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-00Abstract
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
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This Internet-Draft will expire on June 1, 2021.
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Copyright NoticeCopyright (c) 2021 IETF Trust and the persons identified as the document authors. All rights reserved.
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 Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.
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. 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.
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This document defines one extension to Border Gateway Protocol (BGP) to distribute SR policies carrying hot-standby switch.2. Terminology 2.1. Requirements LanguageThe 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. Typically but not limit to, the SR policies carrying Hot-standby are configured by a controller.
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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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Internet-Draft SR Candidate Path Hot switch in BGP February 2021 6. IANA ConsiderationsThis 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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Internet-Draft SR Candidate Path Hot switch in BGP February 2021 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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