Network Working Group
Internet Engineering Task Force (IETF) S. Previdi
Internet-Draft
Request for Comments: 9830 Huawei Technologies
Updates: 9012 (if approved) C. Filsfils
Intended status:
Category: Standards Track K. Talaulikar, Ed.
Expires: 10 August 2025
ISSN: 2070-1721 Cisco Systems
P. Mattes
Microsoft
D. Jain
Google
6 February
July 2025
Advertising Segment Routing Policies in BGP
draft-ietf-idr-sr-policy-safi-13
Abstract
A Segment Routing (SR) Policy is an ordered list of segments (also
referred to as instructions) "instructions") that define a source-routed policy.
An SR Policy consists of one or more candidate paths, each comprising
one or more segment lists. A headend can be provisioned with these
candidate paths using various mechanisms, mechanisms such as CLI, NETCONF, PCEP, Command-Line
Interface (CLI), Network Configuration Protocol (NETCONF), Path
Computation Element Communication Protocol (PCEP), or BGP.
This document specifies how BGP can be used to distribute SR Policy
candidate paths. It introduces a BGP SAFI for advertising a
candidate path of an SR Policy and defines sub-TLVs for the Tunnel
Encapsulation Attribute to signal information related to these
candidate paths.
Furthermore, this document updates RFC9012 RFC 9012 by extending the Color
Extended Community to support additional steering modes over SR
Policy.
Status of This Memo
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provisions of BCP 78 and BCP 79.
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Internet-Drafts are draft documents valid the IETF community. It has
received public review and has been approved for a maximum publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.
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This Internet-Draft will expire on 10 August 2025.
https://www.rfc-editor.org/info/rfc9830.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 6
2. SR Policy Encoding . . . . . . . . . . . . . . . . . . . . . 6
2.1. SR Policy SAFI and NLRI . . . . . . . . . . . . . . . . . 6
2.2. SR Policy and Tunnel Encapsulation Attribute . . . . . . 8
2.3. Applicability of Tunnel Encapsulation Attribute Sub-TLVs . . . . . . . . . . . . . . . . . . . . . . . . 10
2.4. SR Policy Sub-TLVs . . . . . . . . . . . . . . . . . . . 10
2.4.1. Preference Sub-TLV . . . . . . . . . . . . . . . . . 11
2.4.2. Binding SID Sub-TLV . . . . . . . . . . . . . . . . . 11
2.4.3. SRv6 Binding SID Sub-TLV . . . . . . . . . . . . . . 13
2.4.4. Segment List Sub-TLV . . . . . . . . . . . . . . . . 15
2.4.5. Explicit NULL Label Policy Sub-TLV . . . . . . . . . 21
2.4.6. Policy Priority Sub-TLV . . . . . . . . . . . . . . . 23
2.4.7. Policy Candidate Path Name Sub-TLV . . . . . . . . . 23
2.4.8. Policy Name Sub-TLV . . . . . . . . . . . . . . . . . 24
3. Color Extended Community . . . . . . . . . . . . . . . . . . 26
4. SR Policy Operations . . . . . . . . . . . . . . . . . . . . 27
4.1. Advertisement of SR Policies . . . . . . . . . . . . . . 27
4.2. Reception of an SR Policy NLRI . . . . . . . . . . . . . 27
4.2.1. Validation of an SR Policy NLRI . . . . . . . . . . . 28
4.2.2. Eligibility for Local Use of an SR Policy NLRI . . . 28
4.2.3. Propagation of an SR Policy . . . . . . . . . . . . . 29
5. Error Handling and Fault Management . . . . . . . . . . . . . 29
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 30
6.1. Subsequent Address Family Identifiers (SAFI) Parameters . . . . . . . . . . . . . . . . . . . . . . . 31
6.2. BGP Tunnel Encapsulation Attribute Tunnel Types . . . . . 31
6.3. BGP Tunnel Encapsulation Attribute sub-TLVs . . . . . . . 32 Sub-TLVs
6.4. Color Extended Community Flags . . . . . . . . . . . . . 32
6.5. SR Policy Segment List Sub-TLVs . . . . . . . . . . . . . 32
6.6. SR Policy Binding SID Flags . . . . . . . . . . . . . . . 33
6.7. SR Policy SRv6 Binding SID Flags . . . . . . . . . . . . 33
6.8. SR Policy Segment Flags . . . . . . . . . . . . . . . . . 34
6.9. Color Extended Community Color-Only Types . . . . . . . . 34
6.10. SR Policy ENLP Values . . . . . . . . . . . . . . . . . . 35
7. Security Considerations . . . . . . . . . . . . . . . . . . . 35
8. Manageability Considerations . . . . . . . . . . . . . . . . 36
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 36
10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 37
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 38
11.1.
9.1. Normative References . . . . . . . . . . . . . . . . . . 38
11.2. Informational
9.2. Informative References . . . . . . . . . . . . . . . . 40
Acknowledgments
Contributors
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 41
1. Introduction
Segment Routing (SR) [RFC8402] allows a headend node to steer a
packet flow along a specific path. Intermediate per-path states are
eliminated thanks to source routing.
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
segments associated with that SR Policy.
[RFC9256] further details the concepts of SR Policy and steering into
an SR Policy. These apply equally to the SR-MPLS and Segment Routing
for IPv6 (SRv6) data-plane data plane instantiations of Segment Routing using
SR-MPLS and SRv6 Segment Identifiers (SIDs) as described in
[RFC8402]. [RFC8660] describes the representation and processing of
this ordered list of segments as an MPLS label stack for SR-MPLS.
While
[RFC8754] and [RFC8986] describe the same for SRv6 with the use of
the Segment Routing Header (SRH).
The functionality related to SR Policy related functionality described in [RFC9256] can be
conceptually viewed as being incorporated in an SR Policy Module
(SRPM). Following The following is a reminder of the high-level functionality
of SRPM:
* Learning multiple candidate paths (CP) (CPs) for an SR Policy via
various mechanisms (CLI, NETCONF, PCEP, or BGP).
* Selection of the best candidate path for an SR Policy.
* Associating a Binding SID (BSID) to the selected candidate path of
an SR Policy.
* Installation of the selected candidate path and its BSID in the
forwarding plane.
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 policy. SR Policy.
The document describes the functionality provided by BGP and, as
appropriate, provides references for the functionality functionality, which is
outside the scope of BGP (i.e. (i.e., resides within SRPM on the headend
node).
This document specifies a way of representing SR Policy candidate
paths in BGP UPDATE messages. BGP can then be used to propagate the
SR Policy candidate paths to the headend nodes in a network. The
usual BGP rules for BGP propagation and best-path selection are used.
At the headend of a specific policy, this will result in one or more
candidate paths being installed into the "BGP table". These paths
are then passed to the SRPM. The SRPM may compare them to candidate
paths learned via other mechanisms and will choose one or more paths
to be installed in the data plane. BGP itself does not install SR
Policy candidate paths into the data plane.
This document introduces a BGP subsequent address family Subsequent Address Family Identifier
(SAFI) for IPv4 and IPv6 address families. In UPDATE messages of
those AFI/
SAFIs, AFI/SAFIs, the Network Layer Reachability Information (NLRI)
identifies an SR Policy Candidate Path while the attributes encode
the segment lists and other details of that SR Policy Candidate Path.
While
While, for simplicity simplicity, the text in this document states that BGP
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
several other candidate paths provided via BGP (via an NLRI with a
different distinguisher as defined in Section 2.1), PCEP, NETCONF, or
local policy configuration.
Typically, a an SR Policy Controller [RFC9256] defines the set of
policies and advertises them to policy headend routers (typically
ingress routers). These policy advertisements use the BGP extensions
defined in this document. In most cases, the policy advertisement is
tailored for a specific policy headend; consequently, it may be
transmitted over a direct BGP session (i.e., without intermediate BGP
hops) to that headend and is not propagated any further. In such
cases, the policy advertisements will not traverse any Route
Reflector (RR, [RFC4456]) (RR) (see [RFC4456] and Section 4.2.3).
Alternatively, a BGP egress router may advertise SR Policies that
represent paths terminating on itself. In such cases, the router can
send these policies directly to each headend over a dedicated BGP
session, without necessitating any further propagation of the policy.
In some situations, it is undesirable for a controller or BGP egress
router to have a BGP session to each policy headend. In these
situations, BGP Route Reflectors may be used to propagate the
advertisements. In certain other deployments, it may be necessary
for the advertisement to propagate through a sequence of one or more
ASes
Autonomous Systems (ASes) within an SR Domain (refer to Section 7 for
the associated security considerations). To make this possible, an
attribute needs to be attached to the advertisement that enables a
BGP speaker to determine whether it is intended to be a headend for
the advertised policy. This is done by attaching one or more Route
Target Extended Communities to the advertisement [RFC4360].
The BGP extensions for the advertisement of SR Policies include
following components:
* A Subsequent Address Family Identifier (SAFI) whose NLRIs
identifies identify
an SR Policy candidate path.
* A Tunnel Type identifier for SR Policy, Policy and a set of sub-TLVs to be
inserted into the Tunnel Encapsulation Attribute (as defined in
[RFC9012]) specifying segment lists of the SR Policy candidate
path,
path as well as other information about the SR Policy.
