Inter-Domain Routing S. Previdi
Internet-Draft
Intended status: Standards Track K. Talaulikar, Ed.
Expires: 10 September 2023 Cisco Systems
J. Dong
Huawei Technologies
H. Gredler
RtBrick Inc.
J. Tantsura
Microsoft
9 March 2023
Advertisement of Segment Routing Policies using BGP Link-State
draft-ietf-idr-bgp-ls-sr-policy-00
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 10 September 2023.
Copyright Notice
Copyright (c) 2023 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 . . . . . . . . . . . . . . . . . . 11
5.3. SR Candidate Path State TLV . . . . . . . . . . . . . . . 12
5.4. SR Policy Name TLV . . . . . . . . . . . . . . . . . . . 14
5.5. SR Candidate Path Name TLV . . . . . . . . . . . . . . . 15
5.6. SR Candidate Path Constraints TLV . . . . . . . . . . . . 16
5.6.1. SR Affinity Constraint Sub-TLV . . . . . . . . . . . 18
5.6.2. SR SRLG Constraint Sub-TLV . . . . . . . . . . . . . 19
5.6.3. SR Bandwidth Constraint Sub-TLV . . . . . . . . . . . 20
5.6.4. SR Disjoint Group Constraint Sub-TLV . . . . . . . . 20
5.6.5. SR Bidirectional Group Constraint Sub-TLV . . . . . . 22
5.6.6. SR Metric Constraint Sub-TLV . . . . . . . . . . . . 24
5.7. SR Segment List TLV . . . . . . . . . . . . . . . . . . . 25
5.8. SR Segment Sub-TLV . . . . . . . . . . . . . . . . . . . 28
5.8.1. Segment Descriptors . . . . . . . . . . . . . . . . . 30
5.9. SR Segment List Metric Sub-TLV . . . . . . . . . . . . . 36
5.10. SR Segment List Bandwidth Sub-TLV . . . . . . . . . . . . 38
6. Procedures . . . . . . . . . . . . . . . . . . . . . . . . . 38
7. Manageability Considerations . . . . . . . . . . . . . . . . 39
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 39
8.1. BGP-LS NLRI-Types . . . . . . . . . . . . . . . . . . . . 39
8.2. BGP-LS Protocol-IDs . . . . . . . . . . . . . . . . . . . 39
8.3. BGP-LS TLVs . . . . . . . . . . . . . . . . . . . . . . . 40
8.4. BGP-LS SR Policy Protocol Origin . . . . . . . . . . . . 40
8.5. BGP-LS SR Segment Descriptors . . . . . . . . . . . . . . 41
8.6. BGP-LS Metric Type . . . . . . . . . . . . . . . . . . . 42
9. Security Considerations . . . . . . . . . . . . . . . . . . . 43
10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 43
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 43
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 43
12.1. Normative References . . . . . . . . . . . . . . . . . . 43
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12.2. Informative References . . . . . . . . . . . . . . . . . 44
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 46
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 may be active; when multiple 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 a controller
which allows the network operator to optimize several functions and
operations through the use of a controller aware of both topology and
state information.
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 a 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 SR Policy
paths' state 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 [RFC7752]. 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. While
this document focuses on SR Policies, #draft-ietf-idr-bgp-ls-te-lsp#
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-segment-routing-te-policy] that is 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 [RFC7752] is extended to carry the
SR Policy information. New TLVs carried in the Link_State Attribute
defined in [RFC7752] are also defined to carry the attributes of a SR
Policy in the subsequent sections.
The format of "Link-State NLRI" is defined in [RFC7752] 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) //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
An additional "NLRI Type" known as SR Policy Candidate Path NLRI
(value 5) is defined for the advertisement of SR Policy Information.
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.
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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) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Node Descriptor TLV (for the Headend) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// SR Policy Candidate Path Descriptor TLV //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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 [RFC7752].
* "Local Node Descriptor" (TLV 256) as defined in [RFC7752] that
describes the headend node.
* The SR Policy Candidate Path Descriptor TLV is specified in
Section 4.
The Local Node Descriptor TLV MUST include the following Node
Descriptor TLVs:
* BGP Router-ID (TLV 516) [RFC9086], which contains a valid BGP
Identifier of the node originating the SR Policy advertisement.
* Autonomous System Number (TLV 512) [RFC7752], which contains the
ASN or AS Confederation Identifier (ASN) [RFC5065], if
confederations are used, of the node originating the SR Policy
advertisement.
