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Versions: 00

Network Working Group                                         X. Xu, Ed.
Internet-Draft                                                 S. Bryant
Intended status: Standards Track                                  Huawei
Expires: September 10, 2017                                    R. Raszuk
                                                            Bloomberg LP
                                                             U. Chunduri
                                                                  Huawei
                                                            L. Contreras
                                                          Telefonica I+D
                                                                L. Jalil
                                                                 Verizon
                                                            H. Assarpour
                                                                Broadcom
                                                           March 9, 2017


       Unified Source Routing Instruction using MPLS Label Stack
          draft-xu-mpls-unified-source-routing-instruction-00

Abstract

   MPLS-SPRING is an MPLS-based source routing paradigm in which a
   sender of a packet is allowed to partially or completely specify the
   route the packet takes through the network by imposing stacked MPLS
   labels to the packet.  This MPLS -based source routing paradigm could
   actually be leveraged to realize a unified source routing instruction
   for both IPv4 and IPv6 underlays.

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."

   This Internet-Draft will expire on September 10, 2017.







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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
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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
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Packet Forwarding Procedures  . . . . . . . . . . . . . . . .   4
   5.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   7
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   7
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   9

1.  Introduction

   MPLS-SPRING [I-D.ietf-spring-segment-routing-mpls] is a MPLS-based
   source routing paradigm in which a sender of a packet is allowed to
   partially or completely specify the route the packet takes through
   the network by imposing stacked MPLS labels to the packet.  This
   MPLS-based source routing paradigm could actually be leveraged to
   realize a unified source routing instruction for both IPv4 and IPv6
   underlays.  In other words, the source routing instruction
   information contained in IPv4 and IPv6 source routed packets could be
   uniformly encoded as an MPLS label stack.  As a result, there is no
   need any more to develop and implement transport-dependent source
   routing mechanisms for IPv4 and IPv6 respectively.

   The traditional IPv4 and IPv6 source routing mechanisms by use of
   IPv4 Source Routing Options and IPv6 Route Header Type 0 Extension
   respectively have been deprecated due to their obvious security
   vulnerabilities.  IPv6 SPRING [I-D.ietf-6man-segment-routing-header]



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   is a newly proposed IPv6 source routing mechanism in which the source
   route instruction information is encoded as an ordered list of
   128-bit long IPv6 addresses and contained in the Source Routing
   Header (SRH).  Although it has overcome the security vulnerability
   issues associated with the traditional IPv6 source routing mechanism
   as claimed in [I-D.ietf-6man-segment-routing-header], it still has
   the following obvious drawbacks at least: 1) the encapsulation
   overhead is significant especially when the list of the explicit
   routing hops is very long; 2) for those transit IPv6 routers that
   don't support the flow label based load-balancing mechanism yet, the
   ECMP load-balancing effect may be impacted seriously since they could
   not recognize the SRH and therefore could not obtain the five tuple
   of the source routed IPv6 packet; 3) it requires a new forwarding
   logic on basis of the SRH and the forwarding performance associated
   with the IPv6 SRH may still be a big concern for some hardware
   platforms.

   Section 3 describes various use cases for the unified source routing
   and Section 4 describes a typical application scenario and how the
   packet forwarding happens.

1.1.  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].

2.  Terminology

   This memo makes use of the terms defined in [RFC3031] and
   [I-D.ietf-spring-segment-routing-mpls].