* One or more IPv4 address-specific format route target extended
community ([RFC4360]) attached to the SR Policy Candidate Path
advertisement and that indicates the intended headend of such an SR
Policy Candidate Path advertisement.
The SR Policy SAFI route updates utilize the Tunnel Encapsulation
Attribute to signal an SR Policy, which itself functions as a tunnel.
This usage differs notably from the approach described in [RFC9012],
where the Tunnel Encapsulation Attribute is associated with a BGP
route update (e.g., for Internet or VPN routes) to specify the tunnel
used for forwarding traffic. This document does not modify or
supersede the usage of the Tunnel Encapsulation Attribute for
existing AFI/SAFIs AFIs/SAFIs as defined in [RFC9012]. Details regarding the
processing of the Tunnel Encapsulation Attribute for the SR Policy
SAFI are provided in Section Sections 2.2 and Section 2.3.
The northbound advertisement of the operational state of the SR
Policy Candidate Paths as part of BGP-LS BGP - Link State (BGP-LS) [RFC9552]
topology information is specified in [I-D.ietf-idr-bgp-ls-sr-policy]. [SR-BGP-LS].
The signaling of Dynamic and Composite Candidate Paths (sections (Sections 5.2
and 5.3 respectively 5.3, respectively, of [RFC9256]) is outside the scope of this
document.
The Color Extended Community (as defined in [RFC9012]) is used to
steer traffic into an SR Policy, as described in section Section 8.8 of
[RFC9256]. The Section 3 of this document updates [RFC9012] with
modifications to the format of the Flags field of the Color Extended
Community by using the two leftmost bits of that field.
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
2. SR Policy Encoding
2.1. SR Policy SAFI and NLRI
A
The SR Policy SAFI with code point 73 is introduced in this document: the SR Policy SAFI with
codepoint 73. document.
The AFI used MUST be IPv4(1) or IPv6(2).
The SR Policy SAFI uses the NLRI format defined as follows:
+------------------+
| NLRI Length | 1 octet
+------------------+
| Distinguisher | 4 octets
+------------------+
| Policy Color | 4 octets
+------------------+
| Endpoint | 4 or 16 octets
+------------------+
Figure 1: SR Policy SAFI Format
where:
*
Where:
NLRI Length: 1 octet indicating the length expressed in bits as
defined in [RFC4760]. When AFI = 1 1, the value MUST be 96 and 96; when
AFI = 2 2, the value MUST be 192.
*
Distinguisher: 4-octet value uniquely identifying the policy in the
context of <color, endpoint> tuple. The distinguisher has no
semantic value and is solely used by the SR Policy originator to
make unique (from an NLRI perspective) both for multiple candidate
paths of the same SR Policy as well as candidate paths of
different SR Policies (i.e. (i.e., with different segment lists) with
the same Color and Endpoint but meant for different headends. The
distinguisher is the discriminator of the SR Policy candidate path
as specified in section Section 2.5 of [RFC9256].
*
Policy Color: 4 octets that carry an unsigned non-zero integer value
indicating the color of the SR Policy as specified in
section Section 2.1
of [RFC9256]. The color is used to match the color of the
destination prefixes to steer traffic into the SR Policy as
specified in section Section 8 of [RFC9256].
*
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
anycast address). The Endpoint is an IPv4 (4-octet) address or an
IPv6 (16-octet) address according to the AFI of the NLRI. The
address can be either a unicast or an unspecified address (0.0.0.0
for IPv4, :: for IPv6), known as a null endpoint, endpoint as specified in
section
Section 2.1 of [RFC9256].
The color and endpoint are used to automate the steering of BGP
service routes on an SR Policy as described in section Section 8 of
[RFC9256].
The NLRI containing an SR Policy candidate path is carried in a BGP
UPDATE message [RFC4271] using BGP multi-protocol multiprotocol extensions [RFC4760]
with an AFI of 1 or 2 (IPv4 or IPv6) and with a SAFI of 73. The
fault management and error handling in the encoding of the NLRI
is are
specified in Section 5.
An update message that carries the MP_REACH_NLRI or MP_UNREACH_NLRI
attribute with the SR Policy SAFI MUST also carry the BGP mandatory
attributes. In addition, the BGP update message MAY also contain any
of the BGP optional attributes.
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,
independent of the SR Policy AFI. The length field of 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 address. If the next-hop
length is 16, then it is a global IPv6 address; if address. If the next-hop
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
attendant processing is governed by standard BGP procedures as
described in section Section 3 of [RFC4760] and section Section 3 of [RFC2545].
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
the BGP best-path selection algorithm. In other words, this document
leverages the existing BGP propagation and best-path selection rules.
Details of the procedures are described in Section 4.
It has to be noted that if several candidate paths of the same SR
Policy (endpoint, color) are signaled via BGP to a headend, then it
is RECOMMENDED that each NLRI uses use a different distinguisher. If BGP
has installed into the BGP table two advertisements whose respective
NLRIs have the same color and endpoint, but different distinguishers,
both advertisements are passed to the SRPM as different candidate
paths along with their respective originator information (i.e., ASN
Autonomous System Number (ASN) and BGP Router-ID) as described in section
Section 2.4 of [RFC9256]. The ASN would be the ASN of the origin and
the BGP Router-ID is determined in the following order:
* From the Route Origin Community [RFC4360] if present and carrying
an IP Address, or
* As the BGP Originator ID [RFC4456] if present, or
* As the BGP Router-ID of the peer from which the update was
received as a last resort.
The
Section 2.9 of [RFC9256] specifies the selection of the active
candidate path of the SR Policy by the SRPM based on the information
provided to it by BGP.
2.2. SR Policy and Tunnel Encapsulation Attribute
The content of the SR Policy Candidate Path is encoded in the Tunnel
Encapsulation Attribute defined in [RFC9012] using a Tunnel-Type
called SR Policy Type the "SR Policy" type with codepoint code point 15. The use of the SR
Policy Tunnel-type is applicable only for the AFI/SAFI pairs of
(1/73, 2/73). This document specifies the use of the Tunnel
Encapsulation Attribute with the SR Policy Tunnel-Type and the use of
any other Tunnel-Type with the SR Policy SAFI MUST be considered
malformed and handled by the "Treat-as-Withdraw" "treat-as-withdraw" strategy [RFC7606].
The SR Policy Encoding structure is as follows:
SR Policy SAFI NLRI: <Distinguisher, Policy-Color, Endpoint>
Attributes:
Tunnel Encapsulation Attribute (23)
Tunnel Type: SR Policy (15)
Binding SID
Preference
Priority
Policy Name
Policy Candidate Path Name
Explicit NULL Label Policy (ENLP)
Segment List
Weight
Segment
Segment
...
...
Figure 2: SR Policy Encoding
where:
Where:
* The SR Policy SAFI NLRI is defined in Section 2.1.
* The Tunnel Encapsulation Attribute is defined in [RFC9012].
* The Tunnel-Type is set to 15.
* Preference, Binding SID, Priority, Policy Name, Policy Candidate
Path Name, ENLP, Segment-List, Weight, and Segment sub-TLVs are
defined in Section 2.4.
* Additional sub-TLVs may be defined in the future.
A Tunnel Encapsulation Attribute MUST NOT contain more than one TLV
of type "SR Policy"; such updates MUST be considered malformed and
handled by the "Treat-as-Withdraw" "treat-as-withdraw" strategy [RFC7606].
BGP does not need to perform the validation of the tunnel (i.e., SR
Policy) itself as indicated in section Section 6 of [RFC9012]. The
validation of the SR Policy information that is advertised using the
sub-TLVs specified in Section 2.4 is performed by the SRPM.
2.3. Applicability of Tunnel Encapsulation Attribute Sub-TLVs
The Tunnel Egress Endpoint and Color sub-TLVs of the Tunnel
Encapsulation Attribute, as defined in [RFC9012], are not utilized
for SR Policy encodings. Consequently, their values are not relevant
within the context of the SR Policy SAFI NLRI. If these sub-TLVs are
present, a BGP speaker MUST ignore them and MAY remove them from the
Tunnel Encapsulation Attribute during propagation.
Similarly, any other sub-TLVs, including those specified in
[RFC9012], that do not have explicitly defined applicability to the
SR Policy SAFI MUST be ignored by the BGP speaker and MAY be removed
from the Tunnel Encapsulation Attribute during propagation.
2.4. SR Policy Sub-TLVs
This section specifies the sub-TLVs defined for encoding the
information about the SR Policy Candidate Path.
Preference, Binding SID, SRv6 Binding SID, Segment-List, Priority,
Policy Name, Policy Candidate Path Name, and Explicit NULL Label
Policy are all optional sub-TLVs introduced for the BGP Tunnel
Encapsulation Attribute [RFC9012] being defined in this section.
Weight and Segment are sub-TLVs of the Segment-List sub-TLV mentioned
above.
An early draft version of this document included only the Binding SID sub-
TLV
sub-TLV that could be used for both SR-MPLS and SRv6 Binding SIDs.
