rfc9830v1.txt   rfc9830.txt 
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D. Jain D. Jain
Google Google
July 2025 July 2025
Advertising Segment Routing Policies in BGP Advertising Segment Routing Policies in BGP
Abstract Abstract
A Segment Routing (SR) Policy is an ordered list of segments (also A Segment Routing (SR) Policy is an ordered list of segments (also
referred to as "instructions") that define a source-routed policy. referred to as "instructions") that define a source-routed policy.
An SR Policy consists of one or more candidate paths, each comprising An SR Policy consists of one or more Candidate Paths (CPs), each
one or more segment lists. A headend can be provisioned with these comprising one or more segment lists. A headend can be provisioned
candidate paths using various mechanisms such as Command-Line with these CPs using various mechanisms such as Command-Line
Interface (CLI), Network Configuration Protocol (NETCONF), Path Interface (CLI), Network Configuration Protocol (NETCONF), Path
Computation Element Communication Protocol (PCEP), or BGP. Computation Element Communication Protocol (PCEP), or BGP.
This document specifies how BGP can be used to distribute SR Policy This document specifies how BGP can be used to distribute SR Policy
candidate paths. It introduces a BGP SAFI for advertising a CPs. It introduces a BGP SAFI for advertising a CP of an SR Policy
candidate path of an SR Policy and defines sub-TLVs for the Tunnel and defines sub-TLVs for the Tunnel Encapsulation Attribute to signal
Encapsulation Attribute to signal information related to these information related to these CPs.
candidate paths.
Furthermore, this document updates RFC 9012 by extending the Color Furthermore, this document updates RFC 9012 by extending the Color
Extended Community to support additional steering modes over SR Extended Community to support additional steering modes over SR
Policy. Policy.
Status of This Memo Status of This Memo
This is an Internet Standards Track document. This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force This document is a product of the Internet Engineering Task Force
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packet flow along a specific path. Intermediate per-path states are packet flow along a specific path. Intermediate per-path states are
eliminated thanks to source routing. eliminated thanks to source routing.
The headend node is said to steer a flow into an SR Policy [RFC9256]. The headend node is said to steer a flow into an SR Policy [RFC9256].
The packets steered into an SR Policy carry an ordered list of The packets steered into an SR Policy carry an ordered list of
segments associated with that SR Policy. segments associated with that SR Policy.
[RFC9256] further details the concepts of SR Policy and steering into [RFC9256] further details the concepts of SR Policy and steering into
an SR Policy. These apply equally to the SR-MPLS and Segment Routing an SR Policy. These apply equally to the SR-MPLS and Segment Routing
for IPv6 (SRv6) data plane instantiations of Segment Routing using over IPv6 (SRv6) data plane instantiations of Segment Routing using
SR-MPLS and SRv6 Segment Identifiers (SIDs) as described in SR-MPLS and SRv6 Segment Identifiers (SIDs) as described in
[RFC8402]. [RFC8660] describes the representation and processing of [RFC8402]. [RFC8660] describes the representation and processing of
this ordered list of segments as an MPLS label stack for SR-MPLS. this ordered list of segments as an MPLS label stack for SR-MPLS.
[RFC8754] and [RFC8986] describe the same for SRv6 with the use of [RFC8754] and [RFC8986] describe the same for SRv6 with the use of
the Segment Routing Header (SRH). the Segment Routing Header (SRH).
The functionality related to SR Policy described in [RFC9256] can be The functionality related to SR Policy described in [RFC9256] can be
conceptually viewed as being incorporated in an SR Policy Module conceptually viewed as being incorporated in an SR Policy Module
(SRPM). The following is a reminder of the high-level functionality (SRPM). The following is a reminder of the high-level functionality
of SRPM: of SRPM:
* Learning multiple candidate paths (CPs) for an SR Policy via * Learning multiple CPs for an SR Policy via various mechanisms
various mechanisms (CLI, NETCONF, PCEP, or BGP). (CLI, NETCONF, PCEP, or BGP).
* Selection of the best candidate path for an SR Policy. * Selection of the best CP for an SR Policy.
* Associating a Binding SID (BSID) to the selected candidate path of * Associating a Binding SID (BSID) to the selected CP of an SR
an SR Policy. Policy.
* Installation of the selected candidate path and its BSID in the * Installation of the selected CP and its BSID in the forwarding
forwarding plane. plane.
This document specifies the use of BGP to distribute one or more of This document specifies the use of BGP to distribute one or more of
the candidate paths of an SR Policy to the headend of that SR Policy. the CPs of an SR Policy to the headend of that SR Policy. The
The document describes the functionality provided by BGP and, as document describes the functionality provided by BGP and, as
appropriate, provides references for the functionality, which is appropriate, provides references for the functionality, which is
outside the scope of BGP (i.e., resides within SRPM on the headend outside the scope of BGP (i.e., resides within SRPM on the headend
node). node).
This document specifies a way of representing SR Policy candidate This document specifies a way of representing SR Policy CPs in BGP
paths in BGP UPDATE messages. BGP can then be used to propagate the UPDATE messages. BGP can then be used to propagate the SR Policy CPs
SR Policy candidate paths to the headend nodes in a network. The to the headend nodes in a network. The usual BGP rules for BGP
usual BGP rules for BGP propagation and best-path selection are used. propagation and best-path selection are used. At the headend of a
At the headend of a specific policy, this will result in one or more specific policy, this will result in one or more CPs being installed
candidate paths being installed into the "BGP table". These paths into the "BGP table". These paths are then passed to the SRPM. The
are then passed to the SRPM. The SRPM may compare them to candidate SRPM may compare them to CPs learned via other mechanisms and will
paths learned via other mechanisms and will choose one or more paths choose one or more paths to be installed in the data plane. BGP
to be installed in the data plane. BGP itself does not install SR itself does not install SR Policy CPs into the data plane.
Policy candidate paths into the data plane.
This document introduces a BGP Subsequent Address Family Identifier This document introduces a BGP Subsequent Address Family Identifier
(SAFI) for IPv4 and IPv6 address families. In UPDATE messages of (SAFI) for IPv4 and IPv6 address families. In BGP UPDATE messages of
those AFI/SAFIs, the Network Layer Reachability Information (NLRI) those AFI/SAFIs, the Network Layer Reachability Information (NLRI)
identifies an SR Policy Candidate Path while the attributes encode identifies an SR Policy CP while the attributes encode the segment
the segment lists and other details of that SR Policy Candidate Path. lists and other details of that SR Policy CP.
While, for simplicity, the text in this document states that BGP While, for simplicity, the text in this document states that BGP
advertises an SR Policy, it is to be understood that BGP advertises a advertises an SR Policy, it is to be understood that BGP advertises a
candidate path of an SR policy and that this SR Policy might have CP of an SR Policy and that this SR Policy might have several other
several other candidate paths provided via BGP (via an NLRI with a CPs provided via BGP (via an NLRI with a different distinguisher as
different distinguisher as defined in Section 2.1), PCEP, NETCONF, or defined in Section 2.1), PCEP, NETCONF, or local policy
local policy configuration. configuration.
Typically, an SR Policy Controller [RFC9256] defines the set of Typically, an SR Policy Controller [RFC9256] defines the set of
policies and advertises them to policy headend routers (typically policies and advertises them to policy headend routers (typically
ingress routers). These policy advertisements use the BGP extensions ingress routers). These policy advertisements use the BGP extensions
defined in this document. In most cases, the policy advertisement is defined in this document. In most cases, the policy advertisement is
tailored for a specific policy headend; consequently, it may be tailored for a specific policy headend; consequently, it may be
transmitted over a direct BGP session (i.e., without intermediate BGP transmitted over a direct BGP session (i.e., without intermediate BGP
hops) to that headend and is not propagated any further. In such hops) to that headend and is not propagated any further. In such
cases, the policy advertisements will not traverse any Route cases, the policy advertisements will not traverse any Route
Reflector (RR) (see [RFC4456] and Section 4.2.3). Reflector (RR) (see [RFC4456] and Section 4.2.3).
Alternatively, a BGP egress router may advertise SR Policies that Alternatively, a BGP egress router may advertise SR Policies that
represent paths terminating on itself. In such cases, the router can represent paths that terminate on it. In such cases, the router can
send these policies directly to each headend over a dedicated BGP send these policies directly to each headend over a dedicated BGP
session, without necessitating any further propagation of the policy. session, without necessitating any further propagation of the policy.
In some situations, it is undesirable for a controller or BGP egress In some situations, it is undesirable for a controller or BGP egress
router to have a BGP session to each policy headend. In these router to have a BGP session to each policy headend. In these
situations, BGP Route Reflectors may be used to propagate the situations, BGP RRs may be used to propagate the advertisements. In
advertisements. In certain other deployments, it may be necessary certain other deployments, it may be necessary for the advertisement
for the advertisement to propagate through a sequence of one or more to propagate through a sequence of one or more Autonomous Systems
Autonomous Systems (ASes) within an SR Domain (refer to Section 7 for (ASes) within an SR Domain (refer to Section 7 for the associated
the associated security considerations). To make this possible, an security considerations). To make this possible, an attribute needs
attribute needs to be attached to the advertisement that enables a to be attached to the advertisement that enables a BGP speaker to
BGP speaker to determine whether it is intended to be a headend for determine whether it is intended to be a headend for the advertised
the advertised policy. This is done by attaching one or more Route policy. This is done by attaching one or more Route Target extended
Target Extended Communities to the advertisement [RFC4360]. communities to the advertisement [RFC4360].
The BGP extensions for the advertisement of SR Policies include The BGP extensions for the advertisement of SR Policies include
following components: following components:
* A Subsequent Address Family Identifier (SAFI) whose NLRIs identify * A SAFI whose NLRIs identify an SR Policy CP.
an SR Policy candidate path.
* A Tunnel Type identifier for SR Policy and a set of sub-TLVs to be * A Tunnel Type identifier for SR Policy and a set of sub-TLVs to be
inserted into the Tunnel Encapsulation Attribute (as defined in inserted into the Tunnel Encapsulation Attribute (as defined in
[RFC9012]) specifying segment lists of the SR Policy candidate [RFC9012]) specifying segment lists of the SR Policy CP as well as
path as well as other information about the SR Policy. other information about the SR Policy.
* One or more IPv4 address-specific format route target extended * One or more IPv4 address-specific format Route Target extended
community ([RFC4360]) attached to the SR Policy Candidate Path community ([RFC4360]) attached to the SR Policy CP advertisement
advertisement that indicates the intended headend of such an SR that indicates the intended headend of such an SR Policy CP
Policy Candidate Path advertisement. advertisement.
The SR Policy SAFI route updates utilize the Tunnel Encapsulation The SR Policy SAFI route updates utilize the Tunnel Encapsulation
Attribute to signal an SR Policy, which itself functions as a tunnel. Attribute to signal an SR Policy, which itself functions as a tunnel.
This usage differs notably from the approach described in [RFC9012], This usage differs notably from the approach described in [RFC9012],
where the Tunnel Encapsulation Attribute is associated with a BGP where the Tunnel Encapsulation Attribute is associated with a BGP
route update (e.g., for Internet or VPN routes) to specify the tunnel route update (e.g., for Internet or VPN routes) to specify the tunnel
used for forwarding traffic. This document does not modify or used for forwarding traffic. This document does not modify or
supersede the usage of the Tunnel Encapsulation Attribute for supersede the usage of the Tunnel Encapsulation Attribute for
existing AFIs/SAFIs as defined in [RFC9012]. Details regarding the existing AFIs/SAFIs as defined in [RFC9012]. Details regarding the
processing of the Tunnel Encapsulation Attribute for the SR Policy processing of the Tunnel Encapsulation Attribute for the SR Policy
SAFI are provided in Sections 2.2 and 2.3. SAFI are provided in Sections 2.2 and 2.3.
