RFC 2003 (rfc2003) - Page 1 of 14

IP Encapsulation within IP

Network Working Group                                         C. Perkins
Request for Comment: 2003                                            IBM
Category: Standards Track                                   October 1996


                       IP Encapsulation within IP

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.

Abstract

   This document specifies a method by which an IP datagram may be
   encapsulated (carried as payload) within an IP datagram.
   Encapsulation is suggested as a means to alter the normal IP routing
   for datagrams, by delivering them to an intermediate destination that
   would otherwise not be selected by the (network part of the) IP
   Destination Address field in the original IP header.  Encapsulation
   may serve a variety of purposes, such as delivery of a datagram to a
   mobile node using Mobile IP.

1. Introduction

   This document specifies a method by which an IP datagram may be
   encapsulated (carried as payload) within an IP datagram.
   Encapsulation is suggested as a means to alter the normal IP routing
   for datagrams, by delivering them to an intermediate destination that
   would otherwise not be selected based on the (network part of the) IP
   Destination Address field in the original IP header.  Once the
   encapsulated datagram arrives at this intermediate destination node,
   it is decapsulated, yielding the original IP datagram, which is then
   delivered to the destination indicated by the original Destination
   Address field.  This use of encapsulation and decapsulation of a
   datagram is frequently referred to as "tunneling" the datagram, and
   the encapsulator and decapsulator are then considered to be the
   "endpoints" of the tunnel.

   In the most general tunneling case we have

      source ---> encapsulator --------> decapsulator ---> destination

   with the source, encapsulator, decapsulator, and destination being
   separate nodes.  The encapsulator node is considered the "entry



Perkins                     Standards Track