RFC 2075 (rfc2075) - Page 1 of 5

IP Echo Host Service

Network Working Group                                       C. Partridge
Request for Comments: 2075                                           BBN
Category: Experimental                                      January 1997


                          IP Echo Host Service

Status of this Memo

   This memo defines an Experimental Protocol for the Internet
   community.  This memo does not specify an Internet standard of any
   kind.  Discussion and suggestions for improvement are requested.
   Distribution of this memo is unlimited.

Abstract

   This memo describes how to implement an IP echo host.  IP echo hosts
   send back IP datagrams after exchanging the source and destination IP
   addresses.  The effect is that datagrams sent to the echo host are
   sent back to the source, as if they originated at the echo host.

Introduction

   An IP echo host returns IP datagrams to their original source host,
   with the IP source and destination addresses reversed, so that the
   returning datagram appears to be coming from the echo host to the
   original source.  IP echo hosts are tremendously useful for debugging
   applications and protocols.  They allow researchers to create looped
   back conversations across the Internet, exposing their traffic to all
   the vagaries of Internet behavior (congestion, cross traffic,
   variable round-trip times and the like) without having to distribute
   prototype software to a large number of test machines.

   IP echo hosts were heavily used on the Internet in the late 1970s and
   early 1980s to debug various Internet transport and application
   protocols.  But, for reasons unclear, at the current date there are
   no echo hosts on the Internet and few people are even aware of the
   concept.  The goal of this memo is to document the concept in the
   hopes it will be revived.

Implementation Details

   While the basic idea of a echo host is simple, there are a few
   implementation details that require attention.  This section
   describes those implementation details.  The presentation works from
   the simplest to most difficult issues.





Partridge                     Experimental