The northbound advertisement of the operational state of the SR The northbound advertisement of the operational state of the SR
Policy Candidate Paths as part of BGP - Link State (BGP-LS) [RFC9552] Policy CPs as part of BGP - Link State (BGP-LS) [RFC9552] topology
topology information is specified in [SR-BGP-LS]. information is specified in [BGP-LS-SR-POLICY].
The signaling of Dynamic and Composite Candidate Paths (Sections 5.2 The signaling of Dynamic and Composite CPs (Sections 5.2 and 5.3,
and 5.3, respectively, of [RFC9256]) is outside the scope of this respectively, of [RFC9256]) is outside the scope of this document.
document.
The Color Extended Community (as defined in [RFC9012]) is used to The Color Extended Community (as defined in [RFC9012]) is used to
steer traffic into an SR Policy, as described in Section 8.8 of steer traffic into an SR Policy, as described in Section 8.8 of
[RFC9256]. Section 3 of this document updates [RFC9012] with [RFC9256]. Section 3 of this document updates [RFC9012] with
modifications to the format of the Flags field of the Color Extended modifications to the format of the Flags field of the Color Extended
Community by using the two leftmost bits of that field. Community by using the two leftmost bits of that field.
1.1. Requirements Language 1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
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Figure 1: SR Policy SAFI Format Figure 1: SR Policy SAFI Format
Where: Where:
NLRI Length: 1 octet indicating the length expressed in bits as NLRI Length: 1 octet indicating the length expressed in bits as
defined in [RFC4760]. When AFI = 1, the value MUST be 96; when defined in [RFC4760]. When AFI = 1, the value MUST be 96; when
AFI = 2, the value MUST be 192. AFI = 2, the value MUST be 192.
Distinguisher: 4-octet value uniquely identifying the policy in the Distinguisher: 4-octet value uniquely identifying the policy in the
context of <color, endpoint> tuple. The distinguisher has no context of <Color, Endpoint> tuple. The distinguisher has no
semantic value and is solely used by the SR Policy originator to semantic value. It is used by the SR Policy originator to form
make unique (from an NLRI perspective) both for multiple candidate unique NLRIs the following situations:
paths of the same SR Policy as well as candidate paths of
different SR Policies (i.e., with different segment lists) with * to differentiate multiple CPs of the same SR Policy
the same Color and Endpoint but meant for different headends. The
distinguisher is the discriminator of the SR Policy candidate path * to differentiate CPs meant for different headends but having
as specified in Section 2.5 of [RFC9256]. the same Color and Endpoint
The distinguisher is the discriminator of the SR Policy CP as
specified in Section 2.5 of [RFC9256].
Policy Color: 4 octets that carry an unsigned non-zero integer value Policy Color: 4 octets that carry an unsigned non-zero integer value
indicating the color of the SR Policy as specified in Section 2.1 indicating the Color of the SR Policy as specified in Section 2.1
of [RFC9256]. The color is used to match the color of the of [RFC9256]. The Color is used to match the Color of the
destination prefixes to steer traffic into the SR Policy as destination prefixes to steer traffic into the SR Policy as
specified in Section 8 of [RFC9256]. specified in Section 8 of [RFC9256].
Endpoint: a value that identifies the endpoint of a policy. The Endpoint: a value that identifies the Endpoint of a policy. The
Endpoint may represent a single node or a set of nodes (e.g., an Endpoint may represent a single node or a set of nodes (e.g., an
anycast address). The Endpoint is an IPv4 (4-octet) address or an anycast address). The Endpoint is an IPv4 (4-octet) address or an
IPv6 (16-octet) address according to the AFI of the NLRI. The IPv6 (16-octet) address according to the AFI of the NLRI. The
address can be either unicast or an unspecified address (0.0.0.0 address can be either unicast or an unspecified address (0.0.0.0
for IPv4, :: for IPv6), known as a null endpoint as specified in for IPv4, :: for IPv6), known as a null Endpoint as specified in
Section 2.1 of [RFC9256]. Section 2.1 of [RFC9256].
The color and endpoint are used to automate the steering of BGP The Color and Endpoint are used to automate the steering of BGP
service routes on an SR Policy as described in Section 8 of service routes on an SR Policy as described in Section 8 of
[RFC9256]. [RFC9256].
The NLRI containing an SR Policy candidate path is carried in a BGP The NLRI containing an SR Policy CP is carried in a BGP UPDATE
UPDATE message [RFC4271] using BGP multiprotocol extensions [RFC4760] message [RFC4271] using BGP multiprotocol extensions [RFC4760] with
with an AFI of 1 or 2 (IPv4 or IPv6) and with a SAFI of 73. The an AFI of 1 or 2 (IPv4 or IPv6) and with a SAFI of 73. The fault
fault management and error handling in the encoding of the NLRI are management and error handling in the encoding of the NLRI are
specified in Section 5. specified in Section 5.
An update message that carries the MP_REACH_NLRI or MP_UNREACH_NLRI A BGP UPDATE message that carries the MP_REACH_NLRI or
attribute with the SR Policy SAFI MUST also carry the BGP mandatory MP_UNREACH_NLRI attribute with the SR Policy SAFI MUST also carry the
attributes. In addition, the BGP update message MAY also contain any BGP mandatory attributes. In addition, the BGP UPDATE message MAY
of the BGP optional attributes. also contain any of the BGP optional attributes.
The next-hop network address field in SR Policy SAFI (73) updates may The next-hop network address field in SR Policy SAFI (73) updates may
be either a 4-octet IPv4 address or a 16-octet IPv6 address, be either a 4-octet IPv4 address or a 16-octet IPv6 address,
independent of the SR Policy AFI. The length field of the next-hop independent of the SR Policy AFI. The Length field of the next-hop
address specifies the next-hop address family. If the next-hop address specifies the next-hop address family. If the next-hop
length is 4, then the next-hop is an IPv4 address. If the next-hop length is 4, then the next-hop is an IPv4 address. If the next-hop
length is 16, then it is a global IPv6 address. If the next-hop length is 16, then it is a global IPv6 address. If the next-hop
length is 32, then it has a global IPv6 address followed by a link- length is 32, then it has a global IPv6 address followed by a link-
local IPv6 address. The setting of the next-hop field and its local IPv6 address. The setting of the next-hop field and its
attendant processing is governed by standard BGP procedures as attendant processing is governed by standard BGP procedures as
described in Section 3 of [RFC4760] and Section 3 of [RFC2545]. described in Section 3 of [RFC4760] and Section 3 of [RFC2545].
It is important to note that at any BGP speaker receiving BGP updates It is important to note that at any BGP speaker receiving BGP updates
with SR Policy NLRIs, the SRPM processes only the best path as per with SR Policy NLRIs, the SRPM processes only the best path as per
the BGP best-path selection algorithm. In other words, this document the BGP best-path selection algorithm. In other words, this document
leverages the existing BGP propagation and best-path selection rules. leverages the existing BGP propagation and best-path selection rules.
Details of the procedures are described in Section 4. Details of the procedures are described in Section 4.
It has to be noted that if several candidate paths of the same SR It has to be noted that if several CPs of the same SR Policy
Policy (endpoint, color) are signaled via BGP to a headend, then it (Endpoint, Color) are signaled via BGP to a headend, then it is
is RECOMMENDED that each NLRI use a different distinguisher. If BGP RECOMMENDED that each NLRI use a different distinguisher. If BGP has
has installed into the BGP table two advertisements whose respective installed into the BGP table two advertisements whose respective
NLRIs have the same color and endpoint, but different distinguishers, NLRIs have the same Color and Endpoint, but different distinguishers,
both advertisements are passed to the SRPM as different candidate both advertisements are passed to the SRPM as different CPs along
paths along with their respective originator information (i.e., with their respective originator information (i.e., Autonomous System
Autonomous System Number (ASN) and BGP Router-ID) as described in Number (ASN) and BGP Router-ID) as described in Section 2.4 of
Section 2.4 of [RFC9256]. The ASN would be the ASN of the origin and [RFC9256]. The ASN would be the ASN of the origin and the BGP
the BGP Router-ID is determined in the following order: Router-ID is determined in the following order:
* From the Route Origin Community [RFC4360] if present and carrying * From the Route Origin Community [RFC4360] if present and carrying
an IP Address, or an IP Address, or
* As the BGP Originator ID [RFC4456] if present, or * As the BGP ORIGINATOR_ID [RFC4456] if present, or
* As the BGP Router-ID of the peer from which the update was * As the BGP Router-ID of the peer from which the update was
received as a last resort. received as a last resort.
Section 2.9 of [RFC9256] specifies the selection of the active Section 2.9 of [RFC9256] specifies the selection of the active CP of
candidate path of the SR Policy by the SRPM based on the information the SR Policy by the SRPM based on the information provided to it by
provided to it by BGP. BGP.
2.2. SR Policy and Tunnel Encapsulation Attribute 2.2. SR Policy and Tunnel Encapsulation Attribute
The content of the SR Policy Candidate Path is encoded in the Tunnel The content of the SR Policy CP is encoded in the Tunnel
Encapsulation Attribute defined in [RFC9012] using a Tunnel-Type Encapsulation Attribute defined in [RFC9012] using a Tunnel Type
called the "SR Policy" type with code point 15. The use of the SR called the "SR Policy" type with code point 15. The use of the SR
Policy Tunnel-type is applicable only for the AFI/SAFI pairs of Policy Tunnel Type is applicable only for the AFI/SAFI pairs of
(1/73, 2/73). This document specifies the use of the Tunnel (1/73, 2/73). This document specifies the use of the Tunnel
Encapsulation Attribute with the SR Policy Tunnel-Type and the use of Encapsulation Attribute with the SR Policy Tunnel Type and the use of
any other Tunnel-Type with the SR Policy SAFI MUST be considered any other Tunnel Type with the SR Policy SAFI MUST be considered
malformed and handled by the "treat-as-withdraw" strategy [RFC7606]. malformed and handled by the "treat-as-withdraw" strategy [RFC7606].
The SR Policy Encoding structure is as follows: The SR Policy Encoding structure is as follows:
SR Policy SAFI NLRI: <Distinguisher, Policy-Color, Endpoint> SR Policy SAFI NLRI: <Distinguisher, Policy-Color, Endpoint>
Attributes: Attributes:
Tunnel Encapsulation Attribute (23) Tunnel Encapsulation Attribute (23)
Tunnel Type: SR Policy (15) Tunnel Type: SR Policy (15)
Binding SID Binding SID
Preference Preference
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... ...
Figure 2: SR Policy Encoding Figure 2: SR Policy Encoding
Where: Where:
* The SR Policy SAFI NLRI is defined in Section 2.1. * The SR Policy SAFI NLRI is defined in Section 2.1.
* The Tunnel Encapsulation Attribute is defined in [RFC9012]. * The Tunnel Encapsulation Attribute is defined in [RFC9012].
* The Tunnel-Type is set to 15. * The Tunnel Type is set to 15.
