[Docs] [txt|pdf] [Tracker] [WG] [Email] [Nits] [IPR]

Versions: 00 01 02 03 draft-xu-mpls-sr-over-ip

MPLS Working Group                                             S. Bryant
Internet-Draft                                                     X. Xu
Intended status: Standards Track                                 M. Chen
Expires: December 30, 2017                                        Huawei
                                                               A. Farrel
                                                                J. Drake
                                                        Juniper Networks
                                                           June 28, 2017


                A Unified Approach to IP Segment Routing
                   draft-bryant-mpls-unified-ip-sr-00

Abstract

   Segment routing is a new and powerful forwarding paradigm that allows
   packets to be steered through a network on paths other than the
   shortest path derived from the routing protocol.  The approach uses
   information encoded in the packet header and does not make use of a
   signaling protocol to pre-install paths in the network.

   Two different encapsulations have been defined to enable segment
   routing in an MPLS network and in an IPv6 network.  While
   acknowledging that there is a strong need to support segment routing
   in both environments, this document defines a converged, unified
   approach to segment routing that enables a single mechanism to be
   applied in both types of network.  The resulting approach is also
   applicable to IPv4 networks without the need for any changes to the
   IPv4 specification.

   This document makes no changes to the segment routing architecture
   and builds on existing protocol mechanisms such as the encapsulation
   of MPLS within UDP defined in RFC 7510.

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 http://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."



Bryant, et al.          Expires December 30, 2017               [Page 1]


Internet-Draft                Unified IP SR                    June 2017


   This Internet-Draft will expire on December 30, 2017.

Copyright Notice

   Copyright (c) 2017 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
   (http://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  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   3
   3.  The Unified Segment Routing Protocol Stack  . . . . . . . . .   3
   4.  The Segment Routing Instruction Stack . . . . . . . . . . . .   5
     4.1.  SRIS Format . . . . . . . . . . . . . . . . . . . . . . .   5
     4.2.  TTL . . . . . . . . . . . . . . . . . . . . . . . . . . .   6
   5.  UDP/IP Encapsulation. . . . . . . . . . . . . . . . . . . . .   6
   6.  Metadata  . . . . . . . . . . . . . . . . . . . . . . . . . .   6
   7.  Elements of Procedure . . . . . . . . . . . . . . . . . . . .   7
     7.1.  Domain Ingress  . . . . . . . . . . . . . . . . . . . . .   7
     7.2.  Legacy Transit  . . . . . . . . . . . . . . . . . . . . .   8
     7.3.  On-Path Pass-Through SR Nodes . . . . . . . . . . . . . .   8
     7.4.  SR Transit Nodes  . . . . . . . . . . . . . . . . . . . .   8
     7.5.  Penultimate SR Transit  . . . . . . . . . . . . . . . . .   9
     7.6.  Domain Egress . . . . . . . . . . . . . . . . . . . . . .   9
   8.  Modes of Deployment . . . . . . . . . . . . . . . . . . . . .   9
     8.1.  Interconnection of SR Domains . . . . . . . . . . . . . .   9
     8.2.  SR Within and IP Network  . . . . . . . . . . . . . . . .  10
   9.  OAM . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  11
   10. Comparison with SRv6  . . . . . . . . . . . . . . . . . . . .  11
   11. Security Considerations . . . . . . . . . . . . . . . . . . .  12
   12. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  12
   13. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  12
   14. References  . . . . . . . . . . . . . . . . . . . . . . . . .  12
     14.1.  Normative References . . . . . . . . . . . . . . . . . .  12
     14.2.  Informative References . . . . . . . . . . . . . . . . .  13
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  14





Bryant, et al.          Expires December 30, 2017               [Page 2]


Internet-Draft                Unified IP SR                    June 2017


1.  Introduction

   The approach to IPv6 segment routing (SR) described in
   [I-D.ietf-6man-segment-routing-header] can be challenging to
   implement in some types of forwarder, particularly where a large
   number of instructions/segments are needed to specify the required
   behaviour.  Furthermore, the approach does not allow the use of SR
   techniques in legacy IPv4 networks.  In this document we describe a
   low overhead method for running SR in IP networks by using an MPLS
   label stack carried in UDP as a method of encoding the segment
   routing instructions to be executed as the packet traverses the
   network.  We call this Unified Segment Routing (USR).

