Network Working Group S. Previdi
Internet-Draft Individual
Intended status: Standards Track C. Filsfils
Expires: May 17, 2021 K. Talaulikar, Ed.
Cisco Systems
P. Mattes
Microsoft
E. Rosen
Juniper Networks
D. Jain
S. Lin
Google
November 13, 2020
Advertising Segment Routing Policies in BGP
draft-ietf-idr-segment-routing-te-policy-11
Abstract
This document defines a new BGP SAFI with a new NLRI in order to
advertise a candidate path of a Segment Routing (SR) Policy. An SR
Policy is a set of candidate paths, each consisting of one or more
segment lists. The headend of an SR Policy may learn multiple
candidate paths for an SR Policy. Candidate paths may be learned via
a number of different mechanisms, e.g., CLI, NetConf, PCEP, or BGP.
This document specifies the way in which BGP may be used to
distribute SR Policy candidate paths. New sub-TLVs for the Tunnel
Encapsulation Attribute are defined for signaling information about
these candidate paths.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on May 17, 2021.
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Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 5
2. SR Policy Encoding . . . . . . . . . . . . . . . . . . . . . 6
2.1. SR Policy SAFI and NLRI . . . . . . . . . . . . . . . . . 6
2.2. SR Policy and Tunnel Encapsulation Attribute . . . . . . 7
2.3. Remote Endpoint and Color . . . . . . . . . . . . . . . . 8
2.4. SR Policy Sub-TLVs . . . . . . . . . . . . . . . . . . . 9
2.4.1. Preference Sub-TLV . . . . . . . . . . . . . . . . . 9
2.4.2. Binding SID Sub-TLV . . . . . . . . . . . . . . . . . 10
2.4.3. SRv6 Binding SID Sub-TLV . . . . . . . . . . . . . . 11
2.4.4. Segment List Sub-TLV . . . . . . . . . . . . . . . . 13
2.4.5. Explicit NULL Label Policy Sub-TLV . . . . . . . . . 28
2.4.6. Policy Priority Sub-TLV . . . . . . . . . . . . . . . 29
2.4.7. Policy Candidate Path Name Sub-TLV . . . . . . . . . 30
2.4.8. Policy Name Sub-TLV . . . . . . . . . . . . . . . . . 31
3. Color Extended Community . . . . . . . . . . . . . . . . . . 31
4. SR Policy Operations . . . . . . . . . . . . . . . . . . . . 32
4.1. Advertisement of SR Policies . . . . . . . . . . . . . . 32
4.2. Reception of an SR Policy NLRI . . . . . . . . . . . . . 32
4.2.1. Acceptance of an SR Policy NLRI . . . . . . . . . . . 33
4.2.2. Usable SR Policy NLRI . . . . . . . . . . . . . . . . 33
4.2.3. Passing a usable SR Policy NLRI to the SRPM . . . . . 34
4.2.4. Propagation of an SR Policy . . . . . . . . . . . . . 34
5. Error Handling . . . . . . . . . . . . . . . . . . . . . . . 34
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 35
6.1. Existing Registry: Subsequent Address Family Identifiers
(SAFI) Parameters . . . . . . . . . . . . . . . . . . . . 36
6.2. Existing Registry: BGP Tunnel Encapsulation Attribute
Tunnel Types . . . . . . . . . . . . . . . . . . . . . . 36
6.3. Existing Registry: BGP Tunnel Encapsulation Attribute
sub-TLVs . . . . . . . . . . . . . . . . . . . . . . . . 36
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6.4. Existing Registry: Color Extended Community Flags . . . . 37
6.5. New Registry: SR Policy Segment List Sub-TLVs . . . . . . 37
6.6. New Registry: SR Policy Binding SID Flags . . . . . . . . 38
6.7. New Registry: SR Policy SRv6 Binding SID Flags . . . . . 38
6.8. New Registry: SR Policy Segment Flags . . . . . . . . . . 39
6.9. Guidance for Designated Experts . . . . . . . . . . . . . 39
7. Security Considerations . . . . . . . . . . . . . . . . . . . 39
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 40
9. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 40
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 41
10.1. Normative References . . . . . . . . . . . . . . . . . . 41
10.2. Informational References . . . . . . . . . . . . . . . . 42
Appendix A. Deprecated Segment Sub-TLVs . . . . . . . . . . . . 43
A.1. Type B-Deprecated: SID only, in the form of IPv6 address 43
A.2. Type I-Deprecated: IPv6 Node Address with optional SRv6
SID . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
A.3. Type J-Deprecated: IPv6 Address + Interface ID for local
and remote pair for SRv6 with optional SID . . . . . . . 44
A.4. Type K-Deprecated: IPv6 Local and Remote addresses for
SRv6 with optional SID . . . . . . . . . . . . . . . . . 46
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 46
1. Introduction
Segment Routing (SR) [RFC8402] allows a headend node to steer a
packet flow along any path. Intermediate per-flow states are
eliminated thanks to source routing.
The headend node is said to steer a flow into a SR Policy.
The header of a packet steered in an SR Policy is augmented with the
ordered list of segments associated with that SR Policy.
[I-D.ietf-spring-segment-routing-policy] details the concepts of SR
Policy and steering into an SR Policy. These apply equally to the
MPLS and IPv6 (known as SRv6) data plane instantiations of Segment
Routing with their respective representations of segments as SR-MPLS
SID and SRv6 SID as described in [RFC8402].
The SR Policy related functionality described in
[I-D.ietf-spring-segment-routing-policy] can be conceptually viewed
as being incorporated in an SR Policy Module (SRPM). Following is a
reminder of the high-level functionality of SRPM:
o Learning multiple candidate paths for an SR Policy via various
mechanisms (CLI, NetConf, PCEP or BGP).
o Selection of the best candidate path for an SR Policy.
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o Binding BSID to the selected candidate path of an SR Policy.
o Installation of the selected candidate path and its BSID in the
forwarding plane.
This document specifies the way to use BGP to distribute one or more
of the candidate paths of an SR Policy to the headend of that policy.
The document describes the functionality that provided by BGP and, as
appropriate, provides references for the functionality which is
outside the scope of BGP (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 the 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 defines a new BGP address family (SAFI). In UPDATE
messages of that address family, the NLRI identifies an SR Policy
Candidate Path, and the attributes encode the segment lists and other
details of that SR Policy Candidate Path.
While for simplicity we may write that BGP advertises an SR Policy,
it has 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 this document), PCEP, NETCONF or local policy
configuration.
Typically, a controller defines the set of policies and advertise
them to policy head-end routers (typically ingress routers). The
policy advertisement uses BGP extensions defined in this document.
The policy advertisement is, in most but not all of the cases,
tailored for a specific policy head-end. In this case the
advertisement may be sent on a BGP session to that head-end and not
propagated any further.
