Internet DRAFT - draft-hegde-spring-srv6-migration
draft-hegde-spring-srv6-migration
SPRING S. Hegde
Internet-Draft R. Shetty
Intended status: Standards Track R. Bharath
Expires: 18 April 2024 Juniper Networks Inc.
D. Voyer
Bell Canada
23 October 2023
SRv6 Migration Scenarios
draft-hegde-spring-srv6-migration-00
Abstract
SRv6 forwarding plane requires devices to support processing newly
defined Segment Routing extension header. All devices in the network
may not be capable of processing this new header and may require
gradual upgrade. This document specifies mechanisms that to deploy
features such as TI-LFA, in the presence of SRH incapable devices in
the network.
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 RFC 2119 [RFC2119].
Status of This Memo
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This Internet-Draft will expire on 18 April 2024.
Copyright Notice
Copyright (c) 2023 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. TI-LFA with Encapsulation mode . . . . . . . . . . . . . . . 3
3. Decap_only Flavor . . . . . . . . . . . . . . . . . . . . . . 4
4. Backward Compatibility . . . . . . . . . . . . . . . . . . . 4
5. Operational Considerations . . . . . . . . . . . . . . . . . 4
6. Security Considerations . . . . . . . . . . . . . . . . . . . 4
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5
9. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 5
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
10.1. Normative References . . . . . . . . . . . . . . . . . . 5
10.2. Informative References . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 5
1. Introduction
Segment Routing for IPv6 defines new Segment Routing extension header
as defined in [RFC8754]. Legacy devices may not be capable of
processing the SRH. This poses challenges in deploying features such
as TI-LFA, that require anchor nodes to support processing SRH.
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+----+ 10 +----+ 10 +----+ 10 +----+ 10 +----+
| R1 |--------| R2 |--------| R3 |--------| R4 |--------| R5 |
+----+ +----+ +----+ +----+ +----+
\ \ /
\ 10 \ 100 / 60
\ \ /
\ +----+ +----+
+--| R7 |------------------| R8 |
+----+ 30 +----+
/
/
+----+
| R6 |
+----+
* Numbers on the links represent the symmetric link cost
Figure 1: Example topology with locators
Consider the topology diagram above. On R1, The primary path to R5
is R1->R2->R3->R4->R5. The TI-LFA backup path is R1->R7->R8->R4->R5
where R8 is the anchor node.The TI-LFA backup path consists of one
SID in SRH in case of classic SRH [RFC8754] or one additional SID in
the micro-SID container
[I-D.filsfils-spring-net-pgm-extension-srv6-usid]. If device R8 is
not capable of processing SRH or the micro-SID instructions, the TI-
LFA backup path cannot be installed as R8 does not advertise a END
SID or uN SID.
2. TI-LFA with Encapsulation mode
TI-LFA with encapsulation mode imposes an additional IPv6 header on
the packet. This additional header is decapsulated on the anchor
node and lookup done for the inner packet. Many legacy devices are
capable of decapsulating IPv6 header and lookingup inner packet and
forward. The legacy device shuold advertise a SID behaviour which
implies decapsulation and lookup only. Currently defined SIDs END
and END.X from [RFC8986] and un/uA defined in
[I-D.filsfils-spring-net-pgm-extension-srv6-usid] also imply support
for NEXT operation which legacy devices cannot support.
The END.DT6 and END.DX6 SIDs specify decapsulation and lookup.
Reusing these SIDs and advertising them in IGPs have below
disadvantages
- Pure transit nodes will also have to advertise these SIDs where
there are no service routes. This may give false impression that
the transit node is advertising service routes.
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- It is much easier to debug TI-LFA which uses END/END.X uN/uA with
new flavor rather than using SIDs defined for advertising Services.
- When the platform capability is upgraded, its operationally easier
to advertise the ‘END with decap_only’ with END/uN and ‘END.X with
decap_only’ with END.X/UA SIDs respectively.
3. Decap_only Flavor
This document proposes a new flavor for the END/END.X and un/uA SIDs
named decap_only. SIDs with decap_only flavor MUST be used as last
SID in the SRH or as last SID in the last SID container.
Nodes computing TI-LFA backup paths SHOULD use the decap_only
flavored SIDs, if the backup path contains only one SID either
END/uN or END.X/uA. The backup path MUST be installed by the
computing node in the encapsulation mode where the incoming packet
is imposed with additional IPv6 header on failure while exercising
the backup path.
4. Backward Compatibility
TBD
5. Operational Considerations
TBBD
6. Security Considerations
TBD
7. IANA Considerations
This document defines new SRv6 END Point behaviours
Code point Behaviour reference
-----------------------------------------------------------------
TBD1 END with decap_only This document
TBD2 END.X with decap_only This document
Figure 2: IANA Cosepoints
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8. Acknowledgements
9. Contributors
10. References
10.1. Normative References
[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>.
[RFC8754] Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J.,
Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header
(SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020,
<https://www.rfc-editor.org/info/rfc8754>.
[RFC8986] Filsfils, C., Ed., Camarillo, P., Ed., Leddy, J., Voyer,
D., Matsushima, S., and Z. Li, "Segment Routing over IPv6
(SRv6) Network Programming", RFC 8986,
DOI 10.17487/RFC8986, February 2021,
<https://www.rfc-editor.org/info/rfc8986>.
10.2. Informative References
[I-D.filsfils-spring-net-pgm-extension-srv6-usid]
Filsfils, C., Camarillo, P., Cai, D., Voyer, D., Meilik,
I., Patel, K., Henderickx, W., Jonnalagadda, P., Melman,
D. T., Liu, Y., and J. Guichard, "Network Programming
extension: SRv6 uSID instruction", Work in Progress,
Internet-Draft, draft-filsfils-spring-net-pgm-extension-
srv6-usid-15, 12 June 2023,
<https://datatracker.ietf.org/doc/html/draft-filsfils-
spring-net-pgm-extension-srv6-usid-15>.
Authors' Addresses
Shraddha Hegde
Juniper Networks Inc.
Exora Business Park
Bangalore 560103
KA
India
Email: shraddha@juniper.net
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Rajesh Shetty
Juniper Networks Inc.
Email: mrajesh@juniper.net
Bharath R
Juniper Networks Inc.
Email: rbharath@juniper.net
Daniel Voyer
Bell Canada
Email: daniel.voyer@bell.ca
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