3.  Use Cases

   The unified source routing mechanism across MPLS, IPv4 and IPv6 is
   useful at least in the following use cases:

   o  Incremental deployment of the MPLS-SPRING technology.  Since there
      is no need to run any other label distribution protocol (e.g.,
      LDP, see [I-D.filsfils-spring-segment-routing-ldp-interop] for
      more details.) on those non-MPLS-SPRING routers, the network
      provisioning is greatly simplified, which is one of the major
      claimed benefits of the MPLS-SPRING technology (i.e., running a
      single protocol).

   o  MPLS-based Service Function Chaining (SFC)
      [I-D.xu-mpls-service-chaining].  Based on the unified source
      routing mechanism as described in this document, only SFC-related



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      nodes including Service Function Forwarders (SFF), Service
      Functions (SF) and classifiers are required to recognize the SFC
      encapsulation header in the MPLS label stack form, while the
      intermediate routers just need to support vanilla IP forwarding
      (either IPv4 or IPv6).  In other words, it undoubtedly complies
      with the transport-independence requirement as listed in the SFC
      architecture document [RFC7665].

   o  Traffic Engineering scenarios where only a few routers (e.g., the
      entry and exit nodes of each plane in the dual-plane network ) are
      specified as segments of explicit paths.  In this way, only a few
      routers are required to support the MPLS-SPRING capability while
      all the other routers just need to support IP forwarding
      capability, which would significantly reduce the deployment cost
      of this new technology.

   o  A light-weight alternative to IPv6 SPRING technology
      [I-D.ietf-6man-segment-routing-header].  The Source Routing Header
      (SRH) [I-D.ietf-6man-segment-routing-header] consisting of an
      ordered list of 128-bit long IPv6 addresses is now replaced by an
      ordered list of 20-bit long labels (i.e., label stack).  As a
      result, the encapsulation overhead and forwarding performance
      issues associated with the IPv6 SPRING are eliminated.

   o  A new IPv4 source routing mechanism which has overcome the
      security vulnerability issues associated with the traditional IPv4
      source routing mechanism.

4.  Packet Forwarding Procedures






















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     +-----+       +-----+       +-----+        +-----+        +-----+
     |  A  +-------+  B  +-------+  C  +--------+  D  +--------+  H  |
     +-----+       +--+--+       +--+--+        +--+--+        +-----+
                      |             |              |
                      |             |              |
                   +--+--+       +--+--+        +--+--+
                   |  E  +-------+  F  +--------+  G  |
                   +-----+       +-----+        +-----+

          +--------+
          |IP(A->E)|
          +--------+                 +--------+
          |  L(G)  |                 |IP(E->G)|
          +--------+                 +--------+        +--------+
          |  L(H)  |                 |  L(H)  |        |IP(G->H)|
          +--------+                 +--------+        +--------+
          | Packet |     --->        | Packet |  --->  | Packet |
          +--------+                 +--------+        +--------+
                             Figure 1

   As shown in Figure 1, Assume Router A, E, G and H are MPLS-SPRING-
   capable routers while the remaining are only capable of forwarding IP
   packets.  Router A, E, G and H advertise their Segment Routing
   related information via IS-IS or OSPF.  Now assume router A wants to
   send a given IP or MPLS packet via an explicit path of {E->G->H},
   router A would impose an MPLS label stack corresponding to that
   explicit path on the received IP packet.  Since there is no Label
   Switching Path (LSP) towards router E, router A would replace the top
   label indicating router E with an IP-based tunnel for MPLS (e.g.,
   MPLS-over-UDP [RFC7510] or MPLS-over-GRE [RFC4023]) towards router E
   and then send it out.  In other words, router A would pop the top
   label and then encapsulate the MPLS packet with an IP-based tunnel
   towards router E.  When the IP-encapsulated MPLS packet arrives at
   router E, router E would strip the IP-based tunnel header and then
   process the decapsulated MPLS packet accordingly.  Since there is no
   LSP towards router G which is indicated by the current top label of
   the decapsulated MPLS packet, router E would replace the current top
   label with an IP-based tunnel towards router G and send it out.  When
   the packet arrives at router G, router G would strip the IP-based
   tunnel header and then process the decapsulated MPLS packet.  Since
   there is no LSP towards router H, router G would replace the current
   top label with an IP-based tunnel towards router H.  Now the packet
   encapsulated with the IP-based tunnel towards router H is exactly the
   original packet that router A had intended to send towards router H.
   If the packet is an MPLS packet, router G could use any IP-based
   tunnel for MPLS (e.g., MPLS-over-UDP [RFC7510] or MPLS-over-GRE
   [RFC4023]).  If the packet is an IP packet, router G could use any IP
   tunnel for IP (e.g., IP-in-UDP [I-D.xu-intarea-ip-in-udp] or GRE