Alternatively, a router (i.e., a BGP egress router) advertises SR
Policies representing paths to itself. In this case, it is possible
to send the policy to each head-end over a BGP session to that head-
end, without requiring any further propagation of the policy.
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An SR Policy intended only for the receiver will, in most cases, not
traverse any Route Reflector (RR, [RFC4456]).
In some situations, it is undesirable for a controller or BGP egress
router to have a BGP session to each policy head-end. In these
situations, BGP Route Reflectors may be used to propagate the
advertisements, or it may be necessary for the advertisement to
propagate through a sequence of one or more AS. 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
head-end 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:
o A new Subsequent Address Family Identifier (SAFI) whose NLRI
identifies an SR Policy candidate path.
o A new Tunnel Type identifier for SR Policy, and a set of sub-TLVs
to be inserted into the Tunnel Encapsulation Attribute (as defined
in [I-D.ietf-idr-tunnel-encaps]) specifying segment lists of the
SR Policy candidate path, as well as other information about the
SR Policy.
o One or more IPv4 address format route-target extended community
([RFC4360]) attached to the SR Policy advertisement and that
indicates the intended head-end of such SR Policy advertisement.
o The Color Extended Community (as defined in
[I-D.ietf-idr-tunnel-encaps]) and used in order to steer traffic
into an SR Policy, as described in section 8.4 in
[I-D.ietf-spring-segment-routing-policy]. This document
(Section 3) modifies the format of the Color Extended Community by
using the two leftmost bits of the RESERVED 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.
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2. SR Policy Encoding
2.1. SR Policy SAFI and NLRI
A new SAFI is defined: the SR Policy SAFI with codepoint 73. The AFI
used MUST be IPv4(1) or IPv6(2).
The SR Policy SAFI uses a new NLRI defined as follows:
+------------------+
| NLRI Length | 1 octet
+------------------+
| Distinguisher | 4 octets
+------------------+
| Policy Color | 4 octets
+------------------+
| Endpoint | 4 or 16 octets
+------------------+
where:
o NLRI Length: 1 octet of length expressed in bits as defined in
[RFC4760]. When AFI = 1 value MUST be 96 and when AFI = 2 value
MUST be 192.
o 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) multiple candidate paths of
the same SR Policy.
o Policy Color: 4-octet value identifying (with the endpoint) the
policy. The color is used to match the color of the destination
prefixes to steer traffic into the SR Policy as specified in
[I-D.ietf-spring-segment-routing-policy].
o Endpoint: 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 color and endpoint are used to automate the steering of BGP
Payload prefixes on SR Policy as described in
[I-D.ietf-spring-segment-routing-policy].
The NLRI containing the SR Policy candidate path is carried in a BGP
UPDATE message [RFC4271] using BGP multi-protocol extensions
[RFC4760] with an AFI of 1 or 2 (IPv4 or IPv6) and with a SAFI of 73.
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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 the next-hop
length is 16, then it is a global IPv6 address; and 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 3 in [RFC4760].
It is important to note that any BGP speaker receiving a BGP message
with an SR Policy NLRI, will process it only if the NLRI is among the
best-paths 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 head-end, it is
RECOMMENDED that each NLRI 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
and BGP Router-ID) as described in section 2.4 of
[I-D.ietf-spring-segment-routing-policy]. The ASN would be the ASN
of origin and the BGP Router-ID is determined in the following order:
o From the Route Origin Community [RFC4360] if present and carrying
an IP Address
o As the BGP Originator ID [RFC4456] if present
o As the BGP Router-ID of the peer from which the update was
received as a last resort.
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 [I-D.ietf-idr-tunnel-encaps] using
a new Tunnel-Type called SR Policy Type with codepoint 15.
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The SR Policy Encoding structure is as follows:
SR Policy SAFI NLRI: <Distinguisher, Policy-Color, Endpoint>
Attributes:
Tunnel Encaps Attribute (23)
Tunnel Type: SR Policy
Binding SID
SRv6 Binding SID
Preference
Priority
Policy Name
Policy Candidate Path Name
Explicit NULL Label Policy (ENLP)
Segment List
Weight
Segment
Segment
...
...
where:
o SR Policy SAFI NLRI is defined in Section 2.1.
o Tunnel Encapsulation Attribute is defined in
[I-D.ietf-idr-tunnel-encaps].
o Tunnel-Type is set to 15.
o Preference, Binding SID, SRv6 Binding SID, Priority, Policy Name,
Policy Candidate Path Name, ENLP, Segment-List, Weight and Segment
sub-TLVs are defined in this document.
o Additional sub-TLVs may be defined in the future.
A Tunnel Encapsulation Attribute MUST NOT contain more than one TLV
of type "SR Policy".
2.3. Remote Endpoint and Color
The Remote Endpoint and Color sub-TLVs, as defined in
[I-D.ietf-idr-tunnel-encaps], MAY also be present in the SR Policy
encodings.
The Remote Endpoint and Color Sub-TLVs of the Tunnel Encapsulation
Attribute are not used for SR Policy encodings and therefore their
value is irrelevant in the context of the SR Policy SAFI NLRI. If
present, the Remote Endpoint sub-TLV and the Color sub-TLV MUST be
ignored by the BGP speaker.
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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 the new sub-TLVs of the BGP Tunnel Encapsulation Attribute
[I-D.ietf-idr-tunnel-encaps] being defined in this section.
Weight and Segment are sub-TLVs of the new Segment-List sub-TLV
mentioned above.
None of the sub-TLVs defined in the following sub-sections have any
effect on the BGP best-path selection or propagation procedures.
These sub-TLVs are not used by BGP and are instead passed on to SRPM
as SR Policy Candidate Path information for further processing
described in [I-D.ietf-spring-segment-routing-policy] .
2.4.1. Preference Sub-TLV
The Preference sub-TLV is used to carry the preference of the SR
Policy candidate path. The contents of this sub-TLV are used by the
SRPM as described in section 2.7 in
[I-D.ietf-spring-segment-routing-policy].
The Preference sub-TLV is optional and it MUST NOT appear more than
once in the SR Policy encoding.
The Preference sub-TLV has 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) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
o Type: 12
o Length: 6.
o Flags: 1 octet of flags. None are defined at this stage. Flags
SHOULD be set to zero on transmission and MUST be ignored on
receipt.
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o RESERVED: 1 octet of reserved bits. SHOULD be set to zero on
transmission and MUST be ignored on receipt.
o Preference: a 4-octet value.
2.4.2. Binding SID Sub-TLV
The Binding SID sub-TLV is used to signal the binding SID related
information of the SR Policy candidate path. The contents of this
sub-TLV are used by the SRPM as described in section 6 in
[I-D.ietf-spring-segment-routing-policy].
The Binding SID sub-TLV is optional and 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
choice of its SRv6 Endpoint Behavior
[I-D.ietf-spring-srv6-network-programming] to be instantiated is left
to the headend node. It is RECOMMENDED that the SRv6 Binding SID
sub-TLV defined in Section 2.4.3, that enables the specification of
the SRv6 Endpoint Behavior, be used for signaling of an SRv6 Binding
SID for an SR Policy candidate path.