The SRv6 Binding SID TLV was introduced in later versions to support
the advertisement of additional SRv6 capabilities without affecting
backward compatibility for early implementations.
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/sub-TLVs that are specified as single instance, only the first
instance of that TLV/sub-TLV is used and used: the other instances MUST be
ignored and MUST NOT considered to be malformed.
None of the sub-TLVs defined in the following sub-sections subsections have any
effect on the BGP best-path selection or propagation procedures.
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
further processing as described in section Section 2 of [RFC9256].
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
applicability to other AFI/SAFI.
2.4.1. Preference Sub-TLV
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
SRPM as described in section Section 2.7 of [RFC9256].
The Preference sub-TLV is OPTIONAL and OPTIONAL; it MUST NOT appear more than once
in the SR Policy encoding.
The Preference sub-TLV has the following format:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Flags | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Preference (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: Preference sub-TLV
where:
* Sub-TLV
Where:
Type: 12
*
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.
*
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
ignored on receipt.
*
RESERVED: 1 octet of reserved bits. This field MUST be set to zero
on transmission and MUST be ignored on receipt.
*
Preference: a 4-octet value indicating the Preference of the SR
Policy Candidate Path as described in section Section 2.7 of [RFC9256].
2.4.2. Binding SID Sub-TLV
The Binding SID sub-TLV is used to signal the binding SID related BSID-related
information of the SR Policy candidate path. The contents of this
sub-TLV are used by the SRPM as described in section Section 6 in of [RFC9256].
The Binding SID sub-TLV is OPTIONAL and OPTIONAL; it MUST NOT appear more than
once in the SR Policy encoding.
When the Binding SID sub-TLV is used to signal an SRv6 SID, the
selection of the corresponding SRv6 Endpoint Behavior [RFC8986] to be
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
used when signaling an SRv6 Binding SID for an SR Policy candidate
path. The support for the use of this Binding SID sub-TLV for the
signaling of an SRv6 Binding SID is retained primarily for backward
compatibility with implementations that followed early draft versions
of this document that had not defined the SRv6 Binding SID sub-TLV.
The Binding SID sub-TLV has the following format:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Flags | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Binding SID (variable, optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: Binding SID sub-TLV
where:
* Sub-TLV
Where:
Type: 13
*
Length: Specifies the length of the value field (i.e., not including
Type and Length fields) in terms of octets. The value MUST be one of: 18
when a SRv6 BSID is present, 6 when a an SR-MPLS BSID is present, or
2 when no BSID is present.
*
Flags: 1 octet of flags. The following flags are defined in the
registry "SR Policy Binding SID Flags" as described in
Section 6.6:
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|S|I| |
+-+-+-+-+-+-+-+-+
Figure 5: SR Policy Binding SID Flags
where:
- S-Flag: This flag
Where:
* The S-Flag encodes the "Specified-BSID-only" "Specified-BSID-Only" behavior. It is
used by SRPM as described in section Section 6.2.3 in of [RFC9256].
- I-Flag: This flag
* The I-Flag encodes the "Drop Upon Invalid" behavior. It is
used by SRPM as described in section Section 8.2 in of [RFC9256] to define
a specific SR Policy forwarding behavior. The flag indicates
that the SR Policy is to perform the "drop upon invalid"
behavior when no valid candidate path (CP) is available for
this SR Policy. In this situation, the CP with the highest
preference amongst those with the "drop upon invalid" config is
made active to drop traffic steered over the SR Policy.
-
* The unassigned bits in the Flag octet MUST be set to zero upon
transmission and MUST be ignored upon receipt.
*
RESERVED: 1 octet of reserved bits. MUST be set to zero on
transmission and MUST be ignored on receipt.
*
Binding SID: If the length is 2, then no Binding SID is present. If
the length is 6 6, then the Binding SID is encoded in 4 octets using
the format below. Traffic Class (TC), S, and TTL (Total of 12
bits) are RESERVED and MUST be set to zero and MUST be ignored.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: Binding SID Label Encoding
The Label field is validated by the SRPM, SRPM but MUST NOT contain the
reserved MPLS label values (0-15). If the length is 18 18, then the
Binding SID contains a 16-octet SRv6 SID.
2.4.3. SRv6 Binding SID Sub-TLV
The SRv6 Binding SID sub-TLV is used to signal the SRv6 Binding SID
related information of an SR Policy candidate path. It enables the
specification of the SRv6 Endpoint Behavior [RFC8986] to be
instantiated on the headend node. The contents of this sub-TLV are
used by the SRPM as described in section Section 6 in of [RFC9256].
The SRv6 Binding SID sub-TLV is OPTIONAL. More than one SRv6 Binding
SID sub-TLVs sub-TLV MAY be signaled in the same SR Policy encoding to
indicate one or more SRv6 SIDs, each with potentially different SRv6
Endpoint Behaviors to be instantiated.
The SRv6 Binding SID sub-TLV has the following format:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Flags | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SRv6 Binding SID (16 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// SRv6 Endpoint Behavior and SID Structure (optional) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7: SRv6 Binding SID sub-TLV
where:
* Sub-TLV
Where:
Type: 20
*
Length: Specifies the length of the value field (i.e., not including
Type and Length fields) in terms of octets. The value MUST be 26
when the SRv6 Endpoint Behavior and SID Structure is
present else present;
else, it MUST be 18.
*
Flags: 1 octet of flags. The following flags are defined in the
registry "SR Policy SRv6 Binding SID Flags" as described in
Section 6.7:
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|S|I|B| |
+-+-+-+-+-+-+-+-+
Figure 8: SR Policy SRv6 Binding SID Flags
where:
- S-Flag: This flag
Where:
* The S-Flag encodes the "Specified-BSID-only" "Specified-BSID-Only" behavior. It is
used by SRPM as described in section Section 6.2.3 in of [RFC9256].
- I-Flag: This flag
* The I-Flag encodes the "Drop Upon Invalid" behavior. It is
used by SRPM as described in section Section 8.2 in of [RFC9256].
- B-Flag: This flag,
* The B-Flag, when set, indicates the presence of the SRv6 "SRv6
Endpoint Behavior and & SID Structure Structure" encoding specified in
Section 2.4.4.2.4.
-
* The unassigned bits in the Flag octet MUST be set to zero upon
transmission and MUST be ignored upon receipt.
*
RESERVED: 1 octet of reserved bits. This field MUST be set to zero
on transmission and MUST be ignored on receipt.
*
SRv6 Binding SID: Contains a 16-octet SRv6 SID. The value 0 MAY be
used when the controller wants to indicate the desired SRv6
Endpoint Behavior, SID Structure, or flags without specifying the
BSID.
*
SRv6 Endpoint Behavior and SID Structure: Optional, as defined in
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.
2.4.4. Segment List Sub-TLV
The Segment List sub-TLV encodes a single explicit path towards the
endpoint as described in section Section 5.1 of [RFC9256]. The Segment List
sub-TLV includes the elements of the paths (i.e., segments) as well
as an optional Weight sub-TLV.
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.
According to section Section 2 of [RFC9012], the sub-TLV type defines the
size of the length field. Therefore, for the Segment List sub-TLV, a
code point of 128 or higher is used.
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
not matter since each sub-TLV encodes a Segment List.
The Segment List sub-TLV contains zero or more Segment sub-TLVs and
MAY contain a Weight sub-TLV.
The Segment List sub-TLV has the following format:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// sub-TLVs //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 9: Segment List sub-TLV
where:
* Sub-TLV
Where:
Type: 128.
* 128
Length: the The total length (not including the Type and Length fields)
of the sub-TLVs encoded within the Segment List sub-TLV in terms
of octets.
*
RESERVED: 1 octet of reserved bits. This field MUST be set to zero
on transmission and MUST be ignored on receipt.
*
sub-TLVs currently defined:
-
* An optional single Weight sub-TLV.
- sub-TLV
* Zero or more Segment sub-TLVs. sub-TLVs
Validation of an explicit path encoded by the Segment List sub-TLV is
beyond the scope of BGP and performed by the SRPM as described in
section
Section 5 of [RFC9256].
2.4.4.1. Weight Sub-TLV
The Weight sub-TLV specifies the weight associated with a given
segment list. The contents of this sub-TLV are used only by the SRPM
as described in section Section 2.11 of [RFC9256].
The Weight sub-TLV is OPTIONAL and OPTIONAL; it MUST NOT appear more than once
inside the Segment List sub-TLV.
The Weight sub-TLV has the following format:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Flags | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Weight |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 10: Weight sub-TLV
where:
* Sub-TLV
Where:
Type: 9.
* 9
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.
*
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
ignored on receipt.
*
RESERVED: 1 octet of reserved bits. This field MUST be set to zero
on transmission and MUST be ignored on receipt.
*
Weight: 4 octets an unsigned integer value indicating the weight
associated with a segment list as described in section Section 2.11 of
[RFC9256]. A weight value of zero is invalid.
2.4.4.2. Segment Sub-TLVs
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
constitute an explicit path of the SR Policy candidate path. The
contents of these sub-TLVs are used only by the SRPM as described in
section
Section 4 in of [RFC9256].
