Updated 2/24/2009: Added DNS setting info in Method 2
As we expand our networks with computers, a NAS, VoIP devices, Xboxes, PS3s, etc, many of us find we need more wired network ports. A simple solution is to go buy a new network switch. Times are tough though, and reusing an idle device is cheaper than going out and buying a new one.
If you have an old router gathering dust, you can put it to work, save money and keep it out of the landfill. We already described how to turn a wireless router into an access point. This article will show you two ways of using an old router to expand the number of Ethernet ports available on your LAN. The difference between the two methods is in the number of ports that you gain.
I'll refer to the router that is connected to the Internet as the upstream router and the old router that we are converting as the downstream router as shown in Figure 1.
Figure 1: The Basic Setup
Method One - Converting A Router To A Switch
The five steps are:
- [Optional] Put a piece of electric tape over the WAN port so it doesn't get used.
- Disable the DHCP server.
- Change the downstream router's LAN IP.
- [Optional] Turn off the wireless radio on the downstream router.
- Connect an Ethernet cable from a LAN port on the upstream router to a LAN port on the downstream router.
Step 1: Putting a piece of electric tape over the WAN port isn't necessary. But it is a good way to prevent future problems caused by someone plugging a device into that port.
Step 2: Log into the downstream router, look for the DHCP configuration section, and disable the DHCP server. For example, on a Dlink DI-614+, DHCP server configuration is a menu in the Home configuration section as shown in Figure 2.
Figure 2: D-Link DI-614+ DHCP Server controls
Step 3: Change the downstream router's LAN IP to an unused IP in the same subnet as the upstream router. Log into the upstream router and find the DHCP server controls. Figure 3 shows a typical set of DHCP server controls. You can see that 192.168.3.200 - 250 is the range of addresses that will be issued by this router's DHCP server.
Figure 3: Finding the upstream router network
You can use any IP address outside (above or below) this range, except for 0 and 255, which are reserved. You also can't use the IP address used by the upstream router. This is usually 1, which in this case is 192.168.3.1. But if you log into your upstream router's admin screens using an IP address with anything other than 1 as the last octet, i.e. XXX.XXX.XXX.1, then just don't use that address.
Thus, a safe LAN IP address for the downstream router that isn't used by the upstream router is an address from 192.168.3.2 to 192.168.3.199. So I assigned my downstream router a LAN IP of 192.168.3.3 (Figure 4).
Figure 4: Changing the downstream router IP address
Step 4: [Wireless routers only] Disable the downstream router's wireless function. It doesn't hurt to unscrew the antennas from the downstream router as well if they are detachable. This gets them out of the way since you aren't using them anymore. Figure 5 shows the wireless disabled for a D-Link DGL-4300.
Figure 5: Disable the wireless radio
Step 5: Connect the downstream router. Run an Ethernet cable from a LAN port on the upstream router to a LAN port on the downstream router. The LAN ports are the ports that often grouped together and not labeled as WAN or Internet, as shown in Figure 6.
NOTE: For any router manufactured in the last few years, you don't have to worry about using a crossover cable. All current routers have Auto MDI/X ports, which will automatically adjust to the needs of whatever is plugged into them.
Figure 6:Locating the LAN ports
You should now be good to go with three open ports on the downstream router to connect additional devices. Devices connected to the downstream router will get an IP address from the upstream router and access the Internet just as if they were directly connected to the upstream router.
Note that we only gained two network ports because we used one port on the upstream router and one port on the downstream router to connect the two devices. To gain three network ports, we need to get a bit trickier with the downstream router configuration.
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