Linux routing basics
Most of the people doesn’t know that linux/*nix systems can be used as routers. Even there is a project called Linux routing and separate Linux OS for routing purpose alone, that’s the flexibility of Linux. In linux/*nix every work can be done in two ways.
That is one temporary way(after reboots these changes will not be there) and
the other is permanent way(after reboots too the changes will be there).
Creating routes in Linux : Basic Linux routing
Add a route to a network
#route add -net network/mask gw default-gateway
Example
#route add -net 10.10.10.0/24 gw 192.168.0.1
Or
#route add 10.10.10.1 gw 192.168.0.1
Adding default gateway
#route add default gw default-gateway Example #route add default gw 192.168.0.1
Adding a route to specific host
#route add -host host-name gw default-gateway Example: #rotue add -host 2.34.5.6 gw 192.168.0.1Or #route add 2.34.5.6 gw 192.168.0.1
Deleting route to a network
#route del -network network/subnet default-gateway Example #route del -net 10.10.10.0/24 gw 192.168.0.1
Deleting default gateway
#route del default gw default-gatway
Example :
#route del default gw 192.168.0.1
Deleting specific host from routing table
#route del -host ip-add gw default-gateway Example #route del -host 10.10.10.45 gw 192.168.0.1
Seeing routing table
#netstat -rn
#route -n
Note : The old gate way will still remain and may need to be taken out for the system to function properly. Routes are made permanent in Red Hat Linux by adding routes to/etc/sysconfig/static-routes.