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) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
o Type: 13
o Length: specifies the length of the value field not including Type
and Length fields. Can be 2 or 6 or 18.
o Flags: 1 octet of flags. Following flags are defined in the new
registry "SR Policy Binding SID Flags" as described in
Section 6.6:
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|S|I| |
+-+-+-+-+-+-+-+-+
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where:
* S-Flag: This flag encodes the "Specified-BSID-only" behavior.
It is used by SRPM as described in section 6.2.3 in
[I-D.ietf-spring-segment-routing-policy].
* I-Flag: This flag encodes the "Drop Upon Invalid" behavior. It
is used by SRPM as described in section 8.2 in
[I-D.ietf-spring-segment-routing-policy].
* Unused bits in the Flag octet SHOULD be set to zero upon
transmission and MUST be ignored upon receipt.
o RESERVED: 1 octet of reserved bits. SHOULD be set to zero on
transmission and MUST be ignored on receipt.
o Binding SID: if length is 2, then no Binding SID is present. If
length is 6 then the Binding SID is encoded in 4 octets using the
format below. TC, S, TTL (Total of 12 bits) are RESERVED and
SHOULD 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
If length is 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 the SR Policy candidate path. It enables the
specification of the SRv6 Endpoint Behavior
[I-D.ietf-spring-srv6-network-programming] to be instantiated on the
headend node. The contents of this sub-TLV are used by the SRPM as
described in section 6 in [I-D.ietf-spring-segment-routing-policy].
The SRv6 Binding SID sub-TLV is optional. More than one SRv6 Binding
SIDs MAY be signalled 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:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Flags | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SRv6 Binding SID (16 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// SRv6 Endpoint Behavior and SID Structure (optional) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
o Type: TBD
o Length is variable
o Flags: 1 octet of flags. Following flags are defined in the new
registry "SR Policy Binding SID Flags" as described in
Section 6.7:
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|S|I|B| |
+-+-+-+-+-+-+-+-+
where:
* S-Flag: This flag encodes the "Specified-BSID-only" behavior.
It is used by SRPM as described in section 6.2.3 in
[I-D.ietf-spring-segment-routing-policy].
* I-Flag: This flag encodes the "Drop Upon Invalid" behavior. It
is used by SRPM as described in section 8.2 in
[I-D.ietf-spring-segment-routing-policy].
* B-Flag: This flag, when set, indicates the presence of the SRv6
Endpoint Behavior and SID Structure encoding specified in
Section 2.4.4.2.13.
* Unused bits in the Flag octet SHOULD be set to zero upon
transmission and MUST be ignored upon receipt.
o RESERVED: 1 octet of reserved bits. SHOULD be set to zero on
transmission and MUST be ignored on receipt.
o SRv6 Binding SID: Contains a 16-octet SRv6 SID.
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o SRv6 Endpoint Behavior and SID Structure: Optional, as defined in
Section 2.4.4.2.13.
2.4.4. Segment List Sub-TLV
The Segment List sub-TLV encodes a single explicit path towards the
endpoint as described in section 5.1 in
[I-D.ietf-spring-segment-routing-policy]. 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 length due to large
number of segments. Therefore a 2-octet length is required.
According to [I-D.ietf-idr-tunnel-encaps], the first bit of the sub-
TLV codepoint 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, each
sub-TLV encoding a Segment List, does not matter.
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 //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
o Type: 128.
o Length: the total length (not including the Type and Length
fields) of the sub-TLVs encoded within the Segment List sub-TLV.
o RESERVED: 1 octet of reserved bits. SHOULD be set to zero on
transmission and MUST be ignored on receipt.
o sub-TLVs currently defined:
* An optional single Weight sub-TLV.
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* Zero or more Segment 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 5 in [I-D.ietf-spring-segment-routing-policy].
2.4.4.1. Weight Sub-TLV
The Weight sub-TLV specifies the weight associated to a given segment
list. The contents of this sub-TLV are used only by the SRPM as
described in section 2.11 in
[I-D.ietf-spring-segment-routing-policy].
The Weight sub-TLV is optional and 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
o Type: 9.
o Length: 6
o Flags: 1 octet of flags. None are defined at this stage. Flags
SHOULD be set to zero on transmission and MUST be ignored on
receipt.
o RESERVED: 1 octet of reserved bits. SHOULD be set to zero on
transmission and MUST be ignored on receipt.
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 4 in [I-D.ietf-spring-segment-routing-policy].
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The Segment sub-TLVs are optional and MAY appear multiple times in
the Segment List sub-TLV.
[I-D.ietf-spring-segment-routing-policy] defines several Segment
Types:
Type A: SID only, in the form of MPLS Label
Type B: SID only, in the form of IPv6 address
Type C: IPv4 Node Address with optional SID
Type D: IPv6 Node Address with optional SID for SR MPLS
Type E: IPv4 Address and index with optional SID
Type F: IPv4 Local and Remote addresses with optional SID
Type G: IPv6 Address and index for local and remote pair with optional
SID for SR MPLS
Type H: IPv6 Local and Remote addresses with optional SID for SR MPLS
Type I: IPv6 Node Address with optional SID for SRv6
Type J: IPv6 Address and index for local and remote pair with optional
SID for SRv6
Type K: IPv6 Local and Remote addresses for SRv6
The follow sub-sections specify the sub-TLV used for encoding each of
these Segment Types.
2.4.4.2.1. Type A: SID only, in the form of MPLS Label
The Type A Segment Sub-TLV encodes a single SR-MPLS 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
o Type: 1.
o Length is 6.
o Flags: 1 octet of flags as defined in Section 2.4.4.2.12.
o RESERVED: 1 octet of reserved bits. SHOULD be set to zero on
transmission and MUST be ignored on receipt.
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o Label: 20 bits of label value.
o TC: 3 bits of traffic class.
o S: 1 bit of bottom-of-stack.
o TTL: 1 octet of TTL.
The following applies to the Type-1 Segment sub-TLV:
o The S bit SHOULD be zero upon transmission, and MUST be ignored
upon reception.
o If the originator wants the receiver to choose the TC value, it
sets the TC field to zero.
o If the originator wants the receiver to choose the TTL value, it
sets the TTL field to 255.
o If the originator wants to recommend a value for these fields, it
puts those values in the TC and/or TTL fields.
o 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. Type B: SID only, in the form of IPv6 address
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) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
o Type: 13.
o Length is variable.
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o Flags: 1 octet of flags as defined in Section 2.4.4.2.12.
o RESERVED: 1 octet of reserved bits. SHOULD be set to zero on
transmission and MUST be ignored on receipt.
o SRv6 SID: 16 octets of IPv6 address.
o SRv6 Endpoint Behavior and SID Structure: Optional, as defined in
Section 2.4.4.2.13.
