protocol | Adjacent |
| Node |<---------->| Node |
---------- ----------
Figure 1 Management-Based PCE Usage
In networks with composite PCE nodes as specified in section 5.1 of
[RFC4655], PCE is implemented on several routers in the network, and
the PCCs in the network can use the mechanism described in [RFC8231]
to report the SR Policy information to the PCE nodes. An external
component may also need to collect the SR Policy information from all
the PCEs in the network to obtain a global view of the state of all
SR Policy paths in the network.
In multi-area or multi-AS scenarios, each area or AS can have a child
PCE to collect the SR Policies in its domain, in addition, a parent
PCE needs to collect SR Policy information from multiple child PCEs
to obtain a global view of SR Policy paths inside and across the
domains involved.
In another network scenario, a centralized controller is used for
service placement. Obtaining the SR Policy state information is
quite important for making appropriate service placement decisions
with the purpose of both meeting the application's requirements and
utilizing network resources efficiently.
The Network Management System (NMS) may need to provide global
visibility of the SR Policies in the network as part of the network
visualization function.
BGP has been extended to distribute link-state and traffic
engineering information to external components [RFC9552]. Using the
same protocol to collect SR Policy and state information is desirable
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for these external components since this avoids introducing multiple
protocols for network topology information collection. This document
describes a mechanism to distribute SR Policy information (both SR-
MPLS, and SRv6 [RFC8402]) to external components using BGP-LS and
covers both explicit and dynamic candidate paths. The advertisements
of composite candidate path is outside the scope of this document.
While this document focuses on SR Policies,
[I-D.ietf-idr-bgp-ls-te-path] introduces further extension to support
other TE Paths such as MPLS-TE LSPs.
This extensions specified in this document complement the BGP SR
Policy SAFI [I-D.ietf-idr-sr-policy-safi] and
[I-D.ietf-idr-bgp-sr-segtypes-ext] that are used to advertise SR
Policies from controllers to the headend routers using BGP by
enabling the reporting of the operational state of those SR Policies
back from the headend to the controllers.
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. Carrying SR Policy Information in BGP
The "Link-State NLRI" defined in [RFC9552] is extended to carry the
SR Policy information. New TLVs carried in the BGP Link-State
Attribute defined in [RFC9552] are also defined to carry the
attributes of an SR Policy in the subsequent sections.
The format of "Link-State NLRI" is defined in [RFC9552] 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| NLRI Type | Total NLRI Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// Link-State NLRI (variable) //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2 BGP-LS NLRI Format
An additional "NLRI Type" known as SR Policy Candidate Path NLRI
(value 5) is defined for the advertisement of SR Policy Information.
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This SR Policy Candidate Path NLRI is used to report the state
details of individual SR Policy Candidate paths along with their
underlying segment lists.
3. SR Policy Candidate Path NLRI Type
This document defines SR Policy Candidate Path NLRI Type with its
format as shown in the following figure:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+
| Protocol-ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identifier |
| (64 bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Local Node Descriptor TLV (for the Headend) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// SR Policy Candidate Path Descriptor TLV //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3 SR Policy Candidate Path NLRI Format
Where:
* Protocol-ID field specifies the component that owns the SR Policy
state in the advertising node. An additional Protocol-ID "Segment
Routing" (value 9) is introduced by this document to be used for
advertisement of SR Policies.
* "Identifier" is an 8 octet value as defined in [RFC9552].
* "Local Node Descriptor" (TLV 256) [RFC9552] is used as specified
further in this section.
* The SR Policy Candidate Path Descriptor TLV is specified in
Section 4.
The Local Node Descriptor TLV MUST include the following Node
Descriptor TLVs only when the headend node is the BGP-LS Producer:
* BGP Router-ID (TLV 516) [RFC9086], which contains a valid BGP
Identifier of the headend node of the SR Policy.
* Autonomous System Number (TLV 512) [RFC9552], which contains the
ASN or AS Confederation Identifier (ASN) [RFC5065], if
confederations are used, of the headend node of the SR Policy.
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The Local Node Descriptor TLV MUST include at least one of the
following Node Descriptor TLVs:
* IPv4 Router-ID of Local Node (TLV 1028) [RFC9552], which
identifies the headend node of the SR Policy as specified in
section 2.1 of [RFC9256].
* IPv6 Router-ID of Local Node (TLV 1029) [RFC9552], which
identifies the headend node of the SR Policy as specified in
section 2.1 of [RFC9256].
The Local Node Descriptor TLV MAY include the following Node
Descriptor TLVs only when the headend node is the BGP-LS Producer:
* BGP Confederation Member (TLV 517) [RFC9086], which contains the
ASN of the confederation member (i.e. Member-AS Number), if BGP
confederations are used, the headend node of the SR Policy.
* Other Node Descriptors as defined in [RFC9552] to identify the
headend node of the SR Policy. The determination of whether the
IGP Router-ID sub-TLV (TLV 515) contains a 4-octet OSPF Router-ID
or a 6-octet ISO System-ID is to be done based on the length of
that sub-TLV since the Protocol-ID in the NLRI shall always be
"Segment Routing".
When a Path Computation Element (PCE) node is functioning as the BGP-
LS Producer on behalf of one or more headends, it MAY include its own
BGP Router-ID (TLV 516), Autonomous System Number (TLV 512), or BGP
Confederation Member (TLV 517) in the BGP-LS Attribute. The PCE node
MUST NOT include its identifiers in the Node Descriptor TLV in the
NLRI as the Node Descriptor TLV MUST only carry the identifiers of
the SR Policy headend.
4. SR Policy Candidate Path Descriptor
The SR Policy Candidate Path Descriptor TLV identifies a Segment
Routing Policy Candidate Path (CP) as defined in [RFC9256]. It is
used with the Protocol-ID set to Segment Routing to advertise the SR
Policy Candidate Path NLRI Type. It is a mandatory TLV for SR Policy
Candidate Path NLRI type. 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Protocol-origin| Flags | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Endpoint (4 or 16 octets) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Policy Color (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Originator AS Number (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Originator Address (4 or 16 octets) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Discriminator (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4 SR Policy Candidate Path Descriptor Format
Where:
* Type: 554
* Length: variable (valid values are 24, 36 or 48 octets)
* Protocol-Origin: 1-octet field which identifies the protocol or
component which is responsible for the instantiation of this path
as specified in section 2.3 of [RFC9256]. The protocol-origin
codepoints to be used are listed in Section 8.4.
* Flags: 1-octet field with following bit positions defined. Other
bits MUST be cleared by the originator and MUST be ignored by a
receiver.
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|E|O| |
+-+-+-+-+-+-+-+-+
Where:
- E-Flag: Indicates the encoding of endpoint as IPv6 address when
set and IPv4 address when clear
- O-Flag: Indicates the encoding of originator address as IPv6
address when set and IPv4 address when clear
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* Reserved: 2 octets which MUST be set to 0 by the originator and
MUST be ignored by a receiver.
* Endpoint: 4 or 16 octets (as indicated by the flags) containing
the address of the endpoint of the SR Policy as specified in
section 2.1 of [RFC9256].
* Color: 4 octets that indicate the color of the SR Policy as
specified in section 2.1 of [RFC9256].
* Originator ASN: 4 octets to carry the 4-byte encoding of the ASN
of the originator. Refer to section 2.4 of [RFC9256] for details.
* Originator Address: 4 or 16 octets (as indicated by the flags) to
carry the address of the originator. Refer to section 2.4 of
[RFC9256] for details.
* Discriminator: 4 octets to carry the discriminator of the path.
Refer to section 2.5 of [RFC9256] for details.
5. SR Policy State TLVs
This section defines the various TLVs which enable the headend to
report the state at the SR Policy CP level. These TLVs (and their
sub-TLVs) are carried in the optional non-transitive BGP-LS Attribute
defined in [RFC9552] associated with the SR Policy CP NLRI type.
The detailed procedures for the advertisement are described in
Section 6.
5.1. SR Binding SID TLV
The SR Binding SID (BSID) is an optional TLV that is used to report
the BSID and its attributes for the SR Policy CP. The TLV MAY also
optionally contain the Specified BSID value for reporting as
described in section 6.2.3 of [RFC9256]. Only a single instance of
this TLV is advertised for a given CP. If multiple instances are
present, then the first one is considered valid and the rest are
ignored.
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| BSID Flags | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Binding SID (4 or 16 octets) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Specified Binding SID (4 or 16 octets) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5 SR Binding SID TLV Format
Where:
* Type: 1201
* Length: variable (valid values are 12 or 36 octets)
* BSID Flags: 2-octet field that indicates attribute and status of
the Binding SID (BSID) associated with this CP. The following bit
positions are defined and the semantics are described in detail in
section 6.2 of [RFC9256]. Other bits MUST be cleared by the
originator and MUST be ignored by a receiver.
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|D|B|U|L|F| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Where:
- D-Flag: Indicates the dataplane for the BSIDs and if they are
16 octet SRv6 SID when set and are 4 octet SR/MPLS label value
when clear.
- B-Flag: Indicates the allocation of the value in the BSID field
when set and indicates that BSID is not allocated when clear.
