Two Problems
Our two-router setup doesn’t cause problems with simple Internet use including email, web browsing, instant messaging, and most applications, i.e. anything where you initiate the request for data. But you’ll run into two problems when you try to get file and printer sharing going, which I’ll now explain.
Problem 1 is that the multiple subnets in our example LAN cause problems with network browsing. This means when you use My Network Places in Win2000 and XP or Network Neighborhood in earlier versions of Windows, the only computers you’ll see are those connected to the same router. This problem can be solved by using a WINS server, but there are simpler fixes that I’ll describe in the next section.
Problem 2 is caused by each router’s firewall. By default, consumer routers block all unrequested data that tries to travel from WAN port (the Internet) to LAN clients, and passes all outbound data from LAN clients to WAN. The blocking of inbound data requests provides the basic "firewalling" function of a NAT router and keeps computers connected to the router’s LAN ports inaccessible from the Internet. But this inbound filter gets in the way of Microsoft File and Printer sharing when routers are connected together.
Referring to our example LAN in Figure 1, this means wireless router clients will be able to file and printer share with clients of the wired router, but not vice-versa.
NOTE : This same "one-way" action will also complicate access to servers or server-type applications running on any computers connected to the second router. A simple fix for this problem is to connect those computers to the first router, but the file and printer sharing work-arounds shown later can also be used.
