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Re: ipfilter, return-icmp and RFC1122

Subnet-specific broadcast addresses are only broadcast addresses on
the subnet with that address.  If they arrive on another interface
you can do anything you would normally do with any packet addressed
to the same subnet, firewall or not, except that by default the
router shouldn't forward the packet onto the subnet where it would be

You mean that the "don't send ICMPs in response to packets sent to
broadcast addresses" actually means " packets sent to what on the
incoming interface is a broadcast address"?

Yes, that's a good way to put it.

That treatment applies to more than just sending ICMP errors, actually.
If you have an application which receives packets which might be
sent with a broadcast, you would only recognize packets to a subnet
broadcast address as packets addressed to "you" if they arrived on
an interface on that subnet.

Dennis Ferguson

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