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Network Working Group                                      D. Voyer, Ed.
Internet-Draft                                               Bell Canada
Intended status: Informational                               C. Filsfils
Expires: May 22, 2020                                      D. Dukes, Ed.
                                                     Cisco Systems, Inc.
                                                           S. Matsushima
                                                                Softbank
                                                                J. Leddy
                                                  Individual Contributor
                                                                   Z. Li
                                                                  Huawei
                                                             J. Guichard
                                                               Futurewei
                                                       November 19, 2019


       Deployments With Insertion of IPv6 Segment Routing Headers
             draft-voyer-6man-extension-header-insertion-08

Abstract

   SRv6 is deployed in multiple provider networks.

   This document describes the usage of SRH insertion and deletion
   within the SR domain and how security and end-to-end integrity is
   guaranteed.

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 RFC 2119 [RFC2119].

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."




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   This Internet-Draft will expire on May 22, 2020.

Copyright Notice

   Copyright (c) 2019 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
   to this document.  Code Components extracted from this document must
   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.  Deployment Report . . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Deployments . . . . . . . . . . . . . . . . . . . . . . .   3
     2.2.  Vendor and Open-Source Support  . . . . . . . . . . . . .   3
   3.  Deployment Experience With SRH Header Operarion . . . . . . .   4
     3.1.  The SR Domain . . . . . . . . . . . . . . . . . . . . . .   5
   4.  Baseline Usecase  . . . . . . . . . . . . . . . . . . . . . .   5
   5.  Choosing an SRv6 SID Block  . . . . . . . . . . . . . . . . .   6
   6.  Securing the SR Domain  . . . . . . . . . . . . . . . . . . .   7
   7.  MTU within the SR domain  . . . . . . . . . . . . . . . . . .   7
   8.  VPN with SRv6 . . . . . . . . . . . . . . . . . . . . . . . .   7
   9.  TILFA with SRv6 . . . . . . . . . . . . . . . . . . . . . . .   8
     9.1.  SRH Insertion Process . . . . . . . . . . . . . . . . . .   8
     9.2.  The Penultimate SID of the Inserted SRH is of PSP flavor    9
     9.3.  MTU-delta . . . . . . . . . . . . . . . . . . . . . . . .   9
   10. Security Considerations . . . . . . . . . . . . . . . . . . .  10
   11. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  10
   12. Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  10
   13. References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     13.1.  Normative References . . . . . . . . . . . . . . . . . .  10
     13.2.  Informative References . . . . . . . . . . . . . . . . .  11
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11

1.  Introduction

   [I-D.matsushima-spring-srv6-deployment-status] records multiple SRv6
   deployments in multiple networks





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   In each deployment, traffic traversing an SR domain is encapsulated
   in an outer IPv6 header for its journey through the SR domain.

   To implement transport services within the SR domain, insertion or
   removal of an SRH after the outer IPv6 header is performed.  Any
   segment within the SRH is strictly contained within the SR domain.

   The SR domain always preserves the end-to-end integrity of traffic
   traversing it.  No extension header is manipulated, inserted or
   removed from an inner transported packet.  The packet leaving the SR
   domain is exactly the same (except for the hop-limit update) as the
   packet entering the SR domain.

   The SR domain is designed with link MTU sufficiently greater than the
   MTU at the ingress edge of the SR domain.

2.  Deployment Report

   The following deployments are as of November 2019.

2.1.  Deployments

   Six operators have publicly reported SRv6 deployments with commercial
   traffic supported by linerate hardware.  Each deployment follows the
   network design and SRH add/remove behavior described in this
   document.

      Softbank

      China Telecom

      Iliad

      China Unicom

      CERNET2

      MTN Uganda Ltd.

   Further information can be found in
   [I-D.matsushima-spring-srv6-deployment-status]

2.2.  Vendor and Open-Source Support

   Eighteen unique implementations of SRv6 are available from multiple
   vendors and open source initiatives that support the SRH add/remove
   behavior described in this document:




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      Cisco ASR 9000

      Cisco NCS 5500

      Cisco NCS 560

      Cisco NCS 540

      Cisco ASR1000

      Huawei ATN

      Huawei CX600

      Huawei NE40E

      Hauwei ME60

      Huawei NE5000E

      Huawei NE9000

      Huawei NG-OLT MA5800

      Barefoot Tofino 1 NPU

      Barefoot Tofino 2 NPU

      Broadcom Jericho 1, 1+

      Broadcom Jericho 2

      Linux kernel

      FD.io VPP

      Marvell's Prestera Falcon CX 8500 family

      Intel PAC N3000

   Further information can be found in
   [I-D.matsushima-spring-srv6-deployment-status]

3.  Deployment Experience With SRH Header Operarion







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3.1.  The SR Domain

   An SR Domain is defined in [RFC8402].

   Section 5.2 of [I-D.ietf-6man-segment-routing-header] further
   describes the SR domain as a single system with delegation among
   components.  It states:

      All intra SR Domain packets are of the SR Domain.  The IPv6 header
      is originated by a node of the SR Domain, and is destined to a
      node of the SR Domain.