The Local Node Descriptor TLV SHOULD include at least one of the
following Node Descriptor TLVs:
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* IPv4 Router-ID of Local Node (TLV 1028) [RFC7752], which contains
the IPv4 TE Router-ID of the local node when one is provisioned.
* IPv6 Router-ID of Local Node (TLV 1029) [RFC7752], which contains
the IPv6 TE Router-ID of the local node when one is provisioned.
The Local Node Descriptor TLV MAY include the following Node
Descriptor TLVs:
* BGP Confederation Member (TLV 517) [RFC9086], which contains the
ASN of the confederation member (i.e. Member-AS Number), if BGP
confederations are used, of the local node.
* Node Descriptors as defined in [RFC7752].
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:
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) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
* Type: 554
* Length: variable (valid values are 24, 36 or 48 octets)
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* Protocol-Origin: 1-octet field which identifies the protocol or
component which is responsible for the instantiation of this path.
Following protocol-origin codepoints are defined in this document.
+-------+---------------------------------------------------+
| Code | Protocol |
| Point | Origin |
+-------+---------------------------------------------------+
| 1 | PCEP |
| 2 | BGP SR Policy |
| 3 | Configuration (CLI, YANG model via NETCONF, etc.) |
+-------+---------------------------------------------------+
* 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
* 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
* Color: 4 octets that indicate the color of the SR Policy
* 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.
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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 Attribute
"LINK_STATE Attribute" defined in [RFC7752] 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:
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) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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
[RFC9256]. 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|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.
- 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.
* 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 are 4-octet carrying the MPLS Label or 16-octet
carrying the SRv6 SID based on the BSID D-flag. 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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In the case of an SRv6, the Binding SID sub-TLV does not have the
ability to signal the SRv6 Endpoint Behavior [RFC8986] or the
structure of the SID. It is RECOMMENDED that the SRv6 Binding SID
TLV defined in Section 5.2, which enables the specification of the
SRv6 Endpoint Behavior, be used for signaling of an SRv6 Binding SID.
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) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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
[RFC9256]. 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|B|U|F| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
- 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.
- F-Flag: Indicates the BSID value is one allocated dynamically
due to fallback (e.g. when specified BSID is unavailable) when
set.
* 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) defined in [I-D.ietf-idr-bgpls-srv6-ext] are used as sub-TLVs
of the SRv6 Binding SID TLV to optionally indicate the SRv6 Endpoint
behavior and SID structure for the Binding SID value in the 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) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|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
- A-Flag: Indicates the CP is the active path (i.e. one
provisioned in the forwarding plane) for the SR Policy when set
- B-Flag: Indicates the CP is the backup path (i.e. one
identified for path protection of the active path) for the SR
Policy when set
- E-Flag: Indicates that the CP has been evaluated for validity
(e.g. headend may evaluate CPs based on their preferences) when
set
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- V-Flag: Indicates the CP has at least one valid SID-List when
set. 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. Refer to section 8.5 of [RFC9256] for details.
- D-Flag: Indicates the CP was delegated for computation to a
PCE/controller when set
- C-Flag: Indicates the CP was provisioned by a PCE/controller
when set
- I-Flag: Indicates the CP will perform the "drop upon invalid"
behavior when no other active path is available for this SR
Policy and this path is the one with the best preference
amongst the available CPs. Refer to section 8.2 of [RFC9256]
for details.
- T-Flag: Indicates the CP has been marked as eligible for use as
Transit Policy on the headend when set. Refer to section 8.3
of [RFC9256].
- U-Flag: Indicates the SR Policy that the CP belongs to is
dropping traffic as a result of the "drop upon invalid"
behavior being activated.
* 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:
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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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SR Policy Name (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
* Type: 1213
* Length: variable
* SR Policy Name: Symbolic name for the SR Policy 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.
5.5. 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:
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) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
* Type: 1203
* Length: variable
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* 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:
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) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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.
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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| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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. This flag is mutually exclusive with the
U-Flag.
- U-Flag: Indicates that the CP prefers the use of only
unprotected SIDs when set. This flag is mutually exclusive
with the P-Flag.
- A-Flag: Indicates that the CP uses only the SIDs belonging to
the specified SR Algorithm when set
- T-Flag: Indicates that the CP uses only the SIDs belonging to
the specified topology when set
- 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
- F-Flag: Indicates that the CP is fixed once computed and not
modified except on operator intervention.
