Many small office routers are actually a combination of various network devices in a small package, which allows them to be used for other purposes when the routing capability is not desired or needed. You can configure your router as a switch.
Connect your computer to the router using a standard Ethernet cable, even if the router includes wireless access, because configuration changes may affect the wireless signal.
Open a Web browser and enter the router's IP address, usually something similar to 192.168.0.1 or 192.168.1.1.
Enter the username and password for your router. By default, many routers will use "admin" for both the username and password. A Web page showing the status of the router will be displayed if the router is connected correctly and the login was successful.
Set the IP address of the router to an address that will not conflict with the main router on the network. For instance, if the main router is 192.168.0.1, try setting the one to be used as a switch to 192.168.0.2. This setting may be on the status page or the administration page, though it will vary from router to router.
Turn off the DHCP server. This server allows the router to assign IP addresses to the computers connected to it. Because the router will be used as a switch, it no longer needs to perform this function, and the main router on the network will take over this task.
Locate the settings for the DNS server. This server should be turned off as well. It is used to translate IP addresses into the more familiar "www" addresses that are used to go to a Web page. Again, a switch does not need to perform this function.
Turn off any firewall options that the router may have. This may require turning off several settings, depending on the particular router.
Change the mode of your router to gateway or switch if your router has an "Operating Mode" setting.
Remove any port forwarding entries that may have been used for games, peer-to-peer software or other applications.
Configure the wireless portion of your router to function as an access point if this setting is available.
Save all the changes and reboot the router to finish the process. Now that the extra features of the router have been turned off, it will behave more as a switch on your network.
The settings mentioned here may be found in different places on different routers. Have the owner's manual of the router on hand for reference.
Do not leave the password set to the router's default password. While you are in the configuration application, it is a good idea to assign a new one. If your router is of the wireless variety, also change the default SSID, or network name, and enable wireless security. These changes will make it harder for a person with nefarious intentions to gain access to your network.
Be careful when assigning an IP address to the router. If it is the same as another device on the network, it could cause the network to function improperly, or to cease functioning at all.