Re: ICMP responses to broadcasts


J. Noel Chiappa (JNC@XX.LCS.MIT.EDU)
Mon 21 Apr 86 23:59:39-EST


        Mike, sorry, but I think dropping incoming broadcast IP
packets is bogus. This will break at least one existing ICMP message.
(In addition, this won't fix the case where someone sends packets
directly the the gateway with a destination address that translates to
broadcast.)
        My opinion is that the *right* thing is for the gateway's IP
layer to recognize the IP broadcast addresses (thanks to 4.2 the C
gateway recognizes the illegal net.0's as well as net.1's, all 0's,
all 1's, etc) and do the right thing. Network layers should discard
(with an ICMP Host Unreachable error message, if you want) packets
which are sent to a valid IP address which is not an IP broadcast
address but which is the local broadcast address. I.e., a packet
shouldn't get broadcast unless it specifically asks for it.
        IP packets which are addressed to the broadcast address should
be handled as stated in the RFC (if you want a minimal implementation
in the gateway, you can just accept them for local processing only, or
simply ignore them). No ICMP error messages should be returned by
*anyone* in response to any message sent to an IP broadcast address.

        Noel
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