The TLV 2 defined for advertisement of Segment Type B in the earlier
versions of this document has been deprecated to avoid backward
compatibility issues (refer Appendix A for details).
2.4.4.2.3. Type C: IPv4 Node Address with optional SID
The Type C Segment Sub-TLV encodes an IPv4 node address, SR Algorithm
and an optional SR-MPLS 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 | SR Algorithm |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 Node Address (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SR-MPLS SID (optional, 4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
o Type: 3.
o Length is 10 when the SR-MPLS SID is present else is 6.
o Flags: 1 octet of flags as defined in Section 2.4.4.2.12.
o SR Algorithm: 1 octet specifying SR Algorithm as described in
section 3.1.1 in [RFC8402], when A-Flag as defined in
Section 2.4.4.2.12 is present. SR Algorithm is used by SRPM as
described in section 4 in
[I-D.ietf-spring-segment-routing-policy]. When A-Flag is not
encoded, this field SHOULD be set to zero on transmission and MUST
be ignored on receipt.
o IPv4 Node Address: a 4 octet IPv4 address representing a node.
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o SR-MPLS SID: optional, 4 octet field containing label, TC, S and
TTL as defined in Section 2.4.4.2.1.
2.4.4.2.4. Type D: IPv6 Node Address with optional SID for SR MPLS
The Type D Segment Sub-TLV encodes an IPv6 node address, SR Algorithm
and an optional SR-MPLS 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 | SR Algorithm |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// IPv6 Node Address (16 octets) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SR-MPLS SID (optional, 4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
o Type: 4
o Length is 22 when the SR-MPLS SID is present else is 18.
o Flags: 1 octet of flags as defined in Section 2.4.4.2.12.
o SR Algorithm: 1 octet specifying SR Algorithm as described in
section 3.1.1 in [RFC8402], when A-Flag as defined in
Section 2.4.4.2.12 is present. SR Algorithm is used by SRPM as
described in section 4 in
[I-D.ietf-spring-segment-routing-policy]. When A-Flag is not
encoded, this field SHOULD be set to zero on transmission and MUST
be ignored on receipt.
o IPv6 Node Address: a 16 octet IPv6 address representing a node.
o SR-MPLS SID: optional, 4 octet field containing label, TC, S and
TTL as defined in Section 2.4.4.2.1.
2.4.4.2.5. Type E: IPv4 Address + Local Interface ID with optional SID
The Type E Segment Sub-TLV encodes an IPv4 node address, a local
interface Identifier (Local Interface ID) and an optional SR-MPLS
SID. The format is as follows:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Flags | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Local Interface ID (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 Node Address (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SR-MPLS SID (optional, 4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
o Type: 5.
o Length is 14 when the SR-MPLS SID is present else is 10.
o Flags: 1 octet of flags as defined in Section 2.4.4.2.12.
o RESERVED: 1 octet of reserved bits. SHOULD be set to zero on
transmission and MUST be ignored on receipt.
o Local Interface ID: 4 octets of interface index as defined in
[RFC8664].
o IPv4 Node Address: a 4 octet IPv4 address representing a node.
o SR-MPLS SID: optional, 4 octet field containing label, TC, S and
TTL as defined in Section 2.4.4.2.1.
2.4.4.2.6. Type F: IPv4 Local and Remote addresses with optional SID
The Type F Segment Sub-TLV encodes an adjacency local address, an
adjacency remote address and an optional SR-MPLS SID. The format is
as follows:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Flags | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Local IPv4 Address (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Remote IPv4 Address (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SR-MPLS SID (optional, 4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
o Type: 6.
o Length is 14 when the SR-MPLS SID is present else is 10.
o Flags: 1 octet of flags as defined in Section 2.4.4.2.12.
o RESERVED: 1 octet of reserved bits. SHOULD be set to zero on
transmission and MUST be ignored on receipt.
o Local IPv4 Address: a 4 octet IPv4 address.
o Remote IPv4 Address: a 4 octet IPv4 address.
o SR-MPLS SID: optional, 4 octet field containing label, TC, S and
TTL as defined in Section 2.4.4.2.1.
2.4.4.2.7. Type G: IPv6 Address + Interface ID for local and remote
pair with optional SID for SR MPLS
The Type G Segment Sub-TLV encodes an IPv6 Link Local adjacency with
IPv6 local node address, a local interface identifier (Local
Interface ID), IPv6 remote node address , a remote interface
identifier (Remote Interface ID) and an optional SR-MPLS SID. The
format is as follows:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Flags | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Local Interface ID (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// IPv6 Local Node Address (16 octets) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Remote Interface ID (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// IPv6 Remote Node Address (16 octets) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SR-MPLS SID (optional, 4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
o Type: 7
o Length is 46 when the SR-MPLS SID is present else is 42.
o Flags: 1 octet of flags as defined in Section 2.4.4.2.12.
o RESERVED: 1 octet of reserved bits. SHOULD be set to zero on
transmission and MUST be ignored on receipt.
o Local Interface ID: 4 octets of interface index as defined in
[RFC8664].
o IPv6 Local Node Address: a 16 octet IPv6 address.
o Remote Interface ID: 4 octets of interface index as defined in
[RFC8664]. The value MAY be set to zero when the local node
address and interface identifiers are sufficient to describe the
link.
o IPv6 Remote Node Address: a 16 octet IPv6 address. The value MAY
be set to zero when the local node address and interface
identifiers are sufficient to describe the link.
o SR-MPLS SID: optional, 4 octet field containing label, TC, S and
TTL as defined in Section 2.4.4.2.1.
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2.4.4.2.8. Type H: IPv6 Local and Remote addresses with optional SID
for SR MPLS
The Type H Segment Sub-TLV encodes an adjacency local address, an
adjacency remote address and an optional SR-MPLS 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Local IPv6 Address (16 octets) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Remote IPv6 Address (16 octets) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SR-MPLS SID (optional, 4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
o Type: 8
o Length is 38 when the SR-MPLS SID is present else is 34.
o Flags: 1 octet of flags as defined in Section 2.4.4.2.12.
o RESERVED: 1 octet of reserved bits. SHOULD be set to zero on
transmission and MUST be ignored on receipt.
o Local IPv6 Address: a 16 octet IPv6 address.
o Remote IPv6 Address: a 16 octet IPv6 address.
o SR-MPLS SID: optional, 4 octet field containing label, TC, S and
TTL as defined in Section 2.4.4.2.1.