   The method defined is a complementary way of running SR in an IP
   network when compared to [I-D.ietf-6man-segment-routing-header].
   Implementers and deployers should consider the benefits and drawbacks
   of each method and only select the approach defined here where its
   properties are beneficial.

   The format that we propose requires 32 bits per additional
   instruction compared to the 128 bits for the method described in
   [I-D.ietf-6man-segment-routing-header].  The methods are further
   compared in Section 10.

   Although the segment routing instructions (i.e., the segment
   identifiers) are encoded as MPLS labels, this is a hardware
   convenience rather than an indication that the whole MPLS protocol
   stack and in particular the MPLS control protocols need to be
   deployed.  It is a hardware convenience because many hardware
   components are already able to perform lookups based on MPLS labels.

2.  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
   [RFC2119].

3.  The Unified Segment Routing Protocol Stack

   The USR protocol stack is shown below in Figure 1.










Bryant, et al.          Expires December 30, 2017               [Page 3]


Internet-Draft                Unified IP SR                    June 2017


                         +---------------------+
                         |                     |
                         |      IPvX Header    |
                         |                     |
                         +---------------------+
                         |     UDP Header      |
                         |                     |
                         +---------------------+
                         |   Segment Routing   |
                         |  Instruction Stack  |
                         .                     .
                         .                     .
                         +---------------------+
                         |                     |
                         |      Payload        |
                         .                     .
                         .                     .
                         +---------------------+

                      Figure 1: Packet Encapsulation

   The payload may be of any type that, with an appropriate convergence
   layer, can be carried over a packet network.  It is anticipated that
   the most common packet types will be IPv4, IPv6, native MPLS and
   pseudowires [RFC3985].

   Preceding the Payload is the Segment Routing Instruction Stack (SRIS)
   that carries the sequence of instructions to be executed on the
   packet as it traverses the network.  This is the Segment Identifier
   (SID) stack.

   Preceding the SRIS is a UDP header.  The UDP header is included to:

   o  Introduce entropy to allow equal-cost multi-path load balancing
      (ECMP) [RFC2992] in the IP layer [RFC7510].

   o  Provide a protocol multiplexing layer as an alternative to using a
      new IP type/next header.

   o  Allow transit through firewalls and other middleboxes.

   o  Provide disagregation.

   Preceding the UDP header is the IP header which may be IPv4 or IPv6.







Bryant, et al.          Expires December 30, 2017               [Page 4]


Internet-Draft                Unified IP SR                    June 2017


4.  The Segment Routing Instruction Stack

   The core of the protocol encapsulation is the Segment Routing
   Instruction Stack (SRIS).  This consists of a stack of Segment
   Identifiers as described in [I-D.ietf-spring-segment-routing] encoded
   as an MPLS label stack as described in
   [I-D.ietf-spring-segment-routing-mpls].

   The top SRIS entry is the next instruction to be executed.  When the
   node to which this instruction is directed has processed the
   instruction it is removed (popped) from the SRIS, and the next
   instruction processed.

   Each Instruction is encoded in a single Label Stack Entry (LSE) as
   shown in Figure 2.  The basic structure of the LSE is unchanged from
   [RFC3032] and the meanings of the Traffic Class, Bottom of Stack, and
   Time to Live fields are also unchanged.

4.1.  SRIS Format

   As described in [I-D.ietf-spring-segment-routing-mpls], the SRIS uses
   the same format as [RFC3032].  This is a compact representation that
   allows the use of existing data plane hardware.  Its use does not
   imply that MPLS needs to be enabled, or that MPLS protocols need to
   be used.  It is simply a compact, convenient way of carrying the
   instructions (the SIDs) needed to direct how the packet traverses the
   network.

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              Instruction                  | TC  |S|   TTL     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                   Instruction:  Label Value, 20 bits
                   TC:           Traffic Class, 3 bits
                   S:            Bottom of Stack, 1 bit
                   TTL:          Time to Live, 8 bits

                     Figure 2: SRIS Label Stack Entry

   As with [I-D.ietf-spring-segment-routing-mpls] a 32 bit LSE is used
   to carry each SR instruction.  The instruction itself is carried in
   the 20 bit Label Value field.  The TC field has the normal meaning as
   defined in [RFC3032] and modified in [RFC5462].  The S bit has bottom
   of stack semantics defined in [RFC3032].  TTL is discussed in
   Section 4.2.