- U-Flag: Indicates the specified BSID value is unavailable when
set. When clear it indicates that this CP is using the
specified BSID. This flag is ignored when there is no
specified BSID.
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- L-Flag: Indicates the BSID value is from the Segment Routing
Local Block (SRLB) of the headend node when set and is from the
local dynamic label pool when clear.
- F-Flag: Indicates the BSID value is one allocated from dynamic
label pool due to fallback (e.g. when specified BSID is
unavailable) when set and indicates that there has been no
fallback for BSID allocation when clear.
* RESERVED: 2 octets. MUST be set to 0 by the originator and MUST
be ignored by a receiver.
* Binding SID: It indicates the operational or allocated BSID value
based on the status flags.
* Specified BSID: It is used to report the explicitly specified BSID
value regardless of whether it is successfully allocated or not.
The field is set to value 0 when BSID has not been specified.
The BSID fields above depend on the dataplane (SRv6 or MPLS)
indicated by the D-Flag. If D-Flag set (SRv6 dataplane), then the
length of the BSID fields is 16 octets. If the D-Flag is clear (MPLS
dataplane), then the length of the BSID fields is 4 octets. When
carrying the MPLS Label, as shown in the figure below, the TC, S, and
TTL (total of 12 bits) are RESERVED and MUST be set to 0 by the
originator and MUST be ignored by a receiver.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6 SR Binding SID Label Format
In the case of an SRv6, the SR Binding SID sub-TLV does not have the
ability to signal the SRv6 Endpoint Behavior [RFC8986] or the
structure of the SID. Therefore, the SR Binding SID sub-TLV SHOULD
NOT be used for the advertisement of an SRv6 Binding SID. Instead,
the SRv6 Binding SID TLV defined in Section 5.2 SHOULD be used for
signaling of an SRv6 Binding SID. The use of the SR Binding SID sub-
TLV for advertisement of the SRv6 Binding SID is supported only for
backward compatibility with implementations that followed early
versions of this specification.
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5.2. SRv6 Binding SID TLV
The SRv6 Binding SID (BSID) is an optional TLV that is used to report
the SRv6 BSID and its attributes for the SR Policy CP. The TLV MAY
also optionally contain the Specified SRv6 BSID value for reporting
as described in section 6.2.3 of [RFC9256]. Multiple instances of
this TLV may be used to report each of the SRv6 BSIDs associated with
the CP.
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| BSID Flags | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Binding SID (16 octets) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Specified Binding SID (16 octets) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Sub-TLVs (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7 SRv6 Binding SID TLV Format
Where:
* Type: 1212
* Length: variable
* BSID Flags: 2-octet field that indicates attribute and status of
the Binding SID (BSID) associated with this CP. The following bit
positions are defined and the semantics are described in detail in
section 6.2 of [RFC9256]. Other bits MUST be cleared by the
originator and MUST be ignored by a receiver.
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|B|U|F| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Where:
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- B-Flag: Indicates the allocation of the value in the BSID field
when set and indicates that BSID is not allocated when clear.
- U-Flag: Indicates the specified BSID value is unavailable when
set. When clear it indicates that this CP is using the
specified BSID. This flag is ignored when there is no
specified BSID.
- F-Flag: Indicates the BSID value is one allocated dynamically
due to fallback (e.g. when specified BSID is unavailable) when
set and indicates that there has been no fallback for BSID
allocation when clear.
* RESERVED: 2 octets. MUST be set to 0 by the originator and MUST
be ignored by a receiver.
* Binding SID: It indicates the operational or allocated BSID value
based on the status flags.
* Specified BSID: It is used to report the explicitly specified BSID
value regardless of whether it is successfully allocated or not.
The field is set to value 0 when BSID has not been specified.
* Sub-TLVs: variable and contains any other optional attributes
associated with the SRv6 BSID.
The SRv6 Endpoint Behavior TLV (1250) and the SRv6 SID Structure TLV
(1252) MAY optionally be used as sub-TLVs of the SRv6 Binding SID TLV
to indicate the SRv6 Endpoint behavior and SID structure for the
Binding SID value in the TLV. [RFC9514] defines SRv6 Endpoint
Behavior TLV And SRv6 SID Structure TLV.
5.3. SR Candidate Path State TLV
The SR Candidate Path (CP) State TLV provides the operational status
and attributes of the SR Policy at the CP level. Only a single
instance of this TLV is advertised for a given CP. If multiple
instances are present, then the first one is considered valid and the
rest are ignored.
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Priority | RESERVED | Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Preference (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 8 SR Candidate Path State TLV Format
Where:
* Type: 1202
* Length: 8 octets
* Priority: 1-octet value which indicates the priority of the CP.
Refer Section 2.12 of [RFC9256].
* RESERVED: 1 octet. MUST be set to 0 by the originator and MUST be
ignored by a receiver.
* Flags: 2-octet field that indicates attribute and status of the
CP. The following bit positions are defined and the semantics are
described in section 5 of [RFC9256] unless stated otherwise for
individual flags. Other bits MUST be cleared by the originator
and MUST be ignored by a receiver.
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S|A|B|E|V|O|D|C|I|T|U| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Where:
- S-Flag: Indicates the CP is in an administrative shut state
when set and not in administrative shut state when clear.
- A-Flag: Indicates the CP is the active path (i.e. one
provisioned in the forwarding plane as specified in section 2.9
of [RFC9256]) for the SR Policy when set and not the active
path when clear.
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- B-Flag: Indicates the CP is the backup path (i.e. one
identified for path protection of the active path as specified
in section 9.3 of [RFC9256]) for the SR Policy when set and not
the backup path when clear.
- E-Flag: Indicates that the CP has been evaluated for validity
(e.g. headend may evaluate CPs based on their preferences) when
set and has not been evaluated for validity when clear.
- V-Flag: Indicates the CP has at least one valid SID-List when
set and indicates no valid SID-List is available or evaluated
when clear. When the E-Flag is clear (i.e. the CP has not been
evaluated), then this flag MUST be set to 0 by the originator
and ignored by the receiver.
- O-Flag: Indicates the CP was instantiated by the headend due to
an on-demand nexthop trigger based on a local template when set
and that the CP has not been instantiated due to on-demand
nexthop trigger when clear. Refer to section 8.5 of [RFC9256]
for details.
- D-Flag: Indicates the CP was delegated for computation to a
PCE/controller when set and indicates that the CP has not been
delegated for computation when clear.
- C-Flag: Indicates the CP was provisioned by a PCE/controller
when set and indicates that the CP was not provisioned by a
PCE/controller when clear.
- I-Flag: Indicates the CP is to perform the "drop upon invalid"
behavior when no other valid CP is available for this SR Policy
when the flag is set. Refer to section 8.2 of [RFC9256] for
details. When clear, it indicates that the CP is not enabled
for the "drop upon invalid" behavior.
- T-Flag: Indicates the CP has been marked as eligible for use as
a transit policy on the headend when set and not eligible for
use as a transit policy when clear. Transit policy is a policy
whose BSID can be used in the segment list of another SR
Policy. Refer to section 8.3 of [RFC9256] for steering into a
transit policy using its BSID.
- U-Flag: Indicates that this CP is reported as active and is
dropping traffic as a result of the "drop upon invalid"
behavior being activated for the SR Policy when set. When
clear, it indicates that the CP is either dropping traffic as a
result of the "drop upon invalid" behavior. Refer to section
8.2 of [RFC9256] for details.
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* Preference: 4-octet value which indicates the preference of the
CP. Refer to section 2.7 of [RFC9256] for details.
5.4. SR Policy Name TLV
The SR Policy Name TLV is an optional TLV that is used to carry the
symbolic name associated with the SR Policy. Only a single instance
of this TLV is advertised for a given CP. If multiple instances are
present, then the first one is considered valid and the rest are
ignored.
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SR Policy Name (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 9 SR Policy Name TLV Format
Where:
* Type: 1213
* Length: variable
* SR Policy Name: Symbolic name for the SR Policy without a NULL
terminator as specified in section 2.1 of [RFC9256]. It is
RECOMMENDED that the size of the symbolic name be limited to 255
bytes. Implementations MAY choose to truncate long names to 255
bytes when signaling via BGP-LS.
5.5. SR Candidate Path Name TLV
The SR Candidate Path Name TLV is an optional TLV that is used to
carry the symbolic name associated with the candidate path. Only a
single instance of this TLV is advertised for a given CP. If
multiple instances are present, then the first one is considered
valid and the rest are ignored.
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Candidate Path Name (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 10 SR Candidate Path Name TLV Format
Where:
* Type: 1203
* Length: variable
* Candidate Path Name: Symbolic name for the SR Policy candidate
path without a NULL terminator as specified in section 2.6 of
[RFC9256]. It is RECOMMENDED that the size of the symbolic name
be limited to 255 bytes. Implementations MAY choose to truncate
long names to 255 bytes when signaling via BGP-LS.