2.4.4.2.9. Type I: IPv6 Node Address with optional SRv6 SID
The Type I Segment Sub-TLV encodes an IPv6 node address, SR Algorithm
and an optional SRv6 SID. The format is as follows:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Flags | SR Algorithm |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// IPv6 Node Address (16 octets) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// SRv6 SID (optional, 16 octets) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// SRv6 Endpoint Behavior and SID Structure (optional) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
o Type: 14
o Length is variable.
o Flags: 1 octet of flags as defined in Section 2.4.4.2.12.
o SR Algorithm: 1 octet specifying SR Algorithm as described in
section 3.1.1 in [RFC8402], when A-Flag as defined in
Section 2.4.4.2.12 is present. SR Algorithm is used by SRPM as
described in section 4 in
[I-D.ietf-spring-segment-routing-policy]. When A-Flag is not
encoded, this field SHOULD be set to zero on transmission and MUST
be ignored on receipt.
o IPv6 Node Address: a 16 octet IPv6 address.
o SRv6 SID: optional, 16 octet IPv6 address.
o SRv6 Endpoint Behavior and SID Structure: Optional, as defined in
Section 2.4.4.2.13.
The TLV 10 defined for advertisement of Segment Type I in the earlier
versions of this document has been deprecated to avoid backward
compatibility issues (refer Appendix A for details).
2.4.4.2.10. Type J: IPv6 Address + Interface ID for local and remote
pair for SRv6 with optional SID
The Type J Segment Sub-TLV encodes an IPv6 Link Local adjacency with
local node address, a local interface identifier (Local Interface
ID), remote IPv6 node address, a remote interface identifier (Remote
Interface ID) and an optional SRv6 SID. The format is as follows:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Flags | SR Algorithm |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Local Interface ID (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// IPv6 Local Node Address (16 octets) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Remote Interface ID (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// IPv6 Remote Node Address (16 octets) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// SRv6 SID (optional, 16 octets) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// SRv6 Endpoint Behavior and SID Structure (optional) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
o Type: 15
o Length is variable.
o Flags: 1 octet of flags as defined in Section 2.4.4.2.12.
o SR Algorithm: 1 octet specifying SR Algorithm as described in
section 3.1.1 in [RFC8402], when A-Flag as defined in
Section 2.4.4.2.12 is present. SR Algorithm is used by SRPM as
described in section 4 in
[I-D.ietf-spring-segment-routing-policy]. When A-Flag is not
encoded, this field SHOULD be set to zero on transmission and MUST
be ignored on receipt.
o Local Interface ID: 4 octets of interface index as defined in
[RFC8664].
o IPv6 Local Node Address: a 16 octet IPv6 address.
o Remote Interface ID: 4 octets of interface index as defined in
[RFC8664]. The value MAY be set to zero when the local node
address and interface identifiers are sufficient to describe the
link.
o IPv6 Remote Node Address: a 16 octet IPv6 address. The value MAY
be set to zero when the local node address and interface
identifiers are sufficient to describe the link.
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o SRv6 SID: optional, 16 octet IPv6 address.
o SRv6 Endpoint Behavior and SID Structure: Optional, as defined in
Section 2.4.4.2.13.
The TLV 11 defined for advertisement of Segment Type J in the earlier
versions of this document has been deprecated to avoid backward
compatibility issues (refer Appendix A for details).
2.4.4.2.11. Type K: IPv6 Local and Remote addresses for SRv6 with
optional SID
The Type K Segment Sub-TLV encodes an adjacency local address, an
adjacency remote address and an optional 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 | SR Algorithm |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Local IPv6 Address (16 octets) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Remote IPv6 Address (16 octets) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// SRv6 SID (optional, 16 octets) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// SRv6 Endpoint Behavior and SID Structure (optional) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
o Type: 16
o Length is variable.
o Flags: 1 octet of flags as defined in Section 2.4.4.2.12.
o SR Algorithm: 1 octet specifying SR Algorithm as described in
section 3.1.1 in [RFC8402], when A-Flag as defined in
Section 2.4.4.2.12 is present. SR Algorithm is used by SRPM as
described in section 4 in
[I-D.ietf-spring-segment-routing-policy]. When A-Flag is not
encoded, this field SHOULD be set to zero on transmission and MUST
be ignored on receipt.
o Local IPv6 Address: a 16 octet IPv6 address.
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o Remote IPv6 Address: a 16 octet IPv6 address.
o SRv6 SID: optional, 16 octet IPv6 address.
o SRv6 Endpoint Behavior and SID Structure: Optional, as defined in
Section 2.4.4.2.13.
The TLV 12 defined for advertisement of Segment Type K in the earlier
versions of this document has been deprecated to avoid backward
compatibility issues (refer Appendix A for details).
2.4.4.2.12. Segment Flags
The Segment Types sub-TLVs described above MAY contain following
flags in the "Flags" field defined in Section 6.8:
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|V|A|S|B| |
+-+-+-+-+-+-+-+-+
where:
V-Flag: This flag, when set, is used by SRPM for the purpose of
"SID verification" as described in Section 5.1 in
[I-D.ietf-spring-segment-routing-policy].
A-Flag: This flag, when set, indicates the presence of SR
Algorithm id in the "SR Algorithm" field applicable to various
Segment Types. SR Algorithm is used by SRPM as described in
section 4 in [I-D.ietf-spring-segment-routing-policy].
S-Flag: This flag, when set, indicates the presence of the SR-MPLS
or SRv6 SID depending on the segment type.
B-Flag: This flag, when set, indicates the presence of the SRv6
Endpoint Behavior and SID Structure encoding specified in
Section 2.4.4.2.13.
Unused bits in the Flag octet SHOULD be set to zero upon
transmission and MUST be ignored upon receipt.
The following applies to the Segment Flags:
o V-Flag is applicable to all Segment Types.
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o A-Flag is applicable to Segment Types C, D, I, J and K. If A-Flag
appears with Segment Types A, B, E, F, G and H, it MUST be
ignored.
o S-Flag is applicable to Segment Types C, D, E, F, G, H, I, J and
K. If S-Flag appears with Segment Types A or B, it MUST be
ignored.
o B-Flag is applicable to Segment Types B, I, J and K. If B-Flag
appears with Segment Types A, C, D, E, F, G and H, it MUST be
ignored.
2.4.4.2.13. SRv6 SID Endpoint Behavior and Structure
The Segment Types sub-TLVs described above MAY contain the SRv6
Endpoint Behavior and SID Structure
[I-D.ietf-spring-srv6-network-programming] encoding as described
below:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Endpoint Behavior | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LB Length | LN Length | Fun. Length | Arg. Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
Endpoint Behavior: 2 octets. The SRv6 Endpoint Behavior code
point for this SRv6 SID as defined in section 9.2 of
[I-D.ietf-spring-srv6-network-programming]. When set with the
value 0, the choice of SRv6 Endpoint Behavior is left to the
headend.
Reserved: 2 octet of reserved bits. SHOULD 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.
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2.4.5. Explicit NULL Label Policy Sub-TLV
In order to steer an unlabeled IP packet into an SR policy, it is
necessary to create a label stack for that packet, and to push one or
more labels onto that stack.
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 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 4.1 in [I-D.ietf-spring-segment-routing-policy].