* Preference, Binding SID, Priority, Policy Name, Policy Candidate * Preference, Binding SID, Priority, Policy Name, Policy Candidate
Path Name, ENLP, Segment-List, Weight, and Segment sub-TLVs are Path Name, ENLP, Segment-List, Weight, and Segment sub-TLVs are
defined in Section 2.4. defined in Section 2.4.
* Additional sub-TLVs may be defined in the future. * Additional sub-TLVs may be defined in the future.
A Tunnel Encapsulation Attribute MUST NOT contain more than one TLV A Tunnel Encapsulation Attribute MUST NOT contain more than one TLV
of type "SR Policy"; such updates MUST be considered malformed and of type "SR Policy"; such updates MUST be considered malformed and
handled by the "treat-as-withdraw" strategy [RFC7606]. handled by the "treat-as-withdraw" strategy [RFC7606].
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Preference, Binding SID, SRv6 Binding SID, Segment-List, Priority, Preference, Binding SID, SRv6 Binding SID, Segment-List, Priority,
Policy Name, Policy Candidate Path Name, and Explicit NULL Label Policy Name, Policy Candidate Path Name, and Explicit NULL Label
Policy are all optional sub-TLVs introduced for the BGP Tunnel Policy are all optional sub-TLVs introduced for the BGP Tunnel
Encapsulation Attribute [RFC9012] being defined in this section. Encapsulation Attribute [RFC9012] being defined in this section.
Weight and Segment are sub-TLVs of the Segment-List sub-TLV mentioned Weight and Segment are sub-TLVs of the Segment-List sub-TLV mentioned
above. above.
An early draft version of this document included only the Binding SID An early draft version of this document included only the Binding SID
sub-TLV that could be used for both SR-MPLS and SRv6 Binding SIDs. sub-TLV that could be used for both SR-MPLS and SRv6 BSIDs. The SRv6
The SRv6 Binding SID TLV was introduced in later versions to support Binding SID TLV was introduced in later versions to support the
the advertisement of additional SRv6 capabilities without affecting advertisement of additional SRv6 capabilities without affecting
backward compatibility for early implementations. backward compatibility for early implementations.
The fault management and error handling in the encoding of the sub- The fault management and error handling in the encoding of the sub-
TLVs defined in this section are specified in Section 5. For the TLVs defined in this section are specified in Section 5. For the
TLVs/sub-TLVs that are specified as single instance, only the first TLVs/sub-TLVs that are specified as single instance, only the first
instance of that TLV/sub-TLV is used: the other instances MUST be instance of that TLV/sub-TLV is used: the other instances MUST be
ignored and MUST NOT considered to be malformed. ignored and MUST NOT considered to be malformed.
None of the sub-TLVs defined in the following subsections have any None of the sub-TLVs defined in the following subsections have any
effect on the BGP best-path selection or propagation procedures. effect on the BGP best-path selection or propagation procedures.
These sub-TLVs are not used by the BGP path selection process and are These sub-TLVs are not used by the BGP path selection process and are
instead passed on to SRPM as SR Policy Candidate Path information for instead passed on to SRPM as SR Policy Candidate Path information for
further processing as described in Section 2 of [RFC9256]. further processing as described in Section 2 of [RFC9256].
The use of SR Policy Sub-TLVs is applicable only for the AFI/SAFI The use of SR Policy sub-TLVs is applicable only for the AFI/SAFI
pairs of (1/73, 2/73). Future documents may extend their pairs of (1/73, 2/73). Future documents may extend their
applicability to other AFI/SAFI. applicability to other AFI/SAFI.
2.4.1. Preference Sub-TLV 2.4.1. Preference Sub-TLV
The Preference sub-TLV is used to carry the Preference of an SR The Preference sub-TLV is used to carry the Preference of an SR
Policy candidate path. The contents of this sub-TLV are used by the Policy CP. The contents of this sub-TLV are used by the SRPM as
SRPM as described in Section 2.7 of [RFC9256]. described in Section 2.7 of [RFC9256].
The Preference sub-TLV is OPTIONAL; it MUST NOT appear more than once The Preference sub-TLV is OPTIONAL; it MUST NOT appear more than once
in the SR Policy encoding. in the SR Policy encoding.
The Preference sub-TLV has the following format: The Preference sub-TLV has the following format:
0 1 2 3 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 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 | | Type | Length | Flags | RESERVED |
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Type and Length fields) in terms of octets. The value MUST be 6. Type and Length fields) in terms of octets. The value MUST be 6.
Flags: 1 octet of flags. No flags are defined in this document. Flags: 1 octet of flags. No flags are defined in this document.
The Flags field MUST be set to zero on transmission and MUST be The Flags field MUST be set to zero on transmission and MUST be
ignored on receipt. ignored on receipt.
RESERVED: 1 octet of reserved bits. This field MUST be set to zero RESERVED: 1 octet of reserved bits. This field MUST be set to zero
on transmission and MUST be ignored on receipt. on transmission and MUST be ignored on receipt.
Preference: a 4-octet value indicating the Preference of the SR Preference: a 4-octet value indicating the Preference of the SR
Policy Candidate Path as described in Section 2.7 of [RFC9256]. Policy CP as described in Section 2.7 of [RFC9256].
2.4.2. Binding SID Sub-TLV 2.4.2. Binding SID Sub-TLV
The Binding SID sub-TLV is used to signal the BSID-related The Binding SID sub-TLV is used to signal the BSID-related
information of the SR Policy candidate path. The contents of this information of the SR Policy CP. The contents of this sub-TLV are
sub-TLV are used by the SRPM as described in Section 6 of [RFC9256]. used by the SRPM as described in Section 6 of [RFC9256].
The Binding SID sub-TLV is OPTIONAL; it MUST NOT appear more than The Binding SID sub-TLV is OPTIONAL; it MUST NOT appear more than
once in the SR Policy encoding. once in the SR Policy encoding.
When the Binding SID sub-TLV is used to signal an SRv6 SID, the When the Binding SID sub-TLV is used to signal an SRv6 SID, the
selection of the corresponding SRv6 Endpoint Behavior [RFC8986] to be selection of the corresponding SRv6 Endpoint Behavior [RFC8986] to be
instantiated is determined by the headend node. It is RECOMMENDED instantiated is determined by the headend node. It is RECOMMENDED
that the SRv6 Binding SID sub-TLV, as defined in Section 2.4.3, be that the SRv6 Binding SID sub-TLV, as defined in Section 2.4.3, be
used when signaling an SRv6 Binding SID for an SR Policy candidate used when signaling an SRv6 BSID for an SR Policy CP. The support
path. The support for the use of this Binding SID sub-TLV for the for the use of this Binding SID sub-TLV for the signaling of an SRv6
signaling of an SRv6 Binding SID is retained primarily for backward BSID is retained primarily for backward compatibility with
compatibility with implementations that followed early draft versions implementations that followed early draft versions of this document
of this document that had not defined the SRv6 Binding SID sub-TLV. that had not defined the SRv6 Binding SID sub-TLV.
The Binding SID sub-TLV has the following format: The Binding SID sub-TLV has the following format:
0 1 2 3 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 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 | | Type | Length | Flags | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Binding SID (variable, optional) | | Binding SID (variable, optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
skipping to change at line 556 skipping to change at line 555
|S|I| | |S|I| |
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
Figure 5: SR Policy Binding SID Flags Figure 5: SR Policy Binding SID Flags
Where: Where:
* The S-Flag encodes the "Specified-BSID-Only" behavior. It is * The S-Flag encodes the "Specified-BSID-Only" behavior. It is
used by SRPM as described in Section 6.2.3 of [RFC9256]. used by SRPM as described in Section 6.2.3 of [RFC9256].
* The I-Flag encodes the "Drop Upon Invalid" behavior. It is * The I-Flag encodes the "Drop-Upon-Invalid" behavior. It is
used by SRPM as described in Section 8.2 of [RFC9256] to define used by SRPM as described in Section 8.2 of [RFC9256] to define
a specific SR Policy forwarding behavior. The flag indicates a specific SR Policy forwarding behavior. The flag indicates
that the SR Policy is to perform the "drop upon invalid" that the SR Policy is to perform the "Drop-Upon-Invalid"
behavior when no valid candidate path (CP) is available for behavior when no valid CP is available for this SR Policy. In
this SR Policy. In this situation, the CP with the highest this situation, the CP with the highest preference amongst
preference amongst those with the "drop upon invalid" config is those with the "Drop-Upon-Invalid" config is made active to
made active to drop traffic steered over the SR Policy. drop traffic steered over the SR Policy.
* The unassigned bits in the Flag octet MUST be set to zero upon * The unassigned bits in the Flags field MUST be set to zero upon
transmission and MUST be ignored upon receipt. transmission and MUST be ignored upon receipt.
RESERVED: 1 octet of reserved bits. MUST be set to zero on RESERVED: 1 octet of reserved bits. MUST be set to zero on
transmission and MUST be ignored on receipt. transmission and MUST be ignored on receipt.
Binding SID: If the length is 2, then no Binding SID is present. If Binding SID: If the length is 2, then no BSID is present. If the
the length is 6, then the Binding SID is encoded in 4 octets using length is 6, then the BSID is encoded in 4 octets using the format
the format below. Traffic Class (TC), S, and TTL (Total of 12 below. Traffic Class (TC), S, and TTL (Total of 12 bits) are
bits) are RESERVED and MUST be set to zero and MUST be ignored. RESERVED and MUST be set to zero and MUST be ignored.
0 1 2 3 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 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 | | Label | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: Binding SID Label Encoding Figure 6: Binding SID Label Encoding
The Label field is validated by the SRPM but MUST NOT contain the The Label field is validated by the SRPM but MUST NOT contain the
reserved MPLS label values (0-15). If the length is 18, then the reserved MPLS label values (0-15). If the length is 18, then the
Binding SID contains a 16-octet SRv6 SID. BSID contains a 16-octet SRv6 SID.
2.4.3. SRv6 Binding SID Sub-TLV 2.4.3. SRv6 Binding SID Sub-TLV
The SRv6 Binding SID sub-TLV is used to signal the SRv6 Binding SID The SRv6 Binding SID sub-TLV is used to signal the SRv6-BSID-related
related information of an SR Policy candidate path. It enables the information of an SR Policy CP. It enables the specification of the
specification of the SRv6 Endpoint Behavior [RFC8986] to be SRv6 Endpoint Behavior [RFC8986] to be instantiated on the headend
instantiated on the headend node. The contents of this sub-TLV are node. The contents of this sub-TLV are used by the SRPM as described
used by the SRPM as described in Section 6 of [RFC9256]. in Section 6 of [RFC9256].
The SRv6 Binding SID sub-TLV is OPTIONAL. More than one SRv6 Binding The SRv6 Binding SID sub-TLV is OPTIONAL. More than one SRv6 Binding
SID sub-TLV MAY be signaled in the same SR Policy encoding to SID sub-TLV MAY be signaled in the same SR Policy encoding to
indicate one or more SRv6 SIDs, each with potentially different SRv6 indicate one or more SRv6 SIDs, each with potentially different SRv6
Endpoint Behaviors to be instantiated. Endpoint Behaviors to be instantiated.