Bryant, et al.          Expires December 30, 2017               [Page 5]


Internet-Draft                Unified IP SR                    June 2017


4.2.  TTL

   The setting of the TTL is application specific, but the following
   operational consideration should be born in mind.  In SR the size of
   the label stack may be increased within a single routing domain by
   various operations such as the pushing of a binding SID.  Furthermore
   in SR packets are not necessarily constrained to travel on the
   shortest path with that routing domain.  Consideration therefore has
   to be given to possibility of a forwarding loop.  To mitigate against
   this it is RECOMMENDED that the TTL is continuously decremented as
   the packet passes through the SR network regardless of any other
   changes to the network layer encapsulation.

5.  UDP/IP Encapsulation.

   The procedures defined in [RFC7510] are followed.  RFC7510 specifies
   the values to be used in the UDP Source Port, Destination Port, and
   Checksum fields.

   An administrative domain, or set of administrative domains that are
   sufficiently well managed and monitored to be able to safely use IP
   segment routing is likely to comply with the requirements called out
   in [RFC7510] to permit operation with a zero checksum over IPv6.
   However each operator needs to validate the decision on whether or
   not to use a UDP checksum for themselves.

   The [RFC7510] UDP header may be carried over IPv4 or over IPv6.

   The IP source address is the address of the encapsulating device.
   The IP destination address is implied by the instruction at the top
   of the instruction stack.

   If IPv4 is in use fragmentation is not permitted.

6.  Metadata

   There are a number of ways that metadata could be carried:

   o  The metadata could be included in the packet.

   o  A SID could point to locally stored metadata.

   o  Metadata could be carried in a support packet that does not
      include any user data.

   o  Metadata could be provided out of band.

   Metadata is for future study.



Bryant, et al.          Expires December 30, 2017               [Page 6]


Internet-Draft                Unified IP SR                    June 2017


7.  Elements of Procedure

   There are six type of node in an SR domain:

   o  Domain ingress nodes that receive packets and encapsulate them for
      transmission across the domain.  These packets may be native IP
      packets or may already be SR packets.

   o  Legacy transit nodes that are IP routers but are not able to
      perform segment routing.

   o  Transit nodes that are SR capable but that are not identified by a
      SID in the SID stack.

   o  Transit nodes that are SR capable and need to perform SR routing.

   o  The penultimate SR capable node on the path that processes the
      last SID on the stack.

   o  The domain egress node that forwards the payload packet for
      ultimate delivery.

   The following sub-sections describe the processing behavior in each
   case.

7.1.  Domain Ingress

   Domain ingress nodes receive packets from outside the domain and
   encapsulate them to be forwarded across the domain.  Received packets
   may already be MPLS-SR packets (in the case of connecting two MPLS-SR
   networks across a native IP network) or may be IP or MPLS packets.

   In the latter case, the packet is classified by the domain ingress
   node and an MPLS-SR stack is imposed.  In the former case the MPLS-SR
   stack is already in the packet.  The top entry in the stack is popped
   from the stack and retained for use below.

   The packet is then encapsulated in UDP with the destination port set
   to 6635 to indicate "MPLS-UDP" as described in [RFC7510].  The source
   UDP port is set randomly or to provide entropy as described in
   [RFC7510].

   The packet is then encapsulated in IP for transmission across the
   network.  The IP source address is set to the domain ingress node,
   and the destination address is set to the address corresponding to
   the label that was previously popped from the stack.





Bryant, et al.          Expires December 30, 2017               [Page 7]


Internet-Draft                Unified IP SR                    June 2017


   The packet is then sent into the IP network routing the packet
   according to the local FIB and applying hashing to resolve any ECMP
   choices.

7.2.  Legacy Transit

   A legacy transit node is an IP router that has no SR capabilities.
   When such a router receives an MPLS-SR-in-UDP packet it will carry
   out normal TTL processing and if the packet is still live it will
   forward it as it would any other UDP-in-IP packet.  The packet will
   be routed toward the destination indicated in the packet header using
   the local FIB and applying hashing to resolve any ECMP choices.