5.6. SR Candidate Path Constraints TLV
The SR Candidate Path Constraints TLV is an optional TLV that is used
to report the constraints associated with the candidate path. The
constraints are generally applied to a dynamic candidate path which
is computed either by the headend or may be delegated to a
controller. The constraints may also be applied to an explicit path
where the computation entity is expected to validate that the path
satisfies the specified constraints and if not the path is to be
invalidated (e.g., due to topology changes). Only a single instance
of this TLV is advertised for a given CP. If multiple instances are
present, then the first one is considered valid and the rest are
ignored.
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags | RESERVED1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MTID | Algorithm | RESERVED2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| sub-TLVs (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 11 SR Candidate Path Constraints TLV Format
Where:
* Type: 1204
* Length: variable
* Flags: 2-octet field that indicates the constraints that are being
applied to the CP. The following bit positions are defined and
the other bits MUST be cleared by the originator and MUST be
ignored by a receiver.
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|D|P|U|A|T|S|F|H| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Where:
- D-Flag: Indicates that the CP uses SRv6 dataplane when set and
SR/MPLS dataplane when clear
- P-Flag: Indicates that the CP prefers the use of only protected
SIDs when set and indicates that the CP does not prefer the use
of only protected SIDs when clear. This flag is mutually
exclusive with the U-Flag (i.e., both these flags cannot be set
at the same time).
- U-Flag: Indicates that the CP prefers the use of only
unprotected SIDs when set and indicates that the CP does not
prefer the use of only unprotected SIDs when clear. This flag
is mutually exclusive with the P-Flag (i.e., both these flags
cannot be set at the same time).
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- A-Flag: Indicates that the CP uses only the SIDs belonging to
the specified SR Algorithm when set and indicates that the CP
does not use only the SIDs belonging to the specified SR
Algorithm when clear.
- T-Flag: Indicates that the CP uses only the SIDs belonging to
the specified topology when set and indicates that the CP does
not use only the SIDs belonging to the specified topology when
clear.
- S-Flag: Indicates that the use of protected (P-Flag) or
unprotected (U-Flag) SIDs becomes a strict constraint instead
of a preference when set and indicates that there is no strict
constraint (and only a preference) when clear.
- F-Flag: Indicates that the CP is fixed once computed and not
modified except on operator intervention and indicates that the
CP may be modified as part of recomputation when clear.
- H-Flag: Indicates that the CP uses only adjacency SIDs and
traverses hop-by-hop over the links corresponding to those
adjacency SIDs when set and indicates that the CP is not using
only hop-by-hop adjacency SIDs when clear.
* RESERVED1: 2 octets. MUST be set to 0 by the originator and MUST
be ignored by a receiver.
* MTID: Indicates the multi-topology identifier of the IGP topology
that is preferred to be used when the path is set up. When the
T-flag is set then the path is strictly using the specified
topology SIDs only.
* Algorithm: Indicates the algorithm that is preferred to be used
when the path is set up. When the A-flag is set then the path is
strictly using the specified algorithm SIDs only. The algorithm
values are from IGP Algorithm Types registry under the IANA
Interior Gateway Protocol (IGP) Parameters.
* RESERVED2: 1 octet. MUST be set to 0 by the originator and MUST
be ignored by a receiver.
* sub-TLVs: one or more optional sub-TLVs MAY be included in this
TLV to describe other constraints. These sub-TLVs are: SR
Affinity Constraint, SR SRLG Constraint, SR Bandwidth Constraint,
SR Disjoint Group Constraint, SR Bidirectional Group Constraint,
and SR Metric Constraint.
These constraint sub-TLVs are defined below.
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5.6.1. SR Affinity Constraint Sub-TLV
The SR Affinity Constraint sub-TLV is an optional sub-TLV of the SR
CP Constraints TLV that is used to carry the affinity constraints
[RFC2702] associated with the candidate path. The affinity is
expressed in terms of Extended Admin Group (EAG) as defined in
[RFC7308]. Only a single instance of this sub-TLV is advertised for
a given CP. If multiple instances are present, then the first one is
considered valid and the rest are ignored.
The sub-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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Excl-Any-Size | Incl-Any-Size | Incl-All-Size | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Exclude-Any EAG (optional, variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Include-Any EAG (optional, variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Include-All EAG (optional, variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 12 SR Affinity Constraints Sub-TLV Format
Where:
* Type: 1208
* Length: variable, dependent on the size of the Extended Admin
Group. MUST be a multiple of 4 octets.
* Exclude-Any-Size: one octet to indicate the size of Exclude-Any
EAG bitmask size in multiples of 4 octets. (e.g. value 0
indicates the Exclude-Any EAG field is skipped, value 1 indicates
that 4 octets of Exclude-Any EAG is included)
* Include-Any-Size: one octet to indicate the size of Include-Any
EAG bitmask size in multiples of 4 octets. (e.g. value 0
indicates the Include-Any EAG field is skipped, value 1 indicates
that 4 octets of Include-Any EAG is included)
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* Include-All-Size: one octet to indicate the size of Include-All
EAG bitmask size in multiples of 4 octets. (e.g. value 0
indicates the Include-All EAG field is skipped, value 1 indicates
that 4 octets of Include-All EAG is included)
* RESERVED: 1 octet. MUST be set to 0 by the originator and MUST be
ignored by a receiver.
* Exclude-Any EAG: the bitmask used to represent the affinities that
have been excluded from the path.
* Include-Any EAG: the bitmask used to represent the affinities that
have been included in the path.
* Include-All EAG: the bitmask used to represent all the affinities
that have been included in the path.
5.6.2. SR SRLG Constraint Sub-TLV
The SR SRLG Constraint sub-TLV is an optional sub-TLV of the SR CP
Constraints TLV that is used to carry the Shared Risk Link Group
(SRLG) values [RFC4202] that have been excluded from the candidate
path. Only a single instance of this sub-TLV is advertised for a
given CP. If multiple instances are present, then the first one is
considered valid and the rest are ignored.
The sub-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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SRLG Values (variable, multiples of 4 octets) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 13 SR SRLG Constraints Sub-TLV Format
Where:
* Type: 1209
* Length: variable, dependent on the number of SRLGs encoded. MUST
be a multiple of 4 octets.
* SRLG Values: One or more SRLG values. Each SRLG value is of 4
octets.
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5.6.3. SR Bandwidth Constraint Sub-TLV
The SR Bandwidth Constraint sub-TLV is an optional sub-TLV of the SR
CP Constraints TLV that is used to indicate the bandwidth that has
been requested for the candidate path. Only a single instance of
this sub-TLV is advertised for a given CP. If multiple instances are
present, then the first one is considered valid and the rest are
ignored.
The sub-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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Bandwidth |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 14 SR Bandwidth Constraints Sub-TLV Format
Where:
* Type: 1210
* Length: 4 octets
* Bandwidth: 4 octets which specify the desired bandwidth in unit of
bytes per second in IEEE floating point format.
5.6.4. SR Disjoint Group Constraint Sub-TLV
The SR Disjoint Group Constraint sub-TLV is an optional sub-TLV of
the SR CP Constraints TLV that is used to carry the disjointness
constraint associated with the candidate path. The disjointness
between two SR Policy Candidate Paths is expressed by associating
them with the same disjoint group identifier and then specifying the
type of disjointness required between their paths. The computation
is expected to achieve the highest level of disjointness requested
and when that is not possible then fallback to a lesser level
progressively based on the levels indicated. Only a single instance
of this sub-TLV is advertised for a given CP. If multiple instances
are present, then the first one is considered valid and the rest are
ignored.
The sub-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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Request-Flags | Status-Flags | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Disjoint Group Identifier (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 15 SR Disjoint Group Constraints Sub-TLV Format
Where:
* Type: 1211
* Length: Variable. Minimum of 8 octets.
* Request Flags: one octet to indicate the level of disjointness
requested as specified in the form of flags. The following flags
are defined and the other bits MUST be cleared by the originator
and MUST be ignored by a receiver.
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|S|N|L|F|I| |
+-+-+-+-+-+-+-+-+
Where:
- S-Flag: Indicates that SRLG disjointness is requested when set
and indicates that SRLG disjointness is not requested when
clear.
- N-Flag: Indicates that node disjointness is requested when set
and indicates that node disjointness is not requested when
clear.
- L-Flag: Indicates that link disjointness is requested when set
and indicates that the link disjointness is not requested when
clear.
- F-Flag: Indicates that the computation may fallback to a lower
level of disjointness amongst the ones requested when all
cannot be achieved when set and indicates that fallback to a
lower level of disjointness is not allowed when clear.
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- I-Flag: Indicates that the computation may fallback to the
default best path (e.g. IGP path) in case of none of the
desired disjointness can be achieved when set and indicates
that fallback to the default best path is not allowed when
clear.
* Status Flags: one octet to indicate the level of disjointness that
has been achieved by the computation as specified in the form of
flags. The following flags are defined and the other bits MUST be
cleared by the originator and MUST be ignored by a receiver.
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|S|N|L|F|I|X| |
+-+-+-+-+-+-+-+-+
Where:
- S-Flag: Indicates that SRLG disjointness is achieved when set
and indicates that SRLG disjointness is not achieved when
clear.
