Configure Linksys as basic router

0. Do a reset factory settings by pressing for 30 seconds the Reset button on the rear while the router is connected.

1. @ Setup->Basic Setup->Internet Setup->Static IP
Then, put an IP of one of the networks you want to connect, and put it in the same network than the PC in the network you want to reach (PC1). For the Default Gateway of the Router configure the IP of the PC1 so all packets go there. For DNS put the same IP as teh gateway.

2. @ Setup->Advanced Routing, Disable the NAT

3. @ Setup->Basic Setup->Internet Setup->Network Setup, Configure the Local IP Address and subnet mask. This IP must be part of the second network that wants to be connected. The DHCP can be disabled but the Local IP subnet has to be in the same subnet than the second PC (PC2)

4. Configure the PC2 with an IP of the Local subnet and configure its default gateway to point to the Local IP Address ocnfigured in the Step 3.

5. Add a static route in the WLAN Interface, where any IP of the LAN network is routed to the IP of the WAN Interface. For example, the PC1 is 192.168.21.1 and PC2 is 10.0.0.2. The PC1 is the one connected to the WAN, so it would be to add a static route that says IP: 10.0.0.0 mask 255.255.255.0 default gateway 10.0.0.1 where 10.0.0.1 is the IP configured in the WAN interface. Finally select the WAN Interface.

6. Test the ping from PC1 to PC2.

7. @ Administration->Diagnostics there are tools (ping and traceroute) to test connections