7.3.  On-Path Pass-Through SR Nodes

   Just because a node is SR capable and receives an MPLS-SR-in-UDP
   packet does not mean that it performs SR processing on the packet.
   Only routers identified by SIDs in the SR stack need to do such
   processing.

   Routers that are not addressed by the destination address in the IP
   header simply treat the packet as a normal UDP-in-IP packet carrying
   out normal TTL processing and if the packet is still live routing the
   packet according to the local FIB and applying hashing to resolve any
   ECMP choices.

7.4.  SR Transit Nodes

   When a router receives an MPLS-SR-in-UDP packet that is addressed to
   it, it acts as follows:

   o  Perform TTL processing as normal for an IP packet

   o  Determine that the packet is addressed to the local node

   o  Find that the payload is UDP and that the destination port
      indicates MPLS-in-IP

   o  Strip the IP and UDP headers

   o  Pop the top label from the SID stack and retain it for use below

   o  Encapsulate the packet in UDP with the destination port set to
      6635 and the source port set for entropy.

   o  Encapsulate the packet in IP with the IP source address set to
      this transit router, and the destination address set to the




Bryant, et al.          Expires December 30, 2017               [Page 8]


Internet-Draft                Unified IP SR                    June 2017


      address corresponding to the label that was previously popped from
      the stack.

   o  Send the packet into the IP network routing the packet according
      to the local FIB and applying hashing to resolve any ECMP choices.

7.5.  Penultimate SR Transit

   The penultimate SR transit node is only different from the SR transit
   node described in Section 7.4 because it pops the final MPLS-SR SID
   from the stack.  In order to avoid confusion at the egress, the
   router replaces the popped SR label with an explicit null label
   (label value 0 [RFC3032]).  The packet is then encapsulated and sent
   as described in Section 7.4.

7.6.  Domain Egress

   The domain egress strips the IP and UDP headers, pops the explicit
   null label, and forwards the payload packet according to its type and
   the local routing/forwarding mechanisms.

8.  Modes of Deployment

   As previously noted, the procedures described in this document may be
   used to connect islands of SR functionality across an IP backbone, or
   can provide SR function within a native IP network.  This section
   briefly expounds upon those two deployment modes.

8.1.  Interconnection of SR Domains

   Figure 3 shows two SR domains interconnected by an IP network.  The
   procedures described in this document are deployed at border routers
   R1 and R2 and packets are carried across the backbone network in a
   UDP tunnel.

   R1 acts as the domain ingress as described in Section 7.1.  It takes
   the MPLS-SR packet from the SR domain, pops the top label and uses it
   to identify its peer border router R2.  R1 then encapsulates the
   packet in UDP in IP and sends it toward R2.

   Routers within the IP network simply forward the packet using normal
   IP routing.

   R2 acts as a domain egress router as described in Section 7.6.  It
   receives a packet that is addressed to it, strips the IP and UDP
   headers, and acts on the payload SR label stack to continue to route
   the packet.




Bryant, et al.          Expires December 30, 2017               [Page 9]


Internet-Draft                Unified IP SR                    June 2017


                    ________________________
       ______      (                        )      ______
      (      )    (        IP Network        )    (      )
     (        )  (                            )  (        )
    (      --------                          --------      )
   (      | Border |    SR-in-UDP Tunnel    | Border |      )
   (  SR  | Router |========================| Router |  SR  )
   (      |   R1   |                        |   R2   |      )
    (      --------                          --------      )
     (        )  (                            )  (        )
      (______)    (                          )    (______)
                   (________________________)

              Figure 3: SR in UDP to Tunnel Between SR Sites

8.2.  SR Within and IP Network

   Figure 4 shows the procedures defined in this document to provide SR
   function across an IP network.

   R1 receives a native packet and classifies determining that it should
   be sent on the SR path R2-R3-R4-R5.  It imposes a label stack
   accordingly and then acts as a domain ingress as described in
   Section 7.1.  It pops the label for R2, and encapsulates the packet
   in UDP in IP, sets the IP source to R1 and the IP destination to R2,
   and sends the packet into the IP network.

   Routers Ra and Rb are transit routers that simply forward the packets
   using normal IP forwarding.  They may be legacy transit routers (see
   Section 7.2) or on-path pass-through SR nodes (see Section 7.3).