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 |
+-+-+-+-+-+-+-+-+
Where:
Type: 14.
Length: 3.
Flags: 1 octet of flags. None are defined at this stage. Flags
SHOULD be set to zero on transmission and MUST be ignored on
receipt.
RESERVED: 1 octet of reserved bits. SHOULD 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. This field has one of the
following values:
0: Reserved.
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1: Push an IPv4 Explicit NULL label on an unlabeled IPv4
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, 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, and push an IPv6 Explicit NULL label on an unlabeled
IPv6 packet.
4: Do not push an Explicit NULL label.
5 - 255: Reserved.
The ENLP reserved values may be used for future extensions and
implementations SHOULD ignore the ENLP Sub-TLV with these values.
The behavior signaled in this Sub-TLV MAY be overridden by local
configuration. The section 4.1 of
[I-D.ietf-spring-segment-routing-policy] draft describes the
behavior on the headend for handling of 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 upon topological change.
The contents of this sub-TLV are used by the SRPM as described in
section 2.11 in [I-D.ietf-spring-segment-routing-policy].
The Priority sub-TLV is optional and it MUST NOT appear more than
once in the SR Policy encoding.
The Priority sub-TLV has 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Where:
Type: 15
Length: 2.
Priority: a 1-octet value.
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RESERVED: 1 octet of reserved bits. SHOULD 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 Policy Candidate Path Name sub-TLV is described in section
2.6 in [I-D.ietf-spring-segment-routing-policy].
The Policy Candidate Path Name sub-TLV may exceed 255 bytes length
due to long name. Therefore a 2-octet length is required. According
to [I-D.ietf-idr-tunnel-encaps], the first bit of the sub-TLV
codepoint defines the size of the length field. Therefore, for the
Policy Candidate Path Name sub-TLV a code point of 128 or higher is
used.
It is RECOMMENDED that the size of the symbolic name be limited to
255 bytes. Implementations MAY choose to truncate long names to 255
bytes when signaling via BGP.
The Policy Candidate Path Name sub-TLV is optional and it MUST NOT
appear more than once in the SR Policy encoding.
The Policy Candidate Path Name sub-TLV has 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 //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Where:
Type: 129.
Length: Variable.
RESERVED: 1 octet of reserved bits. SHOULD 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 as specified in section
2.6 of [I-D.ietf-spring-segment-routing-policy].
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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 Policy Name sub-TLV is described in section 2.1 of
[I-D.ietf-spring-segment-routing-policy].
The Policy Name sub-TLV may exceed 255 bytes length due to long
policy name. Therefore a 2-octet length is required. According to
[I-D.ietf-idr-tunnel-encaps], the first bit of the sub-TLV codepoint
defines the size of the length field. Therefore, for the Policy Name
sub-TLV a code point of 128 or higher is used.
The Policy Name sub-TLV is optional and it MUST NOT appear more than
once in the SR Policy encoding.
The Policy Name sub-TLV has 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 //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Where:
Type: TBD
Length: Variable.
RESERVED: 1 octet of reserved bits. SHOULD be set to zero on
transmission and MUST be ignored on receipt.
Policy Name: Symbolic name for the policy. It SHOULD be a string
of printable ASCII characters, without a NULL terminator.
3. Color Extended Community
The Color Extended Community as defined in
[I-D.ietf-idr-tunnel-encaps] is used to steer traffic into a policy.
When the Color Extended Community is used for the purpose of steering
the traffic into an SR Policy, two bits from the Flags field (as
defined in [I-D.ietf-idr-tunnel-encaps]) are used as follows:
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1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|C O| RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where CO bits are defined as the "Color-Only" bits.
[I-D.ietf-spring-segment-routing-policy] defines the influence of
these bits on the automated steering of BGP Payload traffic onto SR
Policies.
4. SR Policy Operations
As described in this document, 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 but its installation and use is outside the
scope of BGP. The details of SR Policy installation and use are
specified in [I-D.ietf-spring-segment-routing-policy].
4.1. Advertisement of SR Policies
Typically, but not limited to, an SR Policy is computed by a
controller or a 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 content when these SR policies are
intended for different head-ends.
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-target SHOULD be attached to the
advertisement, where each route-target identifies one or more
intended head-ends 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
case, the NO_ADVERTISE community MUST be attached to the SR Policy
update.
4.2. Reception of an SR Policy NLRI
On reception of an SR Policy NLRI, a BGP speaker first determines if
it is acceptable and then if it is usable.
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4.2.1. Acceptance of an SR Policy NLRI
When a BGP speaker receives an SR Policy NLRI from a neighbor it MUST
first determine if it's acceptable. The following rules apply in
addition to the validation described in Section 5:
o The SR Policy NLRI MUST include a distinguisher, color and
endpoint field which implies that the length of the NLRI MUST be
either 12 or 24 octets (depending on the address family of the
endpoint).
o The SR Policy update MUST have either the NO_ADVERTISE community
or at least one route-target extended community in IPv4-address
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 malformed.
o The Tunnel Encapsulation Attribute MUST be attached to the BGP
Update and MUST have a Tunnel Type TLV set to SR Policy (codepoint
is 15).
A router that receives an SR Policy update that is not valid
according to these criteria MUST treat the update as malformed and
the SR Policy candidate path MUST NOT be passed to the SRPM.
4.2.2. Usable SR Policy NLRI
A SR Policy update that has been determined to be acceptable is
further evaluated for its usability by the receiving node.
An SR Policy NLRI update without any route-target extended community
but having 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. 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 acceptable, 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.
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4.2.3. Passing a usable SR Policy NLRI to the SRPM
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 2.4 in
[I-D.ietf-spring-segment-routing-policy].
When an update for an SR Policy NLRI results in it's becoming
unusable, BGP MUST delete it's corresponding SR Policy candidate path
from the SRPM.
The SRPM applies the rules defined in section 2 in
[I-D.ietf-spring-segment-routing-policy] to determine whether the SR
Policy candidate path is valid and to select the best candidate path
among the valid ones for a given SR Policy.
4.2.4. Propagation of an SR Policy
SR Policy NLRIs that have been determined acceptable and valid can be
evaluated for propagation, even the ones that are not usable.
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 neighbor. An implementation MAY provide an explicit
configuration to override this and enable propagation of acceptable
SR Policy NLRIs to specific EBGP neighbors.
A BGP node advertises a received SR Policy NLRI to its IBGP neighbors
according to normal IBGP propagation rules.
By default, a BGP node receiving an SR Policy NLRI SHOULD NOT remove
route-target extended community before propagation. An
implementation MAY provide support for configuration to filter and/or
remove route-target extended community before propagation.
5. Error Handling
This section describes the error handling actions, as described in
[RFC7606], that are to be performed for handling of BGP update
messages for BGP SR Policy SAFI.
A BGP Speaker MUST perform the following syntactic validation of the
SR Policy NLRI to determine if it is malformed. This includes the
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validation of length of each NLRI and the total length of the
MP_REACH_NLRI and MP_UNREACH_NLRI attributes.