The SRv6 Binding SID sub-TLV has the following format: The SRv6 Binding SID sub-TLV has the following format:
0 1 2 3 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 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
skipping to change at line 640 skipping to change at line 639
|S|I|B| | |S|I|B| |
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
Figure 8: SR Policy SRv6 Binding SID Flags Figure 8: SR Policy SRv6 Binding SID Flags
Where: Where:
* The S-Flag encodes the "Specified-BSID-Only" behavior. It is * The S-Flag encodes the "Specified-BSID-Only" behavior. It is
used by SRPM as described in Section 6.2.3 of [RFC9256]. used by SRPM as described in Section 6.2.3 of [RFC9256].
* The I-Flag encodes the "Drop Upon Invalid" behavior. It is * The I-Flag encodes the "Drop-Upon-Invalid" behavior. It is
used by SRPM as described in Section 8.2 of [RFC9256]. used by SRPM as described in Section 8.2 of [RFC9256].
* The B-Flag, when set, indicates the presence of the "SRv6 * The B-Flag, when set, indicates the presence of the "SRv6
Endpoint Behavior & SID Structure" encoding specified in Endpoint Behavior & SID Structure" encoding specified in
Section 2.4.4.2.4. Section 2.4.4.2.4.
* The unassigned bits in the Flag octet MUST be set to zero upon * The unassigned bits in the Flags field MUST be set to zero upon
transmission and MUST be ignored upon receipt. transmission and MUST be ignored upon receipt.
RESERVED: 1 octet of reserved bits. This field MUST be set to zero RESERVED: 1 octet of reserved bits. This field MUST be set to zero
on transmission and MUST be ignored on receipt. on transmission and MUST be ignored on receipt.
SRv6 Binding SID: Contains a 16-octet SRv6 SID. The value 0 MAY be SRv6 Binding SID: Contains a 16-octet SRv6 SID. The value 0 MAY be
used when the controller wants to indicate the desired SRv6 used when the controller wants to indicate the desired SRv6
Endpoint Behavior, SID Structure, or flags without specifying the Endpoint Behavior, SID Structure, or flags without specifying the
BSID. BSID.
SRv6 Endpoint Behavior and SID Structure: Optional, as defined in SRv6 Endpoint Behavior and SID Structure: Optional, as defined in
Section 2.4.4.2.4. The SRv6 Endpoint Behavior and SID Structure Section 2.4.4.2.4. The SRv6 Endpoint Behavior and SID Structure
MUST NOT be included when the SRv6 SID has not been included. MUST NOT be included when the SRv6 SID has not been included.
2.4.4. Segment List Sub-TLV 2.4.4. Segment List Sub-TLV
The Segment List sub-TLV encodes a single explicit path towards the The Segment List sub-TLV encodes a single explicit path towards the
endpoint as described in Section 5.1 of [RFC9256]. The Segment List Endpoint as described in Section 5.1 of [RFC9256]. The Segment List
sub-TLV includes the elements of the paths (i.e., segments) as well sub-TLV includes the elements of the paths (i.e., segments) as well
as an optional Weight sub-TLV. as an optional Weight sub-TLV.
The Segment List sub-TLV may exceed 255 bytes in length due to a The Segment List sub-TLV may exceed 255 bytes in length due to a
large number of segments. A 2-octet length is thus required. large number of segments. A 2-octet length is thus required.
According to Section 2 of [RFC9012], the sub-TLV type defines the According to Section 2 of [RFC9012], the sub-TLV type defines the
size of the length field. Therefore, for the Segment List sub-TLV, a size of the Length field. Therefore, for the Segment List sub-TLV, a
code point of 128 or higher is used. code point of 128 or higher is used.
The Segment List sub-TLV is OPTIONAL and MAY appear multiple times in The Segment List sub-TLV is OPTIONAL and MAY appear multiple times in
the SR Policy encoding. The ordering of Segment List sub-TLVs does the SR Policy encoding. The ordering of Segment List sub-TLVs does
not matter since each sub-TLV encodes a Segment List. not matter since each sub-TLV encodes a Segment List.
The Segment List sub-TLV contains zero or more Segment sub-TLVs and The Segment List sub-TLV contains zero or more Segment sub-TLVs and
MAY contain a Weight sub-TLV. MAY contain a Weight sub-TLV.
The Segment List sub-TLV has the following format: The Segment List sub-TLV has the following format:
skipping to change at line 749 skipping to change at line 748
Length: Specifies the length of the value field (i.e., not including Length: Specifies the length of the value field (i.e., not including
Type and Length fields) in terms of octets. The value MUST be 6. Type and Length fields) in terms of octets. The value MUST be 6.
Flags: 1 octet of flags. No flags are defined in this document. Flags: 1 octet of flags. No flags are defined in this document.
The Flags field MUST be set to zero on transmission and MUST be The Flags field MUST be set to zero on transmission and MUST be
ignored on receipt. ignored on receipt.
RESERVED: 1 octet of reserved bits. This field MUST be set to zero RESERVED: 1 octet of reserved bits. This field MUST be set to zero
on transmission and MUST be ignored on receipt. on transmission and MUST be ignored on receipt.
Weight: 4 octets an unsigned integer value indicating the weight Weight: 4 octets carrying an unsigned integer value indicating the
associated with a segment list as described in Section 2.11 of weight associated with a segment list as described in Section 2.11
[RFC9256]. A weight value of zero is invalid. of [RFC9256]. A weight value of zero is invalid.
2.4.4.2. Segment Sub-TLVs 2.4.4.2. Segment Sub-TLVs
A Segment sub-TLV describes a single segment in a segment list (i.e., A Segment sub-TLV describes a single segment in a segment list (i.e.,
a single element of the explicit path). One or more Segment sub-TLVs a single element of the explicit path). One or more Segment sub-TLVs
constitute an explicit path of the SR Policy candidate path. The constitute an explicit path of the SR Policy CP. The contents of
contents of these sub-TLVs are used only by the SRPM as described in these sub-TLVs are used only by the SRPM as described in Section 4 of
Section 4 of [RFC9256]. [RFC9256].
The Segment sub-TLVs are OPTIONAL and MAY appear multiple times in The Segment sub-TLVs are OPTIONAL and MAY appear multiple times in
the Segment List sub-TLV. the Segment List sub-TLV.
Section 4 of [RFC9256] defines several Segment Types: Section 4 of [RFC9256] defines several Segment Types:
Type A: SR-MPLS Label Type A: SR-MPLS Label
Type B: SRv6 SID Type B: SRv6 SID
Type C: IPv4 Prefix with optional SR Algorithm Type C: IPv4 Prefix with optional SR Algorithm
Type D: IPv6 Global Prefix with optional SR Algorithm for SR-MPLS Type D: IPv6 Global Prefix with optional SR Algorithm for SR-MPLS
Type E: IPv4 Prefix with Local Interface ID Type E: IPv4 Prefix with Local Interface ID
Type F: IPv4 Addresses for link endpoints as Local, Remote pair Type F: IPv4 Addresses for link Endpoints as Local, Remote pair
Type G: IPv6 Prefix and Interface ID for link endpoints as Local, Type G: IPv6 Prefix and Interface ID for link Endpoints as Local,
Remote pair for SR-MPLS Remote pair for SR-MPLS
Type H: IPv6 Addresses for link endpoints as Local, Remote pair for Type H: IPv6 Addresses for link Endpoints as Local, Remote pair for
SR-MPLS SR-MPLS
Type I: IPv6 Global Prefix with optional SR Algorithm for SRv6 Type I: IPv6 Global Prefix with optional SR Algorithm for SRv6
Type J: IPv6 Prefix and Interface ID for link endpoints as Local, Type J: IPv6 Prefix and Interface ID for link Endpoints as Local,
Remote pair for SRv6 Remote pair for SRv6
Type K: IPv6 Addresses for link endpoints as Local, Remote pair for Type K: IPv6 Addresses for link Endpoints as Local, Remote pair for
SRv6 SRv6
The following subsections specify the sub-TLVs used for Segment Types The following subsections specify the sub-TLVs used for Segment Types
A and B. The other segment types are specified in [RFC9831]. As A and B. The other segment types are specified in [RFC9831]. As
specified in Section 5.1 of [RFC9256], a mix of SR-MPLS and SRv6 specified in Section 5.1 of [RFC9256], a mix of SR-MPLS and SRv6
segments make the segment-list invalid. segments make the segment-list invalid.
2.4.4.2.1. Segment Type A 2.4.4.2.1. Segment Type A
The Type A Segment sub-TLV encodes a single SR-MPLS SID. The format The Type A Segment sub-TLV encodes a single SR-MPLS SID. The format
skipping to change at line 854 skipping to change at line 853
* If the originator wants to recommend a value for these fields, it * If the originator wants to recommend a value for these fields, it
puts those values in the TC and/or TTL fields. puts those values in the TC and/or TTL fields.
* The receiver MAY override the originator's values for these * The receiver MAY override the originator's values for these
fields. This would be determined by local policy at the receiver. fields. This would be determined by local policy at the receiver.
One possible policy would be to override the fields only if the One possible policy would be to override the fields only if the
fields have the default values specified above. fields have the default values specified above.
2.4.4.2.2. Segment Type B 2.4.4.2.2. Segment Type B
The Type B Segment Sub-TLV encodes a single SRv6 SID. The format is The Type B Segment sub-TLV encodes a single SRv6 SID. The format is
as follows: as follows:
0 1 2 3 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 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 | | Type | Length | Flags | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// SRv6 SID (16 octets) // // SRv6 SID (16 octets) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// SRv6 Endpoint Behavior and SID Structure // // SRv6 Endpoint Behavior and SID Structure //
skipping to change at line 890 skipping to change at line 889
RESERVED: 1 octet of reserved bits. This field MUST be set to zero RESERVED: 1 octet of reserved bits. This field MUST be set to zero
on transmission and MUST be ignored on receipt. on transmission and MUST be ignored on receipt.
SRv6 SID: 16 octets of IPv6 address. SRv6 SID: 16 octets of IPv6 address.
SRv6 Endpoint Behavior and SID Structure: Optional, as defined in SRv6 Endpoint Behavior and SID Structure: Optional, as defined in
Section 2.4.4.2.4. The SRv6 Endpoint Behavior and SID Structure Section 2.4.4.2.4. The SRv6 Endpoint Behavior and SID Structure
MUST NOT be included when the SRv6 SID has not been included. MUST NOT be included when the SRv6 SID has not been included.
The Sub-TLV code point 2 defined for the advertisement of Segment The sub-TLV code point 2 defined for the advertisement of Segment
Type B in the earlier draft versions of this document has been Type B in the earlier draft versions of this document has been
deprecated to avoid backward compatibility issues. deprecated to avoid backward compatibility issues.
2.4.4.2.3. SR Policy Segment Flags 2.4.4.2.3. SR Policy Segment Flags
The Segment Types sub-TLVs described above may contain the following The Segment Type sub-TLVs described above may contain the following
SR Policy Segment Flags in their "Flags" field. Also refer to SR Policy Segment Flags in their Flags field. Also refer to
Section 6.8: Section 6.8:
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
|V| |B| | |V| |B| |
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
Figure 13: SR Policy Segment Flags Figure 13: SR Policy Segment Flags
Where: Where:
* When the V-Flag is set, it is used by SRPM for "SID verification" * When the V-Flag is set, it is used by SRPM for "SID verification"
as described in Section 5.1 of [RFC9256]. as described in Section 5.1 of [RFC9256].
