Re: Allocating addresses across routers

[Shawn Mamros <[e-mail]>]

cpeters2 <[e-mail]> writes:
>Hi - I have a little dilemma, but first let me explain where I am at.
>I have configured my AIX4.2 box with a DHCP server (it hands out leases,
>it handles bootp both dynamic and static)  All in all I am pretty pleased
>except for this one little thing.  We have a highly subnetted network
>and I would like to have as FEW DHCP servers as possible which means I
>need to forward client requests across the routers.  My router people
>cringe when I tell them this, they are worried about broadcasts.  Is
>there any other way to do address assignment across a router without
>opening it up to ALL broadcast packets?

There's no need to "open" a router to all broadcast packets.  If your
router supports BOOTP relay agent functionality (and most do these
days), you should be able to specify the set of DHCP servers to which
that relay agent (in this case, the router) will forward DHCP/BOOTP
broadcast client requests.  What happens then is the following:

1) Client broadcasts on its own network.
2) Relay agent (router) picks up that broadcast.
3) Relay agent (upon determining that the broadcast is a UDP packet
   destined for the BOOTP server port) UNICASTS that packet to each
   DHCP server listed.
4) DHCP server(s) respond through the relay agent.

So, broadcasts are confined to the LAN, and all wide area traffic is
unicast.

The notion that one needs "forwarded broadcasts" to do DHCP (or BOOTP)
over a WAN is probably one of the most common misconceptions around.
"It just ain't so..."

-Shawn Mamros
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