Inter-Domain Routing Working Group L. Yang
Internet-Draft H. Li
Intended status: Standards Track Y. Wang
Expires: August 2, 2021 Y. Qiu
M. Chen
H3C Technologies
February 2, 2021
Segment Routing Candidate Path Hot-standby switch in BGP
draft-yang-idr-sr-candidate-path-switch-00
Abstract
Segment Routing is a source routing paradigm that explicitly
indicates the forwarding path for packets at the ingress node. An SR
policy is a set of candidate SR paths consisting of one or more
segment lists with necessary path attributes. If an SR policy has
multiple valid candidate paths, the device chooses the candidate path
with the greatest preference value. If the chosen path fails, the SR
policy must select another candidate path. During path reselection,
packet loss might occur and thus affect service continuity. Therefore
the candidate path hot-standby function occurs, the headend can
compute two candidate paths, one is master and the other is backup,
set them to the forwarding plane, and in this way, the switchover
time is reduced.
This document defines extensions to BGP to distribute hot-standby
switch within SR policies.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on June 1, 2021.
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Copyright Notice
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document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
3. SR Policy for Hot-standby . . . . . . . . . .. . . . . . . . 3
3.1. Path Hot-standby Sub-TLV . . . . . . . . . . . . . . . . . 4
4. Operations . . . . . . . . . . . . . . . . . . . . . . . . . 5
5. Implementation Status . . . . . . . . . . . . . . . . . . . . 6
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
7. Security Considerations . . . . . . . . . . . . . . . . . . . 7
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . 7
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
9.1. Normative References . . . . . . . . . . . . . . . . . . 7
9.2. Informative References . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
Segment routing (SR) [RFC8402] is a source routing paradigm that
explicitly indicates the forwarding path for packets at the ingress
node. The ingress node steers packets into a specific path
according to the Segment Routing Policy (SR Policy) as defined in
[I-D.ietf-spring-segment-routing-policy]. In order to distribute SR
policies to the headend, [I-D.ietf-idr-segment-routing-te-policy]
specifies a mechanism by using BGP.
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An SR Policy includes multiple candidate paths, of which at any time
there is only one active candidate path that is provisioned in the
forwarding plane and used for traffic steering. However, when the
hot-standby is enabled on the policy, another candidate path (with
the secondary greatest preference value) MAY be designated as the
backup for the active candidate path. The active candidate path can
be called the primary candidate path. When the forwarding paths
corresponding to all SID lists of the primary path fails, the backup
path immediately takes over to minimize service interruption.
This document defines one extension to Border Gateway Protocol (BGP)
to distribute SR policies carrying hot-standby switch.
2. Terminology
2.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. SR Policy for hot-standby
As defined in [I-D.ietf-idr-segment-routing-te-policy], the SR
policy encoding structure is as follows:
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
Weight
Segment
Segment
...
...
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As introduced in Section 1, SR policy with hot-standby is expressed
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
Path Hot-standby
Policy Candidate Path Name
Explicit NULL Label Policy (ENLP)
Segment List
Weight
Segment
Segment
...
...
3.1 Path Hot-standby Sub-TLV
A Hot-standby sub-TLV is an Optional sub-TLV. When it appears, it
MUST appear only once at most within a SR Policy SAFI NLRI. If
multiple Hot-standby sub-TLVs appear within a SR Policy SAFI NLRI,
the NLRI MUST be treated as a malformed NLRI.
As per [I-D.ietf-idr-segment-routing-te-policy], when the error
determined allows for the router to skip the malformed NLRI(s) and
continue processing of the rest of the update message, then it MUST
handle such malformed NLRIs as 'Treat-as-withdraw'. This document
does not define new error handling rules for Hot-standby sub-TLV,
and the error handling rules defined in
[I-D.ietf-idr-segment-routing-te-policy] apply to this document.
A Hot-standby sub-TLV associated with a SR policy, The Hot-standby
sub-TLV has the following format:
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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 | Hot-standby | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1. Hot-standby sub-TLV
Where:
Type: to be assigned by IANA.
Length: the total length of the value field not including Type and
Length fields.
Hot-standby: 1 octet of flags. Following flags are defined. Unused
bits in the Flag octet SHOULD be set to zero upon transmission and
MUST be ignored upon receipt.
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|E| |
+-+-+-+-+-+-+-+-+
Where:
E-Flag: 1 bit. Indicates the Policy Candidate Path hot-standby
switch flag.
When E-Flag is set, it represents the switch has been enabled.
Reserved: 8 bits reserved and MUST be set to 0 on transmission and
MUST be ignored on receipt.
When the E-Flag of hot-standby changes, the selection process will
be re-executed, if E-Flag is present, the master and backup
candidate path selected set to data-plane. If E-Flag is absent, only
the master's candidate path will be set to data-plane.
4. Operations
The document does not bring new operation beyond the description of
operations defined in [I-D.ietf-idr-segment-routing-te-policy]. The
existing operations defined in
[I-D.ietf-idr-segment-routing-te-policy] can apply to this document
directly.
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Typically but not limit to, the SR policies carrying Hot-standby are
configured by a controller.
After configuration, the SR policies carrying Hot-standby will be
advertised by BGP update messages. The operation of advertisement
is the same as defined in [I-D.ietf-idr-segment-routing-te-policy],
as well as the reception.
The consumer of the SR policies is not the BGP process. The
operation of sending information to consumers is out of scope of
this document.
5. Implementation Status
This section records the status of known implementations of the
protocol defined by this specification at the time of posting of
this Internet-Draft, and is based on a proposal described in
[RFC7942].
The description of implementations in this section is intended to
assist the IETF in its decision processes in progressing drafts to
RFCs. Please note that the listing of any individual implementation
here does not imply endorsement by the IETF. Furthermore, no effort
has been spent to verify the information presented here that was
supplied by IETF contributors. This is not intended as, and must
not be construed to be, a catalog of available implementations or
their features. Readers are advised to note that other
implementations may exist.
According to [RFC7942], "this will allow reviewers and working
groups to assign due consideration to documents that have the
benefit of running code, which may serve as evidence of valuable
experimentation and feedback that have made the implemented
protocols more mature. It is up to the individual working groups
to use this information as they see fit".
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6. IANA Considerations
This document defines a new Sub-TLV in registries "SR Policy List
Sub- TLVs" [I-D.ietf-idr-segment-routing-te-policy]:
Value Description Reference
---------------------------------------------------------------------
TBA Hot-standby sub-TLV This document
7. Security Considerations
TBA
8. Acknowledgments
Authors would like to thank Changwang Lin for their paraprofessional
comments and help.
9. References
9.1. 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-11 (work in progress), May 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-09 (work in progress),
July 2020.
[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>.
[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>.
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9.2. Informative References
[RFC7942] Sheffer, Y. and A. Farrel, "Improving Awareness of Running
Code: The Implementation Status Section", BCP 205,
RFC 7942, DOI 10.17487/RFC7942, July 2016,
<https://www.rfc-editor.org/info/rfc7942>.
Authors' Addresses
Liping Yang
H3C Technologies
China
Email: liping_yang@h3c.com
Hao Li
H3C Technologies
China
Email: lihao@h3c.com
Yuanxiang Qiu
H3C Technologies
China
Email: qiuyuanxiang@h3c.com
Yang Wang
H3C Technologies
China
Email: wang.a.yang@h3c.com
Mengxiao Chen
H3C Technologies
China
Email: chen.mengxiao@h3c.com
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