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Network Working Group                                    F. Templin, Ed.
Internet-Draft                              Boeing Research & Technology
Updates: RFC2784, RFC2890 (if approved)                   August 5, 2015
Intended status: Informational
Expires: February 6, 2016


                        GRE Tunnel Fragmentation
                  draft-templin-intarea-grefrag-01.txt

Abstract

   GRE tunnels use IPv4 or IPv6 fragmentation of the delivery packet
   when the delivery packet exceeds the tunnel MTU, or when otherwise
   necessary.  This can cause problems when unmitigated IPv4
   fragemntation ensues, or when middleboxes drop IPv6 fragments
   unconditionally.  This document proposes GRE tunnel fragmentation
   which avoids these pitfalls..

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
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   Internet-Drafts are draft documents valid for a maximum of six months
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   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 February 6, 2016.

Copyright Notice

   Copyright (c) 2015 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
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   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
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   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of



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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  GRE Fragmentation Header  . . . . . . . . . . . . . . . . . .   2
   3.  GRE Tunnel Fragmentation Procedures . . . . . . . . . . . . .   3
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   4
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   4
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   4
     7.2.  Informative References  . . . . . . . . . . . . . . . . .   4
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   5

1.  Introduction

   GRE is specified in [RFC2784] and [RFC2890].  In its current
   manifestation, GRE allows for fragmentation of the payload packet
   only if it is an IPv4 packet with the Don't Fragment (DF) bit set to
   0.  GRE also allows for fragmentation of the delivery packet, but
   this can cause problems in some applications.  A third option
   (introduced here) is for the GRE tunnel to perform tunnel
   fragmentation and reassembly on the payload packet.

   In this way, the ingress can fragment the payload packet (while
   treating the payload packet's headers as ordinary data) and
   encapsulate each fragment in a separate delivery header.  The GRE
   header requires a new fragment header field to support this.

   This tunnel fragmentation method was first suggested in Section 3.1.7
   of [RFC2764], and also appears in more recent works
   [I-D.templin-aerolink] [I-D.herbert-gue-fragmentation].

2.  GRE Fragmentation Header

   Figure 1 shows the GRE header as specified in [RFC2784][RFC2890] but
   with a new optional "Fragment Header" and a new control bit "F":












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       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |C| |K|S|F|   Reserved0   | Ver |         Protocol Type         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |      Checksum (optional)      |       Reserved1 (Optional)    |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                         Key (optional)                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                 Sequence Number (Optional)                    |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                 Fragment Header (Optional)                    |
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                 Figure 1: GRE Header with Fragment Header

   In this format, when the "F" bit is set to 1 the GRE header includes
   a Fragment header formatted as specified in Section 4.5 of [RFC2460].

3.  GRE Tunnel Fragmentation Procedures

   GRE tunnel fragmentation treats the entire GRE payload packet
   (including the payload headers) as opaque data.  The GRE tunnel
   ingress breaks the payload packet into N fragments and encapsulates
   each fragment in a separate GRE header and GRE delivery header.  The
   first fragment therefore includes the GRE payload headers and first
   portion of the GRE payload data, while subsequent fragments include
   the remaining portions of the GRE payload data.  The GRE tunnel
   ingress then sends each fragment to the GRE tunnel egress.  Apart
   from the appearance of the Fragment Header within the GRE header, the
   fragmentation procedure is the same as for IPv6 fragmentation.

   When the GRE tunnel egress receives the fragments, it reassembles the
   GRE payload packet by concatenating the data portions of each
   fragment according to their offsets.  Apart from the appearance of
   the Fragment Header within the GRE header, the reassembly procedure
   is the same as for IPv6 reassembly.

   In order to support this fragmentation and reassembly procedure, the
   GRE tunnel ingress must know the maximum sized packet the GRE tunnel
   egress is capable of reassembling, i.e., the Maximum Reassembly Unit
   (MRU).  The GRE tunnnel egress MUST therefore configure a minimum MRU
   of 2KB, and MAY configure a larger MRU.








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4.  IANA Considerations

   This document introduces no IANA considerations.

5.  Security Considerations

   TBD.

6.  Acknowledgements

   TBD

7.  References

7.1.  Normative References

   [RFC0791]  Postel, J., "Internet Protocol", STD 5, RFC 791,
              DOI 10.17487/RFC0791, September 1981,
              <http://www.rfc-editor.org/info/rfc791>.

   [RFC2460]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460,
              December 1998, <http://www.rfc-editor.org/info/rfc2460>.

   [RFC2764]  Gleeson, B., Lin, A., Heinanen, J., Armitage, G., and A.
              Malis, "A Framework for IP Based Virtual Private
              Networks", RFC 2764, DOI 10.17487/RFC2764, February 2000,
              <http://www.rfc-editor.org/info/rfc2764>.

   [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>.

   [RFC2890]  Dommety, G., "Key and Sequence Number Extensions to GRE",
              RFC 2890, DOI 10.17487/RFC2890, September 2000,
              <http://www.rfc-editor.org/info/rfc2890>.

7.2.  Informative References

   [I-D.herbert-gue-fragmentation]
              Herbert, T. and F. Templin, "Fragmentation option for
              Generic UDP Encapsulation", draft-herbert-gue-
              fragmentation-00 (work in progress), March 2015.







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   [I-D.templin-aerolink]
              Templin, F., "Asymmetric Extended Route Optimization
              (AERO)", draft-templin-aerolink-61 (work in progress),
              August 2015.

Author's Address

   Fred L. Templin (editor)
   Boeing Research & Technology
   P.O. Box 3707
   Seattle, WA  98124
   USA

   Email: fltemplin@acm.org





































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