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Network Working Group F. Templin, Ed.
Internet-Draft Boeing Research & Technology
Updates: RFC2784, RFC2890 (if approved) January 26, 2016
Intended status: Informational
Expires: July 29, 2016


GRE Tunnel Fragmentation
draft-templin-intarea-grefrag-02.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 introduces 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.

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This Internet-Draft will expire on July 29, 2016.

Copyright Notice

Copyright (c) 2016 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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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 . . . . . . . . . . . . . . . . . 5
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 5

1. Introduction

GRE is specified in the following RFCs: [RFC2784][RFC2890][RFC7676].
[RFC7588] further discusses GRE fragmentation considerations. 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,
.

[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460,
December 1998, .

[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,
.

[RFC2784] Farinacci, D., Li, T., Hanks, S., Meyer, D., and P.
Traina, "Generic Routing Encapsulation (GRE)", RFC 2784,
DOI 10.17487/RFC2784, March 2000,
.

[RFC2890] Dommety, G., "Key and Sequence Number Extensions to GRE",
RFC 2890, DOI 10.17487/RFC2890, September 2000,
.

[RFC7588] Bonica, R., Pignataro, C., and J. Touch, "A Widely
Deployed Solution to the Generic Routing Encapsulation
(GRE) Fragmentation Problem", RFC 7588,
DOI 10.17487/RFC7588, July 2015,
.

[RFC7676] Pignataro, C., Bonica, R., and S. Krishnan, "IPv6 Support
for Generic Routing Encapsulation (GRE)", RFC 7676,
DOI 10.17487/RFC7676, October 2015,
.



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7.2. Informative References

[I-D.herbert-gue-fragmentation]
Herbert, T. and F. Templin, "Fragmentation option for
Generic UDP Encapsulation", draft-herbert-gue-
fragmentation-02 (work in progress), October 2015.

[I-D.templin-aerolink]
Templin, F., "Asymmetric Extended Route Optimization
(AERO)", draft-templin-aerolink-65 (work in progress),
January 2016.

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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