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Versions: 00 01 03                                                      
Network Working Group                                Yakov Rekhter
Internet Draft                                    Juniper Networks
Expiration Date: March 2002                          Daniel Tappan
                                                     Cisco Systems
                                                        Eric Rosen
                                                     Cisco Systems

                 MPLS Label Stack Encapsulation in GRE


1. Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-

   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.''

   The list of current Internet-Drafts can be accessed at

   The list of Internet-Draft Shadow Directories can be accessed at

2. Abstract

   In certain cases  it may be useful to carry  MPLS packets through a
   GRE tunnel. This document describes how to do that using existing

draft-rekhter-mpls-over-gre-03.txt                              [Page 1]

Internet Draft     draft-rekhter-mpls-over-gre-03.txt     September 2001

3. Encapsulation in GRE

   If one wants to establish a Label Switched Path (LSP) over a set of
   nodes that don't support MPLS, one could encapsulate MPLS header in
   GRE [RFC2784] over the parts of the path that spans these nodes.  The
   protocol type field in the GRE header should be set to the Ethertype
   value for MPLS Unicast (0x8847) or Multicast (0x8848).

   If GRE is extended to carry the Key field [RFC2890], then in
   principle the outer label in the MPLS header could be placed in the
   Key field, the TTL field could be placed in the TTL field of the IP
   header, and the value of the EXP field may  be considered when
   setting the value of the DSCP field of the IP header.  The Protocol
   Type field in the GRE header is set to the L3PID of the LSP.
   Specifically, when the MPLS Label Stack has depth of more than one,
   the Protocol Type field in the GRE header is set to MPLS. Of course,
   one could observe that in terms of the overhead encoding the outer
   label into the Key field doesn't offer any obvious advantages over
   carrying the outer label in the MPLS "shim" header and not using the
   Key field at all.

   One could observe that the above approach also works between directly
   connected nodes. In this case the encoding described in the previous
   paragraph provides (yet another) way to carry MPLS Labels over a
   point-to-point or Ethernet links.  However, in this scenario this
   encoding of MPLS Labels introduces additional bandwidth and
   processing overhead relative to carrying labels just in the MPLS
   "shim" header, and no rational benefits. And it still requires the
   nodes to support MPLS, as forwarding is based on the MPLS Label.

4. Security Considerations

   Security issues are not discussed in this document.

5. Acknowledgements


draft-rekhter-mpls-over-gre-03.txt                              [Page 2]

Internet Draft     draft-rekhter-mpls-over-gre-03.txt     September 2001

6. References


   [RFC2890] "Key and Sequence Number Extensions to GRE", G. Dommety,
   RFC2890, August 2000

7. Author Information

   Yakov Rekhter
   Juniper Networks, Inc.
   1194 N. Mathilda Ave.
   Sunnyvale, CA 94089
   Email: yakov@juniper.net

   Dan Tappan
   Cisco Systems, Inc.
   250 Apollo Drive
   Chelmsford, MA, 01824
   e-mail: tappan@cisco.com

   Eric Rosen
   Cisco Systems, Inc.
   250 Apollo Drive
   Chelmsford, MA, 01824
   e-mail: erosen@cisco.com

draft-rekhter-mpls-over-gre-03.txt                              [Page 3]