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>