When the error determined allows for the router to skip the malformed
NLRI(s) and continue processing of the rest of the update message,
then it MUST handle such malformed NLRIs 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
encoding errors), then the router SHOULD handle such malformed NLRIs
as 'AFI/SAFI disable' when other AFI/SAFI besides SR Policy are being
advertised over the same session. Alternately, the router MUST
perform 'session reset' when the session is only being used for SR
Policy or when it '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 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 [I-D.ietf-idr-tunnel-encaps] 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 of all
valid TLVs/sub-TLVs) is not usable.
An SR Policy update that is determined to be not acceptable, and
therefore malformed, based on 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. A BGP
implementation MUST NOT perform semantic verification of such fields
nor consider the SR Policy update to be invalid or not acceptable/
usable on the basis of such a validation.
An implementation SHOULD log an error for any errors found during the
above validation for further analysis.
6. IANA Considerations
This document requests codepoint allocations for new TLVs/sub-TLVs in
following existing registries:
o Subsequent Address Family Identifiers (SAFI) Parameters registry
o BGP Tunnel Encapsulation Attribute Tunnel Types registry under the
BGP Parameters registry
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o BGP Tunnel Encapsulation Attribute sub-TLVs registry under the BGP
Parameters registry
o Color Extended Community Flags registry under the BGP Extended
Communities registry
This document also requests creation of the following new registries:
o SR Policy Segment List Sub-TLVs under the BGP Parameters registry
o SR Policy Binding SID Flags under the BGP Parameters registry
o SR Policy Segment Flags under the BGP Parameters registry
6.1. Existing Registry: Subsequent Address Family Identifiers (SAFI)
Parameters
This document defines a new SAFI in the registry "Subsequent Address
Family Identifiers (SAFI) Parameters" that has been assigned a
codepoint by IANA as follows:
Codepoint Description Reference
-----------------------------------------------
73 SR Policy SAFI This document
6.2. Existing Registry: BGP Tunnel Encapsulation Attribute Tunnel Types
This document defines a new Tunnel-Type in the registry "BGP Tunnel
Encapsulation Attribute Tunnel Types" that has been assigned a
codepoint by IANA as follows:
Codepoint Description Reference
--------------------------------------------------
15 SR Policy Type This document
6.3. Existing Registry: BGP Tunnel Encapsulation Attribute sub-TLVs
This document defines new sub-TLVs in the registry "BGP Tunnel
Encapsulation Attribute sub-TLVs" that has been assigned codepoints
by IANA as follows:
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Codepoint Description Reference
------------------------------------------------------
12 Preference sub-TLV This document
13 Binding SID sub-TLV This document
14 ENLP sub-TLV This document
15 Priority sub-TLV This document
TBD SRv6 Binding SID sub-TLV This document
128 Segment List sub-TLV This document
129 Policy CP Name sub-TLV This document
TBD Policy Name sub-TLV This document
6.4. Existing Registry: Color Extended Community Flags
This document requests allocations in the registry called "Color
Extended Community Flags" under the "BGP Tunnel Encapsulation
Parameters" grouping.
Following bits are to be allocated:
Bit
Position Description Reference
------------------------------------------------------------------
0-1 Color-only bits This document
6.5. New Registry: SR Policy Segment List Sub-TLVs
This document requests creation of a new registry called "SR Policy
Segment List Sub-TLVs". The allocation policy of this registry is
"Specification Required" according to [RFC8126].
Following initial Sub-TLV codepoints are assigned by this document:
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Value Description Reference
------------------------------------------------------------------------
1 Type A MPLS SID sub-TLV This document
2 Deprecated This document
3 Type C IPv4 Node and SID sub-TLV This document
4 Type D IPv6 Node and SID for SR-MPLS sub-TLV This document
5 Type E IPv4 Node, index and SID sub-TLV This document
6 Type F IPv4 Local/Remote addresses and SID sub-TLV This document
7 Type G IPv6 Node, index for remote and local pair This document
and SID for SR-MPLS sub-TLV
8 Type H IPv6 Local/Remote addresses and SID sub-TLV This document
9 Weight sub-TLV This document
10 Deprecated This document
11 Deprecated This document
12 Deprecated This document
13 Type B SRv6 SID sub-TLV This document
14 Type I IPv6 Node and SID for SRv6 sub-TLV This document
15 Type J IPv6 Node, index for remote and local pair This document
and SID for SRv6 sub-TLV
16 Type K IPv6 Local/Remote addresses and SID for This document
SRv6 sub-TLV
6.6. New Registry: SR Policy Binding SID Flags
This document requests creation of a new registry called "SR Policy
Binding SID Flags". The allocation policy of this registry is
"Specification Required" according to [RFC8126].
Following flags are defined:
Bit Description Reference
-----------------------------------------------------------------
0 Specified-BSID-Only Flag (S-Flag) This document
1 Drop Upon Invalid Flag (I-Flag) This document
2-7 Unassigned
6.7. New Registry: SR Policy SRv6 Binding SID Flags
This document requests creation of a new registry called "SR Policy
SRv6 Binding SID Flags". The allocation policy of this registry is
"Specification Required" according to [RFC8126].
Following flags are defined:
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Bit Description Reference
-----------------------------------------------------------------
0 Specified-BSID-Only Flag (S-Flag) This document
1 Drop Upon Invalid Flag (I-Flag) This document
2 SRv6 Endpoint Behavior &
SID Structure Flag (B-Flag) This document
3-7 Unassigned
6.8. New Registry: SR Policy Segment Flags
This document requests creation of a new registry called "SR Policy
Segment Flags". The allocation policy of this registry is
"Specification Required" according to [RFC8126].
Following Flags are defined:
Bit Description Reference
------------------------------------------------------------------
0 Segment Verification Flag (V-Flag) This document
1 SR Algorithm Flag (A-Flag) This document
2 SID Specified Flag (S-Flag) This document
3 SRv6 Endpoint Behavior &
SID Structure Flag (B-Flag) This document
4-7 Unassigned
6.9. Guidance for Designated Experts
In all cases of review by the Designated Expert (DE) described here,
the DE is expected to ascertain the existence of suitable
documentation (a specification) as described in [RFC8126]. The DE is
also expected to check the clarity of purpose and use of the
requested code points. Additionally, the DE must verify that any
request for one of these code points has been made available for
review and comment within the IETF: the DE will post the request to
the IDR Working Group mailing list (or a successor mailing list
designated by the IESG). If the request comes from within the IETF,
it should be documented in an Internet-Draft. Lastly, the DE must
ensure that any other request for a code point does not conflict with
work that is active or already published within the IETF.
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.
