RHEL default gateway configuration

The default gateway is an essential part of computer networking. When a computer attempts to communicate with another device, it will send packets to the default gateway. The default gateway, which is usually a router, will then direct the packets where they need to go.

Therefore, if a Linux system is not configured with the address of a proper default gateway, it will not know where to send packets to.

In this tutorial, you will learn how to view the currently configured default gateways on Red Hat Enterprise Linux. You will also see how to change the default gateway, in case the IP address or path to the device has changed.

In this tutorial you will learn:

How to view and change the default gateway on an RHEL system

Software Requirements and Linux Command Line Conventions
Category	Requirements, Conventions or Software Version Used
System	Red Hat Enterprise Linux
Software	N/A
Other	Privileged access to your Linux system as root or via the `sudo` command.
Conventions	# – requires given linux commands to be executed with root privileges either directly as a root user or by use of `sudo` command $ – requires given linux commands to be executed as a regular non-privileged user

Viewing default gateway

Let’s start by viewing the currently configured default gateway on the RHEL system. From there, we can see if the correct IP address is being used (or if any is used at all).

The following two commands will do the job.

$ ip r
default via 10.0.2.2 dev enp0s3 
10.0.2.0/24 dev enp0s3 proto kernel scope link src 10.0.2.15 
192.168.122.0/24 dev virbr0 proto kernel scope link src 192.168.122.1 linkdown

Or, for a more thorough output, the routel command…

$ routel
         target            gateway          source    proto    scope    dev tbl
        default           10.0.2.2                                   enp0s3 
      10.0.2.0/ 24                       10.0.2.15   kernel     link enp0s3 
 192.168.122.0/ 24                   192.168.122.1   kernel     link virbr0 
       10.0.2.0          broadcast       10.0.2.15   kernel     link enp0s3 local
      10.0.2.15              local       10.0.2.15   kernel     host enp0s3 local
     10.0.2.255          broadcast       10.0.2.15   kernel     link enp0s3 local
      127.0.0.0          broadcast       127.0.0.1   kernel     link     lo local
     127.0.0.0/ 8            local       127.0.0.1   kernel     host     lo local
      127.0.0.1              local       127.0.0.1   kernel     host     lo local
127.255.255.255          broadcast       127.0.0.1   kernel     link     lo local
  192.168.122.0          broadcast   192.168.122.1   kernel     link virbr0 local
  192.168.122.1              local   192.168.122.1   kernel     host virbr0 local
192.168.122.255          broadcast   192.168.122.1   kernel     link virbr0 local
            ::1                                      kernel              lo 
            ::1              local                   kernel              lo local
        ff00::/ 8                                                    enp0s3 local

As we can observe from both outputs, 10.0.2.2 is the current default gateway.

Change default gateway

Now that we know what our default gateway currently is, let’s see how we would change it.

Defining default gateway using ifcfg files, that is, defining it as per network interface basis takes a precedence over global system wide default gateway configuration defined by /etc/sysconfig/network configuration file.

For a basic configuration we can add new default gateway using GATEWAY="GW IP ADDRESS" directive inside main network config /etc/sysconfig/network file. For example:
```
# cat /etc/sysconfig/network
GATEWAY="10.1.1.1"
```
Make sure you restart Network Manager for the changes to take effect.
```
# systemctl restart NetworkManager.service
```
As it was already mentioned above, adding new default gateway via /etc/sysconfig/network file is system wide and any default configuration using specific ifcfg config file will take precedence. To add a default gateway in Redhat Linux as per network interface basis, edit the appropriate file in /etc/sysconfig/network-scripts
For example, editing the /etc/sysconfig/network-scripts/ifcfg-enp0s3 file will edit the settings for network interface enp0s3.
```
# cat /etc/sysconfig/network-scripts/ifcfg-enp0s3
DEVICE="enp0s3"
ONBOOT=yes
NETBOOT=yes
UUID="452901c2-06e1-4ed9-afa4-f227c7632eed"
BOOTPROTO=none
IPADDR="10.1.1.56"
NETMASK="255.0.0.0"
HWADDR="08:00:27:32:cc:c0"
TYPE=Ethernet
NAME="enp0s3"
GATEWAY="10.1.1.2"
```
Even though we still kept the global default gateway configuration within /etc/sysconfig/network config file, after a network restart we will see that the new default gateway GATEWAY="10.1.1.2" takes precedence:
```
# systemctl restart NetworkManager.service
# routel | grep default
        default           10.1.1.2                   static          enp0s3 
        default        unreachable                   kernel              lo unspec
        default        unreachable                   kernel              lo unspec
```

Closing Thoughts

In this tutorial, you learned how to view the currently configured default gateway in Red Hat Enterprise Linux. We also saw two different methods to change the default gateway, either on a global basis or per individual interface. Having a correctly configured default gateway address is essential for communication across local networks and with devices on the internet.

Viewing default gateway

Change default gateway

Closing Thoughts

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