some points about ubuntu's network.

  1，configuration file:  first you should know some files, /etc/network/interfaces,/etc/resolv.conf, /etc/init.d/networking.
first one /etc/network/interfaces, in it you can set your ip address, set your netmask, set your gateway, like following:

　　auto lo

　　iface lo inet loopback

　　iface eth0 inet static

　　address 192.168.200.***

　　netmask 255.255.255.0

　　gateway 192.168.200.***

　　auto eth0

second, /etc/resolv.conf, in it, we can set nameserver, which is DNS. like following:

nameserver 202.117.***.**

third: /etc/networking

it can restart the net. like following:

sudo /etc/networking restart.

2, /etc/NetworkManager/nm-system-settings.conf, it can set the x-window's network.  The logo is in the desktop.