I have a Centurylink C1000Z DSL modem in transparent bridging mode. It is connected to an Asus N66RT router. The router handles my PPPE connection and contains my ISP credentials. Modem is a simple transparent bridge. I can access and provision the Asus router without a problem my problem is that I need to access the DSL modem's GUI in order to update the firmware. The update is required by my ISP so that my DSL will continue to work after an network upgrade.

ip scheme is 192.168.0.x with a 255.255.255.0 subnet. gateway is 192.168.0.1 (not sure why its not .254)

So how can I look past the gateway at the modem? Could there be a separate subnet local only to the modem for management only?

I would really rather not have to reset the modem to gain access to the GUI. There has GOT to be a way to do this.

Any suggestions?

Gateway is almost always .1 in consumer equipment.

You need to log into your router, find out the DHCP information the WAN address has been configured with (by the modem's DHCP server), then log into that gateway address - generally you plug a computer directly into the modem to do that though.

Yeah I figured it out now. What was confusing me was that I didn't know what the modems management IP was or even if it had one in transparent bridging mode. Since the router in this case is handling the ISP authentication and soliciting an external IP from the ISP DHCP server. Essentially the router is looking directly through the DSL modem at the ISP.  

What I missed (duh) was that the routers WAN port was connected to the modem. Of course I could not see past it! Once I gave my laptop a static IP of 192.168.0.2 and plugged it into the modem LAN port (not the router) I essentially had a small two device network. The modem management network 192.168.0.1 and my laptop 192.168.0.2. They couldn't do shit but talk to each other but that is all I need. So the original management network was still there I just needed to look at through a LAN port and not a WAN port. Incidentally I believe I could use a static route to allow the modem GUI to be accessed but since I rarely need to get into the actual model I'll just use a static IP NIC.

This confirmed I'm no networking genius.