BRUCE@UMDD.UMD.EDU (Bruce Crabill) (09/02/89)
I think the use of a flag that is set based on network level addressing
has validity. This is not to say that you should not use the IP broadcast
format for outgoing traffic, but using network level broadcast information
can be very useful in preventing broadcast storms. Several years ago, I
added this very mechanism to the TCP/IP software that we use on our IBM
mainframes. Basically, each of the network drivers will set a flag in
the packet buffer for incoming packets if the driver detects that it
received the packet as the result of a broadcast. Later on, IP checks
this flag if it is about to forward a packet. If it is on, it drops the
packet. I can see the network destination address on all the currently
supported Ethernet/Pronet drivers, so everything works. If I had a
network interface where I couldn't get to the network destination
address for incoming packets, I would probably also add an additional
check at the IP level using the IP broadcast format (I probably ought
to do that anyway). I don't currently support broadcasts over point-to-
point links (I have mixed feelings about this).
Bruce