Re: broadcast question

 The only device that knows it's a broadcast address is the end router
where the route exists. To everyone else, there's no way to tell whether
it's a route/sub-route/aggregate-route/whatever....

Scott

Dale Shaw wrote:

  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 Tue Mar 02 2010 - 21:42:08 ART