A network gateway is a crucial component in any network infrastructure, acting as an intermediary that routes traffic from a local network to other networks, often the internet. In a Linux environment, configuring a network gateway is essential for ensuring that devices within the local network can communicate with external networks. This article will guide you through the process of setting up a network gateway on a Linux system using practical examples and commands.

Examples:

1. Checking Current Gateway Configuration: Before configuring a new gateway, it's useful to check the current gateway settings.

   ip route show

   This command will display the current routing table, including the default gateway.

2. Setting Up a Static Gateway: To set a static gateway, you can use the ip command. For example, to set the gateway to 192.168.1.1, you would use:

   sudo ip route add default via 192.168.1.1

   This command adds a default route through the specified gateway IP address.

3. Persisting the Gateway Configuration: To ensure that the gateway configuration persists across reboots, you need to add the gateway information to the network configuration file. For systems using netplan (common in Ubuntu 18.04+), you would edit the configuration file located in /etc/netplan/.

   Example netplan configuration:

   network:
    version: 2
    ethernets:
      eth0:
        dhcp4: no
        addresses:
          - 192.168.1.10/24
        gateway4: 192.168.1.1
        nameservers:
          addresses:
            - 8.8.8.8
            - 8.8.4.4

   After editing the file, apply the changes with:

   sudo netplan apply

4. Using iptables for Advanced Gateway Configuration: For more advanced configurations, such as setting up NAT (Network Address Translation), you can use iptables.

   Enable IP forwarding:

   sudo sysctl -w net.ipv4.ip_forward=1

   Add the following rule to iptables to enable NAT:

   sudo iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE

   Save the iptables rules to ensure they persist after a reboot:

   sudo iptables-save | sudo tee /etc/iptables/rules.v4

5. Verifying Gateway Functionality: To verify that the gateway is functioning correctly, you can use the ping command to test connectivity to an external IP address.

   ping -c 4 8.8.8.8

   If the ping is successful, your gateway is correctly routing traffic to external networks.