Normally, Ubuntu doesn’t work very well with DSL modems, and it is needed to go to the network configuration applet and put two DNS servers (from openDNS), 208.67.222.222 and 208.67.220.220. The problem is that after a while, the system removes that configuration automatically leaving you without connection. To overcome this, at the prompt we write
#route -n
and go to the line with a UG flag, and identify the Gateway number. Then we go to network configuration, and set the connection to Static IP, and copy the gateway number to the corresponding box. The IP box is filled with a number we invent, similar to the gateway address, let say
gateway address: 12.31.21.2
we create an IP address 12.31.21.3
The subnet mask should be filled automatically, something like 255.255.255.0. Then we accept and leave the applet (keeping the same DNS numbers), and restart the system (restart the modem if possible).
That should be it.
Raul A. Monsalve 