- N-Flag: Indicates that node disjointness is achieved when set
and indicates that node disjointness was not achieved when
clear.
- L-Flag: Indicates that link disjointness is achieved when set
and indicates that link disjointness was not achieved when
clear.
- F-Flag: Indicates that the computation has fallen back to a
lower level of disjointness than requested when set and
indicates that there has been no fallback to a lower level of
disjointness when clear.
- I-Flag: Indicates that the computation has fallen back to the
best path (e.g. IGP path) and disjointness has not been
achieved when set and indicates that there has been no fallback
to best path when clear.
- X-Flag : Indicates that the disjointness constraint could not
be achieved and hence path has been invalidated when set and
indicates that the path has not been invalidated due to unmet
disjointness constraints when clear.
* RESERVED: 2 octets. MUST be set to 0 by the originator and MUST
be ignored by a receiver.
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* Disjointness Group Identifier: 4-octet value that is the group
identifier for a set of disjoint paths. A PCEP Association Object
[RFC8697] (including its optional TLVs) MAY also be advertised to
convey the disjoint group identifier.
5.6.5. SR Bidirectional Group Constraint Sub-TLV
The SR Bidirectional Group Constraint sub-TLV is an optional sub-TLV
of the SR CP Constraints TLV that is used to carry the bidirectional
constraint associated with the candidate path. The bidirectional
relationship between two SR Policy Candidate Paths is expressed by
associating them with the same bidirectional group identifier and
then specifying the type of bidirectional routing required between
their paths. Only a single instance of this sub-TLV is advertised
for a given CP. If multiple instances are present, then the first
one is considered valid and the rest are ignored.
The sub-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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Bidirectional Group Identifier (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 16 SR Bidirectional Group Constraints Sub-TLV Format
Where:
* Type: 1214
* Length: Variable. Minimum of 8 octets.
* Flags: two octets to indicate the bidirectional path setup
information as specified in the form of flags. The following
flags are defined and the other bits MUST be cleared by the
originator and MUST be ignored by a receiver.
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0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|R|C| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Where:
- R-Flag: Indicates that this CP of the SR Policy forms the
reverse path when the R-Flag is set. If the R-Flag is clear,
this CP forms the forward path.
- C-Flag: Indicates that the bidirectional path is co-routed when
set and indicates that the bidirectional path is not co-routed
when clear.
* RESERVED: 2 octets. MUST be set to 0 by the originator and MUST
be ignored by a receiver.
* Bidirectional Group Identifier: 4-octet value that is the group
identifier for a set of bidirectional paths. A PCEP Association
Object [RFC8697] (including its optional TLVs) MAY also be
advertised to convey the bidirectional group identifier. The PCEP
Association Object MUST NOT be encoded and this sub-TLV skipped
along with an error log, if the object size is such that the
update for a single SR Policy CP NLRI would exceed the supported
BGP message size by the implementation. Refer section 5.3 of
[RFC9552] for discussion on implications of encoding large sets of
information into BGP-LS.
5.6.6. SR Metric Constraint Sub-TLV
The SR Metric Constraint sub-TLV is an optional sub-TLV of the SR CP
Constraints TLV that is used to report the optimization metric of the
CP. For a dynamic path computation, it is used to report the
optimization metric used along with its parameters. For an explicit
path, this sub-TLV MAY be used to report the metric margin or bound
to be used for validation (i.e., the path is invalidated if the
metric is beyond specified values). Multiple instances of this sub-
TLV may be used to report different metric type uses.
The sub-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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Metric Type | Flags | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Metric Margin |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Metric Bound |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 17 SR Metric Constraints Sub-TLV Format
Where:
* Type: 1215
* Length: 12 octets
* Metric Type: 1-octet field which identifies the type of the metric
being used. The Table 1 below lists the metric types introduced
by this document along with reference for each. The reference is
to IS-IS (equivalent also exist for OSPF) specifications where
those metric types are defined for a link while in the SR Policy
context those relate to the candidate path or the segment list.
The metric type code points that may be used in this sub-TLV are
also listed in Section 8.6 of this document. Note that the metric
type in this field is not taken from the "IGP Metric Type"
registry from IANA "IGP Parameters" and is a separate registry
that includes IGP Metric Types as well as metric types specific to
SR Policy path computation.
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+-------+--------------------+---------------------------------+
| Code | | |
| Point | Metric Type | Reference |
+-------+--------------------+---------------------------------+
| 0 | IGP | [RFC5305] Section 3 |
| 1 | Min Unidirectional | [RFC8570] Section 4.2 |
| | Delay | |
| 2 | TE | [RFC5305] Section 3.7 |
| 3 | Hop Count | [RFC5440] Section 7.8 |
| 4 | SID List Length | [RFC8664] Section 4.5 |
| 5 | Bandwidth | [I-D.ietf-lsr-flex-algo-bw-con] |
| | | Section 4 |
| 6 | Avg Unidirectional | [RFC8570] Section 4.1 |
| | Delay | |
| 7 | Unidirectional | [RFC8570] Section 4.3 |
| | Delay Variation | |
| 8 | Loss | [RFC8570] Section 4.4 |
|128-255| User Defined | [I-D.ietf-lsr-flex-algo-bw-con] |
| | | Section 2 |
+-------+--------------------+---------------------------------+
Table 1 BGP-LS SR Policy Metric Types
* Flags: 1-octet field that indicates the validity of the metric
fields and their semantics. The following bit positions are
defined and the other bits MUST be cleared by the originator and
MUST be ignored by a receiver.
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|O|M|A|B| |
+-+-+-+-+-+-+-+-+
Where:
- O-Flag: Indicates that this is the optimization metric being
reported for a dynamic CP when set and indicates that the
metric is not the optimization metric when clear. This bit
MUST NOT be set in more than one instance of this TLV for a
given CP advertisement.
- M-Flag: Indicates that the metric margin allowed is specified
when set and indicates that metric margin allowed is not
specified when clear.
- A-Flag: Indicates that the metric margin is specified as an
absolute value when set and is expressed as a percentage of the
minimum metric when clear.
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- B-Flag: Indicates that the metric bound allowed for the path is
specified when set and indicates that metric bound is not
specified when clear.
* RESERVED: 2 octets. MUST be set to 0 by the originator and MUST
be ignored by a receiver.
* Metric Margin: 4-octet value which indicates the metric margin
when the M-flag is set. The metric margin is specified as either
an absolute value or as a percentage of the minimum computed path
metric based on the A-flag. The metric margin loosens the
criteria for minimum metric path calculation up to the specified
metric to accommodate for other factors such as bandwidth
availability, minimal SID stack depth, and maximizing of ECMP for
the SR path computed.
* Metric Bound: 4-octet value which indicates the maximum metric
that is allowed when the B-flag is set. If the computed path
metric crosses the specified bound value then the path is
considered invalid.
5.7. SR Segment List TLV
The SR Segment List TLV is used to report a single SID-List of a CP.
Multiple instances of this TLV may be used to report multiple SID-
Lists of a CP.
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MTID | Algorithm | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Weight (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| sub-TLVs (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 18 SR Segment List TLV Format
Where:
* Type: 1205
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* Length: variable
* Flags: 2-octet field that indicates attribute and status of the
SID-List.The following bit positions are defined and the semantics
are described in detail in [RFC9256]. Other bits MUST be cleared
by the originator and MUST be ignored by a receiver.
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|D|E|C|V|R|F|A|T|M| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Where:
- D-Flag: Indicates the SID-List is comprised of SRv6 SIDs when
set and indicates it is comprised of SR/MPLS labels when clear.
- E-Flag: Indicates that SID-List is associated with an explicit
candidate path when set and with a dynamic candidate path when
clear. All segment lists of a given candidate path MUST be
either explicit or dynamic and in case of inconsistency, the
receiver MAY consider them all to be dynamic.
- C-Flag: Indicates that SID-List has been computed for a dynamic
path when set. It is always reported as set for explicit
paths. When clear, it indicates that the SID-List has not been
computed for a dynamic path.
- V-Flag: Indicates the SID-List has passed verification or its
verification was not required when set and failed verification
when clear.
- R-Flag: Indicates that the first Segment has been resolved when
set and failed resolution when clear.
- F-Flag: Indicates that the computation for the dynamic path
failed when set and succeeded (or not required in case of
explicit path) when clear.
- A-Flag: Indicates that all the SIDs in the SID-List belong to
the specified algorithm when set and indicates that not all the
SIDs belong to the specified algorithm when clear.
- T-Flag: Indicates that all the SIDs in the SID-List belong to
the specified topology (identified by the multi-topology ID)
when set and indicates that not all the SIDs belong to the
specified topology when clear.
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- M-Flag: Indicates that the SID-list has been removed from the
forwarding plane due to fault detection by a monitoring
mechanism (e.g. BFD) when set and indicates no fault detected
or monitoring is not being done when clear.
* RESERVED: 2 octets. MUST be set to 0 by the originator and MUST
be ignored by a receiver.
* MTID: 2 octets that indicates the multi-topology identifier of the
IGP topology that is to be used when the T-flag is set.
