[comp.dcom.sys.cisco] Directed broadcasts

gutherz@fs06.nas.nasa.gov (Matthew J. Gutherz) (07/06/90)

This is a question about forwarding directed broadcasts.  I do know
this can dangerous.

Does the hardware destination have any effect on directed broadcast
forwarding?

Will the router only forward directed broadcasts that are directed
to one of its interfaces or will it also forward broadcasts that come
in with the hardward broadcast address (FF:FF:FF:FF:FF:FF) ?


Matt

satz@cisco.com (Greg Satz) (07/06/90)

The hardware (MAC) address will determine who receives a packet. The
network layer address (IP) will determine how that packet is handled and
where it is routed. To be a directed broadcast only implies that the IP
destination address contains a well formed IP network number in the network
part and all ones or all zeros (originating host preference) in the host
part. The network mask determines what are network and host parts.

To answer your question, no. The hardware address has no bearing on whether
a directed broadcast will be forwarded. A directed broadcast is only
broadcast on its final hop. Up until then, it is treated like any other
unicast packet.

Greg Satz
cisco