* 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.
* RESERVED2: 1 octet. MUST be set to 0 by the originator and MUST
be ignored by a receiver.
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* sub-TLVs: optional sub-TLVs MAY be included in this TLV to
describe other constraints.
The following constraint sub-TLVs are defined for the SR CP
Constraints TLV.
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) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
* Type: 1211
* Length: 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
- N-Flag: Indicates that node disjointness is requested when set
- L-Flag: Indicates that link disjointness is requested when set
- 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
- 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
* 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.
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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
- N-Flag: Indicates that node disjointness is achieved when set
- L-Flag: Indicates that link disjointness is achieved when set
- F-Flag: Indicates that the computation has fallen back to a
lower level of disjointness than requested when set
- 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
- X-Flag : Indicates that the disjointness constraint could not
be achieved and hence path has been invalidated when set
* RESERVED: 2 octets. MUST be set to 0 by the originator and MUST
be ignored by a receiver.
* Disjointness Group Identifier: 4-octet value that is the group
identifier for a set of disjoint paths
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:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Bidirectional Group Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
* Type: TBD
* Length: 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.
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 set and otherwise it is the forward path when
clear
- C-Flag: Indicates that the bidirectional path is co-routed when
set
* 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
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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:
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
* Type: TBD
* Length: 12 octets
* Metric Type: 1-octet field which identifies the type of the metric
being used. The metric type code points are listed in Section 8.6
of this document.
* 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:
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- O-Flag: Indicates that this is the optimization metric being
reported for a dynamic CP when set. 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.
- 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.
* 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:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MTID | Algorithm | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Weight (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| sub-TLVs (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
* Type: 1205
* 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 an explicit path when set
and indicates a dynamic path when clear.
- C-Flag: Indicates that SID-List has been computed for a dynamic
path when set. It is always reported as set for explicit
paths.
- V-Flag: Indicates the SID-List has passed verification or its
verification was not required when set and failed verification
when clear.
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- 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.
- T-Flag: Indicates that all the SIDs in the SID-List belong to
the specified topology (identified by the multi-topology ID)
when set.
- 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.
* 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 cases
(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, the SR Segment List TLV SHOULD NOT include any SR
Segment sub-TLVs.
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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:
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) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
* Type: 1206
* Length: variable
* Segment Type: 1 octet which indicates the type of segment (refer
Section 5.8.1 for details)
* 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 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S|E|V|R|A| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
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- S-Flag: Indicates the presence of SID value in the SID field
when set and that no value is indicated when clear.
- 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 and failed verification when
clear.
- R-Flag: Indicates the SID has been resolved or did not require
resolution (e.g. because it is not the first SID) when set and
failed resolution when clear.
- 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 [I-D.ietf-idr-bgpls-srv6-ext] are used as sub-sub-
TLVs of the SR Segment sub-TLV to optionally indicate the SRv6
Endpoint behavior and SID structure when advertising the SRv6
specific segment types.
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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.
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 |
+------+-------------------------------------------------------------+
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 |
+-+-+-+-+-+-+-+-+
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.
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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 |
+-+-+-+-+-+-+-+-+
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.
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) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Where:
* Algorithm: 1-octet value that indicates the algorithm used for
picking the SID
* IPv4 Node Address: 4-octet value which carries the IPv4 address
associated with the node
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:
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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) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Where:
* Algorithm: 1-octet value that indicates the algorithm used for
picking the SID
* 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) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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
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:
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 Local Address (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 Remote Address (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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).
5.8.1.8. 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) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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:
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) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Where:
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* Algorithm: 1-octet value that indicates the algorithm used for
picking the SID
* 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) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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
* 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:
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Global IPv6 Local Interface Address (16 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Global IPv6 Remote Interface Address (16 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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:
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
* Type: 1207
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* Length: 16 octets
* Metric Type: 1-octet field which identifies the type of metric.
The metric type code points are listed in Section 8.6 of this
document.
* 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
- 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.
- V-Flag: Indicates that the metric value computed is being
reported when set.
* 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.
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* 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:
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
* Type: TBD
* Length: 4 octets
* Bandwidth: 4 octets which specify the allocated bandwidth in unit
of bytes per second in IEEE floating point format.
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.
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. Then 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
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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 [RFC7752] apply to this document.
In general, the SR Policy head-end nodes are responsible for the
advertisement of SR Policy state information.
