Internet DRAFT - draft-ietf-spring-sr-redundancy-protection
draft-ietf-spring-sr-redundancy-protection
SPRING Working Group X. Geng
Internet-Draft M. Chen
Intended status: Standards Track F. Yang, Ed.
Expires: 21 July 2024 Huawei Technologies
P. Camarillo
Cisco Systems, Inc.
G. Mishra
Verizon Inc.
18 January 2024
SRv6 for Redundancy Protection
draft-ietf-spring-sr-redundancy-protection-03
Abstract
Redundancy Protection is a generalized protection mechanism to
achieve high reliability of service transmission in Segment Routing
network. The mechanism uses the "Live-Live" methodology, with the
aim of enhancing the functionalities of Segment Routing over IPv6.
Inspired by DetNet Packet Replication and Packet Elimination
functions, this document introduces two new Segments to provide
replication and elimination functions on specific network nodes by
leveraging SRv6 Segment programming capabilities.
Status of This Memo
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This Internet-Draft will expire on 21 July 2024.
Copyright Notice
Copyright (c) 2024 IETF Trust and the persons identified as the
document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
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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 . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2.2. Terminology and Conventions . . . . . . . . . . . . . . . 3
3. Redundancy Protection in Segment Routing Scenario . . . . . . 3
4. Segment to Support Redundancy Protection . . . . . . . . . . 5
4.1. Redundancy Segment . . . . . . . . . . . . . . . . . . . 5
4.2. Merging Segment . . . . . . . . . . . . . . . . . . . . . 6
5. Meta Data to Support Redundancy Protection . . . . . . . . . 7
6. Segment Routing Policy to Support Redundancy Protection . . . 8
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
8. Security Considerations . . . . . . . . . . . . . . . . . . . 9
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
10.1. Normative References . . . . . . . . . . . . . . . . . . 9
10.2. Informative References . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction
Redundancy Protection is a generalized protection mechanism to
achieve the high reliability of service transmission in Segment
Routing (SR) network. Specifically, packets of flows are replicated
at a network node into two or more copies, which are transported via
different and disjoint paths in parallel. When copies of packets are
received and merged at one network node, the redundant packets are
determined and eliminated to guarantee only one copy of the packets
is transmitted. The mechanism uses the "Live-Live" methodology,
targeting to enhance the functionalities of Segment Routing over
IPv6(SRv6) [RFC8986]. Inspired by DetNet [RFC8655] Packet
Replication and Packet Elimination Functions, two new Segments are
introduced to provide the replication and elimination functions on
specific network nodes by leveraging SRv6 Segment programming
capabilities. As it is unnecessary to perform switchover of
recieving packets between different paths, redundancy protection can
facilitate to achieve zero packet loss target when failure on either
path happens.
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Redundancy protection provides ultra reliable protection to many
services, for example Cloud VR/Game, IPTV service and other type of
video services, high value private line service etc. In this
document, redundancy protection is applied to point-to-point
services. The mechanism for point-to-multipoint services stays out
of the scope of this document.
SR leverages the source routing paradigm. An ingress node steers a
packet through an ordered list of instructions, called "segments". A
segment can be associated to arbitrary processing of the packet in
the node identified by the segment.
This document extends the Segment Routing to support redundancy
protection in an SRv6 environment, including the definitions of two
new Segments, meta data encapsulation, and a variation of Segment
Routing Policy.
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.
2.2. Terminology and Conventions
SR: Segment Routing
SRv6: Segment Routing over IPv6
SID: Segment Identifier
BSID: Binding SID
Red node: Redundancy node
Mer node: Merging node
FID: Flow Identification
SN: Sequence Number
3. Redundancy Protection in Segment Routing Scenario
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| |
|<--------------- SRv6 Domain ---------------->|
| |
| +-----+ |
| +-----+ R3 +-----+ |
| | +-----+ | |
+-----+ +--+--+ +--+--+ +-----+
-------+ R1 +--------+ Red | | Mer +-------+ R2 +-------
+-----+ +--+--+ +--+--+ +-----+
| +-----+ |
+------+ R4 +-----+
+-----+
Figure 1: Example Scenario of Redundancy Protection in SRv6 Domain
Figure 1 shows an example of redundancy protection used in SRv6
domain. R1, R2, R3, R4, Red and Mer are SR-capable nodes. When a
flow is sent into the SRv6 domain, the process is:
1) R1 receives the traffic flow and encapsulates packets with a list
of segments destined to R2, which is instantiated as an ordered list
of SRv6 SIDs.