The Segment sub-TLVs are OPTIONAL and MAY appear multiple times in
the Segment List sub-TLV.
Section 4 of [RFC9256] defines several Segment Types:
Type A: SR-MPLS Label
Type B: SRv6 SID
Type C: IPv4 Prefix with optional SR Algorithm
Type D: IPv6 Global Prefix with optional SR Algorithm for SR-MPLS
Type E: IPv4 Prefix with Local Interface ID
Type F: IPv4 Addresses for link endpoints as Local, Remote pair
Type G: IPv6 Prefix and Interface ID for link endpoints as Local,
Remote pair for SR-MPLS
Type H: IPv6 Addresses for link endpoints as Local, Remote pair for
SR-MPLS
Type I: IPv6 Global Prefix with optional SR Algorithm for SRv6
Type J: IPv6 Prefix and Interface ID for link endpoints as Local,
Remote pair for SRv6
Type K: IPv6 Addresses for link endpoints as Local, Remote pair for
SRv6
The following sub-sections subsections specify the sub-TLVs used for Segment Types
A and B. The other segment types are specified in
[I-D.ietf-idr-bgp-sr-segtypes-ext]. [RFC9831]. As
specified in section Section 5.1 of [RFC9256], a mix of SR-MPLS and SRv6
segments make the segment-list invalid.
2.4.4.2.1. Segment Type A
The Type A Segment Sub-TLV sub-TLV encodes a single SR-MPLS SID. The format
is as follows and is used to encode MPLS Label fields as specified in
[RFC3032] [RFC5462].: and [RFC5462]:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Flags | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 11: Type A Segment sub-TLV
where:
* Sub-TLV
Where:
Type: 1.
* 1
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.
*
Flags: 1 octet of flags as defined in Section 2.4.4.2.3.
*
RESERVED: 1 octet of reserved bits. This field MUST be set to zero
on transmission and MUST be ignored on receipt.
*
Label: 20 bits of label value.
*
TC: 3 bits of traffic class.
*
S: 1 bit of bottom-of-stack.
*
TTL: 1 octet of TTL.
The following applies to the Type-1 Segment sub-TLV:
* The S bit MUST be zero upon transmission and MUST be ignored upon
reception.
* If the originator wants the receiver to choose the TC value, it
sets the TC field to zero.
* If the originator wants the receiver to choose the TTL value, it
sets the TTL field to 255.
* If the originator wants to recommend a value for these fields, it
puts those values in the TC and/or TTL fields.
* The receiver MAY override the originator's values for these
fields. This would be determined by local policy at the receiver.
One possible policy would be to override the fields only if the
fields have the default values specified above.
2.4.4.2.2. Segment Type B
The Type B Segment Sub-TLV encodes a single SRv6 SID. The format is
as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Flags | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// SRv6 SID (16 octets) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// SRv6 Endpoint Behavior and SID Structure //
// (optional, 8 octets) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 12: Type B Segment sub-TLV
where:
* Sub-TLV
Where:
Type: 13.
* 13
Length: Specifies the length of the value field (i.e., not including
Type and Length fields) in terms of octets. The value MUST be 26
when the SRv6 Endpoint Behavior and SID Structure is
present else present;
else, it MUST be 18.
*
Flags: 1 octet of flags as defined in Section 2.4.4.2.3.
*
RESERVED: 1 octet of reserved bits. This field MUST be set to zero
on transmission and MUST be ignored on receipt.
*
SRv6 SID: 16 octets of IPv6 address.
*
SRv6 Endpoint Behavior and SID Structure: Optional, as defined in
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.
The Sub-TLV code point 2 defined for the advertisement of Segment
Type B in the earlier draft versions of this document has been
deprecated to avoid backward compatibility issues.
2.4.4.2.3. SR Policy Segment Flags
The Segment Types sub-TLVs described above may contain the following
SR Policy Segment Flags in their "Flags" field. Also refer to
Section 6.8:
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|V| |B| |
+-+-+-+-+-+-+-+-+
Figure 22: 13: SR Policy Segment Flags
where:
V-Flag: This flag, when
Where:
* When the V-Flag is set, it is used by SRPM for "SID verification"
as described in Section 5.1 of [RFC9256].
B-Flag: This flag, when
* When the B-Flag is set, it indicates the presence of the SRv6 "SRv6
Endpoint Behavior and & SID Structure Structure" encoding specified in
Section 2.4.4.2.4.
* The unassigned bits in the Flag octet MUST be set to zero upon
transmission and MUST be ignored upon receipt.
The following applies to the Segment Flags:
* V-Flag applies to all Segment Types.
* B-Flag applies to Segment Type B. If B-Flag appears with Segment
Type A A, it MUST be ignored.
2.4.4.2.4. SRv6 SID Endpoint Behavior and Structure
The Segment Types sub-TLVs described above MAY contain the SRv6
Endpoint Behavior and SID Structure [RFC8986] encoding as described
below:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Endpoint Behavior | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LB Length | LN Length | Fun. Length | Arg. Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 23: 14: SRv6 SID Endpoint Behavior and Structure
where:
Where:
Endpoint Behavior: 2 octets. It carries the SRv6 Endpoint Behavior
code point for this SRv6 SID as defined in section Section 10.2 of
[RFC8986]. When set with the value 0xFFFF (i.e., Opaque), the
choice of SRv6 Endpoint Behavior is left to the headend.
Reserved: 2 octets of reserved bits. This field MUST be set to zero
on transmission and MUST be ignored on receipt.
Locator Block Length: 1 octet. SRv6 SID Locator Block length in
bits.
Locator Node Length: 1 octet. SRv6 SID Locator Node length in bits.
Function Length: 1 octet. SRv6 SID Function length in bits.
Argument Length: 1 octet. SRv6 SID Arguments length in bits.
The total of the locator block, locator node, function, and argument
lengths MUST be less than or equal to 128.
2.4.5. Explicit NULL Label Policy Sub-TLV
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
that packet.
The Explicit NULL Label Policy (ENLP) sub-TLV is used to indicate
whether an Explicit NULL Label [RFC3032] must be pushed on an
unlabeled IP packet before any other labels.
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
configuration.
The ENLP sub-TLV is OPTIONAL and OPTIONAL; it MUST NOT appear more than once in
the SR Policy encoding.
The contents of this sub-TLV are used by the SRPM as described in
section
Section 4.1 of [RFC9256].
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Flags | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ENLP |
+-+-+-+-+-+-+-+-+
Figure 24: 15: ELNP sub-TLV Sub-TLV
Where:
Type: 14. 14
Length: Specifies the length of the value field (i.e., not including
Type and Length fields) in terms of octets. The value MUST be 3.
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
ignored on receipt.
RESERVED: 1 octet of reserved bits. This field MUST be set to zero
on transmission and MUST be ignored on receipt.
ENLP (Explicit NULL Label Policy): Indicates whether Explicit NULL
labels are to be pushed on unlabeled IP packets that are being
steered into a given SR policy. The following values have been
currently defined for this field:
-
1: Push an IPv4 Explicit NULL label on an unlabeled IPv4
packet, packet
but do not push an IPv6 Explicit NULL label on an unlabeled
IPv6 packet.
-
2: Push an IPv6 Explicit NULL label on an unlabeled IPv6
packet, packet
but do not push an IPv4 Explicit NULL label on an unlabeled
IPv4 packet.
-
3: Push an IPv4 Explicit NULL label on an unlabeled IPv4
packet, packet
and push an IPv6 Explicit NULL label on an unlabeled IPv6
packet.
-
4: Do not push an Explicit NULL label.
This field can have one of the values as specified in
Section 6.10. The ENLP unassigned values may be used for future
extensions. Implementations adhering to this document MUST ignore
the ENLP Sub-TLV with unrecognized values (viz. other than 1
through 4). The behavior signaled in this Sub-TLV MAY be
overridden by local configuration by the network operator based on
their deployment requirements. The section Section 4.1 of [RFC9256] describes
the behavior on the headend for the handling of the explicit null
label.
2.4.6. Policy Priority Sub-TLV
An operator MAY set the Policy Priority sub-TLV to indicate the order
in which the SR policies are re-computed recomputed upon topological change. The
contents of this sub-TLV are used by the SRPM as described in
section
Section 2.12 of [RFC9256].
The Priority sub-TLV is OPTIONAL and OPTIONAL; it MUST NOT appear more than once
in the SR Policy encoding.
The Priority sub-TLV has the following format:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Priority | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 25: 16: Priority sub-TLV Sub-TLV
Where:
Type: 15
Length: Specifies the length of the value field (i.e., not including
Type and Length fields) in terms of octets.The octets. The value MUST be 2.
Priority: a A 1-octet value indicating the priority as specified in
section
Section 2.12 of [RFC9256].
RESERVED: 1 octet of reserved bits. This field MUST be set to zero
on transmission and MUST be ignored on receipt.
2.4.7. Policy Candidate Path Name Sub-TLV
An operator MAY set the Policy Candidate Path Name sub-TLV to attach
a symbolic name to the SR Policy candidate path.
Usage of the Policy Candidate Path Name sub-TLV is described in section
Section 2.6 of [RFC9256].
