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From: CLYNN@G.BBN.COM.UUCP
Newsgroups: comp.protocols.tcp-ip
Subject: Re:  ICMP echo
Message-ID: <[G.BBN.COM]27-Apr-87.18:54:27.CLYNN>
Date: Mon, 27-Apr-87 18:54:00 EDT
Article-I.D.: <[G.BBN.COM]27-Apr-87.18:54:27.CLYNN>
Posted: Mon Apr 27 18:54:00 1987
Date-Received: Wed, 29-Apr-87 00:43:18 EDT
References: <8704272025.AA00279@braden.isi.edu>
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Bob's statement is a nice start but doesn't mention anything about other
options.  I would like to suggest that it would be more generally useful
if a source route was NOT inverted by the receiver of an echo request
when it formed the echo reply (... that's the way I implemented it ...).
Maybe there should be two versions of source route ...

I would argue that the simplest implementation is the most useful --
just change echo request to echo reply and switch the IP source
and destination and send the packet back without changing the options
in any way (except, of course, for the processing that IP is required
to perform).

By returning the options (which some implimentations don't now do) one
gets to see, for example, information recorded in a record route option
(possibly in addition to a source route) and in a timestamp option.
If you want the time out and back along a specific route (Bob's case)
you can source route the packet out and back to yourself, get the
timestamp info, and have your host return the packet to you (which
should be local delivery).  By not returning along a recorded route
one can (if the gateways implement IP ...) find what route is being
used to reach you from point X in the internet.

It might also be nice to include in this discussion the suggestion
(not originally mine) that the pharse in the ICMP spec (4th paragraph,
page 1) "no ICMP messages are sent about ICMP messages" be amended to
"no ICMP messages are sent about ICMP error messages"; thus allowing
one to get error messages about ICMP ECHO, TIMESTAMP, INFORMATION, etc.,
and their corresponding REPLYs.

Charlie