2) When the packet flow arrives at Red node, known as Redundancy
node, each packet is replicated into two or more copies. Each copy
of the packet is encapsulated with a new segment list, which
represents different disjoint forwarding paths.
3) Meta data information including flow identification (FID) and
sequence number (SN) is used to facilitate elimination of duplicate
packets on Merging node (Mer). Flow identification identifies the
specific flow, and sequence number distinguishes the packet sequence
within a flow. Meta data is either carried in the packet before it
arrives at redundancy node, or added to each of the replicas at the
redundancy node.
4) The multiple replicas go through different paths until they reach
the Mer node. The first received copy of each flow packet is
transmitted from Merging node to R2, and the redundant packets are
eliminated.
5) When there is any failure or packet loss in one path, the service
transmission continues through the other path non-disruptively.
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6) Sometimes, out-of-order packets may occur since service packets
are recovered from different forwarding paths. In this case, the
merging node or other network nodes behind merging node is desired to
include a reordering function, which is implementation specific and
out of the scope of this document.
To minimize the jitter caused by random packet loss, the disjoint
paths are recommended to have similar path forwarding delay.
4. Segment to Support Redundancy Protection
To achieve the packet replication and elimination functions,
Redundancy Segment and Merging Segment, as well as the related SRv6
Endpoint Behavior are introduced.
4.1. Redundancy Segment
Redundancy Segment is the identifier of packets which need to be
replicated on redundancy node. It is a variation of Binding SID
(BSID) to associate with a Redundancy Policy, instantiation of which
provides segment lists of different disjoint paths. Similar to the
relationship between BSID and SR Policy
[I-D.ietf-spring-segment-routing-policy], the use of Redundancy
Segment would trigger the Redundancy Policy instantiation on
redundancy node.
Redundancy Segment is associated with service instructions,
indicating the following operations:
* Steers the packet into the corresponding redundancy policy
* Encapsulates flow identification and sequence number in packets if
the two information is not carried in packets
* Packet replication and segment encapsulation based on the
information of redundancy policy, e.g., the number of replication
copies, an ordered list of segments with a topological instruction
In this document, a new behavior End.R for Redundancy Segment is
defined. An instance of a redundancy SID is associated with a
redundancy policy B and a source address A. In the following
description, End.R behavior is specified in the encapsulation mode.
The End.R behavior in the insertion mode is for further study.
When an SRv6-capable node (N) receives an IPv6 packet whose
destination address matches a local IPv6 address instantiated as an
SRv6 SID (S), and S is a Redundancy SID, N does:
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S01. When an SRH is processed {
S02. If (Segments Left>0) {
S03. Decrement IPv6 Hop Limit by 1
S04. Decrement Segments Left by 1
S05. Update IPv6 DA with Segment List[Segments Left]
S06. Add flow identification and sequence number if indicated*
S07. Duplicate the packets (as number of active SID lists in B)
S08. Push the new IPv6 headers to each replica. The IPv6 header
contains an SRH with the SID list in B
S09. Set the outer IPv6 SA to A
S10. Set the outer IPv6 DA to the first SID of new SRH SL
S11. Set the outer Payload Length, Traffic Class, Flow Label,
Hop Limit and Next-Header fields
S12. Submit the packet to the egress IPv6 FIB lookup
for transmission to the new destination
S13. }
S14. }
* Adding flow identification and sequence number is an optional behavior
for Redundancy Segment. The instruction execution is determined and
explicitly indicated by SR policy or Segment itself.
4.2. Merging Segment
Merging Segment is associated with service instructions, indicates
the following operations:
* Packet merging and elimination: forward the first received packets
and eliminate the redundant packets
In order to eliminate the redundant packet of a flow, merging node
utilizes sequence number to evaluate the redundant status of a
packet. Note that implementation specific mechanism could be applied
to control the amount of state monitored on sequence number, so that
system memory usage can be limited at a reasonable level.
As merging node needs to maintain the state of flows, a centralized
controller should have a knowledge of merging nodes capability, and
never provision the redundancy policy to redundancy node when the
computation result goes beyond the flow recovery capability of
merging node. The capability advertisement of merging node will be
specified separately elsewhere, which is not within the scope of this
document.
A new SRv6 behavior for Merging Segment, End.M, is defined in this
document.
