Internet DRAFT - draft-geng-spring-sr-redundancy-protection
draft-geng-spring-sr-redundancy-protection
SPRING Working Group X. Geng
Internet-Draft M. Chen
Intended status: Standards Track F. Yang, Ed.
Expires: 3 February 2022 Huawei Technologies
P. Camarillo
Cisco Systems, Inc.
G. Mishra
Verizon Inc.
2 August 2021
SRv6 for Redundancy Protection
draft-geng-spring-sr-redundancy-protection-05
Abstract
Redundancy Protection is a generalized protection mechanism to
achieve the high reliability of service transmission in Segment
Routing network. The mechanism inherits the "Live-Live" methodology,
targeting to enhance the functionalities of Segment Routing over
IPv6. Inspired by DetNet Packet Replication and Packet Elimination
functions, two new Segments are introduced to provide replication and
elimination functions on specific network nodes by leveraging SRv6
Segment programming capabilities.
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
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This Internet-Draft will expire on 3 February 2022.
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Copyright Notice
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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 . . . . . . 4
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 . . . 7
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
8. Security Considerations . . . . . . . . . . . . . . . . . . . 8
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
10.1. Normative References . . . . . . . . . . . . . . . . . . 8
10.2. Informative References . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
Redundancy Protection is a generalized protection mechanism to
achieve the high reliability of service transmission in Segment
Routing network. Specifically, packets of flows are replicated at a
network node into two or more copies, which are transported via
different paths in parallel. When copies of packets are received and
merged at one network node, the redundant packets are determined and
further eliminated to guarantee only one copy of packets is
transmitted. The mechanism inherits the "Live-Live" methodology,
targeting to enhance the functionalities of Segment Routing over IPv6
[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
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nodes by leveraging SRv6 Segment programming capabilities. As it is
unnecessary to perform switchover between different paths triggered
by failure detection, redundancy protection can facilitate to achieve
zero packet loss target when failure on either path happens.
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 service.
The mechanism for P2MP service stays out of the scope of this
document.
Segment Routing (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 an arbitrary
processing of the packet in the node identified by the segment.
This document extends the Segment Routing capabilities to support the
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
URLLC: Ultra-Reliable Low-Latency Communication
VR: Virtual Reality
Red Node: Redundancy Node
Mer Node: Merging Node
FID: Flow IDentification
SN: Sequence Number
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3. Redundancy Protection in Segment Routing Scenario
| |
|<------------- SRv6 Domain ------------->|
| |
| +---+ |
| +-----+R3 +-----+ |
| | +---+ | |
+-+-+ +-+-+ +-+-+ +-+-+
-------+R1 +--------+Red| |Mer+--------+R2 +-------
+---+ +-+-+ +-+-+ +---+
| +---+ |
+-----+R4 +-----+
+---+
Figure 1: Example Scenario of Redundancy Protection in SRv6 Domain
This figure 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 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 such as flow identification (FID) and
sequence number (SN) is used to facilitate the packet elimination on
Merging node (Mer). Flow identification identifies the specific
flow, and sequence number distinguishes the packet sequence of a
flow. Meta data is either carried in the packet before it arrives at
Red node, or added to each of the replicas at Red node.
4) The multiple replicas go through different paths until the Mer
node. The first received packet of the flow is transmitted from
Merging Node to R2, and the redundant packets are eliminated.
5) When there is any failures or packet loss in one path, the service
continues undisrupted through the other path without break.
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6) Sometimes, the packet will arrive out of order because of
redundancy protection, the function of reordering may be also
necessary on Merging Node. In such case the Merging node may include
a reordering function, which is implementation specific and out of
the scope of this document.
In this example, service protection is supported by utilizing two
packet flows transmitted over two forwarding paths. It is noted that
there is no limitation of the number of replicas. For a
unidirectional flow, Red node supports replication function, and Mer
node supports elimination function. Reordering function MAY be
required in combination of elimination function on merging node. 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 the
replication function on redundancy node. It is also a variation of
Binding SID, and associated with a Redundancy Policy to provide
segment lists of disjoint paths. Thus, 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 the case of SRv6, 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.
In the case of SRv6, a new behavior End.M for Merging Segment is
defined.
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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> or ==0) {
S03. Acquire the sequence number of received 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 required. Flow identification identifies one
specific flow of redundancy protection, and is usually allocated from
centralized controller to the SR ingress node or redundancy node in
SR network. Sequence number distinguishes the packets within a flow
by specifying the order of packets. It is usually generated at SR
ingress node. If necessary, redundancy node can also facilitate to
add sequence number if required. Thus, encapsulations of flow
identification and sequence number should be specified accordingly.
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 to include more than one 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 the copies 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.
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8. Security Considerations
TBD
9. Acknowledgements
The authors would like to thank Bruno Decraene, Ron Bonica, James
Guichard, Jeffrey Zhang, Balazs Varga for their valuable comments and
discussions.
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>.
[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>.
[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
[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
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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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