   R2 is an SR transit nodes as described in Section 7.4.  It receives a
   packet addressed to it, strips the IP and UDP headers, and processes
   the SR label stack.  It pops the top label and uses it to identify
   the next SR hop which is R3.  R2 then encapsulates the packet in UDP
   in IP setting the IP source to R2 and the IP destination to R3.

   Rc, Rd, and Re are transit routers and perform as Ra and Rb.

   R3 is an SR transit nodes and performs as R2.

   R4 is a penultimate SR transit node as described in Section 7.5.  It
   receives a packet addressed to it, strips the IP and UDP headers, and
   processes the SR label stack.  It pops the top label and uses it to
   identify the next SR hop which is R5.  This was the last label in the
   stack so R4 includes an explicit null label before encapsulating the
   packet in UDP in IP setting the IP source to R4 and the IP
   destination to R5.



Bryant, et al.          Expires December 30, 2017              [Page 10]


Internet-Draft                Unified IP SR                    June 2017


   R5 is the domain egress as described in Section 7.6.  It receives a
   packet addressed to it, strips the IP and UDP headers, and pops the
   explicit null label before forwarding the payload packet.

                    __________________________________
                 __(           IP Network             )__
              __(                                        )__
             (               --        --        --         )
        --------   --   --  |R2|  --  |R3|  --  |R4|  --   --------
       | Ingress| |Ra| |Rb| |  | |Rc| |  | |Rd| |  | |Re| | Egress |
   --->| Router |===========|  |======|  |======|  |======| Router |--->
       |   R1   | |  | |  | |  | |  | |  | |  | |  | |  | |   R5   |
        --------   --   --  |  |  --  |  |  --  |  |  --   --------
             (__             --        --        --       __)
                (__                                    __)
                   (__________________________________)

                     Figure 4: SR Within an IP Network

9.  OAM

   OAM at the payload layer follow the normal OAM procedures for the
   payload.  To the payload the whole SR network looks like a tunnel.

   OAM in the IP domain follows the normal IP procedures.  This can only
   be carried out between IP hops.

   OAM between instruction processing entities i.e. at the SR layer uses
   the procedures documented for MPLS.

10.  Comparison with SRv6

   The format described in [I-D.ietf-6man-segment-routing-header] hereon
   referred to as SRv6 requires an initial 36 octet IPv6 header but
   cannot support IPv4.  USR requires either am initial 36 octet IPv6
   header of an initial 20 octet IPv4 header.

   o SRv6 requires an 8 octet SR header, USR requires a UDP header which
   is also 8 octets.

   o SRv6 requires 16 octets per SID, whereas USR requires only 4 octets
   per SID.

   o The SRv6 SIDs can be a global identifier, but the USR SIDs cannot
   be.

   o SRv6 has an extension to support path repair at the SR level.  This
   is for further study with USR.



Bryant, et al.          Expires December 30, 2017              [Page 11]


Internet-Draft                Unified IP SR                    June 2017


   o SRv6 includes the intended path history in the packet.  USR would
   require the path history to be added as metadata.

11.  Security Considerations

   It is difficult for an attacker to pass a raw MPLS encoded packet
   into a network and operators have considerable experience at
   excluding such packets.

   It is easy for an ingress node to detect any attempt to smuggle IP
   packet into the network since it would see that the UDP destination
   port was set to MPLS.  As noted in Section 6 legitimate packets for
   SR processing within the network could be signed.  SR packets not
   having a destination address terminating in the network would be
   transparently carried and would pose no security risk to the network
   under consideration.

   The security consideration of [I-D.ietf-spring-ipv6-use-cases] and
   [RFC7510] apply.

12.  IANA Considerations

   This document makes no IANA requests.

13.  Acknowledgements

   This draft was inspired by
   [I-D.xu-mpls-unified-source-routing-instruction], and we acknowlegde
   the following authors of that draft: Robert Raszuk, Uma Chunduri,
   Luis M.  Contreras, Luay Jalil, Hamid Assarpour, Gunter Van De Velde,
   Jeff Tantsura, and Shaowen Ma.

14.  References

14.1.  Normative References

   [I-D.ietf-spring-segment-routing]
              Filsfils, C., Previdi, S., Decraene, B., Litkowski, S.,
              and R. Shakir, "Segment Routing Architecture", draft-ietf-
              spring-segment-routing-12 (work in progress), June 2017.

