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: 30 December 2023 C. Lin
New H3C Technologies
M. Koldychev
Cisco Systems, Inc.
28 June 2023
BGP Extensions of SR Policy for Segment List Protection
draft-lp-idr-sr-path-protection-06
Abstract
This document proposes extensions of BGP in order to provide
protection information for segment lists when delivering SR policy
via BGP.
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 30 December 2023.
Copyright Notice
Copyright (c) 2023 IETF Trust and the persons identified as the
document authors. All rights reserved.
Liu, et al. Expires 30 December 2023 [Page 1]
Internet-Draft Segment List Protection June 2023
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 Revised BSD License text as
described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Revised BSD License.
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 Protection Sub-TLV . . . . . . . . . . . . . . . . . 4
3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
3.1. New Registry: Flag Field of Segment List sub-TLV . . . . 6
3.2. Existing Registry: BGP Tunnel Encapsulation Attribute
sub-TLVs . . . . . . . . . . . . . . . . . . . . . . . . 6
4. Security Considerations . . . . . . . . . . . . . . . . . . . 6
5. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
5.1. Normative References . . . . . . . . . . . . . . . . . . 6
5.2. Informative References . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
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.
Liu, et al. Expires 30 December 2023 [Page 2]
Internet-Draft Segment List Protection June 2023
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].
[I-D.ietf-idr-segment-routing-te-policy] specifies BGP extensions for
the advertisement of SR Policy. [I-D.lin-idr-sr-policy-seglist-id]
defines extensions to BGP SR Policy to specify the identifier of
segment list.
This document proposes extensions of BGP in order to provide the
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, 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 |B| RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// sub-TLVs //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: B-Flag in Segment List sub-TLV
Liu, et al. Expires 30 December 2023 [Page 3]
Internet-Draft Segment List Protection June 2023
* B-Flag(Backup Flag): One bit. If set, indicates a pure backup
path. This is a segment list that only carries rerouted traffic
after the protected segment list fails. If this flag is not set,
it indicates that the segment list acts as the active member in
the candidate path that carries normal traffic.
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 Protection 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Backup List ID 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Backup List ID N |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: List Protection 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 octet of ID for the back up segment list, the
segment list id is delivered in Segment List ID Sub-TLV as define
in [I-D.lin-idr-sr-policy-seglist-id]. 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:
Liu, et al. Expires 30 December 2023 [Page 4]
Internet-Draft Segment List Protection June 2023
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 Protection 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 Protection
Weight
Segment
Segment
...
Segment List
...
...
3. IANA Considerations
Liu, et al. Expires 30 December 2023 [Page 5]
Internet-Draft Segment List Protection June 2023
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 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>.
[I-D.lin-idr-sr-policy-seglist-id]
Lin, C., Cheng, W., Yao, L., Talaulikar, K., and M. Chen,
"BGP SR Policy Extensions for Segment List Identifier",
Work in Progress, Internet-Draft, draft-lin-idr-sr-policy-
seglist-id-03, 3 April 2023,
<https://datatracker.ietf.org/doc/html/draft-lin-idr-sr-
policy-seglist-id-03>.
[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>.
Liu, et al. Expires 30 December 2023 [Page 6]
Internet-Draft Segment List Protection June 2023
[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-08, 1
May 2023, <https://datatracker.ietf.org/doc/html/draft-
ietf-pce-multipath-08>.
[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
Email: liu.yao71@zte.com.cn
Shaofu Peng
ZTE
Email: peng.shaofu@zte.com.cn
Changwang Lin
New H3C Technologies
Email: linchangwang.04414@h3c.com
Mike Koldychev
Cisco Systems, Inc.
Email: mkoldych@cisco.com
Liu, et al. Expires 30 December 2023 [Page 7]
