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From: gds@SPAM.ISTC.SRI.COM.UUCP
Newsgroups: comp.protocols.tcp-ip
Subject: Re: ICMP in ISO
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Date: Fri, 17-Apr-87 04:30:24 EST
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     We should not lose sight of the fact that echo mechanisms are embedded in
     many protocols besides ICMP. Both TCP and UDP have echo ports, for
     example.
     ...
     I submit we shouldn't stop at ICMP and should strive for these
     mechanisms at each and every level in the protocol stack.

Dave,

I agree with your points.  However it may be difficult to do this in
practice.  I took a random sampling of hosts I usually ping to measure
their round-trip times and tried connecting to their tcp echo ports
instead.  Out of all the hosts I tried, none but the Unix 4.3 hosts were
listening on the echo port (and even some of them were not listening).

It's trivial to write an echo server, but for some reason most hosts
don't seem to support it.  Transport-level echo services are not
required in the same sense that ICMP echo is required.  If we want to be
assured that we can do debugging at all layers, not only must we push
for debugging protocols at all levels of the protocol stack but
encourage everyone to implement and use these protocols.

--gregbo