Connecting MPLS-SPRING Islands over IP Networks
draft-xu-spring-islands-connection-over-ip-05

Versions: 00 01 02 03 04 05                                             
Network working group                                              X. Xu
Internet Draft                                                    Huawei
Category: Informational                                      S.Sivabalan
                                                                   Cisco

Expires: August 2014                                    February 8, 2014


                 Connecting SPRING Islands over IP Networks

               draft-xu-spring-islands-connection-over-ip-00

Abstract

   Segment Routing (SR) architecture [SR-ARCH] introduces a new MPLS
   paradigm in which a sender of a packet is allowed to partially or
   completely specify the route the packet takes through the network by
   using stacked MPLS labels. The current SR architecture requires an
   end-to-end MPLS Label Switched Path (LSP) between any two SR-enabled
   routers (e.g., two adjacent hops of a given explicit path). In order
   to enable SR to be deployed even when there are non-MPLS routers
   along the path between two SR-enabled routers, it is desirable to
   have an alternative, which allows the use of IP-based tunnels (e.g.,
   GRE tunnels) to connect two SR-enabled routers. This document
   describes a mechanism for such usage.

Status of this Memo

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   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on August 8, 2014.









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Copyright Notice

   Copyright (c) 2013 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   described in the Simplified BSD License.

Conventions used in this document

   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].

Table of Contents


   1. Introduction ................................................ 3
   2. Terminology ................................................. 3
   3. Packet Forwarding Process ................................... 3
   4. Security Considerations ..................................... 4
   5. IANA Considerations ......................................... 4
   6. Acknowledgements ............................................ 4
   7. References .................................................. 4
      7.1. Normative References ................................... 4
      7.2. Informative References  ................................ 4
   Authors' Addresses ............................................. 4















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1. Introduction

   Segment Routing (SR) architecture [SR-ARCH] introduces a new MPLS
   paradigm in which a sender of a packet is allowed to partially or
   completely specify the route the packet takes through the network by
   using stacked MPLS labels. In other words, this new paradigm could
   support source routing by using the MPLS label stack where each MPLS
   label represents a given hop that the packet must go through. Here
   the MPLS label could be either locally significant or globally
   significant.

   The current SR architecture requires an end-to-end MPLS Label
   Switched Path (LSP) between any two SR-enabled routers (e.g., any two
   adjacent hops of a given explicit path). This means that SR cannot be
   implemented if there is a part of the path between those two SR-
   enabled routers that does not support MPLS.

   In order to enable SR to be deployed even when there are non-MPLS
   routers along the path between two SR-enabled routers, it is
   desirable to have an alternative, which allows the use of IP-based
   tunnels (e.g., GRE tunnels) to connect two SR-enabled routers which
   are specified as adjacent hops of a given explicit path. The tunnel
   destination address would be the address of next-hop SR-enabled
   router along the explicit path, and this would cause the packet to be
   delivered to the next explicit hop. In this procedure, the ingress
   and egress of IP-based tunnel themselves must support SR features
   including the MPLS forwarding capability, whereas the transit routers
   along the path between them don't need to support MPLS and SR.

   The above mechanism is beneficial for incrementally deployment of the
   SR technology, especially in the case where only a few specific
   routers (e.g., service function nodes) in addition to Provider Edge
   (PE) routers are actually required to be specified as explicit hops
   of the loose explicit path.

2. Terminology

   This memo makes use of the terms defined in [RFC1195] and [SR-ARCH].

3. Packet Forwarding Process

   Assume a SR-enabled router X prepares to forward a MPLS packet to the
   next node segment Y which is identified by the top label of the MPLS
   packet, if the next-hop router Z which is physically adjacent to X is
   a non-SR router, X would pop the top label (if required) and then
   encapsulate the remaining MPLS packet into an IP-based tunnel(e.g.,



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   GRE) where the tunnel destination is an IP address of Y and the
   tunnel source is an IP address of X. The IP encapsulated packet would
   be forwarded according to the IP forwarding table.

   Upon receipt of that IP encapsulated packet, Y would decapsulate it
   and then process the decapsulated MPLS packet accordingly.

   As for which tunnel encapsulation type should be used by X, it can be
   manually specified on X or dynamically learnt from Y's advertisement
   of its tunnel encapsulation capability. How to advertise tunnel
   encapsulation capability is outside of the scope of this document.

4. Security Considerations

   TBD.

5. IANA Considerations

   No action is required for IANA.

6. Acknowledgements

   Thanks to.

7. References

7.1. Normative References

   [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
             Requirement Levels", BCP 14, RFC 2119, March 1997.

   [SR-ARCH] 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 Architecture", draft-filsfils-rtgwg-
             segment-routing-00 (work in progress), June 2013.

7.2. Informative References

   [RFC4023] Worster, T., Rekhter, Y., and E. Rosen, "Encapsulating MPLS
             in IP or GRE", RFC4023, March 2005.

Authors' Addresses

   Xiaohu Xu
   Huawei Technologies,
   Beijing, China



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   Phone: +86-10-60610041
   Email: xuxiaohu@huawei.com

   Siva Sivabalan
   Cisco Systems

   Email: msiva@cisco.com