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   [RFC2784]).  That original IP or MPLS packet would be forwarded
   towards router H via an IP-based tunnel.  When the encapsulated
   packet arrives at router H, router H would decapsulate it into the
   original packet and then process it accordingly.  Note that in the
   above description, it's assumed that the label associated with each
   prefix-SID advertised by the owner of the prefix-SID is a Penultimate
   Hop Popping (PHP) label (e.g., the NP-flag
   [I-D.ietf-ospf-segment-routing-extensions] associated with the
   corresponding prefix SID is not set).  Figure 2 demostrates the
   packet walk in the case where the label associated with each prefix-
   SID advertised by the owner of the prefix-SID is not a Penultimate
   Hop Popping (PHP) label (e.g., the NP-flag
   [I-D.ietf-ospf-segment-routing-extensions] associated with the
   corresponding prefix SID is set).

     +-----+       +-----+       +-----+        +-----+        +-----+
     |  A  +-------+  B  +-------+  C  +--------+  D  +--------+  H  |
     +-----+       +--+--+       +--+--+        +--+--+        +-----+
                      |             |              |
                      |             |              |
                   +--+--+       +--+--+        +--+--+
                   |  E  +-------+  F  +--------+  G  |
                   +-----+       +-----+        +-----+

          +--------+
          |IP(A->E)|
          +--------+                 +--------+
          |  L(E)  |                 |IP(E->G)|
          +--------+                 +--------+        +--------+
          |  L(G)  |                 |  L(G)  |        |IP(G->H)|
          +--------+                 +--------+        +--------+
          |  L(H)  |                 |  L(H)  |        |  L(H)  |
          +--------+                 +--------+        +--------+
          | Packet |     --->        | Packet |  --->  | Packet |
          +--------+                 +--------+        +--------+
                             Figure 2

   Note that as for which tunnel encapsulation type should be used, it
   could be manually specified on each tunnel ingress routers or be
   learnt from the tunnel egress routers' advertisements of its tunnel
   encapsulation capability.  How to advertise the tunnel encapsulation
   capability using IS-IS or OSPF are specified in
   [I-D.ietf-isis-encapsulation-cap] and
   [I-D.ietf-ospf-encapsulation-cap] respectively.







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5.  Acknowledgements

   Thanks Joel Halpern, Bruno Decraene and Loa Andersson for their
   insightful comments on this draft.

6.  IANA Considerations

   No IANA action is required.

7.  Security Considerations

   TBD.

8.  References

8.1.  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,
              <http://www.rfc-editor.org/info/rfc2119>.

8.2.  Informative References

   [I-D.filsfils-spring-segment-routing-ldp-interop]
              Filsfils, C., Previdi, S., Bashandy, A., Decraene, B.,
              Litkowski, S., Horneffer, M., Milojevic, I., Shakir, R.,
              Ytti, S., Henderickx, W., Tantsura, J., and E. Crabbe,
              "Segment Routing interoperability with LDP", draft-
              filsfils-spring-segment-routing-ldp-interop-03 (work in
              progress), March 2015.

   [I-D.ietf-6man-segment-routing-header]
              Previdi, S., Filsfils, C., Field, B., Leung, I., Linkova,
              J., Aries, E., Kosugi, T., Vyncke, E., and D. Lebrun,
              "IPv6 Segment Routing Header (SRH)", draft-ietf-6man-
              segment-routing-header-05 (work in progress), February
              2017.

