BGP Extensions of SR Policy for Path Protection
draft-lp-idr-sr-path-protection-02
The information below is for an old version of the document.
| Document | Type |
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| Authors | Yao Liu , Shaofu Peng | ||
| Last updated | 2021-12-19 | ||
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draft-lp-idr-sr-path-protection-02
IDR WG Y. Liu
Internet-Draft S. Peng
Intended status: Standards Track ZTE
Expires: 22 June 2022 19 December 2021
BGP Extensions of SR Policy for Path Protection
draft-lp-idr-sr-path-protection-02
Abstract
This document proposes extensions of BGP to provide protection
information of segment lists within a candidate path when delivering
SR policy. And it also extends BGP-LS to provide some extra
information of the segment list in the advertisement.
Status of This Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on 22 June 2022.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. BGP Extensions for Advertising Segment List . . . . . . . . . 3
2.1. Extensions of Segment List sub-TLV . . . . . . . . . . . 3
2.2. List Identifier Sub-TLV . . . . . . . . . . . . . . . . . 4
2.2.1. List Protection Sub-TLV . . . . . . . . . . . . . . . 4
3. BGP-LS Extensions for Distributing Segment List States . . . 7
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
4.1. New Registry: Flag Field of Segment List sub-TLV . . . . 7
4.2. Existing Registry: BGP Tunnel Encapsulation Attribute
sub-TLVs . . . . . . . . . . . . . . . . . . . . . . . . 7
4.3. New Registry: List Identifier Sub-TLVs . . . . . . . . . 8
4.4. Existing Registry: Flag Field of SR Segment List TLV . . 8
5. Security Considerations . . . . . . . . . . . . . . . . . . . 8
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
6.1. Normative References . . . . . . . . . . . . . . . . . . 8
6.2. Informative References . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction
Segment Routing [RFC8402] allows a headend node to steer a packet
flow along any path. [I-D.ietf-spring-segment-routing-policy]
details the concept of SR Policy and steering into an 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 path can be used for path protection, that is, the lower
preference candidate path may be designated as the backup for a
specific or all (active) candidate path(s). Backup candidate path
provide protection only when all the segment lists in the active CP
are invalid.
If a candidate path is associated with a set of Segment-Lists, each
Segment-List is associated with weight for weighted load balancing.
The protection mechanism for SR Policy is not flexible enough. For
example, there're three segment lists(SL1, SL2, SL3) in candidate
path 1, it may be desired that SL1 and SL2 are the primary path, SL3
are the backup path for SL1 and will be active only when SL1 fails.
[I-D.ietf-pce-multipath] proposes extensions to PCEP to specify the
protection relationship between segment lists in the candidate path.
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[I-D.ietf-idr-segment-routing-te-policy] specifies BGP extensions for
the advertisement of SR Policies and each candidate path is carried
in an NLRI. This document proposes extensions of BGP in order to
provide protection information of segment lists when delivering SR
policy.
[I-D.ietf-idr-te-lsp-distribution] describes a mechanism to collect
the SR policy information that is locally available in a node and
advertise it into BGP Link State (BGP-LS) updates. This document
also extends it to provide some extra information of the segment list
in a candidate path in the BGP-LS advertisement.
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
2. BGP Extensions for Advertising Segment List
2.1. Extensions of Segment List sub-TLV
Segment List sub-TLV is introduced in
[I-D.ietf-idr-segment-routing-te-policy] and it includes the elements
of the paths (i.e., segments).
This document introduces a one-bit flag in the RESERVED field.
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 |B| RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// sub-TLVs //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Segment List sub-TLV
B-Flag(Backup Flag): one bit. When set to 0, it indicates that the
segment list acts as the active member in the candidate path. When
set to 1, it indicates that the segment list acts as the backup path
in the candidate path.
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Using segment lists for path protection can be compatible with using
candidate paths. When a path fails, the backup segment list within
the same candidate path is used preferentially for path protection.
If the backup list is also invalid, then other candidate path can be
enabled for protection.
2.2. List Identifier Sub-TLV
This document introduces a new sub-sub-tlv of Segment List sub-TLV,
where,
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| List Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Optional sub-TLVs ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: List Identifier Sub-TLV
* Type: 1 octet. TBD.
* Length: 1 octet, specifies the length of the value field not
including Type and Length fields.
* RESERVED: 2 octet of reserved bits. SHOULD be unset on
transmission and MUST be ignored on receipt.
* List Identifier: 4 octets. It is the identifier of the
corresponding segment list, so that the segment list can be
operated according to the specified Segment List identifier.
* This sub-TLV is optional and it MUST NOT appear more than once
inside the Segment List sub-TLV.
2.2.1. List Protection Sub-TLV
The List Protection Info sub-TLV is an optional sub-TLV of List
Identifier sub-TLV, where:
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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 | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Backup List ID 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Backup List ID N |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: List Protection Info Sub-TLV
* Type: 1 octet. TBD.
* Length: 1 octet, specifies the length of the value field not
including Type and Length fields.
* RESERVED: 2 octet of reserved bits. SHOULD be unset on
transmission and MUST be ignored on receipt.
* Backup List ID: 4 octets. It is the List Identifier of the backup
segment list that protects this segment list. If there're
multiple backup paths, the list ID of each path should be included
in the TLV.
