We often hear from people who have two (or more!) routers in their LAN and are trying to get Microsoft File and Printer sharing running among all their computers. This ProblemSolver will explain why this doesn't work by default and provide some suggestions for working around the problem.
Figure 1 shows a two-router LAN configuration that I'll use as an example. This isn't the only configuration possible, but it will serve to illustrate the points I'll be making.
First, note that the two routers are set to different base addresses - the wired router to 192.168.1.1 and the wireless router to 192.168.2.1. This is essential for multi-router setups, since without the different address ranges, the routers wouldn't be able to properly build their routing tables. These tables control the way that data is handled and ensure that it is sent to the correct router for delivery to its connected clients. The use of different base addresses puts each router's attached clients into different Class C subnets.
TIP: Class C subnets have a maximum of 254 IP addresses, have the same first three "octets" in their addresses (ex. 192.168.3.X) and use a subnet mask of 255.255.255.0.
Next, note that the second router (the wireless) has its WAN port connected to one of the wired router's LAN ports via a normal UTP patch cable, and that it has an IP address in the first router's range. I've shown the wireless router's WAN IP as 192.168.1.100, but it could be any IP address in the 192.168.1.X subnet.
TIP: You don't have to use the 192.168.X subnets shown in the example. You can use any two private IP address ranges as long as they are different.
Note also that you can either assign the second router's WAN IP statically, or just set it to be a DHCP client (obtain automatically). I suggest the latter option, since if you enter the IP address info manually, you'll need to include the Gateway and DNS information, which you might have trouble figuring out.