Network Working Group G. Dommety
Request for Comments: 2890 Cisco Systems
Category: Standards Track September 2000
Key and Sequence Number Extensions to GRE
Status of this Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2000). All Rights Reserved.
Abstract
GRE (Generic Routing Encapsulation) specifies a protocol for
encapsulation of an arbitrary protocol over another arbitrary network
layer protocol. This document describes extensions by which two
fields, Key and Sequence Number, can be optionally carried in the GRE
Header [1].
1. Introduction
The current specification of Generic Routing Encapsulation [1]
specifies a protocol for encapsulation of an arbitrary protocol over
another arbitrary network layer protocol. This document describes
enhancements by which two fields, Key and Sequence Number, can be
optionally carried in the GRE Header [1]. The Key field is intended
to be used for identifying an individual traffic flow within a
tunnel. The Sequence Number field is used to maintain sequence of
packets within the GRE Tunnel.
1.1. Specification Language
The keywords "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 [3].
In addition, the following words are used to signify the requirements
of the specification.
Dommety Standards Track [Page 1]
RFC 2890 Key and Sequence Number Extensions to GRE September 2000
Silently discard
The implementation discards the datagram without further
processing, and without indicating an error to the
sender. The implementation SHOULD provide the
capability of logging the error, including the contents
of the discarded datagram, and SHOULD record the event
in a statistics counter.
2. Extensions to GRE Header
The GRE packet header[1] has the following format:
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| Reserved0 | Ver | Protocol Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Checksum (optional) | Reserved1 (Optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The proposed GRE header will have the following format:
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| Reserved0 | Ver | Protocol Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Checksum (optional) | Reserved1 (Optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Key (optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number (Optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Key Present (bit 2)
If the Key Present bit is set to 1, then it indicates that the
Key field is present in the GRE header. Otherwise, the Key
field is not present in the GRE header.
Sequence Number Present (bit 3)
If the Sequence Number Present bit is set to 1, then it
indicates that the Sequence Number field is present.
Otherwise, the Sequence Number field is not present in the GRE
header.
The Key and the Sequence Present bits are chosen to be
compatible with RFC 1701 [2].
Dommety Standards Track [Page 2]
RFC 2890 Key and Sequence Number Extensions to GRE September 2000
2.1. Key Field (4 octets)
The Key field contains a four octet number which was inserted by the
encapsulator. The actual method by which this Key is obtained is
beyond the scope of the document. The Key field is intended to be
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