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The BGP SR Policy extensions specified in this document enable
traffic engineering and service programming use-cases within the SR
domain as described in [I-D.ietf-spring-segment-routing-policy] . SR
operates within a trusted SR domain [RFC8402] and its security
considerations also apply to BGP sessions when carrying SR Policy
information. The SR Policies distributed by BGP are expected to be
used entirely within this trusted SR domain i.e. within a single AS
or between multiple AS/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 other than SR Policy SAFI may be setup 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 error to an EBGP peering session
outside the SR domain.
Additionally, it may be considered that the export of SR Policy
information as described in this document constitutes a risk to
confidentiality of mission-critical or commercially sensitive
information about the network (more specifically endpoint/node
addresses, SR SIDs and the SR Policies deployed). BGP peerings are
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. 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 and Cheng Li for their comments
and review of this document.
9. Contributors
Arjun Sreekantiah
Cisco Systems
US
Email: asreekan@cisco.com
Acee Lindem
Cisco Systems
US
Email: acee@cisco.com
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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
10. References
10.1. Normative References
[I-D.ietf-idr-tunnel-encaps]
Patel, K., Velde, G., Sangli, S., and J. Scudder, "The BGP
Tunnel Encapsulation Attribute", draft-ietf-idr-tunnel-
encaps-20 (work in progress), November 2020.
[I-D.ietf-spring-segment-routing-policy]
Filsfils, C., Talaulikar, K., Voyer, D., Bogdanov, A., and
P. Mattes, "Segment Routing Policy Architecture", draft-
ietf-spring-segment-routing-policy-09 (work in progress),
November 2020.
[I-D.ietf-spring-srv6-network-programming]
Filsfils, C., Camarillo, P., Leddy, J., Voyer, D.,
Matsushima, S., and Z. Li, "SRv6 Network Programming",
draft-ietf-spring-srv6-network-programming-24 (work in
progress), October 2020.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[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>.
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[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>.
[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>.
[RFC8664] Sivabalan, S., Filsfils, C., Tantsura, J., Henderickx, W.,
and J. Hardwick, "Path Computation Element Communication
Protocol (PCEP) Extensions for Segment Routing", RFC 8664,
DOI 10.17487/RFC8664, December 2019,
<https://www.rfc-editor.org/info/rfc8664>.
10.2. Informational References
[RFC4272] Murphy, S., "BGP Security Vulnerabilities Analysis",
RFC 4272, DOI 10.17487/RFC4272, January 2006,
<https://www.rfc-editor.org/info/rfc4272>.
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[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>.
Appendix A. Deprecated Segment Sub-TLVs
This section describes the encoding of Segment Sub-TLVs that were
specified in a previous version of this document and subsequently
deprecated.
A.1. Type B-Deprecated: SID only, in the form of IPv6 address
The Type B-Deprecated 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) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
o Type: 2.
o Length is 18.
o Flags: 1 octet of flags as defined in Section 2.4.4.2.12.
o RESERVED: 1 octet of reserved bits. SHOULD be set to zero on
transmission and MUST be ignored on receipt.
o SRv6 SID: 16 octets of IPv6 address.
A.2. Type I-Deprecated: IPv6 Node Address with optional SRv6 SID
The Type I-Deprecated Segment Sub-TLV encodes an IPv6 node address,
SR Algorithm and an optional SRv6 SID. The format is as follows:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Flags | SR Algorithm |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// IPv6 Node Address (16 octets) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// SRv6 SID (optional, 16 octets) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
o Type: 10.
o Length is 34 when the SRv6 SID is present else is 18.
o Flags: 1 octet of flags as defined in Section 2.4.4.2.12.
o SR Algorithm: 1 octet specifying SR Algorithm as described in
section 3.1.1 in [RFC8402], when A-Flag as defined in
Section 2.4.4.2.12 is present. SR Algorithm is used by SRPM as
described in section 4 in
[I-D.ietf-spring-segment-routing-policy]. When A-Flag is not
encoded, this field SHOULD be set to zero on transmission and MUST
be ignored on receipt.
o IPv6 Node Address: a 16 octet IPv6 address.
o SRv6 SID: optional, 16 octet IPv6 address.
A.3. Type J-Deprecated: IPv6 Address + Interface ID for local and
remote pair for SRv6 with optional SID
The Type J-Deprecated Segment Sub-TLV encodes an IPv6 Link Local
adjacency with local node address, a local interface identifier
(Local Interface ID), remote IPv6 node address, a remote interface
identifier (Remote Interface ID) and an optional SRv6 SID. The
format is as follows:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Flags | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Local Interface ID (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// IPv6 Local Node Address (16 octets) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Remote Interface ID (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// IPv6 Remote Node Address (16 octets) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// SRv6 SID (optional, 16 octets) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
o Type: 11.
o Length is 58 when the SRv6 SID is present else is 42.
o Flags: 1 octet of flags as defined in Section 2.4.4.2.12.
o RESERVED: 1 octet of reserved bits. SHOULD be set to zero on
transmission and MUST be ignored on receipt.
o Local Interface ID: 4 octets of interface index as defined in
[RFC8664].
o IPv6 Local Node Address: a 16 octet IPv6 address.
o Remote Interface ID: 4 octets of interface index as defined in
[RFC8664]. The value MAY be set to zero when the local node
address and interface identifiers are sufficient to describe the
link.
o IPv6 Remote Node Address: a 16 octet IPv6 address. The value MAY
be set to zero when the local node address and interface
identifiers are sufficient to describe the link.
o SRv6 SID: optional, 16 octet IPv6 address.
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A.4. Type K-Deprecated: IPv6 Local and Remote addresses for SRv6 with
optional SID
The Type K-Deprecated Segment Sub-TLV encodes an adjacency local
address, an adjacency remote address and an optional 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Local IPv6 Address (16 octets) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Remote IPv6 Address (16 octets) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// SRv6 SID (optional, 16 octets) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
o Type: 12.
o Length is 50 when the SRv6 SID is present else is 34.
o Flags: 1 octet of flags as defined in Section 2.4.4.2.12.
o RESERVED: 1 octet of reserved bits. SHOULD be set to zero on
transmission and MUST be ignored on receipt.
o Local IPv6 Address: a 16 octet IPv6 address.
o Remote IPv6 Address: a 16 octet IPv6 address.
o SRv6 SID: optional, 16 octet IPv6 address.
Authors' Addresses
Stefano Previdi
Individual
IT
Email: stefano@previdi.net
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Clarence Filsfils
Cisco Systems
Brussels
BE
Email: cfilsfil@cisco.com
Ketan Talaulikar (editor)
Cisco Systems
India
Email: ketant@cisco.com
Paul Mattes
Microsoft
One Microsoft Way
Redmond, WA 98052
USA
Email: pamattes@microsoft.com
Eric Rosen
Juniper Networks
10 Technology Park Drive
Westford, MA 01886
US
Email: erosen@juniper.net
Dhanendra Jain
Google
Email: dhanendra.ietf@gmail.com
Steven Lin
Google
Email: stevenlin@google.com
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