Pool selection based on Giaddr of different subnet
Simon Hobson
dhcp1 at thehobsons.co.uk
Fri Mar 13 19:37:09 UTC 2009
Dario Aguilar wrote:
>Hi there, I´m trying to configure a pool
>selection based on Giaddr but the problem is
>that Relay Agent IP (Giaddr) doesn't belongs to
>same subnet as the client pool so I guess I need
>to define a class that matches this criteria
>(maybe of sure that I difined in a wrong way).
>This is not working because it´s saying that
>network segment is unknown.
OK, two ways to deal with this :
1) Fix the relay agent !
2) Assuming the GIAddr of the relay agent is
unique to the clients subnet, then simply put an
extra subnet in a shared-network delcaration like
this :
shared-network broken_relay_agent {
subnet 192.168.0.0 netmask 255.255.255.0 { }
subnet 172.17.2.0 netmask 255.255.255.0 {
range ...
...
}
}
What this does is tell the DHCP server that the
two subnets are on the same wire, and so
addresses in each subnet are interchangeable as
far as allocating leases to clients in concerned.
The server will match the GIAddr to one subnet,
find no available leases, but see that leases are
available in the other subnet and allocate from
there.
This will NOT work if the same relay agent serves
other subnets using the same (wrong) GIAddr.
Without the shared-network, you will NOT get the
server to allocate a lease to any client in the
subnet as the server believes that the client is
on a different network.
>class "WAC" {
> match if (binary-to-ascii(10,8, ".", packet(24,4)) = "192.168.0.1");
>}
You don't need the binary to ascii stuff, you can
just use hex something like this :
match if (packet(24,4)) = c0:a8:00:01);
--
Simon Hobson
Visit http://www.magpiesnestpublishing.co.uk/ for books by acclaimed
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