Internet DRAFT - draft-lp-idr-sr-path-protection
draft-lp-idr-sr-path-protection
IDR Working Group Y. Liu
Internet-Draft S. Peng
Intended status: Standards Track ZTE
Expires: 10 September 2023 9 March 2023
BGP Extensions of SR Policy for Segment List Identification and
Protection
draft-lp-idr-sr-path-protection-04
Abstract
This document proposes extensions of BGP in order to provide
identification and protection information of segment lists when
delivering SR policy via BGP.
Status of This Memo
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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. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
3.1. New Registry: Flag Field of Segment List sub-TLV . . . . 7
3.2. Existing Registry: BGP Tunnel Encapsulation Attribute
sub-TLVs . . . . . . . . . . . . . . . . . . . . . . . . 7
3.3. New Registry: List Identifier Sub-TLVs . . . . . . . . . 7
4. Security Considerations . . . . . . . . . . . . . . . . . . . 7
5. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
5.1. Normative References . . . . . . . . . . . . . . . . . . 7
5.2. Informative References . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
Segment Routing [RFC8402] allows a headend node to steer a packet
flow along any path. [RFC9256] 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 two active segment lists(SL1, SL2) in the primary
candidate path CP1, SL1 and SL2 can together carry 80 Gbps. If SL1
fails, CP1 are still the primary path, but the bandwith of CP1 is
probably not enough. If there's a backup segment list for SL1, e.g,
SL3, in CP1, traffic will be load-balanced between SL3 and SL2 after
SL1 fails.
The pcep extensions for segment list identification and protection
relationship among segment lists specification are proposed in
[I-D.ietf-pce-multipath].
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[I-D.ietf-idr-segment-routing-te-policy] specifies BGP extensions for
the advertisement of SR Policy. This document proposes extensions of
BGP in order to provide identification as well as the protection
information of segment lists when delivering SR policy via BGP.
This document proposes extensions of BGP in order to provide
identification and protection information of segment lists when
delivering SR policy via BGP.
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] [RFC8174]
when, and only when, they appear in all capitals, as shown here.
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.
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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. IANA Considerations
3.1. 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).
3.2. 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
3.3. 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. 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].
5. References
5.1. 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-20, 27 July 2022,
<https://datatracker.ietf.org/doc/html/draft-ietf-idr-
segment-routing-te-policy-20>.
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[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>.
[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>.
5.2. Informative References
[I-D.ietf-pce-multipath]
Koldychev, M., Sivabalan, S., Saad, T., Beeram, V. P.,
Bidgoli, H., Yadav, B., Peng, S., and G. S. Mishra, "PCEP
Extensions for Signaling Multipath Information", Work in
Progress, Internet-Draft, draft-ietf-pce-multipath-07, 14
November 2022, <https://datatracker.ietf.org/doc/html/
draft-ietf-pce-multipath-07>.
[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>.
[RFC9256] Filsfils, C., Talaulikar, K., Ed., Voyer, D., Bogdanov,
A., and P. Mattes, "Segment Routing Policy Architecture",
RFC 9256, DOI 10.17487/RFC9256, July 2022,
<https://www.rfc-editor.org/info/rfc9256>.
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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