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
section
Section 2 of [RFC9012], the sub-TLV type defines the size of the
length field. Therefore, for the Policy Candidate Path Name sub-TLV sub-TLV,
a code point of 128 or higher is used.
It is RECOMMENDED that the size of the symbolic name for the
candidate path is be limited to 255 bytes. Implementations MAY choose
to truncate long names to 255 bytes when signaling via BGP.
The Policy Candidate Path Name sub-TLV is OPTIONAL and OPTIONAL; it MUST NOT
appear more than once in the SR Policy encoding.
The Policy Candidate Path Name sub-TLV has the following format:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Policy Candidate Path Name //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 26: 17: Policy Candidate Path Name sub-TLV Sub-TLV
Where:
Type: 129. 129
Length: Specifies the length of the value field (i.e., not including
Type and Length fields) in terms of octets. The value is
variable.
RESERVED: 1 octet of reserved bits. This field MUST be set to zero
on transmission and MUST be ignored on receipt.
Policy Candidate Path Name: Symbolic name for the SR Policy
candidate path without a NULL terminator with encoding as
specified in section Section 2.6 of [RFC9256].
2.4.8. Policy Name Sub-TLV
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
advertised via the SR Policy NLRI.
Usage of the Policy Name sub-TLV is described in section Section 2.1 of
[RFC9256].
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
section
Section 2 of [RFC9012], the sub-TLV type defines the size of the
length field. Therefore, for the Policy Name sub-TLV sub-TLV, a code point
of 128 or higher is used.
It is RECOMMENDED that the size of the symbolic name for the SR
Policy is be limited to 255 bytes. Implementations MAY choose to
truncate long names to 255 bytes when signaling via BGP.
The Policy Name sub-TLV is OPTIONAL and OPTIONAL; it MUST NOT appear more than
once in the SR Policy encoding.
The Policy Name sub-TLV has the following format:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Policy Name //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 27: 18: Policy Name sub-TLV Sub-TLV
Where:
Type: 130
Length: Specifies the length of the value field (i.e., not including
Type and Length fields) in terms of octets. The value is
variable.
RESERVED: 1 octet of reserved bits. This field MUST be set to zero
on transmission and MUST be ignored on receipt.
Policy Name: Symbolic name for the SR Policy without a NULL
terminator with encoding as specified in section Section 2.1 of [RFC9256].
3. Color Extended Community
The Color Extended Community [RFC9012] is used to steer traffic
corresponding to BGP routes into an SR Policy with matching color
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
(IPv4 Labeled Unicast), 2/4 (IPv6 Labeled Unicast), 1/128 (VPN-IPv4
Labeled Unicast), 2/128 (VPN-IPv6 Labeled Unicast), or 25/70
(Ethernet VPN, usually known as EVPN). Use of the Color Extended
Community in BGP UPDATE messages of other AFI/SAFIs is not covered by
[RFC9012] and
[RFC9012]; hence, it is hence outside the scope of this document as well.
Two bits from the Flags field of the Color Extended Community are
used as follows to support the requirements of Color-Only steering as
specified in Section 8.8 of [RFC9256]:
1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|C O| Unassigned |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 28: 19: Color Extended Community Flags
The CO C and O bits together form the Color-Only Type field field, which
indicates the various matching criteria between the BGP NH and the SR
Policy endpoint in addition to the matching of the color value. Following The
following types are defined:
*
Type 0 (bits 00): Specific Endpoint Match: Match. Request a match for the
endpoint that is the BGP NH
* NH.
Type 1 (bits 01): Specific or Null Endpoint Match: Match. Request a match
for either the endpoint that is the BGP NH or a null endpoint
(e.g., like a default gateway)
* gateway).
Type 2 (bits 10): Specific, Null, or Any Endpoint Match: Match. Request a
match for either the endpoint that is the BGP NH or with a null or any endpoint
*
endpoint.
Type 3 (bits 11): reserved Reserved for future use and SHOULD NOT be used.
Upon reception, an implementation MUST treat it like Type 0.
The details of the SR Policy steering mechanisms based on these
Color-Only types are specified in section Section 8.8 of [RFC9256].
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
the steering behaviors over SR Policies when multiple Color Extended
Communities are associated with a BGP route.
4. SR Policy Operations
As mentioned in Section 1, BGP is not the actual consumer of an SR
Policy NLRI. BGP is in charge of the origination and propagation of
the SR Policy NLRI NLRI, but its installation and use are outside the
scope of BGP. The details of SR Policy installation and use are
specified in [RFC9256].
4.1. Advertisement of SR Policies
Typically, but not limited to, an SR Policy is computed by a
controller or a path computation engine Path Computation Engine (PCE) and originated by a BGP
speaker on its behalf.
Multiple SR Policy NLRIs may be present with the same <color,
endpoint> tuple but with different distinguishers when these SR
policies are intended for different headends.
The distinguisher of each SR Policy NLRI prevents undesired BGP route
selection among these SR Policy NLRIs and allows their propagation
across route reflectors [RFC4456].
Moreover, one or more route targets SHOULD be attached to the
advertisement, where each route target identifies one or more
intended headends for the advertised SR Policy update.
If no route target is attached to the SR Policy NLRI, then it is
assumed that the originator sends the SR Policy update directly
(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
Policy update (see further details in Section 4.2.3).
4.2. Reception of an SR Policy NLRI
On reception of an SR Policy NLRI, a BGP speaker first determines if
it is valid as described in Section 4.2.1 and then 4.2.1; then, the BGP speaker
performs the decision process for selection of the best route
(Section 9.1 of [RFC4271]). The key difference from the base BGP
decision process is that BGP does not download the selected best
routes of the SR Policy SAFI into the forwarding and instead forwarding; instead, it
considers them "usable" for passing on to the SRPM for further
processing as described in Section 4.2.2. The selected best route is
"propagated" (Section 9.1.3 of [RFC4271]) as described in
Section 4.2.3 4.2.3, irrespective of its "usability" by the local router.
4.2.1. Validation of an SR Policy NLRI
When a BGP speaker receives an SR Policy NLRI from a neighbor neighbor, it
MUST first perform validation based on the following rules in
addition to the validation described in Section 5:
* The SR Policy NLRI MUST include a distinguisher, color, and
endpoint field which that implies that the length of the NLRI MUST be
either 12 or 24 octets (depending on the address family of the
endpoint).
* The SR Policy update MUST have either the NO_ADVERTISE community
or community,
at least one route target extended community in IPv4-address
format
format, or both. If a router supporting this specification
receives an SR Policy update with no route target extended
communities and no NO_ADVERTISE community, the update MUST be
considered as to be malformed.
* The Tunnel Encapsulation Attribute MUST be attached to the BGP
Update and MUST have a Tunnel Type TLV set to SR Policy (codepoint (code
point is 15).
A router that receives an SR Policy update that is not valid
according to these criteria MUST treat the update as malformed malformed, and
the SR Policy candidate path MUST NOT be passed to the SRPM.
4.2.2. Eligibility for Local Use of an SR Policy NLRI
An SR Policy NLRI update without any that does not have a route target extended
community but having does have the NO_ADVERTISE community is considered
usable.
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
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,
unsigned, non-zero integer. Therefore, the route target extended
community MUST be of the same format.
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
usable on the receiver node.
When the SR Policy tunnel type includes any sub-TLV that is
unrecognized or unsupported, the update SHOULD NOT be considered
usable. An implementation MAY provide an option for ignoring
unsupported sub-TLVs.
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
that, along with the candidate path details, BGP also passes the
originator information for breaking ties in the candidate path
selection process as described in section Section 2.4 of [RFC9256].
When an update for an SR Policy NLRI results in its becoming
unusable, BGP MUST delete its corresponding SR Policy candidate path
from the SRPM.
The SRPM applies the rules defined in section Section 2 of [RFC9256] to
determine whether the SR Policy candidate path is valid and to select
the active candidate path for a given SR Policy.
4.2.3. Propagation of an SR Policy
SR Policy NLRIs that have the NO_ADVERTISE community attached to them
MUST NOT be propagated.
By default, a BGP node receiving an SR Policy NLRI MUST NOT propagate
it to any EBGP External BGP (EBGP) neighbor. An implementation MAY
provide an explicit configuration to override this and enable the
propagation of valid SR Policy NLRIs to specific EBGP neighbors where
the SR domain comprises
multiple-ASes multiple ASes within a single service
provider domain (see Section 7 for details).
A BGP node advertises a received SR Policy NLRI to its IBGP Internal BGP
(IBGP) neighbors according to normal IBGP propagation rules.
By default, a BGP node receiving an SR Policy NLRI SHOULD NOT remove
the route target extended community before propagation. An
implementation MAY provide support for configuration to filter and/or
remove the route target extended community before propagation.
A BGP node MUST NOT alter the SR Policy information carried in the
Tunnel Encapsulation Attribute during propagation.
5. Error Handling and Fault Management
This section describes the error handling error-handling actions, as described in
[RFC7606], that are to be performed for the handling of the BGP
update messages for the BGP SR Policy SAFI.
A BGP Speaker speaker MUST perform the following syntactic validation of 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
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
endpoint address as specified in Section 2.1.