* When the B-Flag is set, it indicates the presence of the "SRv6 * When the B-Flag is set, it indicates the presence of the "SRv6
Endpoint Behavior & SID Structure" encoding specified in Endpoint Behavior & SID Structure" encoding specified in
Section 2.4.4.2.4. Section 2.4.4.2.4.
* The unassigned bits in the Flag octet MUST be set to zero upon * The unassigned bits in the Flags field MUST be set to zero upon
transmission and MUST be ignored upon receipt. transmission and MUST be ignored upon receipt.
The following applies to the Segment Flags: The following applies to the Segment Flags:
* V-Flag applies to all Segment Types. * V-Flag applies to all Segment Types.
* B-Flag applies to Segment Type B. If B-Flag appears with Segment * B-Flag applies to Segment Type B. If B-Flag appears with Segment
Type A, it MUST be ignored. Type A, it MUST be ignored.
2.4.4.2.4. SRv6 SID Endpoint Behavior and Structure 2.4.4.2.4. SRv6 SID Endpoint Behavior and Structure
The Segment Types sub-TLVs described above MAY contain the SRv6 The Segment Type sub-TLVs described above MAY contain the SRv6
Endpoint Behavior and SID Structure [RFC8986] encoding as described Endpoint Behavior and SID Structure [RFC8986] encoding as described
below: below:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Endpoint Behavior | Reserved | | Endpoint Behavior | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LB Length | LN Length | Fun. Length | Arg. Length | | LB Length | LN Length | Fun. Length | Arg. Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 14: SRv6 SID Endpoint Behavior and Structure Figure 14: SRv6 SID Endpoint Behavior and Structure
skipping to change at line 964 skipping to change at line 963
Function Length: 1 octet. SRv6 SID Function length in bits. Function Length: 1 octet. SRv6 SID Function length in bits.
Argument Length: 1 octet. SRv6 SID Arguments length in bits. Argument Length: 1 octet. SRv6 SID Arguments length in bits.
The total of the locator block, locator node, function, and argument The total of the locator block, locator node, function, and argument
lengths MUST be less than or equal to 128. lengths MUST be less than or equal to 128.
2.4.5. Explicit NULL Label Policy Sub-TLV 2.4.5. Explicit NULL Label Policy Sub-TLV
To steer an unlabeled IP packet into an SR policy for the MPLS data To steer an unlabeled IP packet into an SR Policy for the MPLS data
plane, it is necessary to push a label stack of one or more labels on plane, it is necessary to push a label stack of one or more labels on
that packet. that packet.
The Explicit NULL Label Policy (ENLP) sub-TLV is used to indicate The Explicit NULL Label Policy (ENLP) sub-TLV is used to indicate
whether an Explicit NULL Label [RFC3032] must be pushed on an whether an Explicit NULL Label [RFC3032] must be pushed on an
unlabeled IP packet before any other labels. unlabeled IP packet before any other labels.
If an ENLP Sub-TLV is not present, the decision of whether to push an If an ENLP sub-TLV is not present, the decision of whether to push an
Explicit NULL label on a given packet is a matter of local Explicit NULL label on a given packet is a matter of local
configuration. configuration.
The ENLP sub-TLV is OPTIONAL; it MUST NOT appear more than once in The ENLP sub-TLV is OPTIONAL; it MUST NOT appear more than once in
the SR Policy encoding. the SR Policy encoding.
The contents of this sub-TLV are used by the SRPM as described in The contents of this sub-TLV are used by the SRPM as described in
Section 4.1 of [RFC9256]. Section 4.1 of [RFC9256].
0 1 2 3 0 1 2 3
skipping to change at line 1008 skipping to change at line 1007
Flags: 1 octet of flags. No flags are defined in this document. Flags: 1 octet of flags. No flags are defined in this document.
The Flags field MUST be set to zero on transmission and MUST be The Flags field MUST be set to zero on transmission and MUST be
ignored on receipt. ignored on receipt.
RESERVED: 1 octet of reserved bits. This field MUST be set to zero RESERVED: 1 octet of reserved bits. This field MUST be set to zero
on transmission and MUST be ignored on receipt. on transmission and MUST be ignored on receipt.
ENLP (Explicit NULL Label Policy): Indicates whether Explicit NULL ENLP (Explicit NULL Label Policy): Indicates whether Explicit NULL
labels are to be pushed on unlabeled IP packets that are being labels are to be pushed on unlabeled IP packets that are being
steered into a given SR policy. The following values have been steered into a given SR Policy. The following values have been
currently defined for this field: currently defined for this field:
1: Push an IPv4 Explicit NULL label on an unlabeled IPv4 packet 1: Push an IPv4 Explicit NULL label on an unlabeled IPv4 packet
but do not push an IPv6 Explicit NULL label on an unlabeled but do not push an IPv6 Explicit NULL label on an unlabeled
IPv6 packet. IPv6 packet.
2: Push an IPv6 Explicit NULL label on an unlabeled IPv6 packet 2: Push an IPv6 Explicit NULL label on an unlabeled IPv6 packet
but do not push an IPv4 Explicit NULL label on an unlabeled but do not push an IPv4 Explicit NULL label on an unlabeled
IPv4 packet. IPv4 packet.
3: Push an IPv4 Explicit NULL label on an unlabeled IPv4 packet 3: Push an IPv4 Explicit NULL label on an unlabeled IPv4 packet
and push an IPv6 Explicit NULL label on an unlabeled IPv6 and push an IPv6 Explicit NULL label on an unlabeled IPv6
packet. packet.
4: Do not push an Explicit NULL label. 4: Do not push an Explicit NULL label.
This field can have one of the values as specified in This field can have one of the values as specified in
Section 6.10. The ENLP unassigned values may be used for future Section 6.10. The ENLP unassigned values may be used for future
extensions. Implementations adhering to this document MUST ignore extensions. Implementations adhering to this document MUST ignore
the ENLP Sub-TLV with unrecognized values (viz. other than 1 the ENLP sub-TLV with unrecognized values (viz. other than 1
through 4). The behavior signaled in this Sub-TLV MAY be through 4). The behavior signaled in this sub-TLV MAY be
overridden by local configuration by the network operator based on overridden by local configuration by the network operator based on
their deployment requirements. Section 4.1 of [RFC9256] describes their deployment requirements. Section 4.1 of [RFC9256] describes
the behavior on the headend for the handling of the explicit null the behavior on the headend for the handling of the Explicit NULL
label. label.
2.4.6. Policy Priority Sub-TLV 2.4.6. Policy Priority Sub-TLV
An operator MAY set the Policy Priority sub-TLV to indicate the order An operator MAY set the Policy Priority sub-TLV to indicate the order
in which the SR policies are recomputed upon topological change. The in which the SR policies are recomputed upon topological change. The
contents of this sub-TLV are used by the SRPM as described in contents of this sub-TLV are used by the SRPM as described in
Section 2.12 of [RFC9256]. Section 2.12 of [RFC9256].
The Priority sub-TLV is OPTIONAL; it MUST NOT appear more than once The Priority sub-TLV is OPTIONAL; it MUST NOT appear more than once
skipping to change at line 1071 skipping to change at line 1070
Priority: A 1-octet value indicating the priority as specified in Priority: A 1-octet value indicating the priority as specified in
Section 2.12 of [RFC9256]. Section 2.12 of [RFC9256].
RESERVED: 1 octet of reserved bits. This field MUST be set to zero RESERVED: 1 octet of reserved bits. This field MUST be set to zero
on transmission and MUST be ignored on receipt. on transmission and MUST be ignored on receipt.
2.4.7. Policy Candidate Path Name Sub-TLV 2.4.7. Policy Candidate Path Name Sub-TLV
An operator MAY set the Policy Candidate Path Name sub-TLV to attach An operator MAY set the Policy Candidate Path Name sub-TLV to attach
a symbolic name to the SR Policy candidate path. a symbolic name to the SR Policy CP.
Usage of the Policy Candidate Path Name sub-TLV is described in Usage of the Policy Candidate Path Name sub-TLV is described in
Section 2.6 of [RFC9256]. Section 2.6 of [RFC9256].
The Policy Candidate Path Name sub-TLV may exceed 255 bytes in length The Policy Candidate Path Name sub-TLV may exceed 255 bytes in length
due to a long name. A 2-octet length is thus required. According to due to a long name. A 2-octet length is thus required. According to
Section 2 of [RFC9012], the sub-TLV type defines the size of the Section 2 of [RFC9012], the sub-TLV type defines the size of the
length field. Therefore, for the Policy Candidate Path Name sub-TLV, Length field. Therefore, for the Policy Candidate Path Name sub-TLV,
a code point of 128 or higher is used. a code point of 128 or higher is used.
It is RECOMMENDED that the size of the symbolic name for the It is RECOMMENDED that the size of the symbolic name for the CP be
candidate path be limited to 255 bytes. Implementations MAY choose limited to 255 bytes. Implementations MAY choose to truncate long
to truncate long names to 255 bytes when signaling via BGP. names to 255 bytes when signaling via BGP.
The Policy Candidate Path Name sub-TLV is OPTIONAL; it MUST NOT The Policy Candidate Path Name sub-TLV is OPTIONAL; it MUST NOT
appear more than once in the SR Policy encoding. appear more than once in the SR Policy encoding.
The Policy Candidate Path Name sub-TLV has the following format: The Policy Candidate Path Name sub-TLV has the following format:
0 1 2 3 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 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 | RESERVED | | Type | Length | RESERVED |
skipping to change at line 1112 skipping to change at line 1111
Type: 129 Type: 129
Length: Specifies the length of the value field (i.e., not including Length: Specifies the length of the value field (i.e., not including
Type and Length fields) in terms of octets. The value is Type and Length fields) in terms of octets. The value is
variable. variable.
RESERVED: 1 octet of reserved bits. This field MUST be set to zero RESERVED: 1 octet of reserved bits. This field MUST be set to zero
on transmission and MUST be ignored on receipt. on transmission and MUST be ignored on receipt.
Policy Candidate Path Name: Symbolic name for the SR Policy Policy Candidate Path Name: Symbolic name for the SR Policy CP
candidate path without a NULL terminator with encoding as without a NULL terminator with encoding as specified in
specified in Section 2.6 of [RFC9256]. Section 2.6 of [RFC9256].
2.4.8. Policy Name Sub-TLV 2.4.8. Policy Name Sub-TLV
An operator MAY set the Policy Name sub-TLV to associate a symbolic An operator MAY set the Policy Name sub-TLV to associate a symbolic
name with the SR Policy for which the candidate path is being name with the SR Policy for which the CP is being advertised via the
advertised via the SR Policy NLRI. SR Policy NLRI.
Usage of the Policy Name sub-TLV is described in Section 2.1 of Usage of the Policy Name sub-TLV is described in Section 2.1 of
[RFC9256]. [RFC9256].
The Policy Name sub-TLV may exceed 255 bytes in length due to a long The Policy Name sub-TLV may exceed 255 bytes in length due to a long
policy name. A 2-octet length is thus required. According to policy name. A 2-octet length is thus required. According to
Section 2 of [RFC9012], the sub-TLV type defines the size of the Section 2 of [RFC9012], the sub-TLV type defines the size of the
length field. Therefore, for the Policy Name sub-TLV, a code point Length field. Therefore, for the Policy Name sub-TLV, a code point
of 128 or higher is used. of 128 or higher is used.