   [I-D.ietf-spring-segment-routing-mpls]
              Filsfils, C., Previdi, S., Bashandy, A., Decraene, B.,
              Litkowski, S., and R. Shakir, "Segment Routing with MPLS
              data plane", draft-ietf-spring-segment-routing-mpls-10
              (work in progress), June 2017.





Bryant, et al.          Expires December 30, 2017              [Page 12]


Internet-Draft                Unified IP SR                    June 2017


   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC3032]  Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y.,
              Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack
              Encoding", RFC 3032, DOI 10.17487/RFC3032, January 2001,
              <http://www.rfc-editor.org/info/rfc3032>.

   [RFC5462]  Andersson, L. and R. Asati, "Multiprotocol Label Switching
              (MPLS) Label Stack Entry: "EXP" Field Renamed to "Traffic
              Class" Field", RFC 5462, DOI 10.17487/RFC5462, February
              2009, <http://www.rfc-editor.org/info/rfc5462>.

   [RFC7510]  Xu, X., Sheth, N., Yong, L., Callon, R., and D. Black,
              "Encapsulating MPLS in UDP", RFC 7510,
              DOI 10.17487/RFC7510, April 2015,
              <http://www.rfc-editor.org/info/rfc7510>.

14.2.  Informative References

   [I-D.ietf-6man-segment-routing-header]
              Previdi, S., Filsfils, C., Raza, K., Leddy, J., Field, B.,
              daniel.voyer@bell.ca, d., daniel.bernier@bell.ca, d.,
              Matsushima, S., Leung, I., Linkova, J., Aries, E., Kosugi,
              T., Vyncke, E., Lebrun, D., Steinberg, D., and R. Raszuk,
              "IPv6 Segment Routing Header (SRH)", draft-ietf-6man-
              segment-routing-header-06 (work in progress), March 2017.

   [I-D.ietf-spring-ipv6-use-cases]
              Brzozowski, J., Leddy, J., Filsfils, C., Maglione, R., and
              M. Townsley, "IPv6 SPRING Use Cases", draft-ietf-spring-
              ipv6-use-cases-11 (work in progress), June 2017.

   [I-D.xu-mpls-spring-islands-connection-over-ip]
              Xu, X., Raszuk, R., Chunduri, U., Contreras, L., and L.
              Jalil, "Connecting MPLS-SPRING Islands over IP Networks",
              draft-xu-mpls-spring-islands-connection-over-ip-00 (work
              in progress), October 2016.

   [I-D.xu-mpls-unified-source-routing-instruction]
              Xu, X., Bryant, S., Raszuk, R., Chunduri, U., Contreras,
              L., Jalil, L., Assarpour, H., Velde, G., Tantsura, J., and
              S. Ma, "Unified Source Routing Instruction using MPLS
              Label Stack", draft-xu-mpls-unified-source-routing-
              instruction-01 (work in progress), June 2017.




Bryant, et al.          Expires December 30, 2017              [Page 13]


Internet-Draft                Unified IP SR                    June 2017


   [RFC2992]  Hopps, C., "Analysis of an Equal-Cost Multi-Path
              Algorithm", RFC 2992, DOI 10.17487/RFC2992, November 2000,
              <http://www.rfc-editor.org/info/rfc2992>.

   [RFC3985]  Bryant, S., Ed. and P. Pate, Ed., "Pseudo Wire Emulation
              Edge-to-Edge (PWE3) Architecture", RFC 3985,
              DOI 10.17487/RFC3985, March 2005,
              <http://www.rfc-editor.org/info/rfc3985>.

Authors' Addresses

   Stewart Bryant
   Huawei

   Email: stewart.bryant@gmail.com


   Xiaohu Xu
   Huawei

   Email: xuxiaohu@huawei.com


   Mach Chen
   Huawei

   Email: mach.chen@huawei.com


   Adrian Farrel
   Juniper Networks

   Email: afarrel@juniper.net


   John Drake
   Juniper Networks

   Email: jdrake@juniper.net












Bryant, et al.          Expires December 30, 2017              [Page 14]


Html markup produced by rfcmarkup 1.129d, available from https://tools.ietf.org/tools/rfcmarkup/