Browse Prior Art Database

IP Echo Host Service (RFC2075)

IP.com Disclosure Number: IPCOM000002627D
Original Publication Date: 1997-Jan-01
Included in the Prior Art Database: 2000-Sep-13
Document File: 5 page(s) / 12K

Publishing Venue

Internet Society Requests For Comment (RFCs)

Related People

C. Partridge: AUTHOR

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.

This text was extracted from a ASCII document.
This is the abbreviated version, containing approximately 23% of the total text.

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.

The most straightforward situation is when an echo host receives an

IP datagram with no options and whose protocol field has a value

other than 1 (ICMP). In this case, the echo host modifies the header

by exchanging the source and destination addresses, decrements the

TTL by one and updates the IP header checksum. The host then

transmits the updated IP datagram back to the original source of the

datagram.

NOTE: If the TTL is zero or less after decrementing, the datagram

MUST not be echoed. In general, an echo host is required to do

all the vari...