It is RECOMMENDED that the size of the symbolic name for the SR It is RECOMMENDED that the size of the symbolic name for the SR
Policy be limited to 255 bytes. Implementations MAY choose to Policy be limited to 255 bytes. Implementations MAY choose to
truncate long names to 255 bytes when signaling via BGP. truncate long names to 255 bytes when signaling via BGP.
The Policy Name sub-TLV is OPTIONAL; it MUST NOT appear more than The Policy Name sub-TLV is OPTIONAL; it MUST NOT appear more than
once in the SR Policy encoding. once in the SR Policy encoding.
The Policy Name sub-TLV has the following format: The Policy Name sub-TLV has the following format:
skipping to change at line 1167 skipping to change at line 1166
RESERVED: 1 octet of reserved bits. This field MUST be set to zero RESERVED: 1 octet of reserved bits. This field MUST be set to zero
on transmission and MUST be ignored on receipt. on transmission and MUST be ignored on receipt.
Policy Name: Symbolic name for the SR Policy without a NULL Policy Name: Symbolic name for the SR Policy without a NULL
terminator with encoding as specified in Section 2.1 of [RFC9256]. terminator with encoding as specified in Section 2.1 of [RFC9256].
3. Color Extended Community 3. Color Extended Community
The Color Extended Community [RFC9012] is used to steer traffic The Color Extended Community [RFC9012] is used to steer traffic
corresponding to BGP routes into an SR Policy with matching color corresponding to BGP routes into an SR Policy with matching Color
value. The Color Extended Community MAY be carried in any BGP UPDATE value. The Color Extended Community MAY be carried in any BGP UPDATE
message whose AFI/SAFI is 1/1 (IPv4 Unicast), 2/1 (IPv6 Unicast), 1/4 message whose AFI/SAFI is 1/1 (IPv4 Unicast), 2/1 (IPv6 Unicast), 1/4
(IPv4 Labeled Unicast), 2/4 (IPv6 Labeled Unicast), 1/128 (VPN-IPv4 (IPv4 Labeled Unicast), 2/4 (IPv6 Labeled Unicast), 1/128 (VPN-IPv4
Labeled Unicast), 2/128 (VPN-IPv6 Labeled Unicast), or 25/70 Labeled Unicast), 2/128 (VPN-IPv6 Labeled Unicast), or 25/70
(Ethernet VPN, usually known as EVPN). Use of the Color Extended (Ethernet VPN, usually known as EVPN). Use of the Color Extended
Community in BGP UPDATE messages of other AFI/SAFIs is not covered by Community in BGP UPDATE messages of other AFI/SAFIs is not covered by
[RFC9012]; hence, it is outside the scope of this document as well. [RFC9012]; hence, it is outside the scope of this document as well.
Two bits from the Flags field of the Color Extended Community are Two bits from the Flags field of the Color Extended Community are
used as follows to support the requirements of Color-Only steering as used as follows to support the requirements of Color-Only steering as
skipping to change at line 1189 skipping to change at line 1188
1 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|C O| Unassigned | |C O| Unassigned |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 19: Color Extended Community Flags Figure 19: Color Extended Community Flags
The C and O bits together form the Color-Only Type field, which The C and O bits together form the Color-Only Type field, which
indicates the various matching criteria between the BGP NH and the SR indicates the various matching criteria between the BGP Next Hop (NH)
Policy endpoint in addition to the matching of the color value. The and the SR Policy Endpoint in addition to the matching of the Color
following types are defined: value. The following types are defined:
Type 0 (bits 00): Specific Endpoint Match. Request a match for the Type 0 (bits 00): Specific Endpoint Match. Request a match for the
endpoint that is the BGP NH. Endpoint that is the BGP NH.
Type 1 (bits 01): Specific or Null Endpoint Match. Request a match Type 1 (bits 01): Specific or Null Endpoint Match. Request a match
for either the endpoint that is the BGP NH or a null endpoint for either the Endpoint that is the BGP NH or a null Endpoint
(e.g., a default gateway). (e.g., a default gateway).
Type 2 (bits 10): Specific, Null, or Any Endpoint Match. Request a Type 2 (bits 10): Specific, Null, or Any Endpoint Match. Request a
match for either the endpoint that is the BGP NH or a null or any match for either the Endpoint that is the BGP NH or a null or any
endpoint. Endpoint.
Type 3 (bits 11): Reserved for future use and SHOULD NOT be used. Type 3 (bits 11): Reserved for future use and SHOULD NOT be used.
Upon reception, an implementation MUST treat it like Type 0. Upon reception, an implementation MUST treat it like Type 0.
The details of the SR Policy steering mechanisms based on these The details of the SR Policy steering mechanisms based on these
Color-Only types are specified in Section 8.8 of [RFC9256]. Color-Only types are specified in Section 8.8 of [RFC9256].
One or more Color Extended Communities MAY be associated with a BGP One or more Color Extended Communities MAY be associated with a BGP
route update. Sections 8.4.1, 8.5.1, and 8.8.2 of [RFC9256] specify route update. Sections 8.4.1, 8.5.1, and 8.8.2 of [RFC9256] specify
the steering behaviors over SR Policies when multiple Color Extended the steering behaviors over SR Policies when multiple Color Extended
skipping to change at line 1229 skipping to change at line 1228
the SR Policy NLRI, but its installation and use are outside the the SR Policy NLRI, but its installation and use are outside the
scope of BGP. The details of SR Policy installation and use are scope of BGP. The details of SR Policy installation and use are
specified in [RFC9256]. specified in [RFC9256].
4.1. Advertisement of SR Policies 4.1. Advertisement of SR Policies
Typically, but not limited to, an SR Policy is computed by a Typically, but not limited to, an SR Policy is computed by a
controller or a Path Computation Engine (PCE) and originated by a BGP controller or a Path Computation Engine (PCE) and originated by a BGP
speaker on its behalf. speaker on its behalf.
Multiple SR Policy NLRIs may be present with the same <color, Multiple SR Policy NLRIs may be present with the same <Color,
endpoint> tuple but with different distinguishers when these SR Endpoint> tuple but with different distinguishers when these SR
policies are intended for different headends. policies are intended for different headends.
The distinguisher of each SR Policy NLRI prevents undesired BGP route The distinguisher of each SR Policy NLRI prevents undesired BGP route
selection among these SR Policy NLRIs and allows their propagation selection among these SR Policy NLRIs and allows their propagation
across route reflectors [RFC4456]. across RRs [RFC4456].
Moreover, one or more route targets SHOULD be attached to the Moreover, one or more route targets SHOULD be attached to the
advertisement, where each route target identifies one or more advertisement, where each route target identifies one or more
intended headends for the advertised SR Policy update. intended headends for the advertised SR Policy update.
If no route target is attached to the SR Policy NLRI, then it is If no route target is attached to the SR Policy NLRI, then it is
assumed that the originator sends the SR Policy update directly assumed that the originator sends the SR Policy update directly
(e.g., through a BGP session) to the intended receiver. In such a (e.g., through a BGP session) to the intended receiver. In such a
case, the NO_ADVERTISE community [RFC1997] MUST be attached to the SR case, the NO_ADVERTISE community [RFC1997] MUST be attached to the SR
Policy update (see further details in Section 4.2.3). Policy update (see further details in Section 4.2.3).
skipping to change at line 1266 skipping to change at line 1265
processing as described in Section 4.2.2. The selected best route is processing as described in Section 4.2.2. The selected best route is
"propagated" (Section 9.1.3 of [RFC4271]) as described in "propagated" (Section 9.1.3 of [RFC4271]) as described in
Section 4.2.3, irrespective of its "usability" by the local router. Section 4.2.3, irrespective of its "usability" by the local router.
4.2.1. Validation of an SR Policy NLRI 4.2.1. Validation of an SR Policy NLRI
When a BGP speaker receives an SR Policy NLRI from a neighbor, it When a BGP speaker receives an SR Policy NLRI from a neighbor, it
MUST first perform validation based on the following rules in MUST first perform validation based on the following rules in
addition to the validation described in Section 5: addition to the validation described in Section 5:
* The SR Policy NLRI MUST include a distinguisher, color, and * The SR Policy NLRI MUST include a distinguisher, Color, and
endpoint field that implies that the length of the NLRI MUST be Endpoint field that implies that the length of the NLRI MUST be
either 12 or 24 octets (depending on the address family of the either 12 or 24 octets (depending on the address family of the
endpoint). Endpoint).
* The SR Policy update MUST have either the NO_ADVERTISE community, * The SR Policy update MUST have either the NO_ADVERTISE community,
at least one route target extended community in IPv4-address at least one Route Target extended community in IPv4-address
format, or both. If a router supporting this specification format, or both. If a router supporting this specification
receives an SR Policy update with no route target extended receives an SR Policy update with no Route Target extended
communities and no NO_ADVERTISE community, the update MUST be communities and no NO_ADVERTISE community, the update MUST be
considered to be malformed. considered to be malformed.
* The Tunnel Encapsulation Attribute MUST be attached to the BGP * The Tunnel Encapsulation Attribute MUST be attached to the BGP
Update and MUST have a Tunnel Type TLV set to SR Policy (code UPDATE message and MUST have a Tunnel Type TLV set to SR Policy
point is 15). (code point is 15).
A router that receives an SR Policy update that is not valid A router that receives an SR Policy update that is not valid
according to these criteria MUST treat the update as malformed, and according to these criteria MUST treat the update as malformed, and
the SR Policy candidate path MUST NOT be passed to the SRPM. the SR Policy CP MUST NOT be passed to the SRPM.
4.2.2. Eligibility for Local Use of an SR Policy NLRI 4.2.2. Eligibility for Local Use of an SR Policy NLRI
An SR Policy NLRI update that does not have a route target extended An SR Policy NLRI update that does not have a Route Target extended
community but does have the NO_ADVERTISE community is considered community but does have the NO_ADVERTISE community is considered
usable. usable.
If one or more route targets are present, then at least one route If one or more route targets are present, then at least one route
target MUST match the BGP Identifier of the receiver for the update target MUST match the BGP Identifier of the receiver for the update
to be considered usable. The BGP Identifier is defined in [RFC4271] to be considered usable. The BGP Identifier is defined in [RFC4271]
as a 4-octet IPv4 address and is updated by [RFC6286] as a 4-octet, as a 4-octet IPv4 address and is updated by [RFC6286] as a 4-octet,
unsigned, non-zero integer. Therefore, the route target extended unsigned, non-zero integer. Therefore, the Route Target extended
community MUST be of the same format. community MUST be of the same format.
If one or more route targets are present and none matches the local If one or more route targets are present, and none matches the local
BGP Identifier, then, while the SR Policy NLRI is valid, it is not BGP Identifier, then, while the SR Policy NLRI is valid, the SR
usable on the receiver node. Policy NLRI is not usable on the receiver node.
When the SR Policy tunnel type includes any sub-TLV that is When the SR Policy tunnel type includes any sub-TLV that is
unrecognized or unsupported, the update SHOULD NOT be considered unrecognized or unsupported, the update SHOULD NOT be considered
usable. An implementation MAY provide an option for ignoring usable. An implementation MAY provide an option for ignoring
unsupported sub-TLVs. unsupported sub-TLVs.
Once BGP on the receiving node has determined that the SR Policy NLRI Once BGP on the receiving node has determined that the SR Policy NLRI
is usable, it passes the SR Policy candidate path to the SRPM. Note is usable, it passes the SR Policy CP to the SRPM. Note that, along
that, along with the candidate path details, BGP also passes the with the CP details, BGP also passes the originator information for
originator information for breaking ties in the candidate path breaking ties in the CP selection process as described in Section 2.4
selection process as described in Section 2.4 of [RFC9256]. of [RFC9256].
