Generic Routing Encapsulation (GRE) (RFC1701)
Original Publication Date: 1994-Oct-01
Included in the Prior Art Database: 2000-Sep-12
Internet Society Requests For Comment (RFCs)
S. Hanks: AUTHOR [+3]
This document specifies a protocol for performing encapsulation of an arbitrary network layer protocol over another arbitrary network layer protocol.
Network Working Group S. Hanks
Request for Comments: 1701 NetSmiths, Ltd.
Category: Informational T. Li
Generic Routing Encapsulation (GRE)
Status of this Memo
This memo provides information for the Internet community. This memo
does not specify an Internet standard of any kind. Distribution of
this memo is unlimited.
This document specifies a protocol for performing encapsulation of an
arbitrary network layer protocol over another arbitrary network layer
A number of different proposals [RFC 1234, RFC 1226] currently exist
for the encapsulation of one protocol over another protocol. Other
types of encapsulations [RFC 1241, SDRP, RFC 1479] have been proposed
for transporting IP over IP for policy purposes. This memo describes
a protocol which is very similar to, but is more general than, the
above proposals. In attempting to be more general, many protocol
specific nuances have been ignored. The result is that this proposal
is may be less suitable for a situation where a specific "X over Y"
encapsulation has been described. It is the attempt of this protocol
to provide a simple, general purpose mechanism which is reduces the
problem of encapsulation from its current O(n^2) problem to a more
manageable state. This proposal also attempts to provide a
lightweight encapsulation for use in policy based routing. This memo
explicitly does not address the issue of when a packet should be
encapsulated. This memo acknowledges, but does not address problems
with mutual encapsulation [RFC 1326].
In the most general case, a system has a packet that needs to be
encapsulated and routed. We will call this the payload packet. The
payload is first encapsulated in a GRE packet, which possibly also
includes a route. The resulting GRE packet can then be encapsulated
in some other protocol and then forwarded. We will call this outer
protocol the delivery protocol. The algorithms for processing this
packet are discussed later.
The entire encapsulated packet would then have the form: