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Segment Routing for Redundancy Protection
draft-geng-spring-sr-redundancy-protection-03

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This is an older version of an Internet-Draft whose latest revision state is "Replaced".
Authors Xuesong Geng , Mach Chen , Fan Yang , Pablo Camarillo , Gyan Mishra
Last updated 2021-05-10 (Latest revision 2021-02-22)
Replaced by draft-ietf-spring-sr-redundancy-protection
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draft-geng-spring-sr-redundancy-protection-03
SPRING Working Group                                             X. Geng
Internet-Draft                                                   M. Chen
Intended status: Standards Track                            F. Yang, Ed.
Expires: November 11, 2021                           Huawei Technologies
                                                            P. Camarillo
                                                     Cisco Systems, Inc.
                                                               G. Mishra
                                                            Verizon Inc.
                                                            May 10, 2021

               Segment Routing for Redundancy Protection
             draft-geng-spring-sr-redundancy-protection-03

Abstract

   Redundancy protection provides a mechanism to achieve the high
   reliability of the service transmission in network.  This document
   extends the capabilities in SR paradigm to support the redundancy
   protection in a DetNet environment, including the definitions of new
   Segments and a variation of Segment Routing Policy.  The new
   mechanism applies equally to both Segment Routing with MPLS data
   plane (SR-MPLS) and Segment Routing with IPv6 data plane (SRv6).

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
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on November 11, 2021.

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Copyright Notice

   Copyright (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
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   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
     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
       4.1.1.  SR over MPLS  . . . . . . . . . . . . . . . . . . . .   5
       4.1.2.  SRv6  . . . . . . . . . . . . . . . . . . . . . . . .   6
     4.2.  Merging Segment . . . . . . . . . . . . . . . . . . . . .   7
       4.2.1.  SR over MPLS  . . . . . . . . . . . . . . . . . . . .   7
       4.2.2.  SRv6  . . . . . . . . . . . . . . . . . . . . . . . .   7
   5.  Meta Data to Support Redundancy Protection  . . . . . . . . .   8
   6.  Segment Routing Policy to Support Redundancy Protection . . .   8
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   9
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     10.1.  Normative References . . . . . . . . . . . . . . . . . .   9
     10.2.  Informative References . . . . . . . . . . . . . . . . .  10
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

   Redundancy Protection provides a mechanism to achieve the high
   reliability of the service transmission in network.  Specifically,
   packets of flows are replicated into two or more copies, which are
   transported through different paths in parallel.  When copies of
   packets are merged at network node, the redundant packets are
   eliminated to guarantee one copy of the flow is successfully
   transmitted.

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   Redundancy protection targets to the services especially requires
   ultra reliable transmission, for example 5G URLLC services including
   Cloud VR/Game, remote surgery, harbor crane lifting, and differential
   protection in electrical utilities etc.  Redundancy protection can
   also be used as Packet Replication and Elimination Function for
   Deterministic Networking defined in [RFC8655].  At last, it also
   bring values to the existing services in legacy network, for example
   IPTV service and financial private line in fixed broadband network,
   as well as the video service in data center interconnect.

   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 capabilities in SR paradigm to support the
   redundancy protection in a DetNet environment, including the
   definitions of new Segments and a variation of Segment Routing
   Policy.  The new mechanism applies equally to both Segment Routing
   with MPLS data plane (SR-MPLS) [RFC8660] and Segment Routing with
   IPv6 data plane (SRv6) [RFC8986].

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

   This document uses the terminology defined in [RFC8402] [RFC8964],
   and it also introduces the following new terms:

   Redundancy Node: the start point of redundancy protection, which is a
   network device that could implement packet replication.

   Merging Node: the end point of redundancy protection, which is a
   network node that could implement packet elimination.

   Redundancy Policy: an extended SR policy which includes more than one
   active segment lists to support redundancy protection.

   Flow Identification: information in the SR packet to indicate one
   flow.

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   Sequence Number: information in the SR packet to indicate the packet
   sequence of one flow.

   Editor's Note: Similar mechanism is defined as "Service Protection"
   in the [RFC8655].  In this document, we define a new term "Redundancy
   Protection" to distinguish with other service protection method.
   Some of the terms are similar as [RFC8655].

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 in 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 forwarding paths (e.g., Disjoint Paths).  The
   last SID in the segment list is always a SID instantiated on the
   Merging node (Mer) .

   3) At the same time, the Flow Identification and Sequence Number are
   added to each of the replicas.  Flow identification identifies the
   specific flow, and sequence number distinguishes the packet sequence
   of a flow.

   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.

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   5) When there is any failures or packet loss in one path, the service
   continues undisrupted through the other path without break.

   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.  This 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 SR over MPLS
   forwarding behavior and SRv6 Endpoint Behavior are introduced.

4.1.  Redundancy Segment

   Redundancy Segment is a variation of Binding SID, and associated with
   a Redundancy Policy on the redundancy node.  Redundancy segment is
   associated with service instructions, indicating the following
   operations:

   o  Steering the packet into the corresponding redundancy policy

   o  Flow identification and sequence number encapsulation in packets

   o  Packet replication and segment encapsulation based on the
      information of redundancy policy, e.g., the number of replication
      copies, a segment or an ordered list of segments with a
      topological instruction

4.1.1.  SR over MPLS

   In the case of SR over MPLS, IETF Deterministic Networking working
   group has defined Packet Replication/Elimination/Ordering Functions
   in DetNet MPLS data plane [RFC8964].  The support of redundancy
   protection in SR over MPLS data plane keeps consistent with the PRF
   and REF functions defined in DetNet MPLS data plane.

