Internet DRAFT - draft-geng-spring-redundancy-policy
draft-geng-spring-redundancy-policy
SPRING F. Yang
Internet-Draft X. Geng
Intended status: Standards Track T. Zhou
Expires: 14 September 2023 Huawei
G. Mishra
Verizon Inc.
13 March 2023
Redundancy Policy for Redundancy Protection
draft-geng-spring-redundancy-policy-05
Abstract
This document introduces a variant of SR Policy called Redundancy
Policy, in order to instruct the replication of service packets and
assign more than one redundancy forwarding paths used for redundancy
protection.
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 .
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
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
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This Internet-Draft will expire on 14 September 2023.
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. Terminology and Conventions . . . . . . . . . . . . . . . . . 3
3. Redundancy Policy . . . . . . . . . . . . . . . . . . . . . . 3
3.1. Identification of Redundancy Policy . . . . . . . . . . . 3
3.2. Structure of Redundancy Policy . . . . . . . . . . . . . 3
3.3. Flag of a Candidate Path . . . . . . . . . . . . . . . . 4
3.4. Behavior of Redundancy Policy . . . . . . . . . . . . . . 5
3.5. BSID and Redundancy Policy . . . . . . . . . . . . . . . 5
3.6. Steering into a Redundancy Policy . . . . . . . . . . . . 6
3.7. Protocol Extensions . . . . . . . . . . . . . . . . . . . 6
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
5. Security Considerations . . . . . . . . . . . . . . . . . . . 6
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
6.1. Normative References . . . . . . . . . . . . . . . . . . 6
6.2. Informative References . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
Redundancy protection [I-D.ietf-spring-sr-redundancy-protection] is a
generalized protection mechanism by replicating and transmitting
copies of flow packets on redundancy node over multiple different and
disjoint paths, and further eliminating the redundant packets at
merging node. This document introduces Redundancy Policy to support
redundancy protection, which is a variant of SR Policy
[I-D.ietf-spring-segment-routing-policy]. Redundancy Policy
instructs the replication of service packets and assigns more than
one equivalent forwarding paths used for redundancy protection.
Redundancy Policy applies equally to both MPLS data plane (SR-MPLS)
[RFC8660] and Segment Routing with IPv6 data plane (SRv6) [RFC8986].
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2. Terminology and Conventions
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.
The other terminologies used in this document are:
Redundancy Node: the start point of redundancy protection, where the
network node replicates the flow packets.
Merging Node: the end point of redundancy protection, where the
network node eliminates and ordering(optionally) the flow packets.
Redundancy Policy: an extended SR Policy which instructs more than
one redundancy forwarding paths to support packet redundant
transmission.
3. Redundancy Policy
Redundancy Policy is used to enable packet replication and
instantiation more than one active ordered lists of segments between
redundancy node and merging node to steer the same flow through
different paths in an SR domain.
3.1. Identification of Redundancy Policy
Redundancy Policy is a variant of SR Policy and also identified
through the tuple <headend, color, endpoint>. Specifically, a
redundancy policy is identified by <redundancy node, color, merging
node>. Redundancy node is specified as IPv4/IPv6 address of headend
of Redundancy Policy, which is the node to perform packet
replication. Merging node is specified as IPv4/IPv6 address of
endpoint of Redundancy Policy, which is the node to perform packet
elimination. The value of color specifies the intent of the
redundancy policy is "redundancy protection for high reliability",
which indicates service packets are replicated into multiple copies
and carried on different forwarding paths .
3.2. Structure of Redundancy Policy
Redundancy policy shares the basic structure and elements with SR
Policy and its information model is shown in the following:
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Redundancy policy POL1 <R Node= R1, Color = 1, M Node = M1>
Candidate-path CP1 <protocol-origin = 20, originator
= 100:1.1.1.1, discriminator = 1>
Flag Redundancy
Preference 200
SID-List1 <SID11...SID1i>
SID-List2 <SID21...SID2j>
Candidate-path CP2 <protocol-origin = 20, originator
= 100:2.2.2.2, discriminator = 2>
Preference 100
Weight W3, SID-List3 <SID31...SID3i>
The Redundancy Policy POL1 is identified by the tuple <redundancy
node, color, merging node>, in which R1 is the redundancy node, M1 is
the merging node, and Color 1 represents the intent of redundancy
protection. Two candidate-paths CP1 and CP2 instruct the ordered
segment lists from redundancy node to merging node. In candidate
path CP1, a new attribute Flag is added to indicate the type of
candidate path. When the candidate path is indicated with the flag
of redundancy, the attribute Weight is not applicable to the SID-
Lists and all SID Lists of the candidate path are used for redundancy
forwarding. Regarding the other attributes of candidate path such as
originator, preference, priority, segment-list etc, the definitions
apply the same as [I-D.ietf-spring-segment-routing-policy].
3.3. Flag of a Candidate Path
Flag is an optional attribute of a candidate path, which is used to
indicate the type of a candidate path is for redundancy forwarding.
