ICMP Broadcast


URBANIAK@G.BBN.COM
21 Sep 1988 11:17-EDT


broadcast ICMP echo request is certainly guaranteed to provoke a
massive collision (if many IP implementations respond), but this
is not synonymous with being obnoxious or being a VERY BAD idea.
I think I would call it an unusual, potentially dangerous action.
If viewed as another LAN management tool, it can be useful, as
mentioned, to locate quickly all active IP stations on a
broadcast LAN. I see this as a useful, off-hours verification
against address assignment databases. Certainly I would wish to
request users not to issue such broadcasts, but I'm not sure that
users stations should be mandated not to respond to a broadcast
request. (Being one of many tools, you might conclude that the
safest network behaviour is to constrain the IP behaviour. But
maybe this is just a user behaviour prophylactic, not a protocol
design goal. don't you really want an implementation switch:
do/don't respond to IP broadcast ICMP Echo, for individual sites
to set?)

Also, massive LAN collisions are not necessarily to be avoided,
they are to be managed, which might mean avoidance during prime
time to some sites. Generating a test massive collision with IP
broadcast might tell you how different implementations behave,
which are more/less robust, what the settling time for this
incident is for a given LAN, how your network components are
responding. My view is that many production LANs permit some wee
hour testing or preventive maintenance and learning on the real
live network.

I'm not sure how much of real LAN management might not be
considered to be "unusual" and "potentially dangerous" from the
perspective of a user who was yet to benefit immediately and
directly.

Walter doc Urbaniak. Urbaniak@BBN.COM (800 station Ethernet)



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