Setting a Default Gateway for Redhat / CentOS systems?

There are two possible ways for adding a default gateway.

Option 1: You can add a gateway definition to  the /etc/sysconfig/network file. This definition will apply to all network interfaces.

Let’s say that your gateway is 192.168.4.1,  then you need to add the following line to /etc/sysconfig/network file.
GATEWAY=192.168.4.1

Option 2: You can define a default gateway for a specific interface. For this approach you need to modify your nterface definition. Let’s say we want to modify eth0 then you need to add the same definition to the  /etc/sysconfig/network-scripts/ifcfg-eth0 file.

For both options, your modifications will be activated after you restart your networking service.

root@centos ~]# /etc/init.d/networking restart

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2. KVM And Bridge Network Definition On Ubuntu
3. Ubuntu KVM Virtualization Host: Networking
4. Disabling SELinux on CentOS
5. Configuring an additional Yum repository.