When the candidate path with flag of redundancy is selected as the
active candidate path, this SR Policy is identified as the Redundancy
Policy. Flag of a candidate path is an 8-bit bitmap. The table
below specifies the current definition of Flag:
+----------------------------------+
| Bitmap | Flag | Description |
+----------------------------------+
| 0 | R | Redundancy paths |
+----------------------------------+
| 1-7 | U | Reserved |
+----------------------------------+
Figure 2: Flag
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3.4. Behavior of Redundancy Policy
When the SR policy is identified as a redundancy policy, network node
uses rules to compute and select the valid active ordered segment-
lists for redundancy forwarding. The specific rules are:
* The candidate paths are selected to determine the best path of an
SR policy. Preference, Protocol-Origin, and other tie-breaking
rules defined in section 2.9 of
[I-D.ietf-spring-segment-routing-policy] are evaluated until only
one valid best path is selected.
* In a redundancy policy, the candidate path with a flag of
redundancy is always selected as the best path in the first place.
* When the selected active candidate path is with a flag of
redundancy, all the segment-lists of the candidate path are used
as the active segment-lists for redundancy forwarding, where each
active segment-list carries an entire copy of service packets.
* Weight is not applicable for the segment-lists in a candidate path
with a flag of redundancy. Redundancy policy has no purpose of
weighted load-balancing.
* The candidate path without a flag of redundancy in the same SR
policy with the candidate paths with a flag, is considered as the
backup path, which allowing provisioning of multiple path options.
Take the information model in section 3.2 as an example, preference
value 200 of CP1 is higher than preference value 100 of CP2, thus CP1
is selected as the active candidate path. Because CP1 is with the
flag of redundancy, both Segment-List1 and Segment-List2 are selected
as the active Segment-Lists for redundancy forwarding. After service
packets are replicated, each segment-list forwards each replicas of
service packets. When CP1 becomes invalid and fallbacks to CP2, CP2
provides the backup path to the redundancy forwarding.
3.5. BSID and Redundancy Policy
Redundancy policy can be optionally associated with a Binding
Segment. Redundancy SID defined in
[I-D.ietf-spring-sr-redundancy-protection] can be the Binding SID of
redundancy policy. In other words, Redundancy SID triggers the
instantiation of redundancy policy in the forwarding plane on
redundancy node.
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3.6. Steering into a Redundancy Policy
A packet is steered into a Redundancy Policy at a redundancy node in
following ways:
* Incoming packets have an active SID matching the Redundancy SID at
the redundancy node.
* Per-destination Steering: incoming packets match a BGP/Service
route which recurses on a Redundancy Policy.
* Per-flow Steering: incoming packets match or recurse on a
forwarding array of where some of the entries are Redundancy
Policy.
* Policy-based Steering: incoming packets match a routing policy
which redirects them on a Redundancy Policy.
3.7. Protocol Extensions
Similar to SR Policy, Redundancy Policy requires the control plane
protocol extensions to distribute candidate paths and other
information. New sub-TLVs are expected to be defined to encode new
information of Redundancy Policy Candidate Paths in BGP
[I-D.ietf-idr-segment-routing-te-policy] and PCEP
[I-D.ietf-pce-segment-routing-policy-cp].
4. IANA Considerations
TBD
5. Security Considerations
TBD
6. References
6.1. Normative References
[I-D.ietf-spring-segment-routing-policy]
Filsfils, C., Talaulikar, K., Voyer, D., Bogdanov, A., and
P. Mattes, "Segment Routing Policy Architecture", Work in
Progress, Internet-Draft, draft-ietf-spring-segment-
routing-policy-22, 22 March 2022,
<https://datatracker.ietf.org/doc/html/draft-ietf-spring-
segment-routing-policy-22>.
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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>.
[RFC8660] Bashandy, A., Ed., Filsfils, C., Ed., Previdi, S.,
Decraene, B., Litkowski, S., and R. Shakir, "Segment
Routing with the MPLS Data Plane", RFC 8660,
DOI 10.17487/RFC8660, December 2019,
<https://www.rfc-editor.org/info/rfc8660>.
[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>.
6.2. Informative 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.ietf-pce-segment-routing-policy-cp]
Koldychev, M., Sivabalan, S., Barth, C., Peng, S., and H.
Bidgoli, "PCEP extension to support Segment Routing Policy
Candidate Paths", Work in Progress, Internet-Draft, draft-
ietf-pce-segment-routing-policy-cp-09, 7 March 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-pce-
segment-routing-policy-cp-09>.
[I-D.ietf-spring-sr-redundancy-protection]
Geng, X., Chen, M., Yang, F., Camarillo, P., and G. S.
Mishra, "SRv6 for Redundancy Protection", Work in
Progress, Internet-Draft, draft-ietf-spring-sr-redundancy-
protection-02, 23 September 2022,
<https://datatracker.ietf.org/doc/html/draft-ietf-spring-
sr-redundancy-protection-02>.
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Authors' Addresses
Fan Yang
Huawei
156 Beiqing Rd.
Beijing
100095
China
Email: shirley.yangfan@huawei.com
Xuesong Geng
Huawei
156 Beiqing Rd.
Beijing
100095
China
Email: gengxuesong@huawei.com
Tianran Zhou
Huawei
156 Beiqing Rd.
Beijing
100095
China
Email: zhoutianran@huawei.com
Gyan Mishra
Verizon Inc.
Email: gyan.s.mishra@verizon.com
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