Default gateway on CentOS

On Cent OS you can check the routing table with the following command:

$ route -n

The above command prints a table like this below:

Kernel IP routing table
Destination     Gateway        Genmask         Flags Metric Ref    Use Iface
10.254.1.0      0.0.0.0        255.255.255.0   U     0      0        0 eth0
192.168.185.0   0.0.0.0        255.255.255.0   U     0      0        0 eth1
0.0.0.0         192.168.185.2  0.0.0.0         UG    0      0        0 eth1

The last line of the table indicates the default gateway of the machine. In this case:

0.0.0.0         192.168.185.2  0.0.0.0         UG    0      0        0 eth1

Change default gateway

You can control default gateway using route command:

$ route del default gw <default_gateway_ip>
$ route add default gw <default_gateway_ip>

Keep in mind that this changes are only temporary. To change default gateway permanently you need to edit the file /etc/sysconfig/network and change to:

GATEWAY=<new_default_gateway_ip>

With many interfaces on the same sub-net it's also possible choose the preferred route to the default gateway with below command:

GATEWAYDEV=<network_interface>