One of the many tasks that a typical router can perform is bridging, or connecting two networks to perform as one. Normally this task is done in unison with the routing task, but in a network that is using a separate router, you may want to configure an additional router to act as a bridge only.
Connect your computer to the router using an Ethernet cable. The cable should be plugged into one of the LAN ports, not the port labeled "WAN" or "Internet."
Follow the instructions in the router's manual to log in to the router's configuration application. This is done by entering the IP address of the router into the address bar of a Web browser. The IP address of the router will be something like 192.168.0.1 or 192.168.1.1. Next, enter the username and password for the router. If successful, the main configuration page for the router will open in the window of the browser. There will be an assortment of links on this page that will allow you to customize how the router operates.
Locate the page that allows you to set the IP address of the router. This should be set to something other than the default address, and it must not be the same as any other device on the network.
Find the settings for the DHCP and DNS servers that are built into the router. Both severs will need to be disabled because the main router on the network will now be in charge of assigning IP addresses and translating network addresses.
Disable all of the access controls and the firewall of the router to be used as a bridge. The main router will also perform these tasks.
Remove all of the entries in the "Port forwarding" section of the router. These settings are designed to allow certain applications easier access to the Internet on specific ports and are no longer necessary.
Save all of the settings you have changed and reboot the router for the changes to take effect. With all of the routing features of the unit disabled, the router can now act as a bridge on your network.
If you cannot access the router using the default password, and the new password is not available, it may be necessary to reset the router to its default configuration. On most routers, there will be a tiny push-button for this specific purpose. After the password is reset to the default, it is advisable to change it immediately, in order to make your network less vulnerable to security compromises.