RFC 1702 (rfc1702) - Page 1 of 4

Generic Routing Encapsulation over IPv4 networks

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Network Working Group                                           S. Hanks
Request for Comments: 1702                               NetSmiths, Ltd.
Category: Informational                                            T. Li
                                                            D. Farinacci
                                                               P. Traina
                                                           cisco Systems
                                                            October 1994


            Generic Routing Encapsulation over IPv4 networks

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.

Introduction

   In an earlier memo [RFC 1701], we described GRE, a mechanism for
   encapsulating arbitrary packets within an arbitrary transport
   protocol.  This is a companion memo which describes the use of GRE
   with IP.  This memo addresses the case of using IP as the delivery
   protocol or the payload protocol and the special case of IP as both
   the delivery and payload.  This memo also describes using IP
   addresses and autonomous system numbers as part of a GRE source
   route.

IP as a delivery protocol

   GRE packets which are encapsulated within IP will use IP protocol
   type 47.

IP as a payload protocol

   IP packets will be encapsulated with a Protocol Type field of 0x800.

   For the Address Family value of 0x800, the Routing Information field
   will consist of a list of IP addresses and indicates an IP source
   route.  The first octet of the Routing Information field constitute a
   8 bit integer offset from the start of the Source Route Entry (SRE),
   called the SRE Offset.  The SRE Offset indicates the first octet of
   the next IP address.  The SRE Length field consists of the total
   length of the IP Address List in octets.







Hanks, Li, Farinacci & Traina
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