Updating routing tables in linux
The default gateway is traditionally a dedicated network router.
On Linux, BSD, and other Unix-like systems, the route command is used to view and make changes to the kernel routing table.
I am able to change gateway of an existing entry using "ip route change" command as below but not able to change metrics. Here is a website page that has the commands to edit IP addresses using the ifconfig command.
I don't know all the commands off the top of my head, but hopefully this page will help you.
adds a default route (which will be used if no other route matches).
All packets using this route will be gatewayed through "mango-gw".