   [I-D.ietf-isis-encapsulation-cap]
              Xu, X., Decraene, B., Raszuk, R., Chunduri, U., Contreras,
              L., and L. Jalil, "Advertising Tunnelling Capability in
              IS-IS", draft-ietf-isis-encapsulation-cap-00 (work in
              progress), October 2016.







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   [I-D.ietf-ospf-encapsulation-cap]
              Xu, X., Decraene, B., Raszuk, R., Chunduri, U., Contreras,
              L., and L. Jalil, "Advertising Tunnelling Capability in
              OSPF", draft-ietf-ospf-encapsulation-cap-01 (work in
              progress), October 2016.

   [I-D.ietf-ospf-segment-routing-extensions]
              Psenak, P., Previdi, S., Filsfils, C., Gredler, H.,
              Shakir, R., Henderickx, W., and J. Tantsura, "OSPF
              Extensions for Segment Routing", draft-ietf-ospf-segment-
              routing-extensions-12 (work in progress), March 2017.

   [I-D.ietf-spring-segment-routing-mpls]
              Filsfils, C., Previdi, S., Bashandy, A., Decraene, B.,
              Litkowski, S., Horneffer, M., Shakir, R.,
              jefftant@gmail.com, j., and E. Crabbe, "Segment Routing
              with MPLS data plane", draft-ietf-spring-segment-routing-
              mpls-07 (work in progress), February 2017.

   [I-D.xu-intarea-ip-in-udp]
              Xu, X., Lee, Y., and F. Yongbing, "Encapsulating IP in
              UDP", draft-xu-intarea-ip-in-udp-04 (work in progress),
              December 2016.

   [I-D.xu-mpls-service-chaining]
              Xu, X., Bryant, S., Assarpour, H., Shah, H., Contreras,
              L., and d. daniel.bernier@bell.ca, "Service Chaining using
              MPLS Source Routing", draft-xu-mpls-service-chaining-00
              (work in progress), October 2016.

   [RFC2784]  Farinacci, D., Li, T., Hanks, S., Meyer, D., and P.
              Traina, "Generic Routing Encapsulation (GRE)", RFC 2784,
              DOI 10.17487/RFC2784, March 2000,
              <http://www.rfc-editor.org/info/rfc2784>.

   [RFC3031]  Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
              Label Switching Architecture", RFC 3031,
              DOI 10.17487/RFC3031, January 2001,
              <http://www.rfc-editor.org/info/rfc3031>.

   [RFC4023]  Worster, T., Rekhter, Y., and E. Rosen, Ed.,
              "Encapsulating MPLS in IP or Generic Routing Encapsulation
              (GRE)", RFC 4023, DOI 10.17487/RFC4023, March 2005,
              <http://www.rfc-editor.org/info/rfc4023>.







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   [RFC4817]  Townsley, M., Pignataro, C., Wainner, S., Seely, T., and
              J. Young, "Encapsulation of MPLS over Layer 2 Tunneling
              Protocol Version 3", RFC 4817, DOI 10.17487/RFC4817, March
              2007, <http://www.rfc-editor.org/info/rfc4817>.

   [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>.

   [RFC7665]  Halpern, J., Ed. and C. Pignataro, Ed., "Service Function
              Chaining (SFC) Architecture", RFC 7665,
              DOI 10.17487/RFC7665, October 2015,
              <http://www.rfc-editor.org/info/rfc7665>.

Authors' Addresses

   Xiaohu Xu (editor)
   Huawei

   Email: xuxiaohu@huawei.com


   Stewart Bryant
   Huawei

   Email: stewart.bryant@gmail.com


   Robert Raszuk
   Bloomberg LP

   Email: robert@raszuk.net


   Uma Chunduri
   Huawei

   Email: uma.chunduri@gmail.com


   Luis M. Contreras
   Telefonica I+D

   Email: luismiguel.contrerasmurillo@telefonica.com






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   Luay Jalil
   Verizon

   Email: luay.jalil@verizon.com


   Hamid Assarpour
   Broadcom

   Email: hamid.assarpour@broadcom.com









































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