* Algorithm: 1 octet that indicates the algorithm of the SIDs used
in the SID-List when the A-flag is set. The algorithm values are
from IGP Algorithm Types registry under the IANA Interior Gateway
Protocol (IGP) Parameters.
* RESERVED: 1 octet. MUST be set to 0 by the originator and MUST be
ignored by a receiver.
* Weight: 4-octet field that indicates the weight associated with
the SID-List for weighted load-balancing. Refer to section 2.2
and 2.11 of [RFC9256].
* Sub-TLVs: variable and contains the ordered set of Segments and
any other optional attributes associated with the specific SID-
List.
The SR Segment sub-TLV (defined in Section 5.8) MUST be included as
an ordered set of sub-TLVs within the SR Segment List TLV when the
SID-List is not empty. A SID-List may be empty in certain situations
(e.g. for a dynamic path) where the headend has not yet performed the
computation and hence not derived the segments required for the path.
In such cases where the SID-LIST is empty, the SR Segment List TLV
SHOULD NOT include any SR Segment sub-TLVs.
5.8. SR Segment Sub-TLV
The SR Segment sub-TLV describes a single segment in a SID-List. One
or more instances of this sub-TLV in an ordered manner constitute a
SID-List for an SR Policy candidate path. It is a sub-TLV of the SR
Segment List TLV and it 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Segment Type | RESERVED | Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SID (4 or 16 octets) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Segment Descriptor (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Sub-TLVs (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 19 SR Segment Sub-TLV Format
Where:
* Type: 1206
* Length: variable
* Segment Type: 1 octet which indicates the type of segment.
Initial values are specified by this document (see Section 5.8.1
for details). Additional segment types are possible, but out of
scope for this document.
* RESERVED: 1 octet. MUST be set to 0 by the originator and MUST be
ignored by a receiver.
* Flags: 2-octet field that indicates attribute and status of the
Segment and its SID. The following bit positions are defined and
the semantics are described in section 5 of [RFC9256]. Other bits
MUST be cleared by the originator and MUST be ignored by a
receiver.
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S|E|V|R|A| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Where:
- S-Flag: Indicates the presence of SID value in the SID field
when set and that no value is indicated when clear.
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- E-Flag: Indicates the SID value is explicitly provisioned value
(locally on headend or via controller/PCE) when set and is a
dynamically resolved value by headend when clear
- V-Flag: Indicates the SID has passed verification or did not
require verification when set. When V-Flage is clear, it
indicates the SID has failed verification.
- R-Flag: Indicates the SID has been resolved or did not require
resolution (e.g. because it is not the first SID) when set.
When R-Flage is clear, it indicates the SID has failed
resolution.
- A-Flag: Indicates that the Algorithm indicated in the Segment
descriptor is valid when set. When clear, it indicates that
the headend is unable to determine the algorithm of the SID.
* SID: 4 octets carrying the MPLS Label or 16 octets carrying the
SRv6 SID based on the Segment Type. When carrying the MPLS Label,
as shown in the figure below, the TC, S, and TTL (total of 12
bits) are RESERVED and MUST be set to 0 by the originator and MUST
be ignored by a receiver.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
* Segment Descriptor: variable size Segment descriptor based on the
type of segment (refer to Section 5.8.1 for details)
* Sub-Sub-TLVs: variable and contains any other optional attributes
associated with the specific segment.
The SRv6 Endpoint Behavior TLV (1250) and the SRv6 SID Structure TLV
(1252) defined in [RFC9514] are used as sub-sub-TLVs of the SR
Segment sub-TLV. These two sub-sub-TLVs are used to optionally
indicate the SRv6 Endpoint behavior and SID structure when
advertising the SRv6 specific segment types.
5.8.1. Segment Descriptors
Section 4 of [RFC9256] defines multiple types of segments and their
description. This section defines the encoding of the Segment
Descriptors for each of those Segment types to be used in the Segment
sub-TLV describes previously in Section 5.8.
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The following types are currently defined and their mapping to the
respective segment types defined in [RFC9256]:
+------+-------------------------------------------------------------+
| Type | Segment Description |
+------+-------------------------------------------------------------+
| 1 | (Type A) SR-MPLS Label |
| 2 | (Type B) SRv6 SID as IPv6 address |
| 3 | (Type C) SR-MPLS Prefix SID as IPv4 Node Address |
| 4 | (Type D) SR-MPLS Prefix SID as IPv6 Node Global Address |
| 5 | (Type E) SR-MPLS Adjacency SID as IPv4 Node Address & Local |
| | Interface ID |
| 6 | (Type F) SR-MPLS Adjacency SID as IPv4 Local & Remote |
| | Interface Addresses |
| 7 | (Type G) SR-MPLS Adjacency SID as pair of IPv6 Global |
| | Address & Interface ID for Local & Remote nodes |
| 8 | (Type H) SR-MPLS Adjacency SID as pair of IPv6 Global |
| | Addresses for the Local & Remote Interface |
| 9 | (Type I) SRv6 END SID as IPv6 Node Global Address |
| 10 | (Type J) SRv6 END.X SID as pair of IPv6 Global Address & |
| | Interface ID for Local & Remote nodes |
| 11 | (Type K) SRv6 END.X SID as pair of IPv6 Global Addresses |
| | for the Local & Remote Interface |
+------+-------------------------------------------------------------+
Table 2 SR Segment Types
5.8.1.1. Type 1: SR-MPLS Label
The Segment is SR-MPLS type and is specified simply as the label.
The format of its Segment Descriptor 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
+-+-+-+-+-+-+-+-+
| Algorithm |
+-+-+-+-+-+-+-+-+
Figure 20 Type 1 Segment Descriptor
Where:
* Algorithm: 1-octet value that indicates the algorithm used for
picking the SID. This is valid only when the A-flag has been set
in the Segment TLV. The algorithm values are from IGP Algorithm
Types registry under the IANA Interior Gateway Protocol (IGP)
Parameters.
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5.8.1.2. Type 2: SRv6 SID
The Segment is SRv6 type and is specified simply as the SRv6 SID
address. The format of its Segment Descriptor 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
+-+-+-+-+-+-+-+-+
| Algorithm |
+-+-+-+-+-+-+-+-+
Figure 21 Type 2 Segment Descriptor
Where:
* Algorithm: 1-octet value that indicates the algorithm used for
picking the SID. This is valid only when the A-flag has been set
in the Segment TLV. The algorithm values are from IGP Algorithm
Types registry under the IANA Interior Gateway Protocol (IGP)
Parameters.
5.8.1.3. Type 3: SR-MPLS Prefix SID for IPv4
The Segment is SR-MPLS Prefix SID type and is specified as an IPv4
node address. The format of its Segment Descriptor 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
+-+-+-+-+-+-+-+-+
| Algorithm |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 Node Address (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 22 Type 3 Segment Descriptor
Where:
* Algorithm: 1-octet value that indicates the algorithm used for
picking the SID. The algorithm values are from IGP Algorithm
Types registry under the IANA Interior Gateway Protocol (IGP)
Parameters.
* IPv4 Node Address: 4-octet value which carries the IPv4 address
associated with the node
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5.8.1.4. Type 4: SR-MPLS Prefix SID for IPv6
The Segment is SR-MPLS Prefix SID type and is specified as an IPv6
global address. The format of its Segment Descriptor 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
+-+-+-+-+-+-+-+-+
| Algorithm |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv6 Node Global Address (16 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 23 Type 4 Segment Descriptor
Where:
* Algorithm: 1-octet value that indicates the algorithm used for
picking the SID. The algorithm values are from IGP Algorithm
Types registry under the IANA Interior Gateway Protocol (IGP)
Parameters.
* IPv6 Node Global Address: 16-octet value which carries the IPv6
global address associated with the node
5.8.1.5. Type 5: SR-MPLS Adjacency SID for IPv4 with an Interface ID
The Segment is SR-MPLS Adjacency SID type and is specified as an IPv4
node address along with the local interface ID on that node. The
format of its Segment Descriptor 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 Node Address (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Local Interface ID (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 24 Type 5 Segment Descriptor
Where:
* IPv4 Node Address: 4-octet value which carries the IPv4 address
associated with the node
* Local Interface ID: 4-octet value which carries the local
interface ID of the node identified by the Node Address
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5.8.1.6. Type 6: SR-MPLS Adjacency SID for IPv4 with an Interface
Address
The Segment is SR-MPLS Adjacency SID type and is specified as a pair
of IPv4 local and remote addresses. The format of its Segment
Descriptor 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 Local Address (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 Remote Address (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 25 Type 6 Segment Descriptor
Where:
* IPv4 Local Address: 4-octet value which carries the local IPv4
address associated with the node
* IPv4 Remote Address: 4-octet value which carries the remote IPv4
address associated with the node's neighbor. This is optional and
MAY be set to 0 when not used (e.g. when identifying point-to-
point links).
5.8.1.7. Type 7: SR-MPLS Adjacency SID for IPv6 with an interface ID
The Segment is SR-MPLS Adjacency SID type and is specified as a pair
of IPv6 global address and interface ID for local and remote nodes.
