On Jan 10, 2006, at 3:48 PM, Peter wrote:

> Doesn't broadcasting work in groups ? And a node must be enabled to
> receive broadcast by giving it an address in the group (in addition to
> the normal address) ?

No, that's "multicasting."

Everything receives broadcasts.  There was a bunch of trouble
in the early internet days because unix was brain-dead and thought
the broadcast IP address was 0.0.0.0.  It would receive a broadcast
to 255.255.255.255, and decide that it wanted to be a router and
forward that packet, since it was obviously not for IT (did I mention
that unix was brain dead at the time?)  So it would
then ARP for 255.255.255.255 in an attempt to find out what ethernet
address to forward it to.  Of course, this was on an ethernet, and a
network segment with one unix workstation probably had a bunch
of them, and they'd ALL be trying to ARP for 255.255.255.255 AT THE
SAME TIME.  The ARP packets of course were broadcasts received by
everyone, so this ate up a lot of collective CPU cycles.  The most
amusing melt-down I heard of happened when some helpful device
decided to ANSWER the arp request for the broadcast IP address with
the ethernet broadcast (seems reasonable, eh?  But consider what
happens next when the broken workstations actually FORWARD the
packets to that ethernet address!)

And that's why cisco made a lot of money selling routers when some
people were trying to build large networks with nothing but bridges
and repeaters (routers stop hardware broadcasts!)

BillW
-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist