Making Additional IPs as Source IPs

When you buy a server with the main IP and assign additional IPs, they are routed statically. Therefore, no gateway or broadcast addresses are needed when configuring the IPs on your NIC.

However, when using additional IPs, the default route of the server is still via the gateway of your primary IP. So, how do you reroute all traffic via an additional IP?

In this example, we are using a Cloud Hosting server with CentOS 7 OS. The main IP is The additional IP is, and we have already assigned it to our server via Terminal.

Note: Once you assign additional IPs to the server, do not forget to perform stop/start of the server to complete routing. Otherwise, you might not see the desired results.

All in all, changing the default route is not complicated. It can be done temporarily or permanently.

The temporary solution

Check the network configuration:

ip a

Inspect the results:

Server terminal demonstrating network configuration results.

Add the additional IP:

ip addr add dev eth0

Check the network configuration again:

Server terminal demonstrating network configuration results after adding additional IP.

We can see that the IP address was added successfully.

As we check using a different computer/server, we can see that the IP address gives ping replies:

Server terminal demonstrating that added IPs ping successfully.

Now, check the default route:

ip r
Server terminal showing a default IP route.

Let’s change the default route of the source IP:

ip r change default via src

Inspect the results:

Server terminal showing changed default route of source IP.

That’s it! The traffic has been rerouted to go via the additional IP.

Note: After you perform a network service restart or after you restart the server, the changes will be reverted back to defaults.

The permanent solution

It is just as easy to apply the permanent solution.

Let’s edit the


file (if your network interface name is eth0):

vi /etc/sysconfig/network-scripts/ifcfg-eth0

Note: Since we use a Cloud server as an example, we need to configure the IP address statically.

Here is how our configuration looks in our example:

Server terminal showing IP configuration results.

Make sure there are no mistakes in this file. We suggest you configure the static IP first and then restart the network service. Afterward, configure the second IP in the same file and then add the SRCADDR (source address). Otherwise, you might lose connection to your server. In such a case, use the virtual console via the Heficed Terminal to reach your server.

Check the results:

ip r
Server terminal showing results after adding IPs as source IPs.

To keep the changes permanent after a server reboot, edit the file:

vi /etc/cloud/cloud.cfg

Add the following line:

 config: disabled

Save the file and restart the server.

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