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:
According to the local routing table shown above, a default gateway is 192.168.91.2, and traffic is forwarded to the gateway via eth0.
Change a default gateway to another IP address
In order to change a default gateway to another IP address, try below command:
Obviously, a default gateway's IP address should come from the subnet associated with the interface connected to the default gateway, in this example, 192.168.91.0/24. Otherwise, the command will fail with the following error.
Also, keep in mind that the default route change made by ip command will be lost after rebooting.
Set a default gateway permanently on CentOS
You will need to update /etc/sysconfig/network accordingly.
Again, be aware that the IP addressed specified here should match with the subnet (192.168.91.0/24) 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=
Whether you edit /etc/sysconfig/network or /etc/sysconfig/network-scripts/ifcfg-ethX, don't forget to restart network service as follows, or reboot your CentOS for the change to take effect.
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