As defined in [I-D.ietf-idr-segment-routing-te-policy], the SR Policy
encoding structure is as follows:
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SR Policy SAFI NLRI: <Distinguisher, Policy-Color, Endpoint>
Attributes:
Tunnel Encaps Attribute (23)
Tunnel Type: SR Policy
Binding SID
Preference
Priority
Policy Name
Explicit NULL Label Policy (ENLP)
Segment List
Weight
Segment
Segment
...
Segment List
...
...
The new SR Policy encoding structure with List Identifier sub-TLV is
shown as below:
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
List Identifier
List Protection Info
Weight
Segment
Segment
...
Segment List
...
...
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3. BGP-LS Extensions for Distributing Segment List States
[I-D.ietf-idr-te-lsp-distribution] describes a mechanism to collect
the SR Policy information that is locally available in a node and
advertise it into BGP Link State (BGP-LS) updates. The SR Policy
information includes status of the candidate path, e.g, whether the
candidate path is administrative shut or not.
SR Segment List TLV is defined in [I-D.ietf-idr-te-lsp-distribution]
to to report the SID-List(s) of a candidate path. Figure 4 shows the
flags in SR Segment List TLV.
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|D|E|C|V|R|F|A|T|M|S|B| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: Flag Field of SR Segment List TLV
The D,E,C,V,R,F,A,M flags are defined in
[I-D.ietf-idr-te-lsp-distribution].
This document introduces two new flags, where,
* S-Flag : Indicates the segment list is in administrative shut
state when set.
* B-Flag : Indicates the segment list is the backup path within the
candidate path when set, otherwise it is the active path.
4. IANA Considerations
4.1. New Registry: Flag Field of Segment List sub-TLV
This document introduces a one-bit flag field in the Segment List
sub-TLV [I-D.ietf-idr-segment-routing-te-policy] for the Backup Flag
(B-Flag).
4.2. Existing Registry: BGP Tunnel Encapsulation Attribute sub-TLVs
This document defines a new sub-TLV in the registry "SR Policy List
Sub-TLVs" [I-D.ietf-idr-segment-routing-te-policy] to be assigned by
IANA:
Codepoint Description Reference
-------------------------------------------------------------
TBD List Identifier Sub-TLV This document
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4.3. New Registry: List Identifier Sub-TLVs
This document requests the creation of a new registry called "List
Identifier Sub-TLVs" under the "BGP Tunnel Encapsulation" registry.
Following initial Sub-TLV codepoint are assigned by this document.
Codepoint Description Reference
-------------------------------------------------------------
TBD List Protection Sub-TLV This document
4.4. Existing Registry: Flag Field of SR Segment List TLV
This document requests bit 9 and bit 10 in the flag field of "SR
Segment List TLV" [I-D.ietf-idr-te-lsp-distribution] under the "BGP-
LS Node Descriptor, Link Descriptor, Prefix Descriptor, and Attribute
TLVs" registry.
Bit Description Reference
------------------------------------------------------------------
9 Administrative Shut State Flag(S-Flag) This document
10 Backup Path State Flag(B-Flag) This document
5. Security Considerations
Procedures and protocol extensions defined in this document do not
affect the security considerations discussed in
[I-D.ietf-idr-segment-routing-te-policy] and
[I-D.ietf-idr-te-lsp-distribution].
6. References
6.1. Normative References
[I-D.ietf-idr-segment-routing-te-policy]
Previdi, S., Filsfils, C., Talaulikar, K., Mattes, P.,
Jain, D., and S. Lin, "Advertising Segment Routing
Policies in BGP", Work in Progress, Internet-Draft, draft-
ietf-idr-segment-routing-te-policy-14, 10 November 2021,
<https://datatracker.ietf.org/doc/html/draft-ietf-idr-
segment-routing-te-policy-14>.
[I-D.ietf-idr-te-lsp-distribution]
Previdi, S., Talaulikar, K., Dong, J., Chen, M., Gredler,
H., and J. Tantsura, "Distribution of Traffic Engineering
(TE) Policies and State using BGP-LS", Work in Progress,
Internet-Draft, draft-ietf-idr-te-lsp-distribution-16, 22
October 2021, <https://datatracker.ietf.org/doc/html/
draft-ietf-idr-te-lsp-distribution-16>.
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[I-D.ietf-spring-segment-routing-policy]
Filsfils, C., Talaulikar, K., Voyer, D., Bogdanov, A., and
P. Mattes, "Segment Routing Policy Architecture", Work in
Progress, Internet-Draft, draft-ietf-spring-segment-
routing-policy-14, 25 October 2021,
<https://datatracker.ietf.org/doc/html/draft-ietf-spring-
segment-routing-policy-14>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
6.2. Informative References
[I-D.ietf-pce-multipath]
Koldychev, M., Sivabalan, S., Saad, T., Beeram, V. P.,
Bidgoli, H., Yadav, B., and S. Peng, "PCEP Extensions for
Signaling Multipath Information", Work in Progress,
Internet-Draft, draft-ietf-pce-multipath-03, 25 October
2021, <https://datatracker.ietf.org/doc/html/draft-ietf-
pce-multipath-03>.
[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>.
Authors' Addresses
Yao Liu
ZTE
Nanjing
China
Email: liu.yao71@zte.com.cn
Shaofu Peng
ZTE
Nanjing
China
Email: peng.shaofu@zte.com.cn
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