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SPRING Working Group                                             X. Geng
Internet-Draft                                                   M. Chen
Intended status: Standards Track                                 F. Yang
Expires: August 26, 2021                             Huawei Technologies
                                                       February 22, 2021


               Segment Routing for Redundancy Protection
             draft-geng-spring-sr-redundancy-protection-02

Abstract

   Redundancy protection is one of the mechanisms to achieve service
   protection, following the principle of PREOF (Packet
   Replication/Elimination/Ordering Function).  To empower the Segment
   Routing with the capability of redundancy protection, two types of
   Segment including Redundancy Segment and Merging Segment are
   introduced.  The instantiation of Redundancy and Merging Segments can
   be applied to both segment routing over MPLS (SR-MPLS) and segment
   routing over IPv6 (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
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   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 August 26, 2021.








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Copyright Notice

   Copyright (c) 2021 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   described in the Simplified BSD License.

Table of Contents

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

1.  Introduction

   Service protection defined in [RFC8655] is initially required from
   the use cases in a variety of industries described in [RFC8578].
   Together with other two techniques Resource allocation and Explicit
   routes, it targets to provide the deterministic flow transmission.
   Meanwhile, with the emerge of Cloud VR, Cloud Game, High-Definition
   Video applications running in the Internet, SLA (Service Level
   Agreement) guarantee becomes an important issue which requires new
   technologies and solutions for network.




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   Redundancy Protection is one of the mechanisms to achieve service
   protection, following the principle of PREOF (Packet Replication/
   Elimination/Ordering Function) defined in [RFC8655].  Specifically,
   replicates the packets of flows into two or more copies, transports
   different copies through different paths in parallel, eliminates and
   orders the packets at end to provide redundancy protection.

   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, 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).

2.  Terminology and Conventions

   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
   [I-D.ietf-spring-srv6-network-programming] and[RFC2119].

   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 and ordering
   (optionally).

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

   Flow Identification: information in SR data service to indicate one
   flow.

   Sequence Number: information in SR data service 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].






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3.  Redundancy Protection in Segment Routing Scenario

                |                                        |
                |<-------------- SR Domain ------------->|
                |                                        |
                |            +-----+R3+-----+            |
              +---+        +-+-+          +-+-+        +---+
       -------|R1 |--------|Red|          |Mer|--------|R2 |-------
              +---+        +-+-+          +-+-+        +---+
                             +-----+R4+-----+

   Figure 1: Example Scenario of Redundancy Protection in SR Domain

   This figure shows an example of redundancy protection used in SR
   domain.  When a flow is sent into SR 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 a stack of MPLS
   labels or an ordered list of SRv6 SIDs.  R1, R2, R3, R4, Red and Mer
   are SR-capable nodes.

   2) R1 encapsulates the flow identification and sequence number to the
   packets.  Flow identification identifies the specific flow, and
   sequence number distinguishes the packet sequence of a flow.

   3) When the packet flow arrives in Red node, known as Redundancy
   Node, one flow is replicated into two copies.  Each copy of flow is
   encapsulated with different newly-defined list of SIDs, and the last
   SID is always pointed to the SID of Mer node, known as Merging Node.

   4) When the original flow and replicated flow go through different
   paths till 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 happened in one path, the service
   continues to deliver 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 necessary in
   the Merging Node.

   In this example, service protection is supported by utilizing two
   packet flows transmitted over two forwarding paths.  For a
   unidirectional flow, Red node supports replication function, and Mer
   node supports elimination and ordering functions.





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4.  Segment to Support Redundancy Protection

   To achieve the Packet Replication/Elimination/Ordering Function,
   Redundancy Segment and Merging Segment are introduced.

4.1.  Redundancy Segment

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

   o  Steering the packet into the corresponding redundancy policy

   o  Packet replication and encapsulation based on the redundancy
      policy, e.g., the number of replication copies

4.1.1.  SR over MPLS

   In the case of SR over MPLS, when the Active Segment is a Redundancy
   Segment, a redundancy policy is associated.  According to the
   information of candidate paths in redundancy policy, packets are
   replicated, and the Incoming redundancy segment is swapped with
   different stacks of MPLS labels to forward the packet in different
   paths.

4.1.2.  SRv6

   In the case of SRv6, a new behavior End.R for Redundancy Segment is
   defined.  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.          Create two new IPv6 headers with SRH-1 and SRH-2 respectively
S07.          Insert different policy-instructed segment lists into SRH-1 and SRH-2
S08.          Create a duplication of the incoming packet
S09.          Encapsulate the original packet with the new IPv6+SRH-1 header
S10.          Encapsulate the duplicate packet with the new IPv6+SRH-2 header
S11.          Set IPv6 SA as the local address of this node
S12.          Set IPv6 DA of IPv6+SRH-1 to the first segment of SRH-1 SL
S13.          Set IPv6 DA of IPv6+SRH-2 to the first segment of SRH-2 SL
S14.          Copy flow identification and sequence number from current SRH to SRH-1
S15.          Copy flow identification and sequence number from current SRH to SRH-2
S16.          Set the outer Payload Length, Traffic Class, Flow Label,Hop Limit and Next-Header fields
S17.          Submit the packet to the egress IPv6 FIB lookup and transmit
S18.     }
S19.     ELSE {
S20.          Drop the packet
S21.     }
S22.  }

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

   o  Packet ordering(optional): reorder the packets if the packet
      arrives out of order

4.2.1.  SR over MPLS

   In the case of SR over MPLS, when the Active Segment is a Merging
   Segment and this packet is not a redundant packet, a CONTINUE
   operation is applied.  Incoming merging segment is swapped with next
   segment.

4.2.2.  SRv6

   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==0)   {
S03.          Acquire the sequence number of received packet and lookup it in a local table
S04.             If (the sequence number is not existed in table ) {
S05.                   Store the packet and record the 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 the
   specific flow with target of redundancy protection.  Sequence number
   distinguishes the packets within a flow by specifying the order of
   packets.  The flow identification and sequence number is RECOMMENDED
   to be added at the ingress of SR domain, and MUST be added before the
   redundancy node.  The flow identification and sequence number is
   carried in the service packets along the different paths to merging
   node.  Merging node removes flow identifier and sequence number once
   the elimination and ordering is accomplished.  Thus, an encapsulation
   of flow identification and sequence number is required to be defined
   in both SR over MPLS and SRv6 data plane.

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 and ordering (optional).  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 could also be used to




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   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-srv6-network-programming]
              Filsfils, C., Camarillo, P., Leddy, J., Voyer, D.,
              Matsushima, S., and Z. Li, "SRv6 Network Programming",
              draft-ietf-spring-srv6-network-programming-28 (work in
              progress), December 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>.

10.2.  Informative 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-09 (work in progress),
              November 2020.




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   [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>.

   [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>.

Authors' Addresses

   Xuesong Geng
   Huawei Technologies
   Beijing
   China

   Email: gengxuesong@huawei.com


   Mach(Guoyi) Chen
   Huawei Technologies
   Beijing
   China

   Email: mach.chen@huawei.com


   Fan Yang
   Huawei Technologies
   Beijing
   China

   Email: shirley.yangfan@huawei.com













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