When an update for an SR Policy NLRI results in its becoming When an update for an SR Policy NLRI results in its becoming
unusable, BGP MUST delete its corresponding SR Policy candidate path unusable, BGP MUST delete its corresponding SR Policy CP from the
from the SRPM. SRPM.
The SRPM applies the rules defined in Section 2 of [RFC9256] to The SRPM applies the rules defined in Section 2 of [RFC9256] to
determine whether the SR Policy candidate path is valid and to select determine whether the SR Policy CP is valid and to select the active
the active candidate path for a given SR Policy. CP for a given SR Policy.
4.2.3. Propagation of an SR Policy 4.2.3. Propagation of an SR Policy
SR Policy NLRIs that have the NO_ADVERTISE community attached to them SR Policy NLRIs that have the NO_ADVERTISE community attached to them
MUST NOT be propagated. MUST NOT be propagated.
By default, a BGP node receiving an SR Policy NLRI MUST NOT propagate By default, a BGP node receiving an SR Policy NLRI MUST NOT propagate
it to any External BGP (EBGP) neighbor. An implementation MAY it to any External BGP (EBGP) neighbor. An implementation MAY
provide an explicit configuration to override this and enable the provide an explicit configuration to override this and enable the
propagation of valid SR Policy NLRIs to specific EBGP neighbors where propagation of valid SR Policy NLRIs to specific EBGP neighbors where
the SR domain comprises multiple ASes within a single service the SR domain comprises multiple ASes within a single service
provider domain (see Section 7 for details). provider domain (see Section 7 for details).
A BGP node advertises a received SR Policy NLRI to its Internal BGP A BGP node advertises a received SR Policy NLRI to its Internal BGP
(IBGP) neighbors according to normal IBGP propagation rules. (IBGP) neighbors according to normal IBGP propagation rules.
By default, a BGP node receiving an SR Policy NLRI SHOULD NOT remove By default, a BGP node receiving an SR Policy NLRI SHOULD NOT remove
the route target extended community before propagation. An the Route Target extended community before propagation. An
implementation MAY provide support for configuration to filter and/or implementation MAY provide support for configuration to filter and/or
remove the route target extended community before propagation. remove the Route Target extended community before propagation.
A BGP node MUST NOT alter the SR Policy information carried in the A BGP node MUST NOT alter the SR Policy information carried in the
Tunnel Encapsulation Attribute during propagation. Tunnel Encapsulation Attribute during propagation.
5. Error Handling and Fault Management 5. Error Handling and Fault Management
This section describes the error-handling actions, as described in This section describes the error-handling actions, as described in
[RFC7606], that are to be performed for the handling of the BGP [RFC7606], that are to be performed for the handling of the BGP
update messages for the BGP SR Policy SAFI. UPDATE messages for the BGP SR Policy SAFI.
A BGP speaker MUST perform the following syntactic validation of the A BGP speaker MUST perform the following syntactic validation of the
SR Policy NLRI to determine if it is malformed. This includes the SR Policy NLRI to determine if it is malformed. This includes the
validation of the length of each NLRI and the total length of the validation of the length of each NLRI and the total length of the
MP_REACH_NLRI and MP_UNREACH_NLRI attributes. It also includes the MP_REACH_NLRI and MP_UNREACH_NLRI attributes. It also includes the
validation of the consistency of the NLRI length with the AFI and the validation of the consistency of the NLRI length with the AFI and the
endpoint address as specified in Section 2.1. Endpoint address as specified in Section 2.1.
When the error determined allows for the router to skip the malformed When the error determined allows for the router to skip the malformed
NLRI(s) and continue the processing of the rest of the update NLRI(s) and continue the processing of the rest of the BGP UPDATE
message, then it MUST handle such malformed NLRIs as 'treat-as- message, then it MUST handle such malformed NLRIs as 'treat-as-
withdraw'. In other cases, where the error in the NLRI encoding withdraw'. In other cases, where the error in the NLRI encoding
results in the inability to process the BGP update message (e.g., results in the inability to process the BGP UPDATE message (e.g.,
length-related encoding errors), then the router SHOULD handle such length-related encoding errors), then the router SHOULD handle such
malformed NLRIs as "AFI/SAFI disable" when other AFIs/SAFIs besides malformed NLRIs as "AFI/SAFI disable" when other AFIs/SAFIs besides
SR Policy are being advertised over the same session. Alternately, SR Policy are being advertised over the same session. Alternately,
the router MUST perform "session reset" when the session is only the router MUST perform "session reset" when the session is only
being used for SR Policy or when a "AFI/SAFI disable" action is not being used for SR Policy or when a "AFI/SAFI disable" action is not
possible. possible.
The validation of the TLVs/sub-TLVs introduced in this document and The validation of the TLVs/sub-TLVs introduced in this document and
defined in their respective subsections of Section 2.4 MUST be defined in their respective subsections of Section 2.4 MUST be
performed to determine if they are malformed or invalid. The performed to determine if they are malformed or invalid. The
skipping to change at line 1447 skipping to change at line 1446
+=======+================+===========+ +=======+================+===========+
| Value | Description | Reference | | Value | Description | Reference |
+=======+================+===========+ +=======+================+===========+
| 73 | SR Policy SAFI | RFC 9830 | | 73 | SR Policy SAFI | RFC 9830 |
+-------+----------------+-----------+ +-------+----------------+-----------+
Table 1: BGP SAFI Code Point Table 1: BGP SAFI Code Point
6.2. BGP Tunnel Encapsulation Attribute Tunnel Types 6.2. BGP Tunnel Encapsulation Attribute Tunnel Types
This document registers a Tunnel-Type code point in the "BGP Tunnel This document registers a Tunnel Type code point in the "BGP Tunnel
Encapsulation Attribute Tunnel Types" registry under the "Border Encapsulation Attribute Tunnel Types" registry under the "Border
Gateway Protocol (BGP) Tunnel Encapsulation" registry group. Gateway Protocol (BGP) Tunnel Encapsulation" registry group.
+=======+=============+===========+ +=======+=============+===========+
| Value | Description | Reference | | Value | Description | Reference |
+=======+=============+===========+ +=======+=============+===========+
| 15 | SR Policy | RFC 9830 | | 15 | SR Policy | RFC 9830 |
+-------+-------------+-----------+ +-------+-------------+-----------+
Table 2: Tunnel Type Code Point Table 2: Tunnel Type Code Point
6.3. BGP Tunnel Encapsulation Attribute Sub-TLVs 6.3. BGP Tunnel Encapsulation Attribute Sub-TLVs
This document defines sub-TLVs in the "BGP Tunnel Encapsulation This document defines sub-TLVs in the "BGP Tunnel Encapsulation
Attribute Sub-TLVs" registry under the "Border Gateway Protocol (BGP) Attribute Sub-TLVs" registry under the "Border Gateway Protocol (BGP)
Tunnel Encapsulation" registry group. Tunnel Encapsulation" registry group.
+=======+====================================+===========+ +=======+==========================+===========+===================+
| Value | Description | Reference | | Value | Description | Reference | Change Controller |
+=======+====================================+===========+ +=======+==========================+===========+===================+
| 12 | Preference sub-TLV | RFC 9830 | | 12 | Preference sub-TLV | RFC 9830 | IETF |
+-------+------------------------------------+-----------+ +-------+--------------------------+-----------+-------------------+
| 13 | Binding SID sub-TLV | RFC 9830 | | 13 | Binding SID sub-TLV | RFC 9830 | IETF |
+-------+------------------------------------+-----------+ +-------+--------------------------+-----------+-------------------+
| 14 | ENLP sub-TLV | RFC 9830 | | 14 | ENLP sub-TLV | RFC 9830 | IETF |
+-------+------------------------------------+-----------+ +-------+--------------------------+-----------+-------------------+
| 15 | Priority sub-TLV | RFC 9830 | | 15 | Priority sub-TLV | RFC 9830 | IETF |
+-------+------------------------------------+-----------+ +-------+--------------------------+-----------+-------------------+
| 20 | SRv6 Binding SID sub-TLV | RFC 9830 | | 20 | SRv6 Binding SID sub-TLV | RFC 9830 | IETF |
+-------+------------------------------------+-----------+ +-------+--------------------------+-----------+-------------------+
| 128 | Segment List sub-TLV | RFC 9830 | | 128 | Segment List sub-TLV | RFC 9830 | IETF |
+-------+------------------------------------+-----------+ +-------+--------------------------+-----------+-------------------+
| 129 | Policy Candidate Path Name sub-TLV | RFC 9830 | | 129 | Policy Candidate Path | RFC 9830 | IETF |
+-------+------------------------------------+-----------+ | | Name sub-TLV | | |
| 130 | Policy Name sub-TLV | RFC 9830 | +-------+--------------------------+-----------+-------------------+
+-------+------------------------------------+-----------+ | 130 | Policy Name sub-TLV | RFC 9830 | IETF |
+-------+--------------------------+-----------+-------------------+
Table 3: BGP Tunnel Encapsulation Attribute Sub-TLV Table 3: BGP Tunnel Encapsulation Attribute Sub-TLV Code Points
Code Points
6.4. Color Extended Community Flags 6.4. Color Extended Community Flags
This document defines the use of 2 bits in the "Color Extended This document defines the use of 2 bits in the "Color Extended
Community Flags" registry under the "Border Gateway Protocol (BGP) Community Flags" registry under the "Border Gateway Protocol (BGP)
Tunnel Encapsulation" registry group. Tunnel Encapsulation" registry group.
+==============+========================+===========+ +==============+========================+===========+
| Bit Position | Description | Reference | | Bit Position | Description | Reference |
+==============+========================+===========+ +==============+========================+===========+
skipping to change at line 1553 skipping to change at line 1552
registry group. The registration policy of this registry is registry group. The registration policy of this registry is
"Standards Action" (see [RFC8126]). "Standards Action" (see [RFC8126]).
The following flags are defined: The following flags are defined:
+=====+===================================+===========+ +=====+===================================+===========+
| Bit | Description | Reference | | Bit | Description | Reference |
+=====+===================================+===========+ +=====+===================================+===========+
| 0 | Specified-BSID-Only Flag (S-Flag) | RFC 9830 | | 0 | Specified-BSID-Only Flag (S-Flag) | RFC 9830 |
+-----+-----------------------------------+-----------+ +-----+-----------------------------------+-----------+
| 1 | Drop Upon Invalid Flag (I-Flag) | RFC 9830 | | 1 | Drop-Upon-Invalid Flag (I-Flag) | RFC 9830 |
+-----+-----------------------------------+-----------+ +-----+-----------------------------------+-----------+
| 2-7 | Unassigned | | 2-7 | Unassigned |
+-----+-----------------------------------------------+ +-----+-----------------------------------------------+
Table 6: SR Policy Binding SID Flags Table 6: SR Policy Binding SID Flags
6.7. SR Policy SRv6 Binding SID Flags 6.7. SR Policy SRv6 Binding SID Flags
This document creates a new registry called "SR Policy SRv6 Binding This document creates a new registry called "SR Policy SRv6 Binding
SID Flags" under the "Border Gateway Protocol (BGP) Tunnel SID Flags" under the "Border Gateway Protocol (BGP) Tunnel
Encapsulation" registry group. The registration policy of this Encapsulation" registry group. The registration policy of this
registry is "Standards Action" (see [RFC8126]). registry is "Standards Action" (see [RFC8126]).
