Oct 102014

A default gateway is a remote host or router that your Linux host forwards traffic to when the destination IP address of outgoing traffic does not match any route in your local routing table. Configuring a default gateway on CentOS is quite straightforward.
If you wish to change a default gateway temporarily at run time, you can use ip command.
First things first. To check what default gateway you are using currently:
$ ip route show dev eth0  proto kernel  scope link  src dev eth0 scope link metric 1002
default via dev eth0
According to the local routing table shown above, a default gateway is, and traffic is forwarded to the gateway via eth0.
In order to change a default gateway to another IP address:
$ sudo ip route replace default via dev eth0
Obviously, a default gateway’s IP address should come from the subnet associated with the interface connected to the default gateway, in this example, Otherwise, the command will fail with the following error.
RTNETLINK answers: No such process
Also, keep in mind that the default route change made by ip command will be lost after rebooting.
In order to set a default gateway permanently on CentOS, you will need to update /etc/sysconfig/network accordingly.
$ sudo vi /etc/sysconfig/network
Again, be aware that the IP addressed specified here should match with the subnet ( associated with a default route interface.
Another option to set a default gateway persistently on CentOS is to edit /etc/sysconfig/network-scripts/ifcfg-<default_interface_name>, and add “GATEWAY=<gateway_ip>” there. If the default interface is “eth0”, you will need to edit /etc/sysconfig/network-scripts/ifcfg-eth0. If you choose to use this method, you need to refer to this post to get familiar with this option.
Whether you edit /etc/sysconfig/network or /etc/sysconfig/network-scripts/ifcfg-ethX, don’t forget to restart networkservice as follows, or reboot your CentOS for the change to take effect.