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   In SR over MPLS, Redundancy Segment acts as DetNet S-Label to
   explicitly identify the replication function on redundancy node.
   Redundancy segment is allocated from redundancy node, and is
   provisioned to the ingress node of SR domain by the controller plane
   via PCEP, BGP, or NetConf protocols.

   When the Active Segment is a Redundancy Segment, a NEXT operation is
   performed and a redundancy policy is associated.  Via redundancy
   policy, flow identification is assigned to redundancy node and acts
   as the elimination serivce label (S-Label).  Sequence number is
   generated and encapsulated in DetNet Control Word (d-CW).  The
   packets of a flow is replicated to multiple replicas, and
   encapsulated with a new MPLS label stack including the d-CW, S-Label
   and forwarding sub-layer LSPs, determined by the candidate paths of
   redundancy policy.

4.1.2.  SRv6

   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:

S01.When an SRH is processed {
S02.   If (Segments Left == 0) {
S03.        Remove the IPv6 header
S04    }
S05.   If (Segments Left>0)   {
S06.        Decrement IPv6 Hop Limit by 1
S07.        Decrement Segments Left by 1
S08.        Update IPv6 DA with Segment List[Segments Left]
S09.   }
S10.   Add flow identification and sequence number to packet
S11.   Duplicate the packets (as many replicas as active SID lists in B)
S12.   Push the new IPv6 headers to each replica. The IPv6 header
       contains an SRH with a different SID List
S13.   Set the outer IPv6 SA to A
S14.   Set the outer IPv6 DA to the first SID of new SRH SL
S15.   Set the outer Payload Length, Traffic Class, Flow Label,
       Hop Limit and Next-Header fields
S16.   Submit the packet to the egress IPv6 FIB lookup
       for transmission to the new destination
S17.}

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4.2.  Merging Segment

   Merging Segment is associated with service instructions, indicates
   the following operations:

   o  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.

4.2.1.  SR over MPLS

   In the case of SR over MPLS, being consistent with [RFC8964], Merging
   Segment always stays at last of MPLS label stack as DetNet S-Label.
   When the Active Segment is a Merging Segment, a NEXT operation is
   performed.  The packet is identified to a particular flow according
   to the service label.  Sequence number encapsulated in DetNet control
   word is used to determine whether the packet is redundant.

4.2.2.  SRv6

   In the case of SRv6, a new behavior End.M for Merging Segment is
   defined.

   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:

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 S01. When an SRH is processed {
 S02.  If (Segments Left==0)   {
 S03.    Acquire the sequence number of received packet and look it up
 S04.      If (state of this sequence number == 0) {
 S05.       Set the state of this sequence number to 1
 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 the
   specific flow with target of redundancy protection.  Sequence number
   distinguishes the packets within a flow by specifying the order of
   packets.  Thus, the encapsulation of flow identification and sequence
   number is required in both SR over MPLS and SRv6 data plane.

   In SR over MPLS, being consistent with [RFC8964], flow identification
   is identified by either redundancy service or merging service, and is
   encapsulated as the DetNet service label.  Note that, the DetNet
   service label can be different and swapped in the packet
   transmission.  Sequence number is encapsulated in DetNet Control Word
   (d-CW).

   In SRv6, flow identification and sequence number is added at the
   redundancy node and carried in the packets along the different paths
   to merging node.  Merging node removes flow identifier and sequence
   number once the elimination and ordering (optional) is accomplished.

6.  Segment Routing Policy to Support Redundancy Protection

   Redundancy Policy is a variation of SR Policy, and is identified
   through the tuple <redundancy node, redundancy ID, merging node>.
   Redundancy node is specified as IPv4/IPv6 address of the headend,
   which is able to do packet replication.  Merging node is specified as
   IPv4/IPv6 address of the endpoint, which is able to do packet
   elimination.  Redundancy ID could be a specified value of "color"
   define in section 2.1 of [I-D.ietf-spring-segment-routing-policy],
   which indicates the SR policy as a redundancy policy.  Redundancy ID

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   could also be used to distinguish different redundancy policies
   sharing the same redundancy node and merging node.

   Redundancy Policy 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 paths.  In redundancy policy,
   Redundancy Segment MUST be specified, and the last segment of each
   ordered list of segments MUST be Merging Segment.

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.

8.  Security Considerations

   TBD

9.  Acknowledgements

   The authors would like to thank Bruno Decraene, Ron Bonica, and James
   Guichard for their valuable comments.

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", draft-
              ietf-spring-segment-routing-policy-11 (work in progress),
              April 2021.

   [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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   [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>.

   [RFC8964]  Varga, B., Ed., Farkas, J., Berger, L., Malis, A., Bryant,
              S., and J. Korhonen, "Deterministic Networking (DetNet)
              Data Plane: MPLS", RFC 8964, DOI 10.17487/RFC8964, January
              2021, <https://www.rfc-editor.org/info/rfc8964>.

   [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

   [I-D.ietf-spring-sr-service-programming]
              Clad, F., Xu, X., Filsfils, C., Bernier, D., Li, C.,
              Decraene, B., Ma, S., Yadlapalli, C., Henderickx, W., and
              S. Salsano, "Service Programming with Segment Routing",
              draft-ietf-spring-sr-service-programming-04 (work in
              progress), March 2021.

   [RFC8578]  Grossman, E., Ed., "Deterministic Networking Use Cases",
              RFC 8578, DOI 10.17487/RFC8578, May 2019,
              <https://www.rfc-editor.org/info/rfc8578>.

   [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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