The following flags are defined: The following flags are defined:
+=====+===================================+===========+ +=====+===================================+===========+
| Bit | Description | Reference | | Bit | Description | Reference |
+=====+===================================+===========+ +=====+===================================+===========+
| 0 | Specified-BSID-Only Flag (S-Flag) | RFC 9830 | | 0 | Specified-BSID-Only Flag (S-Flag) | RFC 9830 |
+-----+-----------------------------------+-----------+ +-----+-----------------------------------+-----------+
| 1 | Drop Upon Invalid Flag (I-Flag) | RFC 9830 | | 1 | Drop-Upon-Invalid Flag (I-Flag) | RFC 9830 |
+-----+-----------------------------------+-----------+ +-----+-----------------------------------+-----------+
| 2 | SRv6 Endpoint Behavior & SID | RFC 9830 | | 2 | SRv6 Endpoint Behavior & SID | RFC 9830 |
| | Structure Flag (B-Flag) | | | | Structure Flag (B-Flag) | |
+-----+-----------------------------------+-----------+ +-----+-----------------------------------+-----------+
| 3-7 | Unassigned | | 3-7 | Unassigned |
+-----+-----------------------------------------------+ +-----+-----------------------------------------------+
Table 7: SR Policy SRv6 Binding SID Flags Table 7: SR Policy SRv6 Binding SID Flags
6.8. SR Policy Segment Flags 6.8. SR Policy Segment Flags
skipping to change at line 1638 skipping to change at line 1637
| 3 | Unassigned | RFC 9830 | | 3 | Unassigned | RFC 9830 |
+------+---------------------------------------+-----------+ +------+---------------------------------------+-----------+
Table 9: Color Extended Community Color-Only Types Table 9: Color Extended Community Color-Only Types
6.10. SR Policy ENLP Values 6.10. SR Policy ENLP Values
IANA will maintain a new registry under the "Segment Routing" IANA will maintain a new registry under the "Segment Routing"
registry group with the registration policy of "Standards Action" registry group with the registration policy of "Standards Action"
(see [RFC8126]). The new registry is called "SR Policy ENLP Values" (see [RFC8126]). The new registry is called "SR Policy ENLP Values"
and contains the code points allocated to the "ENLP" field defined in and contains the code points allocated to the ENLP field defined in
Section 2.4.5. The registry contains the following code points: Section 2.4.5. The registry contains the following code points:
+=======+===================================+===========+ +=======+===================================+===========+
| Code | Description | Reference | | Code | Description | Reference |
| Point | | | | Point | | |
+=======+===================================+===========+ +=======+===================================+===========+
| 0 | Reserved (not to be used) | RFC 9830 | | 0 | Reserved | RFC 9830 |
+-------+-----------------------------------+-----------+ +-------+-----------------------------------+-----------+
| 1 | Push an IPv4 Explicit NULL label | RFC 9830 | | 1 | Push an IPv4 Explicit NULL label | RFC 9830 |
| | on an unlabeled IPv4 packet but | | | | on an unlabeled IPv4 packet but | |
| | do not push an IPv6 Explicit NULL | | | | do not push an IPv6 Explicit NULL | |
| | label on an unlabeled IPv6 packet | | | | label on an unlabeled IPv6 packet | |
+-------+-----------------------------------+-----------+ +-------+-----------------------------------+-----------+
| 2 | Push an IPv6 Explicit NULL label | RFC 9830 | | 2 | Push an IPv6 Explicit NULL label | RFC 9830 |
| | on an unlabeled IPv6 packet but | | | | on an unlabeled IPv6 packet but | |
| | do not push an IPv4 Explicit NULL | | | | do not push an IPv4 Explicit NULL | |
| | label on an unlabeled IPv4 packet | | | | label on an unlabeled IPv4 packet | |
skipping to change at line 1688 skipping to change at line 1687
The BGP SR Policy extensions specified in this document enable The BGP SR Policy extensions specified in this document enable
traffic engineering and service programming use cases within an SR traffic engineering and service programming use cases within an SR
domain as described in [RFC9256]. SR operates within a trusted SR domain as described in [RFC9256]. SR operates within a trusted SR
domain [RFC8402]; its security considerations also apply to BGP domain [RFC8402]; its security considerations also apply to BGP
sessions when carrying SR Policy information. The SR Policies sessions when carrying SR Policy information. The SR Policies
distributed by BGP are expected to be used entirely within this distributed by BGP are expected to be used entirely within this
trusted SR domain, which comprises a single AS or multiple ASes / trusted SR domain, which comprises a single AS or multiple ASes /
domains within a single provider network. Therefore, precaution is domains within a single provider network. Therefore, precaution is
necessary to ensure that the SR Policy information advertised via BGP necessary to ensure that the SR Policy information advertised via BGP
sessions is limited to nodes in a secure manner within this trusted sessions is limited to nodes in a secure manner within this trusted
SR domain. BGP peering sessions for address families other than SR SR domain. BGP peering sessions for address families other than
Policy SAFI may be set up to routers outside the SR domain. The those that use the SR Policy SAFI may be set up to routers outside
isolation of BGP SR Policy SAFI peering sessions may be used to the SR domain. The isolation of BGP SR Policy SAFI peering sessions
ensure that the SR Policy information is not advertised by accident may be used to ensure that the SR Policy information is not
or in error to an EBGP peering session outside the SR domain. advertised by accident or in error to an EBGP peering session outside
the SR domain.
Additionally, it may be a consideration that the export of SR Policy Additionally, it may be a consideration that the export of SR Policy
information, as described in this document, constitutes a risk to information, as described in this document, constitutes a risk to
confidentiality of mission-critical or commercially sensitive confidentiality of mission-critical or commercially sensitive
information about the network (more specifically endpoint/node information about the network (more specifically endpoint/node
addresses, SR SIDs, and the SR Policies deployed). BGP peerings are addresses, SR SIDs, and the SR Policies deployed). BGP peerings are
not automatic and require configuration; thus, it is the not automatic and require configuration; thus, it is the
responsibility of the network operator to ensure that only trusted responsibility of the network operator to ensure that only trusted
nodes (that include both routers and controller applications) within nodes (that include both routers and controller applications) within
the SR domain are configured to receive such information. the SR domain are configured to receive such information.
skipping to change at line 1812 skipping to change at line 1812
DOI 10.17487/RFC9012, April 2021, DOI 10.17487/RFC9012, April 2021,
<https://www.rfc-editor.org/info/rfc9012>. <https://www.rfc-editor.org/info/rfc9012>.
[RFC9256] Filsfils, C., Talaulikar, K., Ed., Voyer, D., Bogdanov, [RFC9256] Filsfils, C., Talaulikar, K., Ed., Voyer, D., Bogdanov,
A., and P. Mattes, "Segment Routing Policy Architecture", A., and P. Mattes, "Segment Routing Policy Architecture",
RFC 9256, DOI 10.17487/RFC9256, July 2022, RFC 9256, DOI 10.17487/RFC9256, July 2022,
<https://www.rfc-editor.org/info/rfc9256>. <https://www.rfc-editor.org/info/rfc9256>.
9.2. Informative References 9.2. Informative References
[BGP-LS-SR-POLICY]
Previdi, S., Talaulikar, K., Ed., Dong, J., Gredler, H.,
and J. Tantsura, "Advertisement of Segment Routing
Policies using BGP Link-State", Work in Progress,
Internet-Draft, draft-ietf-idr-bgp-ls-sr-policy-16, 3
March 2025, <https://datatracker.ietf.org/doc/html/draft-
ietf-idr-bgp-ls-sr-policy-16>.
[BGP-YANG-MODEL] [BGP-YANG-MODEL]
Jethanandani, M., Patel, K., Hares, S., and J. Haas, "YANG Jethanandani, M., Patel, K., Hares, S., and J. Haas, "YANG
Model for Border Gateway Protocol (BGP-4)", Work in Model for Border Gateway Protocol (BGP-4)", Work in
Progress, Internet-Draft, draft-ietf-idr-bgp-model-18, 21 Progress, Internet-Draft, draft-ietf-idr-bgp-model-18, 21
October 2024, <https://datatracker.ietf.org/doc/html/ October 2024, <https://datatracker.ietf.org/doc/html/
draft-ietf-idr-bgp-model-18>. draft-ietf-idr-bgp-model-18>.
[RFC4272] Murphy, S., "BGP Security Vulnerabilities Analysis", [RFC4272] Murphy, S., "BGP Security Vulnerabilities Analysis",
RFC 4272, DOI 10.17487/RFC4272, January 2006, RFC 4272, DOI 10.17487/RFC4272, January 2006,
<https://www.rfc-editor.org/info/rfc4272>. <https://www.rfc-editor.org/info/rfc4272>.
skipping to change at line 1844 skipping to change at line 1852
[RFC9552] Talaulikar, K., Ed., "Distribution of Link-State and [RFC9552] Talaulikar, K., Ed., "Distribution of Link-State and
Traffic Engineering Information Using BGP", RFC 9552, Traffic Engineering Information Using BGP", RFC 9552,
DOI 10.17487/RFC9552, December 2023, DOI 10.17487/RFC9552, December 2023,
<https://www.rfc-editor.org/info/rfc9552>. <https://www.rfc-editor.org/info/rfc9552>.
[RFC9831] Talaulikar, K., Ed., Filsfils, C., Previdi, S., Mattes, [RFC9831] Talaulikar, K., Ed., Filsfils, C., Previdi, S., Mattes,
P., and D. Jain, "Segment Routing Segment Types Extensions P., and D. Jain, "Segment Routing Segment Types Extensions
for BGP SR Policy", RFC 9831, DOI 10.17487/RFC9831, July for BGP SR Policy", RFC 9831, DOI 10.17487/RFC9831, July
2025, <https://www.rfc-editor.org/info/rfc9831>. 2025, <https://www.rfc-editor.org/info/rfc9831>.
[SR-BGP-LS]
Previdi, S., Talaulikar, K., Ed., Dong, J., Gredler, H.,
and J. Tantsura, "Advertisement of Segment Routing
Policies using BGP Link-State", Work in Progress,
Internet-Draft, draft-ietf-idr-bgp-ls-sr-policy-16, 3
March 2025, <https://datatracker.ietf.org/doc/html/draft-
ietf-idr-bgp-ls-sr-policy-16>.
[SR-POLICY-YANG] [SR-POLICY-YANG]
Raza, K., Ed., Saleh, T., Shunwan, Z., Voyer, D., Durrani, Raza, K., Ed., Saleh, T., Shunwan, Z., Voyer, D., Durrani,
M., Matsushima, S., and V. Beeram, "YANG Data Model for M., Matsushima, S., and V. Beeram, "YANG Data Model for
Segment Routing Policy", Work in Progress, Internet-Draft, Segment Routing Policy", Work in Progress, Internet-Draft,
draft-ietf-spring-sr-policy-yang-04, 22 November 2024, draft-ietf-spring-sr-policy-yang-04, 22 November 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-spring- <https://datatracker.ietf.org/doc/html/draft-ietf-spring-
sr-policy-yang-04>. sr-policy-yang-04>.
Acknowledgments Acknowledgments
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