Setting up LAN-WAN Connection between Two Routers: TP-Link WR840N

To establish a LAN-WAN connection between two TP-Link WR840N routers, you must configure the secondary router to act as a distinct network node rather than a simple switch. This setup allows the second router to manage its own subnet while connecting to the primary router’s internet source via an Ethernet cable plugged into the WAN port. By keeping the LAN ports isolated on the secondary device, you prevent IP conflicts and double NAT issues that often plague home networks.

Understanding the LAN-WAN Topology

A LAN-to-WAN configuration creates a hierarchical network structure. The primary router serves as the main gateway for your internet service provider (ISP) connection. It handles DHCP (Dynamic Host Configuration Protocol) for devices directly connected to it. The secondary router connects to this primary network but maintains its own separate internal network segment. This is ideal if you want to isolate specific devices, such as IoT gadgets or guest machines, from your main local area network. Unlike a LAN-to-LAN setup, which effectively merges two routers into one large switch, the WAN method preserves network boundaries. In a LAN-to-LAN scenario, both routers share the same IP range, and the secondary router’s routing features are disabled. However, for a true LAN-WAN link, the secondary router acts as a client to the primary network. This requires careful attention to IP addressing to ensure the two subnets do not overlap. If both routers use the default 192.168.0.x or 192.168.1.x ranges, they will conflict immediately upon connection. Therefore, changing the secondary router’s LAN IP address is the most critical step in this process.

Preparing the Secondary Router

Before connecting any cables, you must configure the secondary TP-Link WR840N while it is disconnected from the primary network. This prevents accidental interference with your existing internet connection. Start by connecting a computer directly to one of the LAN ports of the secondary router using an Ethernet cable. Power on the secondary router only. Open a web browser and navigate to the router’s default login page. For most TP-Link models, this is http://tplinkwifi.net or the default IP address printed on the label, typically 192.168.0.1. Log in with the admin credentials. If you have previously changed these, use the updated password; otherwise, reset the router to factory defaults if you are unsure. Once logged in, locate the Network settings. You need to change the LAN IP address of the secondary router so it does not clash with the primary router. If your primary router uses 192.168.0.1, set the secondary router’s LAN IP to 192.168.0.2 or 192.168.0.254. Ensure the Subnet Mask remains 255.255.255.0. Save the changes. The router will likely reboot, and you will lose connection temporarily. You must now access the management interface using the new IP address you just assigned. It is also wise to check the Wireless Settings on the secondary router. Assign a unique SSID (network name) and a different Wi-Fi channel than the primary router to reduce interference. While not strictly required for the wired WAN connection, distinct channels improve performance for wireless clients attached to the secondary unit.

Configuring the Primary Router

The primary router generally requires minimal configuration for this setup, provided it is already functioning correctly. Ensure that the primary router’s DHCP server is enabled. This service assigns IP addresses to devices connected to it. Since the secondary router will request an IP from the primary router via its WAN port, the primary DHCP server must be active to provide that address. Verify that the primary router’s firewall is not blocking incoming connections unnecessarily, though standard home configurations usually allow this traffic. There is no need to change the primary router’s IP address unless it conflicts with other devices on your network. Simply note down its IP address, as this will serve as the Default Gateway for the secondary router later. For those interested in expanding their network further, understanding how different devices interact is crucial. You might find relevant information in our guide on Connecting Windows, Share ChromeOS to ensure your client devices can communicate across these segments if needed.

Physical Connection and Final Steps

Now that both routers are configured, perform the physical connection. Take an Ethernet cable and plug one end into a LAN port on the primary router. Plug the other end into the WAN (Internet) port on the secondary TP-Link WR840N. Do not use a LAN port on the secondary router for this initial connection. Power on the secondary router. Wait for it to boot completely. Check the LED indicators; the Internet/WAN light should illuminate, indicating a successful link to the primary router. To verify connectivity, log into the secondary router’s management interface again using the new LAN IP address you set earlier. Navigate to the Status or Network Map section. Look for the WAN status. It should show "Connected" or display an IP address assigned by the primary router. If the WAN status shows "Disconnected" or 0.0.0.0, check the cable integrity and ensure the primary router’s DHCP is still active. Sometimes, simply restarting both routers resolves temporary handshake failures. Once connected, devices plugged into the secondary router’s LAN ports or connected via its Wi-Fi will receive IPs from the primary router’s pool, but they will be behind the secondary router’s NAT (Network Address Translation). This setup ensures that the secondary router provides internet access while maintaining a separate administrative boundary. If you encounter issues where the secondary router becomes inaccessible, refer to troubleshooting steps for unreachable secondary nodes. See our article on Devices: Secondary Router Unreachable for detailed diagnostics.

Frequently Asked Questions

Why do I need to change the secondary router's IP address?

You must change the IP to prevent subnet conflicts. If both routers share the same IP range, they will fight for control of the network traffic, causing connectivity loss for all devices.

Can I use Wi-Fi to connect the two routers in a LAN-WAN setup?

No, a standard LAN-WAN connection requires a physical Ethernet cable between the primary’s LAN port and the secondary’s WAN port. Using Wi-Fi would require a WDS or Repeater mode, which is a different topology.

Will this setup create double NAT?

Yes, a LAN-WAN connection inherently creates double NAT because each router performs its own network address translation. This may affect online gaming or port forwarding requirements.

What happens if I plug the cable into a LAN port on the secondary router?

If you plug into a LAN port on the secondary router, you are creating a LAN-to-LAN bridge, not a LAN-WAN connection. This disables the secondary router’s routing capabilities and turns it into a simple switch.

How do I access the secondary router if I forget the new IP?

You can perform a hard reset by holding the reset button on the back of the router for 10 seconds. This restores the default IP address found on the device label.