How to configure DNS on a router with two fiber optic cables

To configure DNS on a router with two fiber optic connections, assign DNS servers to each WAN interface and ensure proper routing or failover settings so all devices use the correct DNS.

Step 1: Access Your Router's Admin Panel

Open a web browser and navigate to your router's gateway IP (commonly 192.168.0.1 or 192.168.1.1) and log in with your administrator credentials . For routers like TP-Link, Netgear, Asus, or MikroTik, the DNS settings are usually under WAN, Internet, or Network Settings .

Step 2: Identify WAN Interfaces

With two fiber optic connections, your router may have dual WAN ports or use a WAN + secondary WAN (failover/load balancing) configuration. Identify which interface corresponds to each fiber connection. Label them as WAN1 and WAN2 for clarity.

Step 3: Assign DNS Servers

• Navigate to the DNS settings for each WAN interface.
• Switch from Automatic/ISP-assigned to Manual.
• Enter your preferred Primary and Secondary DNS servers for each WAN. For example, you can use 8.8.8.8 and 1.1.1.1 for Google and Cloudflare DNS .
• If your router supports IPv6, configure IPv6 DNS as well to prevent bypassing IPv4 DNS settings .

Step 4: Configure Routing or Failover

• If using load balancing, ensure both WAN interfaces are active and DNS queries can route through either connection.
• If using failover, set the primary WAN to handle DNS queries and the secondary WAN as backup. The router should automatically switch DNS queries to the secondary WAN if the primary fails .

Step 5: Apply and Reboot

• Save the DNS settings and apply changes.
• Reboot the router to clear cached DNS entries and ensure all devices use the updated DNS servers .

Step 6: Test DNS Resolution

• From a connected device, ping a domain name (e.g., ping google.com) to verify DNS resolution.
• Optionally, use router diagnostic tools to confirm that DNS queries are correctly routed through both fiber connections.

Additional Tips

• For advanced setups, consider DNS over TLS or DNS over HTTPS to encrypt queries, supported on routers like OpenWrt or FRITZ!Box .
• If using multiple subnets or secondary routers, ensure DHCP and DNS are coordinated to avoid conflicts .
• Document your DNS IPs and WAN assignments for troubleshooting. By following these steps, your router will properly handle DNS queries across both fiber optic connections, ensuring reliable name resolution and network performance.