When the error determined allows for the router to skip the malformed
NLRI(s) and continue the processing of the rest of the update
message, then it MUST handle such malformed NLRIs as 'Treat-as- 'treat-as-
withdraw'. In other cases, where the error in the NLRI encoding
results in the inability to process the BGP update message (e.g.
length related (e.g.,
length-related encoding errors), then the router SHOULD handle such
malformed NLRIs as 'AFI/SAFI disable' "AFI/SAFI disable" when other AFI/SAFI AFIs/SAFIs besides
SR Policy are being advertised over the same session. Alternately,
the router MUST perform 'session reset' "session reset" when the session is only
being used for SR Policy or when it 'AFI/SAFI disable' a "AFI/SAFI disable" action is not
possible.
The validation of the TLVs/sub-TLVs introduced in this document and
defined in their respective sub-sections subsections of Section 2.4 MUST be
performed to determine if they are malformed or invalid. The
validation of the Tunnel Encapsulation Attribute itself and the other
TLVs/sub-TLVs specified in Section 13 of [RFC9012] MUST be done as
described in that document. In case of any error detected, either at
the attribute or its TLV/sub-TLV level, the "treat-as-withdraw"
strategy MUST be applied. This is because an SR Policy update
without a valid Tunnel Encapsulation Attribute (comprising (comprised of all
valid TLVs/sub-TLVs) is not usable.
An SR Policy update that is determined not to be not valid, and therefore
malformed, valid (and,
therefore, malformed) based on the rules described in Section 4.2.1
MUST be handled by the "treat-as-withdraw" strategy.
The validation of the individual fields of the TLVs/sub-TLVs defined
in Section 2.4 are beyond the scope of BGP as they are handled by the
SRPM as described in the individual TLV/sub-TLV sub-sections. subsections. A BGP
implementation MUST NOT perform semantic verification of such fields
nor consider the SR Policy update to be invalid or not usable based
on such validation.
An implementation SHOULD log any errors found during the above
validation for further analysis.
6. IANA Considerations
This document uses code point allocations from the following existing
registries:
* Subsequent
registries in the "Subsequent Address Family Identifiers (SAFI) Parameters
Parameters" registry group:
* BGP Tunnel Encapsulation Attribute Tunnel Types The "SAFI Values" registry under
This document uses code point allocations from the
BGP following existing
registries in the "Border Gateway Protocol (BGP) Tunnel Encapsulation
Encapsulation" registry group:
* BGP The "BGP Tunnel Encapsulation Attribute sub-TLVs Tunnel Types" registry under the BGP
* The "BGP Tunnel Encapsulation Attribute Sub-TLVs" registry
* Color The "Color Extended Community Flags registry under the BGP Tunnel
Encapsulation Flags" registry
This document also requests the creation of creates the following new
registries: registries in the "Border
Gateway Protocol (BGP) Tunnel Encapsulation" registry group:
* SR The "SR Policy Segment List Sub-TLVs under the BGP Tunnel Encapsulation Sub-TLVs" registry
* SR The "SR Policy Binding SID Flags under the BGP Tunnel Encapsulation Flags" registry
* SR The "SR Policy SRv6 Binding SID Flags under the BGP Tunnel
Encapsulation Flags" registry
* SR The "SR Policy Segment Flags under the BGP Tunnel Encapsulation Flags" registry
* Color The "Color Extended Community Color-Only Types Types" registry under
This document creates the BGP
Tunnel Encapsulation following new registry in the "Segment
Routing" registry group:
* SR The "SR Policy ENLP Values under the Segment Routing Values" registry
6.1. Subsequent Address Family Identifiers (SAFI) Parameters
This document introduces registers a SAFI code point in the "SAFI Values"
registry of the "Subsequent Address Family Identifiers (SAFI)
Parameters" that has been assigned a code
point by IANA. The entry needs to be updated registry group as follows:
Code Point
+=======+================+===========+
| Value | Description | Reference
----------------------------------------------- |
+=======+================+===========+
| 73 | SR Policy SAFI This document | RFC 9830 |
+-------+----------------+-----------+
Table 1: BGP SAFI Code Point
6.2. BGP Tunnel Encapsulation Attribute Tunnel Types
This document introduces registers a Tunnel-Type code point in the registry "BGP Tunnel
Encapsulation Attribute Tunnel Types" that has been assigned a
codepoint by IANA. The entry needs to be updated as follows:
Code Point registry under the "Border
Gateway Protocol (BGP) Tunnel Encapsulation" registry group.
+=======+=============+===========+
| Value | Description | Reference
-------------------------------------------------- |
+=======+=============+===========+
| 15 | SR Policy This document | RFC 9830 |
+-------+-------------+-----------+
Table 2: Tunnel Type Code Point
6.3. BGP Tunnel Encapsulation Attribute sub-TLVs Sub-TLVs
This document defines sub-TLVs in the registry "BGP Tunnel Encapsulation
Attribute sub-TLVs" that have been assigned code points
by IANA as follows via Sub-TLVs" registry under the early allocation process which needs to be
made permanent:
Code Point "Border Gateway Protocol (BGP)
Tunnel Encapsulation" registry group.
+=======+====================================+===========+
| Value | Description | Reference
------------------------------------------------------------ |
+=======+====================================+===========+
| 12 | Preference sub-TLV This document | RFC 9830 |
+-------+------------------------------------+-----------+
| 13 | Binding SID sub-TLV This document | RFC 9830 |
+-------+------------------------------------+-----------+
| 14 | ENLP sub-TLV This document | RFC 9830 |
+-------+------------------------------------+-----------+
| 15 | Priority sub-TLV This document | RFC 9830 |
+-------+------------------------------------+-----------+
| 20 | SRv6 Binding SID sub-TLV This document | RFC 9830 |
+-------+------------------------------------+-----------+
| 128 | Segment List sub-TLV This document | RFC 9830 |
+-------+------------------------------------+-----------+
| 129 | Policy Candidate Path Name sub-TLV This document | RFC 9830 |
+-------+------------------------------------+-----------+
| 130 | Policy Name sub-TLV This document | RFC 9830 |
+-------+------------------------------------+-----------+
Table 3: BGP Tunnel Encapsulation Attribute Sub-TLV
Code Points
6.4. Color Extended Community Flags
This document defines the use of 2 bits in the registry called "Color Extended
Community Flags" registry under the "BGP "Border Gateway Protocol (BGP)
Tunnel Encapsulation" registry that have been assigned by IANA via the early allocation
process to form the Color-Only Types field which needs to be made
permanent: group.
+==============+========================+===========+
| Bit Position | Description | Reference
------------------------------------------------------------------ |
+==============+========================+===========+
| 0-1 | Color-only Types Field This document | RFC 9830 |
+--------------+------------------------+-----------+
Table 4: Color Extended Community Flag Bits
6.5. SR Policy Segment List Sub-TLVs
This document requests the creation of creates a new registry called "SR Policy Segment List
Sub-TLVs" under the "BGP "Border Gateway Protocol (BGP) Tunnel
Encapsulation"
registry. registry group. The allocation registration policy of this
registry is "IETF Review"
according to [RFC8126].
Following (see [RFC8126]).
The following initial Sub-TLV codepoints sub-TLV code points are assigned by this
document:
+========+========================+===========+
| Value | Description | Reference
----------------------------------------------------- |
+========+========================+===========+
| 0 | Reserved This document | RFC 9830 |
+--------+------------------------+-----------+
| 1 | Segment Type A sub-TLV This document | RFC 9830 |
+--------+------------------------+-----------+
| 2 | Deprecated This document | RFC 9830 |
+--------+------------------------+-----------+
| 3-8 | Unassigned |
+--------+------------------------+-----------+
| 9 | Weight sub-TLV This document | RFC 9830 |
+--------+------------------------+-----------+
| 10 | Deprecated This document | RFC 9830 |
+--------+------------------------+-----------+
| 11 | Deprecated This document | RFC 9830 |
+--------+------------------------+-----------+
| 12 | Deprecated This document | RFC 9830 |
+--------+------------------------+-----------+
| 13 | Segment Type B sub-TLV This document | RFC 9830 |
+--------+------------------------+-----------+
| 14-255 | Unassigned |
+--------+------------------------------------+
Table 5: SR Policy Segment List Sub-TLV
Code Points
6.6. SR Policy Binding SID Flags
This document requests the creation of creates a new registry called "SR Policy Binding SID
Flags" under the "BGP "Border Gateway Protocol (BGP) Tunnel Encapsulation"
registry.
registry group. The allocation registration policy of this registry is
"Standards Action" according to [RFC8126]. (see [RFC8126]).
The following flags are defined:
+=====+===================================+===========+
| Bit | Description | Reference
----------------------------------------------------------------- |
+=====+===================================+===========+
| 0 | Specified-BSID-Only Flag (S-Flag) This document | RFC 9830 |
+-----+-----------------------------------+-----------+
| 1 | Drop Upon Invalid Flag (I-Flag) This document | RFC 9830 |
+-----+-----------------------------------+-----------+
| 2-7 | Unassigned |
+-----+-----------------------------------------------+
Table 6: SR Policy Binding SID Flags
6.7. SR Policy SRv6 Binding SID Flags
This document requests the creation of creates a new registry called "SR Policy SRv6 Binding
SID Flags" under the "BGP "Border Gateway Protocol (BGP) Tunnel
Encapsulation"
registry. registry group. The allocation registration policy of this
registry is "Standards Action" according to [RFC8126]. (see [RFC8126]).
