I have a D-Link DSL-2500U ADSL modem. Its default IP is 192.168.1.1 and default login/password for the web interface is admin/admin. If I plug in the Ethernet cable to the NIC of a computer (that runs Windows XP), assign the IP 192.168.1.2, then I can access the web interface at http://192.168.1.1 in the browser.
My modem is configured to work in bridge mode. If I also plug in the phone line that comes from the splitter and change the NIC settings on computer to obtain an IP addres automatically over DHCP, I get a real IP (and also a default gateway, which implies a default route) from my ISP. Everything is well, Internet works, except the fact that I can't access the web interface of the modem anymore, unless I unplug the phone line, restard the modem and change the NIC settings back as described above. I assume this happens because the IP packets for 192.168.1.1 destination go to the ISP gateway via the default route instead of going to the modem.
Until now I used to have ~8Mbps download, so I know for sure that my modem and my phone line can handle it. Recently my ISP raised the download speed up to 20Mbps, but I'm still getting only ~8 as before. I know I need to have ADSL2+ support. My modem supports it and this is enabled, I can see that in the web interface. But I would want to be able to access the web interface when the modem is running in bridging mode and my Internet connection is working, so I could see the maximum link speed, just in case that my ISP forgot to increase the speed on the DSLAM port.
How can I access the web interface in this scenario?