In message <199808272141.RAA22050@jekyll.piermont.com>, "Perry E. Metzger" writ
es:
>
>"Michael K. Sanders" writes:
>> >BTW, you know there *is* a standard ICMP message to let you get the
>> >local netmask by broadcasting...
>> 
>> "Broadcasting to what"? 
>
>To the local net.
>
>You presumably get answers from the local routers and hosts if they
>know what the netmask is.

Right, but if you have a CIDR network then the broadcast address is an
unknown... You could just send the ICMP to the gateway and hope it's
implemented (is it required by any standards?), but I don't think
relying on a broadcast is a good idea.