      All inter domain packets are encapsulated for the part of the
      packet journey that is within the SR Domain.  The outer IPv6
      header is originated by a node of the SR Domain, and is destined
      to a node of the SR Domain.

   In other words, all packets within the SR domain have a source and
   destination address within the SR Domain.

   The SR domain is secured as per Section 5.1 of
   [I-D.ietf-6man-segment-routing-header] and no external packet can
   enter the domain with a destination address equal to a segment of the
   domain.

   In other words, no node outside the SR domain may send packets to,
   nor make direct use of, segments within the SR domain.

4.  Baseline Usecase

   The following abstract illustration shows the SR Domain, how traffic
   is encapsulated when traversing the SR domain, and (in subequent
   sections) how an SRH is inserted and processed for a packet
   traversing the SR domain.  It is representative of all deployments in
   Section 2.1.
















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              + * * * * * * * * * * * * * * * * * * * * +

              *                                         *
      [1]----[3]--------[5]----------------[6]---------[4]---[2]
              *          |                  |           *
                         |                  |
              *          |                  |           *
                        [7]----------------[8]
              *                                         *

              + * * * * * * *  SR Domain  * * * * * * * +

                                 Figure 1

   o  3 and 4 are SR Domain edge routers

   o  5, 6, 7, and 8 are all SR Domain routers

   o  1 and 2 are hosts outside the SR Domain

   Since all inter domain packets are encapsulated for the part of the
   packet journey that is within the SR Domain, a packet sent from 1 and
   destined to 2 is encapsulated in an outer IP v6 header between nodes
   3 and 4.

5.  Choosing an SRv6 SID Block

   Without revealing the specifics of each deployment, the following
   well-known technique can be used:

      Obtain a GUA block from the respective registry (e.g.
      PPPP:PPP0::/28)

      Sub-allocate a block for SID allocation (e.g.
      PPPP:PPPB:BB00::/40)

      Allocate a /64 SID locator to each node in the domain that needs
      to provide network instruction (e.g. node 4 gets
      PPPP:PPPB:BB00:0004::/64 as a SID locator)

   Vendors and operators have automated the process of locator
   selection, the details of which are outside the scope of this
   document.








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6.  Securing the SR Domain

   The security measures defined in
   [I-D.ietf-6man-segment-routing-header] Section 5.1 are applied.

   Protection level 1: filter external traffic entering the SR domain.
   For example, node 4 (on its interface from node 2) applies an ingress
   ACL that drops any packet with DA within the PPPP:PPPB:BB00::/40
   block.

   Protection level 2: filter internal traffic.  For example, node 4 (on
   its interface from node 6) applies an ingress ACL that drops any
   packet with DA in PPPP:PPPB:BB00:0004::/64 block if SA is not within
   the block PPPP:PPP0::/28

   Vendors and operators have automated the application of these
   protection levels, the details of which are outside the scope of this
   document.

7.  MTU within the SR domain

   The deployments, Section 2.1, leverage the extensively used practice
   of ensuring an MTU within the domain is bigger than the MTU on the
   external links of the domain.

   More specifically, the MTU difference (MTU-Delta) is designed to be
   larger than the maximum encapsulation overhead deemed required by the
   deployment.

   The exact number is operator specific and is outside the scope of
   this document.  Some indications on how to plan this are provided in
   the following sections.

   Any packet exceeding the MTU of a link generates an IPv6 ICMP error
   message "packet too big" back to the source of the packet.

8.  VPN with SRv6

   The deployments involve the creation of commercial SRv6-based VPN
   traffic as described in [I-D.ietf-bess-srv6-services].

   The salient point to note is that no SRH needs to be inserted to
   realize an SRv6 VPN service.

   The ingress PE encapsulates the inner packet in an outer header and
   sets the outer DA to the END.DT/DX SID signaled by the egress PE.





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   MTU-Delta must be >= 40 bytes to allow for the outer IPv6
   encapsulation without fragmentation.

9.  TILFA with SRv6

   The deployments involve the delivery of sub-50msec TILFA protection
   to the commercial SRv6-based VPN traffic transported by the operator
   network [I-D.ietf-rtgwg-segment-routing-ti-lfa].

   In these deployments, when a failure is detected, the Point of Local
   Repair (PLR) inserts an SRH implementing the precomputed TILFA backup
   path.

   The following salient points are discussed:

      SRH insertion process

      The penultimate SID of the inserted SRH is of PSP flavor

      MTU-delta planning

9.1.  SRH Insertion Process

   When an SRH is inserted by an intermediate node it walks the IPv6
   header chain to the first header after the IPv6 header and inserts
   the SRH prior to that header.

      +---------------+------------
      |  IPv6 header  | IPv4 header
      |  VPN Service  |
      | Next Header = |
      |      IPv4     |
      +---------------+------------
                      ^-SRH insertion here

                                 Figure 2

   An SR Policy headend within the SR domain inserts an SRH as follows:

   1.  Determine where to insert the SRH.

   2.  Copy the destination address from the IPv6 header to Segment
       List[0] of the SRH to be inserted.  This ensures the original
       destination address is restored upon execution of the final
       segment in the inserted SRH.