The format of its Segment Descriptor 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv6 Local Node Global Address (16 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Local Node Interface ID (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv6 Remote Node Global Address (16 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Remote Node Interface ID (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 26 Type 7 Segment Descriptor
Where:
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* IPv6 Local Node Global Address: 16-octet value which carries the
IPv6 global address associated with the local node
* Local Node Interface ID : 4-octet value which carries the
interface ID of the local node identified by the Local Node
Address
* IPv6 Remote Node Global Address: 16-octet value which carries the
IPv6 global address associated with the remote node. This is
optional and MAY be set to 0 when not used (e.g. when identifying
point-to-point links).
* Remote Node Interface ID: 4-octet value which carries the
interface ID of the remote node identified by the Remote Node
Address. This is optional and MAY be set to 0 when not used (e.g.
when identifying point-to-point links).
5.8.1.8. Type 8: SR-MPLS Adjacency SID for IPv6 with an Interface
Address
The Segment is SR-MPLS Adjacency SID type and is specified as a pair
of IPv6 Global addresses for local and remote interface addresses.
The format of its Segment Descriptor 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Global IPv6 Local Interface Address (16 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Global IPv6 Remote Interface Address (16 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 27 Type 8 Segment Descriptor
Where:
* IPv6 Local Address: 16-octet value which carries the local IPv6
address associated with the node
* IPv6 Remote Address: 16-octet value which carries the remote IPv6
address associated with the node's neighbor
5.8.1.9. Type 9: SRv6 END SID as IPv6 Node Address
The Segment is SRv6 END SID type and is specified as an IPv6 global
address. The format of its Segment Descriptor is as follows:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+
| Algorithm |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv6 Node Global Address (16 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 28 Type 9 Segment Descriptor
Where:
* Algorithm: 1-octet value that indicates the algorithm used for
picking the SID. The algorithm values are from IGP Algorithm
Types registry under the IANA Interior Gateway Protocol (IGP)
Parameters.
* IPv6 Node Global Address: 16-octet value which carries the IPv6
global address associated with the node
5.8.1.10. Type 10: SRv6 END.X SID as an Anterface ID
The Segment is SRv6 END.X SID type and is specified as a pair of IPv6
global address and interface ID for local and remote nodes. The
format of its Segment Descriptor 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv6 Local Node Global Address (16 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Local Node Interface ID (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv6 Remote Node Global Address (16 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Remote Node Interface ID (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 29 Type 10 Segment Descriptor
Where:
* IPv6 Local Node Global Address: 16-octet value which carries the
IPv6 global address associated with the local node
* Local Node Interface ID: 4-octet value which carries the interface
ID of the local node identified by the Local Node Address
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* IPv6 Remote Node Global Address: 16-octet value which carries the
IPv6 global address associated with the remote node. This is
optional and MAY be set to 0 when not used (e.g. when identifying
point-to-point links).
* Remote Node Interface ID: 4-octet value which carries the
interface ID of the remote node identified by the Remote Node
Address. This is optional and MAY be set to 0 when not used (e.g.
when identifying point-to-point links).
5.8.1.11. Type 11: SRv6 END.X SID as an Interface Address
The Segment is SRv6 END.X SID type and is specified as a pair of IPv6
Global addresses for local and remote interface addresses. The
format of its Segment Descriptor 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Global IPv6 Local Interface Address (16 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Global IPv6 Remote Interface Address (16 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 30 Type 11 Segment Descriptor
Where:
* IPv6 Local Address: 16-octet value which carries the local IPv6
address associated with the node
* IPv6 Remote Address: 16-octet value which carries the remote IPv6
address associated with the node's neighbor
5.9. SR Segment List Metric Sub-TLV
The SR Segment List Metric sub-TLV reports the computed metric of the
specific SID-List. It is used to report the type of metric and its
computed value by the computation entity (i.e., either the headend or
the controller when the path is delegated) when available. More than
one instance of this sub-TLV may be present in SR Segment List to
report metric values of different metric types. The metric margin
and bound may be optionally reported using this sub-TLV when this
information is not being reported using the SR Metric Constraint sub-
TLV (refer to Section 5.6.6) at the SR CP level.
It is a sub-TLV of the SR Segment List TLV and 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Metric Type | Flags | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Metric Margin |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Metric Bound |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Metric Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 31 SR Segment List Metric Sub-TLV Format
Where:
* Type: 1207
* Length: 16 octets
* Metric Type: 1-octet field which identifies the type of metric.
The Table 1 in Section 5.6.6 lists the metric types introduced by
this document. The metric type code points that may be used in
this sub-TLV are also listed in Section 8.6 of this document.
Note that the metric type in this field is not taken from the "IGP
Metric Type" registry from IANA "IGP Parameters" and is a separate
registry that includes IGP Metric Types as well as metric types
specific to SR Policy path computation.
* Flags: 1-octet field that indicates the validity of the metric
fields and their semantics. The following bit positions are
defined and the other bits MUST be cleared by the originator and
MUST be ignored by a receiver.
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|M|A|B|V| |
+-+-+-+-+-+-+-+-+
Where:
- M-Flag: Indicates that the metric margin allowed for this path
computation is specified when set and indicates that metric
margin allowed is not specified when clear.
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- A-Flag: Indicates that the metric margin is specified as an
absolute value when set and is expressed as a percentage of the
minimum metric when clear.
- B-Flag: Indicates that the metric bound allowed for the path is
specified when set and indicates that metric bound is not
specified when clear.
- V-Flag: Indicates that the metric value computed is being
reported when set and indicates that the computed metric value
is not being reported when clear.
* RESERVED: 2 octets. MUST be set to 0 by the originator and MUST
be ignored by a receiver.
* Metric Margin: 4-octet value which indicates the metric margin
value when the M-flag is set. The metric margin is specified as
either an absolute value or as a percentage of the minimum
computed path metric based on the A-flag. The metric margin
loosens the criteria for minimum metric path calculation up to the
specified metric to accomodate for other factors such as bandwidth
availability, minimal SID stack depth, and maximizing of ECMP for
the SR path computed.
* Metric Bound: 4-octet value which indicates the maximum metric
value that is allowed when the B-flag is set. If the computed
path metric crosses the specified bound value then the path is
considered invalid.
* Metric Value: 4-octet value which indicates the metric of the
computed path when the V-flag is set. This value is available and
reported when the computation is successful and a valid path is
available.
5.10. SR Segment List Bandwidth Sub-TLV
The SR Segment List Bandwidth sub-TLV is an optional sub-TLV used to
report the bandwidth allocated to the specific SID-List by the path
computation entity. Only a single instance of this sub-TLV is
advertised for a given Segment List. If multiple instances are
present, then the first one is considered valid and the rest are
ignored.
It is a sub-TLV of the SR Segment List TLV and 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Bandwidth |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 32 SR Segment List Bandwidth Sub-TLV Format
Where:
* Type: 1216
* Length: 4 octets
* Bandwidth: 4 octets which specify the allocated bandwidth in unit
of bytes per second in IEEE floating point format.
5.11. SR Segment List Identifier Sub-TLV
The SR Segment List Identifier sub-TLV is an optional sub-TLV used to
report an identifier associated with the specific SID-List. Only a
single instance of this sub-TLV is advertised for a given Segment
List. If multiple instances are present, then the first one is
considered valid and the rest are ignored.
It is a sub-TLV of the SR Segment List TLV and 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Segment List Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 33 SR Segment List Identifier Sub-TLV Format
Where:
* Type: 1217
* Length: 4 octets
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* Segment List Identifier: 4 octets which carry a 32-bit unsigned
non-zero number that serves as the identifier associated with the
segment list. A value of 0 indicates that there is no identifier
associated with the Segment List. The scope of this identifier is
the SR Policy Candidate path.
6. Procedures
The BGP-LS advertisements for the SR Policy CP NLRI type are
generally originated by the headend node for the SR Policies that are
instantiated on its local node (i.e., the headend is the BGP-LS
Producer). The BGP-LS Producer may also be a node (e.g., a PCE) that
is advertising on behalf of the headend.
For the reporting of SR Policy Candidate Paths, the NLRI descriptor
TLV as specified in Section 4 is used. An SR Policy candidate path
(CP) may be instantiated on the headend node via a local
configuration, PCEP, or BGP SR Policy signaling and this is indicated
via the SR Protocol Origin. When a PCE node is the BGP-LS Producer,
it uses the "reported via PCE" variants of the SR Protocol Origin so
as to distinguish them from advertisements by headend nodes. The SR
Policy Candidate Path's state and attributes are encoded in the BGP-
LS Attribute field as SR Policy State TLVs and sub-TLVs as described
in Section 5. The SR Candidate Path State TLV as defined in
Section 5.3 is included to report the state of the CP. The SR BSID
TLV as defined in Section 5.1 or Section 5.2 is included to report
the BSID of the CP when one is either specified or allocated by the
headend. The constraints and the optimization metric for the SR
Policy Candidate Path are reported using the SR Candidate Path
Constraints TLV and its sub-TLVs as described in Section 5.6. The SR
Segment List TLV is included for each of the SID-List(s) associated
with the CP. Each SR Segment List TLV in turn includes SR Segment
sub-TLV(s) to report the segment(s) and their status. The SR Segment
List Metric sub-TLV is used to report the metric values at an
individual SID List level.