The following flags are defined:
+=====+===================================+===========+
| Bit | Description | Reference
----------------------------------------------------------------- |
+=====+===================================+===========+
| 0 | Specified-BSID-Only Flag (S-Flag) This document | RFC 9830 |
+-----+-----------------------------------+-----------+
| 1 | Drop Upon Invalid Flag (I-Flag) This document | RFC 9830 |
+-----+-----------------------------------+-----------+
| 2 | SRv6 Endpoint Behavior & SID | RFC 9830 |
| | Structure Flag (B-Flag) This document | |
+-----+-----------------------------------+-----------+
| 3-7 | Unassigned |
+-----+-----------------------------------------------+
Table 7: SR Policy SRv6 Binding SID Flags
6.8. SR Policy Segment Flags
This document requests the creation of creates a new registry called "SR Policy Segment Flags"
under the "BGP "Border Gateway Protocol (BGP) Tunnel Encapsulation" registry.
registry group. The allocation registration policy of this registry is "IETF
Review" according to
[RFC8126]. (see [RFC8126]).
The following flags are defined:
+=====+====================================+===========+
| Bit | Description | Reference
------------------------------------------------------------------ |
+=====+====================================+===========+
| 0 | Segment Verification Flag (V-Flag) This document | RFC 9830 |
+-----+------------------------------------+-----------+
| 1-2 | Unassigned |
+-----+------------------------------------+-----------+
| 3 | SRv6 Endpoint Behavior & SID | RFC 9830 |
| | Structure Flag (B-Flag) This document | |
+-----+------------------------------------+-----------+
| 4-7 | Unassigned |
+-----+------------------------------------------------+
Table 8: SR Policy Segment Flags
6.9. Color Extended Community Color-Only Types
This document requests the creation of creates a new registry called "Color Extended Community
Color-Only Types" under the "BGP "Border Gateway Protocol (BGP) Tunnel
Encapsulation" registry group for assignment of codepoints code points (values 0
through 3) in the Color-Only Type field of the Color Extended
Community Flags field. The allocation registration policy of this registry is
"Standards Action" according to [RFC8126]. (see [RFC8126]).
The following types are defined:
+======+=======================================+===========+
| Type | Description | Reference
----------------------------------------------------------- |
+======+=======================================+===========+
| 0 | Specific Endpoint Match This document | RFC 9830 |
+------+---------------------------------------+-----------+
| 1 | Specific or Null Endpoint Match This document | RFC 9830 |
+------+---------------------------------------+-----------+
| 2 | Specific, Null, or Any Endpoint Match This document | RFC 9830 |
+------+---------------------------------------+-----------+
| 3 | Unassigned This document | RFC 9830 |
+------+---------------------------------------+-----------+
Table 9: Color Extended Community Color-Only Types
6.10. SR Policy ENLP Values
Note to IANA (RFC editor to remove this before publication): The new
registry creation request below is also present in the draft-ietf-
pce-segment-routing-policy-cp.
IANA is requested to process the
registry creation via the first of these two documents to reach
publication stage and the authors of the other document would update
the IANA considerations suitably.
This document requests IANA to will maintain a new registry under the "Segment Routing"
registry group with the allocation registration policy of "Standards Action" [RFC8126].
(see [RFC8126]). The new registry is called "SR Policy ENLP Values"
and contains the codepoints code points allocated to the "ENLP" field defined in
Section 2.4.5. The registry contains the following
codepoints, with initial values, to be assigned by IANA with the
reference set to this document:
+-------+-----------------------------------+---------------+ code points:
+=======+===================================+===========+
| Code | Description | Reference |
| Point | Description | Reference |
+-------+-----------------------------------+---------------+
+=======+===================================+===========+
| 0 | Reserved (not to be used) | This document RFC 9830 |
+-------+-----------------------------------+-----------+
| 1 | Push an IPv4 Explicit NULL label | This document RFC 9830 |
| | on an unlabeled IPv4 packet, packet but | |
| | do not push an IPv6 Explicit NULL | |
| | label on an unlabeled IPv6 packet | |
+-------+-----------------------------------+-----------+
| 2 | Push an IPv6 Explicit NULL label | This document RFC 9830 |
| | on an unlabeled IPv6 packet, packet but | |
| | do not push an IPv4 Explicit NULL | |
| | label on an unlabeled IPv4 packet | |
+-------+-----------------------------------+-----------+
| 3 | Push an IPv6 Explicit NULL label | This document RFC 9830 |
| | on an unlabeled IPv6 packet, packet and | |
| | push an IPv4 Explicit NULL label | |
| | on an unlabeled IPv4 packet | |
+-------+-----------------------------------+-----------+
| 4 | Do not push an Explicit NULL | This document RFC 9830 |
| | label | |
+-------+-----------------------------------+-----------+
| 5-255 | Unassigned | |
+-------+-----------------------------------+---------------+
+-------+-----------------------------------------------+
Table 10: SR Policy ENLP Values
7. Security Considerations
The security mechanisms of the base BGP security model apply to the
extensions described in this document as well. See the Security
Considerations section of [RFC4271] for a discussion of BGP security.
Also, refer to [RFC4272] and [RFC6952] for analysis of security
issues for BGP.
The BGP SR Policy extensions specified in this document enable
traffic engineering and service programming use-cases use cases within an SR
domain as described in [RFC9256]. SR operates within a trusted SR
domain [RFC8402] and [RFC8402]; its security considerations also apply to BGP
sessions when carrying SR Policy information. The SR Policies
distributed by BGP are expected to be used entirely within this
trusted SR domain domain, which comprises a single AS or multiple ASes/ ASes /
domains within a single provider network. Therefore, precaution is
necessary to ensure that the SR Policy information advertised via BGP
sessions is limited to nodes in a secure manner within this trusted
SR domain. BGP peering sessions for address-families address families other than SR
Policy SAFI may be set up to routers outside the SR domain. The
isolation of BGP SR Policy SAFI peering sessions may be used to
ensure that the SR Policy information is not advertised by accident
or in error to an EBGP peering session outside the SR domain.
Additionally, it may be considered a consideration that the export of SR Policy
information, as described in this document, constitutes a risk to
confidentiality of mission-critical or commercially sensitive
information about the network (more specifically endpoint/node
addresses, SR SIDs, and the SR Policies deployed). BGP peerings are
not automatic and require configuration; thus, it is the
responsibility of the network operator to ensure that only trusted
nodes (that include both routers and controller applications) within
the SR domain are configured to receive such information.
8. Manageability Considerations
The specification of BGP models is an ongoing work based on
[I-D.ietf-idr-bgp-model] and
[BGP-YANG-MODEL]; its future extensions are expected to cover the SR
Policy SAFI. Existing BGP operational procedures also apply to the
SAFI specified in this document. The management, operations, and
monitoring of BGP speakers and the SR Policy SAFI sessions between
them are not very different from other BGP sessions and can be
managed using the same data models.
The YANG data model for the operation and management of SR Policies
[I-D.ietf-spring-sr-policy-yang]
[SR-POLICY-YANG] reports the SR Policies provisioned via BGP SR
Policy SAFI along with their operational states.
9. Acknowledgments
The authors of this document would like to thank Shyam Sethuram, John
Scudder, Przemyslaw Krol, Alex Bogdanov, Nandan Saha, Bruno Decraene,
Gurusiddesh Nidasesi, Kausik Majumdar, Zafar Ali, Swadesh Agarwal,
Jakob Heitz, Viral Patel, Peng Shaofu, Cheng Li, Martin Vigoureux,
John Scudder, Vincent Roca, Brian Haberman, Mohamed Boucadair,
Shunwan Zhuang, Andrew Alston, Jeffrey (Zhaohui) Zhang, Nagendra
Nainar, Rajesh Melarcode Venkateswaran, Nat Kao, Boris Hassanov,
Vincent Roca, Russ Housley, and Dan Romascanu for their comments and
review of this document. The authors would like to thank Susan Hares
for her detailed shepherd review that helped in improving the
document.
10. Contributors
Eric Rosen
Juniper Networks
US
Email: erosen@juniper.net
Arjun Sreekantiah
Cisco Systems
US
Email: asreekan@cisco.com
Acee Lindem
Cisco Systems
US
Email: acee@cisco.com
Siva Sivabalan
Cisco Systems
US
Email: msiva@cisco.com
Imtiyaz Mohammad
Arista Networks
India
Email: imtiyaz@arista.com
Gaurav Dawra
Cisco Systems
US
Email: gdawra.ietf@gmail.com
Peng Shaofu
ZTE Corporation
China
Email: peng.shaofu@zte.com.cn
Steven Lin
Calix
USA
Email: steven.lin@calix.com
11. References
11.1.
