Two NIC WAN failover

How to configure failover for a WAN connection using two network interface cards (NICs) on a system using Netplan

Netplan can be used to configure failover for a WAN connection using two network interface cards (NICs) on a system. By defining two NICs in your Netplan configuration and using routing policies, you can create a primary connection and a backup connection. When the primary connection fails, traffic can be automatically switched to the backup NIC.

Here's a breakdown of how to set up a failover network with Netplan:

1. Identify Your NICs: Determine the names of your network interface cards (e.g., eth0, eth1, wlan0). You can use ip addr or nmcli to list active interfaces.

2. Configure Netplan (YAML):

   • Create a Netplan configuration file (usually in /etc/netplan/).

   • Define two ethernet interfaces in the netplan file, one for the primary WAN connection and one for the backup WAN connection.

   • Set up static IP addresses or utilize DHCP as needed for each interface.

   • Use the routing-policy section to define the order in which routes are applied. This will determine which NIC is used for traffic when both are available.

   • Set the primary NIC as the primary route with a higher priority, and the backup NIC as a lower priority route.

3. Apply Netplan Changes: Run netplan apply in your terminal to apply the new configuration and restart the network services.

4. Test Failover: Simulate a failure of the primary NIC (e.g., unplug the cable or manually disable the interface) to verify that traffic automatically switches to the backup connection.

Example Netplan YAML Configuration (Simplified):

network:
  version: 2
  renderer: networkd
  ethernets:
    eth0:  # Primary WAN NIC
      dhcp4: yes
      dhcp6: no
      match:
        macaddress: "your-mac-address-here"
      routes:
        - to: "0.0.0.0/0"
          on-link: true
          gateway: 192.168.1.1 # Example Gateway
          metric: 100 # Higher Metric (Priority)
    eth1:  # Backup WAN NIC
      dhcp4: yes
      dhcp6: no
      match:
        macaddress: "your-mac-address-here"
      routes:
        - to: "0.0.0.0/0"
          on-link: true
          gateway: 192.168.2.1 # Example Gateway
          metric: 200 # Lower Metric (Priority)

Explanation:

• ethernets: Defines the configuration for Ethernet interfaces.

• dhcp4: Sets whether to use DHCP for IPv4 (enable for dynamic IP, disable for static).

• dhcp6: Sets whether to use DHCP for IPv6.

• match: Used to identify the NIC based on its MAC address.

• routes: Defines the routing rules.

• to: Specifies the destination network (0.0.0.0/0 represents all networks).

• on-link: Indicates whether to use this route on the same subnet.

• gateway: The IP address of the gateway.