Expanding a Home Network

I've been working on a few different posts and haven't quite got the finishing touches on them, but I felt I should get this one out there.  In the past week, I have been asked to help out with expanding a home network using an old router at least four times.  With many ISPs providing routers, people are often finding themselves with an extra router.   So its only natural that they look to reusing an old router when trying to expand their wired or wireless network.

There are several approaches to adding a second router to a home network, in this post I'll look at the simplest and  probably the most common way.  Which is cascading a second router to operate as a WAP or switch.

 Whether you are using a wired or wireless router, the basic setup of the routers will be the same and can be done in five simple steps.

1.  Determine the DHCP range used by the main router.
2. Connect a computer to the secondary router and login into its administration console.
   You do not want to have the secondary router connected to anything else at this time.  Additionally, you want to perform a factory reset to ensure that there are no old settings that could causes problems.
3. Set the internal IP address of the secondary router to an IP address on the subnet as the main router, but outside of the DHCP range used by the main router.
4. Disable the DHCP and DNS service on the secondary router.
   You want to have just one DHCP and DNS service running locally and that is best left to the main router.
5. Connect a LAN port of the main router to a LAN port of the secondary router. 
   Wiring the routers together this way results in the secondary router operating just as a switch and avoids multiple subnets and firewall issues.  The down side is that the WAN/internet port on the secondary router will go unused, effectively losing a network port. 

Once these steps are done you should be able to connect your computers or printers to either router and not notice a difference.  With this setup up, the main router will always act as the DHCP server and hand out IP addresses and all the systems will be on the same subnet.

If your second router is a wireless router and you wish to have it also function as a WAP, that can be taken care of in just a few more steps.  You can perform these steps at the same time as your initial setup or since we've statically assigned the secondary router an IP address from the main router's subnet, you can do them later.

1. Determine the SSID, channel and encryption key used by the main router.
2. Log into the secondary router.
3. Set the SSID and encryption key to what is used by the main router.
   Doing this allows you to setup the wireless configuration on the computers once for your whole LAN.
4. Set the the wireless channel to a different, non-overlapping channel.
   This will reduce the interference between the multiple WAPs.

At this point you should have wired and wireless connectivity through both routers, which is almost seamless.  There are a couple of small issues to keep in mind with this setup. Since the two routers are operating independent wireless networks, when you roam from one router to the other, your computer will have to negotiate the wireless connection with the new router.  This should normally happen quickly, but some sensitive connections may be broken (such as VPN connections).  Additionally, if your routers provide a wireless isolation mode or a hotspot mode, this will need to be set at each router.

As I said, this is the most basic setup and won't provide a solution for everyone.  In particular, this configuration requires an Ethernet connection between the two routers, which some people would like to avoid.  There are several options for tackling that problem and I hope to discuss them in a future post.  If there are any other configurations that you would like explored, let me know and I'll see what I can pull together.