multiple subnets on the same interface

[Andi Kleen]

For various reasons I'm trying to give one client on a dhcpd
3.0.5/Linux 2.6.25rc7 served subnet an IP address on a different
network.  This means there are not multiple interfaces with
different nets, but a single interface with multiple networks
configured.

I configured the additional network on the interface and
everything works great when I configure the client to use a static
IP address.

But I have a little trouble to get dhcpd to automatically serve
the different IP.

I tried the two obvious ways

subnet normal subnet  { 
        range normal subnet;

        host special-client {
                hardware ethernet mac-address-of-client;
                fixed-address ip-in-different-subnet;
                options routers router-in-different-subnet;
        }
}


and to define two different subnets which would point 
to the same interface. dhcpd didn't like either. For the first
option it just ignored the host declaration with the special
IP address and stubbornly served out an address in the normal
subnet.  I also cleared out the leases database manually
from the old address while dhcpd was stopped, but that also didn't
help.

And for the second option it would complain about
not being able to find the additional subnet, while it was clearly
on the interface.

Is there a way to make this work?

Thanks,

-Andi