9.1. Normative References
[RFC1997] Chandra, R., Traina, P., and T. Li, "BGP Communities
Attribute", RFC 1997, DOI 10.17487/RFC1997, August 1996,
<https://www.rfc-editor.org/info/rfc1997>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC2545] Marques, P. and F. Dupont, "Use of BGP-4 Multiprotocol
Extensions for IPv6 Inter-Domain Routing", RFC 2545,
DOI 10.17487/RFC2545, March 1999,
<https://www.rfc-editor.org/info/rfc2545>.
[RFC3032] Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y.,
Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack
Encoding", RFC 3032, DOI 10.17487/RFC3032, January 2001,
<https://www.rfc-editor.org/info/rfc3032>.
[RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
Border Gateway Protocol 4 (BGP-4)", RFC 4271,
DOI 10.17487/RFC4271, January 2006,
<https://www.rfc-editor.org/info/rfc4271>.
[RFC4360] Sangli, S., Tappan, D., and Y. Rekhter, "BGP Extended
Communities Attribute", RFC 4360, DOI 10.17487/RFC4360,
February 2006, <https://www.rfc-editor.org/info/rfc4360>.
[RFC4760] Bates, T., Chandra, R., Katz, D., and Y. Rekhter,
"Multiprotocol Extensions for BGP-4", RFC 4760,
DOI 10.17487/RFC4760, January 2007,
<https://www.rfc-editor.org/info/rfc4760>.
[RFC5462] Andersson, L. and R. Asati, "Multiprotocol Label Switching
(MPLS) Label Stack Entry: "EXP" Field Renamed to "Traffic
Class" Field", RFC 5462, DOI 10.17487/RFC5462, February
2009, <https://www.rfc-editor.org/info/rfc5462>.
[RFC6286] Chen, E. and J. Yuan, "Autonomous-System-Wide Unique BGP
Identifier for BGP-4", RFC 6286, DOI 10.17487/RFC6286,
June 2011, <https://www.rfc-editor.org/info/rfc6286>.
[RFC7606] Chen, E., Ed., Scudder, J., Ed., Mohapatra, P., and K.
Patel, "Revised Error Handling for BGP UPDATE Messages",
RFC 7606, DOI 10.17487/RFC7606, August 2015,
<https://www.rfc-editor.org/info/rfc7606>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
Decraene, B., Litkowski, S., and R. Shakir, "Segment
Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
July 2018, <https://www.rfc-editor.org/info/rfc8402>.
[RFC8660] Bashandy, A., Ed., Filsfils, C., Ed., Previdi, S.,
Decraene, B., Litkowski, S., and R. Shakir, "Segment
Routing with the MPLS Data Plane", RFC 8660,
DOI 10.17487/RFC8660, December 2019,
<https://www.rfc-editor.org/info/rfc8660>.
[RFC8754] Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J.,
Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header
(SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020,
<https://www.rfc-editor.org/info/rfc8754>.
[RFC8986] Filsfils, C., Ed., Camarillo, P., Ed., Leddy, J., Voyer,
D., Matsushima, S., and Z. Li, "Segment Routing over IPv6
(SRv6) Network Programming", RFC 8986,
DOI 10.17487/RFC8986, February 2021,
<https://www.rfc-editor.org/info/rfc8986>.
[RFC9012] Patel, K., Van de Velde, G., Sangli, S., and J. Scudder,
"The BGP Tunnel Encapsulation Attribute", RFC 9012,
DOI 10.17487/RFC9012, April 2021,
<https://www.rfc-editor.org/info/rfc9012>.
[RFC9256] Filsfils, C., Talaulikar, K., Ed., Voyer, D., Bogdanov,
A., and P. Mattes, "Segment Routing Policy Architecture",
RFC 9256, DOI 10.17487/RFC9256, July 2022,
<https://www.rfc-editor.org/info/rfc9256>.
11.2. Informational
9.2. Informative References
[I-D.ietf-idr-bgp-ls-sr-policy]
Previdi, S., Talaulikar, K., 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-10, 9 December 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-idr-bgp-
ls-sr-policy-10>.
[I-D.ietf-idr-bgp-model]
[BGP-YANG-MODEL]
Jethanandani, M., Patel, K., Hares, S., and J. Haas, "YANG
Model for Border Gateway Protocol (BGP-4)", Work in
Progress, Internet-Draft, draft-ietf-idr-bgp-model-18, 21
October 2024, <https://datatracker.ietf.org/doc/html/
draft-ietf-idr-bgp-model-18>.
[I-D.ietf-idr-bgp-sr-segtypes-ext]
Talaulikar, K., Filsfils, C., Previdi, S., Mattes, P., and
D. Jain, "Segment Routing Segment Types Extensions for BGP
SR Policy", Work in Progress, Internet-Draft, draft-ietf-
idr-bgp-sr-segtypes-ext-06, 7 November 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-idr-bgp-
sr-segtypes-ext-06>.
[I-D.ietf-spring-sr-policy-yang]
Raza, S. K., Saleh, T., Shunwan, Z., Voyer, D., Durrani,
M., Matsushima, S., and V. P. Beeram, "YANG Data Model for
Segment Routing Policy", Work in Progress, Internet-Draft,
draft-ietf-spring-sr-policy-yang-04, 22 November 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-spring-
sr-policy-yang-04>.
[RFC4272] Murphy, S., "BGP Security Vulnerabilities Analysis",
RFC 4272, DOI 10.17487/RFC4272, January 2006,
<https://www.rfc-editor.org/info/rfc4272>.
[RFC4456] Bates, T., Chen, E., and R. Chandra, "BGP Route
Reflection: An Alternative to Full Mesh Internal BGP
(IBGP)", RFC 4456, DOI 10.17487/RFC4456, April 2006,
<https://www.rfc-editor.org/info/rfc4456>.
[RFC6952] Jethanandani, M., Patel, K., and L. Zheng, "Analysis of
BGP, LDP, PCEP, and MSDP Issues According to the Keying
and Authentication for Routing Protocols (KARP) Design
Guide", RFC 6952, DOI 10.17487/RFC6952, May 2013,
<https://www.rfc-editor.org/info/rfc6952>.
[RFC9552] Talaulikar, K., Ed., "Distribution of Link-State and
Traffic Engineering Information Using BGP", RFC 9552,
DOI 10.17487/RFC9552, December 2023,
<https://www.rfc-editor.org/info/rfc9552>.
[RFC9831] Talaulikar, K., Ed., Filsfils, C., Previdi, S., Mattes,
P., and D. Jain, "Segment Routing Segment Types Extensions
for BGP SR Policy", RFC 9831, DOI 10.17487/RFC9831, July
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,
March 2025, <https://datatracker.ietf.org/doc/html/draft-
ietf-idr-bgp-ls-sr-policy-16>.
[SR-POLICY-YANG]
Raza, K., Ed., Saleh, T., Shunwan, Z., Voyer, D., Durrani,
M., Matsushima, S., and V. Beeram, "YANG Data Model for
Segment Routing Policy", Work in Progress, Internet-Draft,
draft-ietf-spring-sr-policy-yang-04, 22 November 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-spring-
sr-policy-yang-04>.
Acknowledgments
The authors of this document would like to thank Shyam Sethuram, John
Scudder, Przemyslaw Krol, Alex id Bogdanov, Nandan Saha, Bruno
Decraene, Gurusiddesh Nidasesi, Kausik Majumdar, Zafar Ali, Swadesh
Agarwal, Jakob Heitz, Viral Patel, Peng Shaofu, Cheng Li, Martin
Vigoureux, John Scudder, Vincent Roca, Brian Haberman, Mohamed
Boucadair, Shunwan Zhuang, Andrew Alston, Jeffrey (Zhaohui) Zhang,
Nagendra Nainar, Rajesh Melarcode Venkateswaran, Nat Kao, Boris
Hassanov, Vincent Roca, Russ Housley, and Dan Romascanu for their
comments and review of this document. The authors would like to
thank Susan Hares for her detailed shepherd review that helped in
improving the document.
Contributors
Eric Rosen
Juniper Networks
United States of America
Email: erosen@juniper.net
Arjun Sreekantiah
Cisco Systems
United States of America
Email: asreekan@cisco.com
Acee Lindem
Cisco Systems
United States of America
Email: acee@cisco.com
Siva Sivabalan
Cisco Systems
United States of America
Email: msiva@cisco.com
Imtiyaz Mohammad
Arista Networks
India
Email: imtiyaz@arista.com
Gaurav Dawra
Cisco Systems
United States of America
Email: gdawra.ietf@gmail.com
Peng Shaofu
ZTE Corporation
China
Email: peng.shaofu@zte.com.cn
Steven Lin
Calix
United States of America
Email: steven.lin@calix.com
Authors' Addresses
Stefano Previdi
Huawei Technologies
Italy
Email: stefano@previdi.net
Clarence Filsfils
Cisco Systems
Brussels
Belgium
Email: cfilsfil@cisco.com
Ketan Talaulikar (editor)
Cisco Systems
India
Email: ketant.ietf@gmail.com
Paul Mattes
Microsoft
One Microsoft Way
Redmond, WA 98052
United States of America
Email: pamattes@microsoft.com
Dhanendra Jain
Google
Email: dhanendra.ietf@gmail.com