Re: broadcast question

Hi,

On Wed, Mar 3, 2010 at 3:24 AM, Jersey Guy <guy.jersey_at_gmail.com> wrote:
> All,
> Let's say I have four /26 networks carved out of the same /24, sitting on
> the same router's LAN interfaces. From a remote location, I wish to send a
> broadcast to all four /26 networks. To save WAN bandwidth, can i send a
> single broadcast to the /24 network and somehow have the router pass the
> broadcast on to the four /24s? How can this be accomplished?

Try putting four 'ip helper-address' commands on the remote router's
interface that's closest to the source of the broadcast, then enable
"ip directed-broadcast" (possibly with an ACL to restrict senders) on
the same interface.

The 'ip helper-address' commands should reference the broadcast
addresses corresponding to each /26.

You can't just send it to the top level /24 as a packet destined for
its broadcast (.255) will correspond to only one of the /26s (the last
one) by the time the router with the connected interfaces receives it.

NB: I have not tested the above solution. 'ip helper-address' is
normally used for converting broadcasts to unicasts, so I'm not sure
if the router will care that the destination address is a directed
broadcast.

cheers,
Dale

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Received on Wed Mar 03 2010 - 09:03:08 ART