D-link DSL-320B modem fails to connect to router.

[#1]

Having spent much time trying to connect the plusnet supplied DSL-320B modem to my existing Buffalo Airstation wireless router I thought I would post a query here. I have not tried the suggestion in http://community.plus.net/forum/index.php/topic,36358.msg330468.html so that may solve the problem but it still warrants discussion.
The modem says that it has some form of built in firewall/routing and a dhcp server for the internal LAN. When connecting this to a PC the internet settings are as follows:
IP: 87.112.32.1
Subnet mask: 255.255.255.255
Gateway: 192.168.1.1
DHCP server: 192.168.1.1
DNS: 212.159.6.9
I'm not an expert but this looks like it shouldn't work as the gateway/subnet mask are incompatible. It seems that the modem is directly transferring IP, subnet and DNS from the adsl but supplying it's own gateway and DHCP server. Has anyone used this modem or got any ideas to try?
Many thanks.

[#2]

Quote from: mncooper

The modem says that it has some form of built in firewall/routing and a dhcp server for the internal LAN.

I thought that your DSL-320B "modem" is a "router".  As such it performs network address translation separating Internet (WAN) IP addresses from local (LAN) addresses.  However, it seems that it performs a half-bridge connection when it functions as a 'modem', passing on the Internet IP address to your PC/router in your LAN.
So, within your LAN, communications take place using the 192.168.1.0/255.255.255.0 subnet and that's how you can access your modem's admin GUI.  From the Internet communications (inbound) take place using your 87.112.32.1 IP address.
From the link you posted it seems that your modem requires MAC address spoofing, although I am not sure if this is mandatory.  Unfortunately, I do not have your devices available to me to experiment and confirm settings.  If MAC address spoofing is necessary, then you'll also need to set this up at your router (as opposed to your PC) if you are connecting a router to your DSL-320B.
Hope this helps.

[#3]

I am not at my parents (who have this connection) again until this weekend when I will try mac spoofing as the Buffalo router does have that facility.
The interesting question is why is this necessary? Afaics there is no updated firmware for the DSL-320B but I would expect it to either work as a modem providing IP pass-through or as a router rather than with some kind of mish-mash of the two. There seem to be two subnets in operation depending on the desired direction of data flow.
Is it something I should (try to) chase up with d-link?

[#4]

I'm not familiar with your modem.  You seem to want to use it in a full bridge mode (no MAC spoofing is required).  However, without going through the documentation I have no idea if D-Link offer a full bridge mode.  Certain modem implementations can only manage a half-bridge set up.  Even if it does manage to provide a fully bridged mode, some/most manufacturers do not formally support full bridge operation, although the device will do it if you type the right string in the browser.
In full bridge mode the modem will perform no PPP authentication with the ISP, no NAT-ing, no DHCP and no DNS services for machines in your LAN.  Just ATM encapsulation of the packets generated in your LAN.  PPPoE authentication will take place at the router (or your PC if you do not use a router) and DNS resolution will take place at the ISP side.  To access the modem in full bridge mode you will need to set your PC with a static IP address in the same subnet (e.g. 192.168.1.0/255.255.255.0) that the modem is listening for LAN connections.
Alternatively, if you set your modem to use the same subnet as your router's LAN subnet, then you can connect a patch cable from the modem (assuming that it has more than one ethernet port) to one of the router's switch ports.  Then connect your PC to the router normally (using DHCP) and point your PC at the LAN IP address of the modem, which will now go through your router.
In full bridge the modem is transparent (i.e. invisible network wise) from the Internet and can only be ping-ed or tracerouted from the LAN.
Hope this helps.