   3.  Increase the IPv6 header payload length field by the length in
       bytes of the inserted SRH.



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       If the resulting payload length exceeds 2^16 bytes generate an
       ICMP "Packet To Big" error message to the source with an MTU of
       2^16 minus the length in bytes of the SRH and discard the packet.
       Note: this does not occur in reported deployments given the MTU
       design constraint.

   4.  Set the SRH next header field to the value in the next header
       field of the header that will precede the SRH.

   5.  Set the next header field of the header that will precede the SRH
       to the routing extension header (43)

   6.  Set the IPv6 destination address to the first segment in the
       segment list of the SRH to be inserted.  This segment may or may
       not be present in the SRH depending on the use of a reduced SRH,
       see section 4.1.1 of [I-D.ietf-6man-segment-routing-header].

   7.  Insert the SRH into the packet at the location it should be
       inserted and resubmit the packet to the IPv6 module for
       transmission to the new destination.

9.2.  The Penultimate SID of the Inserted SRH is of PSP flavor

   The TILFA protection service is essentially a transparent service: it
   seeks to make the loss of a link, node or SRLG invisible to the
   transport service.  It is also a very transient service as it only
   lasts a few hundreds of msec while the IGP converges.

   Consistent with this transparent service definition, the deployments
   leverage a TILFA computation that ensures that the penultimate SID of
   the inserted SRH is of PSP flavor.

9.3.  MTU-delta

   The vendors reporting the listed deployments have collectively
   deployed TILFA in tens of SR-MPLS networks, in 6 SRv6 networks and
   have simulated their SRv6 algorithm in tens of collected real
   topologies.  The inferred experience is that the probability that a
   TILFA backup path requires more than 2 SRv6 SIDs is very rare.

   MTU-Delta must be >= 80 bytes.

      40 bytes (VPN service)

      + 8 (SRH) (TILFA)

      + 2 * 16 (2 TILFA SID's)




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   The maximum encapsulation size of any node within the SR domain is
   limited to a specific value, this maximum is used to calculate the
   maximum link MTU of interfaces ingress to the SR domain.

10.  Security Considerations

   Section 6 describes the method of securing the SR domain in the
   deployments listed.

   All security considerations discussed in
   [I-D.ietf-6man-segment-routing-header] are equally applicable when an
   SRH insertion is performed.

11.  IANA Considerations

   This document doesn't introduce any IANA request.

12.  Contributors

   The authors would like to thank the following for their
   contributions: Robert Raszuk, Stefano Previdi, Stefano Salsano,
   Antonio Cianfrani, David Lebrun, Olivier Bonaventure, Prem
   Jonnalagadda, Milad Sharif, Hani Elmalky, Ahmed Abdelsalam, Arthi
   Ayyangar, Dirk Steinberg, Wim Henderickx.

13.  References

13.1.  Normative References

   [I-D.ietf-6man-segment-routing-header]
              Filsfils, C., Dukes, D., Previdi, S., Leddy, J.,
              Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header
              (SRH)", draft-ietf-6man-segment-routing-header-26 (work in
              progress), October 2019.

   [I-D.ietf-bess-srv6-services]
              Dawra, G., Filsfils, C., Brissette, P., Agrawal, S.,
              Leddy, J., Voyer, D., daniel.bernier@bell.ca, d.,
              Steinberg, D., Raszuk, R., Decraene, B., Matsushima, S.,
              Zhuang, S., and J. Rabadan, "SRv6 BGP based Overlay
              services", draft-ietf-bess-srv6-services-00 (work in
              progress), October 2019.

   [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>.




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   [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>.

13.2.  Informative References

   [I-D.ietf-rtgwg-segment-routing-ti-lfa]
              Litkowski, S., Bashandy, A., Filsfils, C., Decraene, B.,
              Francois, P., daniel.voyer@bell.ca, d., Clad, F., and P.
              Camarillo, "Topology Independent Fast Reroute using
              Segment Routing", draft-ietf-rtgwg-segment-routing-ti-
              lfa-01 (work in progress), March 2019.

   [I-D.matsushima-spring-srv6-deployment-status]
              Matsushima, S., Filsfils, C., Ali, Z., and Z. Li, "SRv6
              Implementation and Deployment Status", draft-matsushima-
              spring-srv6-deployment-status-02 (work in progress),
              October 2019.

Authors' Addresses

   Daniel Voyer (editor)
   Bell Canada
   Canada

   Email: daniel.voyer@bell.ca


   Clarence Filsfils
   Cisco Systems, Inc.
   Belgium

   Email: cfilsfil@cisco.com


   Darren Dukes (editor)
   Cisco Systems, Inc.
   Ottawa
   Canada

   Email: ddukes@cisco.com









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   Satoru Matsushima
   Softbank
   Japan

   Email: satoru.matsushima@g.softbank.co.jp


   John Leddy
   Individual Contributor
   USA

   Email: john@leddy.net


   Zhenbin Li
   Huawei
   China

   Email: lizhenbin@huawei.com


   James Guichard
   Futurewei
   USA

   Email: james.n.guichard@futurewei.com

























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