[Moderator edit (TH): Resolved. See this thread for details]
I have the following setup:
Linksys AM300 ADSL Modem in Half-Bridge Mode
Linksys WRT54GL with DD-WRT v23 SP2 installed obtaining the external IP from the ADSL modem
X-Net ADSL Connection with dynamic IP
Previous to this week, this setup ran flawlessly until a couple of days ago it stopped working properly.
What is happening is that the modem is connecting fine & picking up the assigned Internet IP, Subnet and Gateway addresses as normal and connectivity from the modem works fine. Also, the DHCP on the modem works (to a point) and the router picks up an IP address, subnet and gateway from the modem. However, while the modem is getting a subnet mask of 255.0.0.0, the router picks up a subnet of 22.214.171.124!!??
The only thing that has changed is that previous to last week, X-Net were giving out 58.x.x.x ip addresses, and a 58.x.x.x gateway address. However, as of this week, I am getting a 118.x.x.x ip address and a 58.x.x.x gateway, which is a little odd.
I'm wondering if somehow this is screwing up the DHCP on the modem and causing it to serve up an incorrect subnet mask to the router?
I think there might be a bigger problem however as even if I manually specify the correct IP details on my modem (& don't use DHCP), it still doesn't work (unless half-bridging requires DHCP in some way that I don't understand).
I tried obtaining IP details from the modem with my PC and I get the same result, so I don't think the fault lies with the router. I have tried resetting the modem to factory defaults and configuring it again from scratch to no avail. I am also running the latest firmware that I can find (1.19.02).
I've setup double-nat at the moment, which works ok, but is not what I want in the long term.
I've tried creating a post on the Linksys community forum, but for some reason it won't let me create a new post!
So, does anyone have any ideas?