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When an SRv6-capable node (N) receives an IPv6 packet whose
destination address matches a local IPv6 address instantiated as an
SRv6 SID (S), and S is a Merging SID, N does:
S01. When an SRH is processed {
S02. If (Segments Left>=0) {
S03. Read the SN from the packet and look it up in table
S04. If (this sequence number does not exist in the table) {
S05. Store this sequence number in table
S06. Remove the outer IPv6+SRH header
S07. Decrement IPv6 Hop Limit by 1 in inner SRH
S08. Decrement Segments Left by 1 in inner SRH
S09. Update IPv6 DA with Segment List[Segments Left] in inner SRH
S10. Submit the packet to the egress IPv6 FIB lookup and transmit
S11. }
S12. ELSE {
S13. Drop the packet
S14. }
S15. }
S16. }
5. Meta Data to Support Redundancy Protection
To support the redundancy protection function, flow identification
and sequence number are added in the packet and further used at
merging node when the merging function is executed. Flow
identification identifies one specific flow of redundancy protection,
and is usually allocated from centralized controller to SR ingress
node or redundancy node in SR network. Note that flow identification
can also be allocated and advertised by merging node. BGP, PCEP or
Netconf protocols can facilitate the advertisement and distribution
of flow identification among controller, redundancy node and merging
node. Sequence number distinguishes the packets within a flow by
specifying the order of packets. Not like the uniqueness of flow
identification to one specific flow, sequence number keeps changing
to each packet within a flow. It is RECOMMENDED to add the sequence
number in forwarding plane as performance and scalability is
required.
Figure 2 suggests an encapsulation of flow identification and
sequence number in Segment Routing Header (SRH)[RFC8754] when
redundancy protection is used in SRv6 network.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Header | Hdr Ext Len | Routing Type | Segments Left |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Last Entry | Flags | Tag (Sequence Number) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Merging Segment (Locator+Function+Arg:Flow ID) ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ... ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Segment List[n] (128 bits) ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2 Encapsulation of Flow Identification and Sequence Number
Since the flow identification is only used at merging node to
identify the specific flow of redundancy protection, it is
encapsulated in the Arguments of Merging Segment in SRH. The length
of flow identification is not limited, however in practice it is
suggested to be 16 bits.
All the duplicates of the same packet need to be tagged for
deduplication at the merging node. For this purpose, we will use a
sequence number. It is RECOMMENDED to encode the seq number in the
Tag field of the SRH, with a length of 16bits.
6. Segment Routing Policy to Support Redundancy Protection
Redundancy Policy is a variation of SR Policy to conduct the replicas
to multiple disjoint paths for redundancy protection. It extends SR
policy [I-D.ietf-spring-segment-routing-policy] to include more than
one active and parallel ordered lists of segments between redundancy
node and merging node, and all the ordered lists of segments are used
at the same time to steer each copy of flow into different disjoint
paths.
7. IANA Considerations
This document requires registration of End.R behavior and End.M
behavior in "SRv6 Endpoint Behaviors" sub-registry of "Segment
Routing Parameters" registry.
IANA maintains The "SRv6 Endpoint Behaviors" sub-registry of the
"Segment Routing Parameters" registry. IANA is reuqested to make two
new assignments from the First Come First Served portion of the
registry as follows:
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Value | Hex | Endpoint Behavior | Reference | Change Controller
------+-------+-------------------+------------+------------------
TBD1 | xTBD1 | End.R | [This.I-D] | IETF
TBD1 | xTBD1 | End.M | [This.I-D] | IETF
8. Security Considerations
TBD
9. Acknowledgements
The authors would like to thank Bruno Decraene, Ron Bonica, James
Guichard, Jeffrey Zhang, Balazs Varga, Adrian Farrel for their
valuable comments and discussions.
10. References
10.1. 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>.
[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>.
[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
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[RFC8655] Finn, N., Thubert, P., Varga, B., and J. Farkas,
"Deterministic Networking Architecture", RFC 8655,
DOI 10.17487/RFC8655, October 2019,
<https://www.rfc-editor.org/info/rfc8655>.
Authors' Addresses
Xuesong Geng
Huawei Technologies
China
Email: gengxuesong@huawei.com
Mach(Guoyi) Chen
Huawei Technologies
China
Email: mach.chen@huawei.com
Fan Yang
Huawei Technologies
China
Email: shirley.yangfan@huawei.com
Pablo Camarillo Garvia
Cisco Systems, Inc.
Spain
Email: pcamaril@cisco.com
Gyan Mishra
Verizon Inc.
Email: gyan.s.mishra@verizon.com
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