Re: ICMP's & IP src addrs


jqj@hogg.cc.uoregon.edu
Sat, 17 Sep 88 07:24:29 PDT


>Flame: An ICMP echo to a broadcast address should get no response!
>What an incredibly obnoxious thing to do!

        What do you mean it should get no response? It is a legal broadcast
        that all machines should reply to.

Recall that broadcast was not originally part of the IP design, and indeed
that many media that support IP do not support hardware broadcast. As such,
it is to be expected that the "proper" behavior of various protocols in
response to broadcasts is not well defined in the specs. IP broadcast was
added mostly to support the functionality provided by Ethernet broadcast. In
any CSMA environment (though not on a TR!) a broadcast ICMP echo request is
a VERY BAD idea since it is guaranteed to generate a massive collision as
everyone tries to answer at once. Designers of broadcast request-response
Ethernet protocols almost always go to great effort to insure that the
number of legitimate respondents is bounded, and preferably 1 (cf proxy
ARP).

If the spec doesn't forbid it, it should.



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