IDR WG Yao. Liu
Internet-Draft Shaofu. Peng
Intended status: Standards Track ZTE Corporation
Expires: April 17, 2021 October 14, 2020
BGP extensions of SR policy for path protection
draft-lp-idr-sr-path-protection-00
Abstract
This document proposes extensions of BGP in order to provide path
protection within a candidate path when delivering SR policy. And it
also extends BGP-LS to provide some extra information of the segment
list in a candidate path in the advertisement.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. BGP Extensions for Advertising Segment List . . . . . . . . . 3
2.1. Extensions of Segment List sub-TLV . . . . . . . . . . . 3
2.2. List Identifier Sub-TLV . . . . . . . . . . . . . . . . . 3
2.2.1. List Protection Sub-TLV . . . . . . . . . . . . . . . 4
3. BGP-LS Extensions for Distributing Segment List States . . . 5
4. Security Considerations . . . . . . . . . . . . . . . . . . . 5
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
6. Normative References . . . . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6
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 concepts 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.
When SR policies are involved and a strict compliance of the policy
is required, an end-to-end protection should be preferred over a
local repair mechanism.
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).
Despite using candidate path for protection, protection at segment
list level within an candidate path is also useful.
[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, if candidate path is used for protection ,the BGP origin
must generate multiple NLRIs. If protection at segment list level is
possible, only one NLRI is needed which makes the advertisement more
simple.
On the other hand, protection in and between candidate path can be
combined together to provide a more comprehensive protection
mechanism.
This document proposes extensions of BGP in order to provide path
protection in an candidate path when delivering SR policy.
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[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.
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.
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,
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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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| List Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Optional 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
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 Identifier Sub-TLV
Type: 1 octet. TBD.
Length: 1 octet, specifies the length of the value field not
including Type and Length fields.
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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.
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 meaning of the D,E,C,V,R,F,A,M can be found in
[I-D.ietf-idr-te-lsp-distribution] section 6.5.
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. 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].
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5. IANA Considerations
TBD
6. Normative References
[I-D.ietf-idr-segment-routing-te-policy]
Previdi, S., Filsfils, C., Talaulikar, K., Mattes, P.,
Rosen, E., Jain, D., and S. Lin, "Advertising Segment
Routing Policies in BGP", draft-ietf-idr-segment-routing-
te-policy-09 (work in progress), May 2020.
[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", draft-ietf-idr-te-
lsp-distribution-13 (work in progress), April 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-08 (work in progress),
July 2020.
[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
Liu Yao
ZTE Corporation
Nanjing
China
Email: liu.yao71@zte.com.cn
Peng Shaofu
ZTE Corporation
Nanjing
China
Email: peng.shaofu@zte.com.cn
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