7. Manageability Considerations
The Existing BGP operational and management procedures apply to this
document. No new procedures are defined in this document. The
considerations as specified in [RFC9552] apply to this document.
In general, the SR Policy head-end nodes are responsible for the
advertisement of SR Policy state information.
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8. IANA Considerations
This section describes the code point allocation by IANA for this
document.
8.1. BGP-LS NLRI-Types
IANA maintains a registry called "BGP-LS NLRI-Types" in the "Border
Gateway Protocol - Link State (BGP-LS) Parameters" registry group.
The following table lists the status of code points that have been
allocated by IANA:
+------+-------------------------------+---------------+
| Type | NLRI Type | Reference |
+------+-------------------------------+---------------+
| 5 | SR Policy Candidate Path NLRI | this document |
+------+-------------------------------+---------------+
Table 3 NLRI Type Codepoint
8.2. BGP-LS Protocol-IDs
IANA maintains a registry called "BGP-LS Protocol-IDs" in the "Border
Gateway Protocol - Link State (BGP-LS) Parameters" registry group.
The following Protocol-ID codepoints have been allocated by IANA:
+-------------+----------------------------------+---------------+
| Protocol-ID | NLRI information source protocol | Reference |
+-------------+----------------------------------+---------------+
| 9 | Segment Routing | this document |
+-------------+----------------------------------+---------------+
Table 4 Protocol ID Codepoint
8.3. BGP-LS TLVs
IANA maintains a registry called "BGP-LS NLRI and Attribute TLVs" in
the "Border Gateway Protocol - Link State (BGP-LS) Parameters"
registry group.
The following table lists the status of TLV code points that have
been allocated by IANA and others that are pending allocation:
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+-------+----------------------------------------+---------------+
| Code | Description | Value defined |
| Point | | in |
+-------+----------------------------------------+---------------+
| 554 | SR Policy CP Descriptor | this document |
| 1201 | SR Binding SID | this document |
| 1202 | SR CP State | this document |
| 1203 | SR CP Name | this document |
| 1204 | SR CP Constraints | this document |
| 1205 | SR Segment List | this document |
| 1206 | SR Segment | this document |
| 1207 | SR Segment List Metric | this document |
| 1208 | SR Affinity Constraint | this document |
| 1209 | SR SRLG Constraint | this document |
| 1210 | SR Bandwidth Constraint | this document |
| 1211 | SR Disjoint Group Constraint | this document |
| 1212 | SRv6 Binding SID | this document |
| 1213 | SR Policy Name | this document |
| 1214 | SR Bidirectional Group Constraint | this document |
| 1215 | SR Metric Constraint | this document |
| 1216 | SR Segment List Bandwidth | this document |
| 1217 | SR Segment List Identifier | this document |
+-------+----------------------------------------+---------------+
Table 5 NLRI and Attribute TLVs Codepoint
8.4. SR Policy Protocol Origin
Note to IANA (RFC editor to remove this before publication): The new
registry creation request below is also present in the draft-ietf-
pce-segment-routing-policy-cp. IANA is requested to process the
registry creation via the first of these two documents to reach
publication stage and the authors of the other document would update
the IANA considerations suitably. The initial allocations in this
document are a super-set of the initial allocations in draft-ietf-
pce-segment-routing-policy-cp.
This document requests IANA to maintain a new registry under "Segment
Routing" registry group with the allocation policy of "Expert Review"
[RFC8126] using the guidelines for Designated Experts as specified in
[RFC9256]. The new registry is called "SR Policy Protocol Origin"
and should have the reference to this document and
[I-D.ietf-pce-segment-routing-policy-cp]. This registry contains the
codepoints allocated to the "Protocol Origin" field defined in
Section 4.
The registry contains the following codepoints, with initial values,
to be assigned by IANA with the reference set to this document:
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+---------+--------------------------------------+---------------+
| Code | | |
| Point | Protocol Origin | Reference |
+---------+--------------------------------------+---------------+
| 0 | Reserved (not to be used) | this document |
| 1 | PCEP | this document |
| 2 | BGP SR Policy | this document |
| 3 | Configuration (CLI, YANG model via | this document |
| | NETCONF, etc.) | this document |
| 4-9 | Unassigned | this document |
| 10 | PCEP reported via PCE/PCEP | this document |
| 11-19 | Unassigned | this document |
| 20 | BGP SR Policy reported via PCE/PCEP | this document |
| 21-29 | Unassigned | this document |
| 30 | Configuration (CLI, YANG model via | this document |
| | NETCONF, etc.) reported via PCE/PCEP | this document |
| 31-250 | Unassigned | this document |
| 251-255 | Private Use (not to be assigned by | this document |
| | IANA | this document |
+---------+--------------------------------------+---------------+
Table 6 SR Policy Protocol Origin Codepoint
8.5. BGP-LS SR Segment Descriptors
This document requests IANA to maintain a new registry under "Border
Gateway Protocol - Link State (BGP-LS) Parameters" registry group
with the allocation policy of "Expert Review" [RFC8126] using the
guidelines for Designated Experts as specified in [RFC9552]. The new
registry is called "SR Segment Descriptor Types" and contains the
codepoints allocated to the "Segment Type" field defined in
Section 5.8 and described in Section 5.8.1. The registry contains
the following codepoints, with initial values, to be assigned by IANA
with the reference set to this document:
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+--------+-----------------------------------------------------------+
| Code | Segment Description |
| Point | |
+--------+-----------------------------------------------------------+
| 0 | Reserved (not to be used) |
| 1 | (Type A) SR-MPLS Label |
| 2 | (Type B) SRv6 SID as IPv6 address |
| 3 | (Type C) SR-MPLS Prefix SID as IPv4 Node Address |
| 4 | (Type D) SR-MPLS Prefix SID as IPv6 Node Global Address |
| 5 | (Type E) SR-MPLS Adjacency SID as IPv4 Node Address & |
| | Local Interface ID |
| 6 | (Type F) SR-MPLS Adjacency SID as IPv4 Local & Remote |
| | Interface Addresses |
| 7 | (Type G) SR-MPLS Adjacency SID as pair of IPv6 Global |
| | Address & Interface ID for Local & Remote nodes |
| 8 | (Type H) SR-MPLS Adjacency SID as pair of IPv6 Global |
| | Addresses for the Local & Remote Interface |
| 9 | (Type I) SRv6 END SID as IPv6 Node Global Address |
| 10 | (Type J) SRv6 END.X SID as pair of IPv6 Global Address & |
| | Interface ID for Local & Remote nodes |
| 11 | (Type K) SRv6 END.X SID as pair of IPv6 Global Addresses |
| | for the Local & Remote Interface |
| 12-255 | Unassigned |
+--------+-----------------------------------------------------------+
Table 7 SR Segment Descriptor Types Codepoint
8.6. BGP-LS SR Policy Metric Type
This document requests IANA to maintain a new registry under "Border
Gateway Protocol - Link State (BGP-LS) Parameters" registry group
with the allocation policy of "Expert Review" [RFC8126] using the
guidelines for Designated Experts as specified in [RFC9552]. The new
registry is called "BGP-LS SR Policy Metric Type" and contains the
codepoints allocated to the "metric type" field defined in
Section 5.9. The registry contains the following codepoints, with
initial values, to be assigned by IANA with the reference set to this
document:
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+---------+--------------------------------+---------------------+
| Code | | |
| Point | Metric Type | Reference |
+---------+--------------------------------+---------------------+
| 0 | IGP | this document |
| 1 | Min Unidirectional Delay | this document |
| 2 | TE | this document |
| 3 | Hop Count | this document |
| 4 | SID List Length | this document |
| 5 | Bandwidth | this document |
| 6 | Avg Unidirectional Delay | this document |
| 7 | Unidirectional Delay Variation | this document |
| 8 | Loss | this document |
| 9-120 | Unassigned | this document |
| 128-255 | User Defined | this document |
+---------+--------------------------------+---------------------+
Table 8 SR Policy Metric Type Codepoint
9. Security Considerations
Procedures and protocol extensions defined in this document do not
affect the base BGP security model. See [RFC6952] for details. The
security considerations of the base BGP-LS specification as described
in [RFC9552] also apply.
The BGP-LS SR Policy extensions specified in this document enable
traffic engineering and service programming use-cases within an SR
domain as described in [RFC9256]. SR operates within a trusted SR
domain [RFC8402] and its security considerations also apply to BGP
sessions when carrying SR Policy information. The SR Policies
advertised to controllers and other applications via BGP-LS are
expected to be used entirely within this trusted SR domain, i.e.,
within a single AS or between multiple ASes/domains within a single
provider network. Therefore, precaution is necessary to ensure that
the SR Policy information advertised via BGP sessions is limited to
nodes and/or controllers/applications in a secure manner within this
trusted SR domain. The general guidance for BGP-LS with respect to
isolation of BGP-LS sessions from BGP sessions for other address-
families (refer security considerations of [RFC9552]) may be used to
ensure that the SR Policy information is not advertised by accident
or error to an EBGP peering session outside the SR domain.