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 |
+------+-------------------------------+---------------+
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:
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+-------------+----------------------------------+---------------+
| Protocol-ID | NLRI information source protocol | Reference |
+-------------+----------------------------------+---------------+
| 9 | Segment Routing | this document |
+-------------+----------------------------------+---------------+
8.3. BGP-LS TLVs
IANA maintains a registry called "Node Anchor, Link Descriptor and
Link 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:
+-------+----------------------------------------+---------------+
| 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 |
| TBD | SR Bidirectional Group Constraint | this document |
| TBD | SR Metric Constraint | this document |
| TBD | SR Segment List Bandwidth | this document |
+-------+----------------------------------------+---------------+
8.4. BGP-LS SR Policy Protocol Origin
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 [RFC9029]. The new
registry is called "SR Policy Protocol Origin" and 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
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document:
+---------+---------------------------------------------------+
| Code | |
| Point | Protocol Origin |
+---------+---------------------------------------------------+
| 0 | Reserved (not to be used) |
| 1 | PCEP |
| 2 | BGP SR Policy |
| 3 | Configuration (CLI, YANG model via NETCONF, etc.) |
| 4-250 | Unassigned |
| 251-255 | Private Use (not to be assigned by IANA) |
+---------+---------------------------------------------------+
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 [RFC9029]. 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 |
+--------+-----------------------------------------------------------+
8.6. BGP-LS 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 [RFC9029]. The new
registry is called "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:
+------------+------------------------------------------+
| Code Point | Metric Type |
+------------+------------------------------------------+
| 0 | IGP Metric |
| 1 | Min Unidirectional Link Delay [RFC7471] |
| 2 | TE Metric [RFC3630] |
| 3 | Hop Count (refer [RFC5440]) |
| 4 | SID List Length |
| 5-250 | Unassigned |
| 251-255 | Private Use (not to be assigned by IANA) |
+------------+------------------------------------------+
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9. Security Considerations
Procedures and protocol extensions defined in this document do not
affect the BGP security model. See [RFC6952] for details.
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, and
Aravind Babu Mahendra Babu for their review and valuable comments.
12. References
12.1. Normative References
[I-D.ietf-idr-bgpls-srv6-ext]
Dawra, G., Filsfils, C., Talaulikar, K., Chen, M.,
Bernier, D., and B. Decraene, "BGP Link State Extensions
for SRv6", Work in Progress, Internet-Draft, draft-ietf-
idr-bgpls-srv6-ext-14, 17 February 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-idr-
bgpls-srv6-ext-14>.
[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>.
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[RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and
S. Ray, "North-Bound Distribution of Link-State and
Traffic Engineering (TE) Information Using BGP", RFC 7752,
DOI 10.17487/RFC7752, March 2016,
<https://www.rfc-editor.org/info/rfc7752>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[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>.
[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>.
[RFC9029] Farrel, A., "Updates to the Allocation Policy for the
Border Gateway Protocol - Link State (BGP-LS) Parameters
Registries", RFC 9029, DOI 10.17487/RFC9029, June 2021,
<https://www.rfc-editor.org/info/rfc9029>.
[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>.
12.2. Informative References
[I-D.ietf-idr-segment-routing-te-policy]
Previdi, S., Filsfils, C., Talaulikar, K., Mattes, P.,
Jain, D., and S. Lin, "Advertising Segment Routing
Policies in BGP", Work in Progress, Internet-Draft, draft-
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Internet-Draft Advertising SR Policies using BGP-LS March 2023
ietf-idr-segment-routing-te-policy-20, 27 July 2022,
<https://datatracker.ietf.org/doc/html/draft-ietf-idr-
segment-routing-te-policy-20>.
[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>.
[RFC3630] Katz, D., Kompella, K., and D. Yeung, "Traffic Engineering
(TE) Extensions to OSPF Version 2", RFC 3630,
DOI 10.17487/RFC3630, September 2003,
<https://www.rfc-editor.org/info/rfc3630>.
[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>.
[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>.
[RFC7471] Giacalone, S., Ward, D., Drake, J., Atlas, A., and S.
Previdi, "OSPF Traffic Engineering (TE) Metric
Extensions", RFC 7471, DOI 10.17487/RFC7471, March 2015,
<https://www.rfc-editor.org/info/rfc7471>.
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Internet-Draft Advertising SR Policies using BGP-LS March 2023
[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>.
Authors' Addresses
Stefano Previdi
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
Microsoft
Email: jefftant.ietf@gmail.com
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