I have a server with multiple network interfaces. Out of that two of them were connected to two different networks. My requirement is to route the internet traffic through the second interface. The Server is running with CentOS 7 operating system. The second interface is connected to a network with higher internet bandwidth and the first interface is connected to a network with lower bandwidth. So I have to make the second interface as the primary/default interface.
The details of the network interfaces are given below.
Details of first interface:
Interface name -> eno2
IP Address: 192.168.0.208
Gateway 192.168.0.1
Internet Provider : ISP01
Details of second interface:
Interface name -> eno3
IP Address: 172.31.0.208
Gateway 172.31.0.1
Internet Provider : ISP02
The diagrammatic view of the server and network connections are given below.
Problem statement:
The internet traffic is going through the first interface. I want to change it to the second interface.
How to check the route of the internet traffic ?
This can be checked by using the traceroute command. Execute the following commands and check hops. If it is going through the gateway of the first network, means traffic is routed through the first interface. If it is going through the gateway of the second network, means that the traffic is routed through the second interface.
traceroute google.com
When I executed this command, I got the following output that proves that the traffic was going through the first interface. 192.168.0.1 is the gateway of the first interface. You can see the details in the below screenshot.
How to list the default traffic routes ?
To list the existing routes in the system, type the following command in the terminal.
ip route list
This will list all the routes and that shows the default routes also. The following screenshot shows the details of the routes in my system.
In the above image, you can see two default routes. The first one has a priority of 102 and second one with priority 103. So based on the priority, the traffic goes through the first interface (gateway 192.168.0.1, ISP-01).
How to change the default / primary route ?
In my case there were two default routes. So making one interface as the default or primary route will solve the problem.
This can be enabled by configuring the DEFROUTE parameter in the network interface settings. The network interface configurations are present in the following directory.
/etc/sysconfig/network-scripts
In this directory, you can see files that starts with ifcfg-. In my case, the two files that I have to deal with are ifcfg-eno2 and ifcfg-eno3.
In this file, there will be a parameter DEFROUTE. If it is configured with value “yes” means that interface is a default route. If the value is “no” means it is not a default interface.
So make DEFROUTE=no in the first interface (ifcfg-eno2) and DEFROUTE=yes in the second interface (ifcfg-eno3).
Restart the network after making these changes. The command is shared below.
service network restart
Now check the route list and see the default route/s. The command is given below.
ip route list
The screenshot from my system is shared below.
Now you can see that the second interface (gateway 172.31.0.1 & ISP-02) became the default interface and the first interface got removed from the default list. It is present in the available interfaces, but not the default interface.
Now let us test the internet traffic through traceroute command. As per our configuration, the traffic should go through the second interface. The command is given below.
traceroute google.com
The screenshot from my system is given below.
As per the screenshot, the traffic is going as expected based on our configuration. It is going through the second interface.
The steps for Ubuntu and other operating systems are also similar. Here I have explained based on CentOS & RHEL operating systems.
Hope this article helps someone. 🙂
