Sometimes, you need to expand a Wi-Fi network, whether it is to accommodate more devices or you're adding an extra office. What follows is a quick guide on the items you need to plan in advance and a few things to look out for when another wireless router is added to your network. It is a general guide, as opposed to being tied to specific brands of Wi-Fi routers.
The first part is to decide how to connect the two routers together. The best solution is to have a cat 5e cable running from a port on one router to a port on the new router. This may mean a little bit of extra work. In our case, the cable had been run already and ports were installed at both ends of the office. The original intent was to use one end as the server/switch room and the other end as the print room. We simply re-used the printer outlet and plugged the new Wi-Fi router into the old printer outlet. Using cable is probably the best way to go; there are Wi-Fi routers that can be re-configured to act as range extenders, but this tends to suffer from the drawback that you lose a slice of the spectrum (and hence throughput) that could otherwise be used.
If you use DHCP, then the next step is to decide where the DHCP server should reside: on the new router, on the existing router, or on a server. Alternatively you could switch DHCP off and assign every device an IP address. If you keep DHCP, then you may want to exclude some devices, such as (for example) the new router, any NAS that is on the network, and any servers that require fixed IP addresses. Whatever you decide, ensure that you have DHCP on one router only.
You probably want to make sure your new router is on the same subnet as the existing router. It is best to assign the IP address of the new router as a permanent one, in which case you should exclude it from the DHCP range. The assumption is that this is a SOHO network, which by definition will be a small network, in which case putting the router on the same subnet will be sufficient.
Alternatively, you could create another subnet. This would mean extra work in configuring routes, and may cause issues with printing to any printer that is on the other subnet. Unless you have some good reason to operate separate subnets, it is probably best not to do it on a SOHO network.
You also need to decide what SSID you want to use, or whether you want the same SSID. Sometimes having a different SSID can assist in isolating issues. You will know pretty quickly which router has a problem. There are no strict rules on whether you keep the same SSID for both routers or use different ones for each router.
A few words of caution: Selecting ports and channels
Some routers have a separate port that is labelled Internet. If you are adding a second router, then you do not use this port. You use one of the standard Ethernet ports instead.
Before starting out, make sure you know how many devices will be on the subnet. The best way to check this is to log in to the existing router and see what IP addresses are currently in use. You may be surprised that the network that you thought had just a couple of laptops and a server is actually home also to several tablets and a couple of smartphones. Check before you begin.
Make sure both routers auto select which channel to use. Usually, a wireless router will first scan the channels, looking for a vacant one to use. Depending on the algorithm, they will usually pick a channel that is separated in frequency to a neighbouring Wi-Fi router.
If you do manually set the channels, then beware of the following scenario. A neighbouring Wi-Fi is set up with a hidden SSID and also has a manually selected channel. Your Wi-Fi may now experience interference, particularly if the neighbouring Wi-Fi network is using your channel. In this case, the throughput will be reduced, and isolating why this is occurring could take some time. Setting the router to auto-select the channel mitigates this issue.
In summary, adding a Wi-Fi router to a SOHO network is not complicated. All it needs is some planning beforehand, and careful configuration of the wireless components.
Scott Reeves has worked for Hewlett Packard on HP-UX servers and SANs, and has worked in similar areas in the past at IBM. Currently he works as an independent IT consultant, specializing in Wi-Fi networks and SANs.