Just because you're using a router doesn't mean you need to be firewalled. If your router doesn't have UPnP or reliable UPnp which means a program can request it to open a listening port for it whilst the program is open, then the best thing to do is port forward it. Routers generally use NAT which is not a firewall per se but behaves a little like one in respect to how it may affect LW.

Did you do a static ip before you created the port forward rule for your router? If not before, the process won't work & would need to be cancelled & done again. And since NAT is based on ip, the ip of the 2nd computer would be used for the port forward rule for that one. Remember each computer will need a separate different port.

Setting up a Static ip

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