Stefan Hegnauer wrote:

> I can use LAN1 without any problems, i.e. connect to m0n0wall, to the
> internet, get DHCP leases, anything.
> 
> Hooking up the same computer (XP box) to LAN2 I cannot even get a DHCP
> lease. Wireshark on the XP box shows that DHCP requests are sent from the XP
> box, but not answered by m0n0. Trying to ping m0n0 from LAN2 results in ARP
> broadcasts that are not answered by m0n0 - nothing, not a peep. 
> Trying to ping my XP box (this time with a static IP of 192.168.100.2) from
> m0n0 does not give any replies, and wireshark does also not see them (and
> the XP firewall is off).
> 
> I am running m0n0wall 1.3b14 (although I tried similar setups with earlier
> versions, and no success as well).

Two questions out of sheer curiosity:

- what does the m0n0 route table look like?

- have you tried to reboot the m0n0 box after switching from interface 1 
to interface 2 with the XP box?

The reason I ask the second question is because many times (with Cisco 
and other branded routers, and some switches for that matter), if I move 
a device from one physical interface to another, the ARP cache requires 
a flush in order to realize that the device has moved.

May also be worth flushing the Windows ARP cache entry as well, but I 
don't think that this will be the problem in this case, as XP will see 
the two m0n0 IP's as separate ARP entries anyhow.

Steve