Additionally, it may be considered that the export of SR Policy
information, as described in this document, constitutes a risk to
confidentiality of mission-critical or commercially sensitive
information about the network (more specifically endpoint/node
addresses, SR SIDs, and the SR Policies deployed). BGP peerings are
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not automatic and require configuration. Thus, it is the
responsibility of the network operator to ensure that only trusted
nodes (that include both routers and controller applications) within
the SR domain are configured to receive such information.
10. Contributors
The following people have substantially contributed to the editing of
this document:
Clarence Filsfils
Cisco Systems
Email: cfilsfil@cisco.com
Mach (Guoyi) Chen
Huawei Technologies
Email: mach.chen@huawei.com
11. Acknowledgements
The authors would like to thank Dhruv Dhody, Mohammed Abdul Aziz
Khalid, Lou Berger, Acee Lindem, Siva Sivabalan, Arjun Sreekantiah,
Dhanendra Jain, Francois Clad, Zafar Ali, Stephane Litkowski, Aravind
Babu Mahendra Babu, Geetanjalli Bhalla, Ahmed Bashandy, Mike
Koldychev, Samuel Sidor, Alex Tokar, Rajesh Melarcode Venkatesswaran,
Lin Changwang, and Liu Yao for their review and valuable comments.
The authors would also like to thank Susan Hares for her shepherd
review of the document and helpful comments to improve this document.
12. References
12.1. 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>.
[RFC5440] Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation
Element (PCE) Communication Protocol (PCEP)", RFC 5440,
DOI 10.17487/RFC5440, March 2009,
<https://www.rfc-editor.org/info/rfc5440>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
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[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[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>.
[RFC8697] Minei, I., Crabbe, E., Sivabalan, S., Ananthakrishnan, H.,
Dhody, D., and Y. Tanaka, "Path Computation Element
Communication Protocol (PCEP) Extensions for Establishing
Relationships between Sets of Label Switched Paths
(LSPs)", RFC 8697, DOI 10.17487/RFC8697, January 2020,
<https://www.rfc-editor.org/info/rfc8697>.
[RFC8986] Filsfils, C., Ed., Camarillo, P., Ed., Leddy, J., Voyer,
D., Matsushima, S., and Z. Li, "Segment Routing over IPv6
(SRv6) Network Programming", RFC 8986,
DOI 10.17487/RFC8986, February 2021,
<https://www.rfc-editor.org/info/rfc8986>.
[RFC9086] Previdi, S., Talaulikar, K., Ed., Filsfils, C., Patel, K.,
Ray, S., and J. Dong, "Border Gateway Protocol - Link
State (BGP-LS) Extensions for Segment Routing BGP Egress
Peer Engineering", RFC 9086, DOI 10.17487/RFC9086, August
2021, <https://www.rfc-editor.org/info/rfc9086>.
[RFC9256] Filsfils, C., Talaulikar, K., Ed., Voyer, D., Bogdanov,
A., and P. Mattes, "Segment Routing Policy Architecture",
RFC 9256, DOI 10.17487/RFC9256, July 2022,
<https://www.rfc-editor.org/info/rfc9256>.
[RFC9514] Dawra, G., Filsfils, C., Talaulikar, K., Ed., Chen, M.,
Bernier, D., and B. Decraene, "Border Gateway Protocol -
Link State (BGP-LS) Extensions for Segment Routing over
IPv6 (SRv6)", RFC 9514, DOI 10.17487/RFC9514, December
2023, <https://www.rfc-editor.org/info/rfc9514>.
[RFC9552] Talaulikar, K., Ed., "Distribution of Link-State and
Traffic Engineering Information Using BGP", RFC 9552,
DOI 10.17487/RFC9552, December 2023,
<https://www.rfc-editor.org/info/rfc9552>.
12.2. Informative References
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[I-D.ietf-idr-bgp-ls-te-path]
Previdi, S., Talaulikar, K., Dong, J., Gredler, H., and J.
Tantsura, "Advertisement of Traffic Engineering Paths
using BGP Link-State", Work in Progress, Internet-Draft,
draft-ietf-idr-bgp-ls-te-path-02, 11 November 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-idr-bgp-
ls-te-path-02>.
[I-D.ietf-idr-bgp-sr-segtypes-ext]
Talaulikar, K., Filsfils, C., Previdi, S., Mattes, P., and
D. Jain, "Segment Routing Segment Types Extensions for BGP
SR Policy", Work in Progress, Internet-Draft, draft-ietf-
idr-bgp-sr-segtypes-ext-06, 7 November 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-idr-bgp-
sr-segtypes-ext-06>.
[I-D.ietf-idr-sr-policy-safi]
Previdi, S., Filsfils, C., Talaulikar, K., Mattes, P., and
D. Jain, "Advertising Segment Routing Policies in BGP",
Work in Progress, Internet-Draft, draft-ietf-idr-sr-
policy-safi-10, 7 November 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-idr-sr-
policy-safi-10>.
[I-D.ietf-lsr-flex-algo-bw-con]
Hegde, S., Britto, W., Shetty, R., Decraene, B., Psenak,
P., and T. Li, "Flexible Algorithms: Bandwidth, Delay,
Metrics and Constraints", Work in Progress, Internet-
Draft, draft-ietf-lsr-flex-algo-bw-con-16, 25 November
2024, <https://datatracker.ietf.org/doc/html/draft-ietf-
lsr-flex-algo-bw-con-16>.
[I-D.ietf-pce-segment-routing-policy-cp]
Koldychev, M., Sivabalan, S., Barth, C., Peng, S., and H.
Bidgoli, "Path Computation Element Communication Protocol
(PCEP) Extensions for Segment Routing (SR) Policy
Candidate Paths", Work in Progress, Internet-Draft, draft-
ietf-pce-segment-routing-policy-cp-18, 14 October 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-pce-
segment-routing-policy-cp-18>.
[RFC2702] Awduche, D., Malcolm, J., Agogbua, J., O'Dell, M., and J.
McManus, "Requirements for Traffic Engineering Over MPLS",
RFC 2702, DOI 10.17487/RFC2702, September 1999,
<https://www.rfc-editor.org/info/rfc2702>.
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[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>.
[RFC4655] Farrel, A., Vasseur, J.-P., and J. Ash, "A Path
Computation Element (PCE)-Based Architecture", RFC 4655,
DOI 10.17487/RFC4655, August 2006,
<https://www.rfc-editor.org/info/rfc4655>.
[RFC5065] Traina, P., McPherson, D., and J. Scudder, "Autonomous
System Confederations for BGP", RFC 5065,
DOI 10.17487/RFC5065, August 2007,
<https://www.rfc-editor.org/info/rfc5065>.
[RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic
Engineering", RFC 5305, DOI 10.17487/RFC5305, October
2008, <https://www.rfc-editor.org/info/rfc5305>.
[RFC6952] Jethanandani, M., Patel, K., and L. Zheng, "Analysis of
BGP, LDP, PCEP, and MSDP Issues According to the Keying
and Authentication for Routing Protocols (KARP) Design
Guide", RFC 6952, DOI 10.17487/RFC6952, May 2013,
<https://www.rfc-editor.org/info/rfc6952>.
[RFC7308] Osborne, E., "Extended Administrative Groups in MPLS
Traffic Engineering (MPLS-TE)", RFC 7308,
DOI 10.17487/RFC7308, July 2014,
<https://www.rfc-editor.org/info/rfc7308>.
[RFC8231] Crabbe, E., Minei, I., Medved, J., and R. Varga, "Path
Computation Element Communication Protocol (PCEP)
Extensions for Stateful PCE", RFC 8231,
DOI 10.17487/RFC8231, September 2017,
<https://www.rfc-editor.org/info/rfc8231>.
[RFC8570] Ginsberg, L., Ed., Previdi, S., Ed., Giacalone, S., Ward,
D., Drake, J., and Q. Wu, "IS-IS Traffic Engineering (TE)
Metric Extensions", RFC 8570, DOI 10.17487/RFC8570, March
2019, <https://www.rfc-editor.org/info/rfc8570>.
[RFC8664] Sivabalan, S., Filsfils, C., Tantsura, J., Henderickx, W.,
and J. Hardwick, "Path Computation Element Communication
Protocol (PCEP) Extensions for Segment Routing", RFC 8664,
DOI 10.17487/RFC8664, December 2019,
<https://www.rfc-editor.org/info/rfc8664>.
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Authors' Addresses
Stefano Previdi
Individual
Email: stefano@previdi.net
Ketan Talaulikar (editor)
Cisco Systems
India
Email: ketant.ietf@gmail.com
Jie Dong
Huawei Technologies
Huawei Campus, No. 156 Beiqing Rd.
Beijing
100095
China
Email: jie.dong@huawei.com
Hannes Gredler
RtBrick Inc.
Email: hannes@rtbrick.com
Jeff Tantsura
Nvidia
Email: jefftant.ietf@gmail.com
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