Re: No echo from the NIC


Ken Pogran (pogran@ccq.bbn.com)
Wed, 5 Aug 87 8:41:40 EDT


Regarding PINGing and the report that the NIC has elected to turn
off ICMP echo replies ("He said they were getting too many ECHO
requests and that it was loading the machine down. ICMP ECHO
request/reply has been a usefull debugging tool. I hope this
doesn't start a trend."):

This issue is only about thirteen or fourteen years old. Perhaps
Mike Padlipsky will supply us with the correct bibliographic
reference; back in the NCP days he wrote an RFC entitled
something like, "... but my NCP costs $500 a day!" complaining
about incessant NCP ECHO requests from TENEX hosts that were
causing the MIT-Multics Network Daemon to wake up constantly to
send ECHO REPLYs. The solution for us at MIT, back then, was
two-fold: 1) Get the TENEXes to stop frequent pinging which was
being done for the sole purpose of keeping track who was really
up on the ARPANET and who was not, and 2) move the Multics
ECHO-processing code into an interrupt handler and out of a
process that needed to be awakend for each echo. Both were
accomplished.

Yes, pings are nice. They provide you with assurance that
someone is really there. As the Internet grows though (and we're
over 250 truly active nets, now), unnecessary or gratuitous pings
are a waste of everyone's cycles -- hosts, gateways, PSNs. And
at a well-known, heavily-used host like the NIC -- imagine the
horror experienced by a system manager who, trying to respond to
user complaints of slow service, does a profile of where his
cycles are going and discovers that a substantial fraction is
going into ICMP ECHO replying! (I haven't talked with the NIC,
so my description here is purely hypothetical.) Here, clearly,
is a way to "buy back" cycles that can be used to improve service
to users.

Is it going to start a trend? Given the ever-increasing number
of nets out there, we might indeed begin to see more "defensive"
moves made by major service hosts who begin to perceive completely
open, full, and friendly participation as a drain on their
resources.

Food for thought.

Ken Pogran



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