where is the route table put

["万建明"<mingjwan youth njust edu cn>]

the content of my route table is wrong .
so I have to modify them using the following command
route add default gw myip 
route del default gw oldip
but every time i reboot the computer or turn on the computer .The content of the route table returned to the old one.
How can i change it permanently. Where is the file that contain the route .