Shareaza

It may seem a weird question because I don't know what exactly am I asking.

When people do need to configure port forwarding? I have connected my two PCs to internet without port forwarding. In what situation this won't work? Is it because of old routers which don't do NAT?

It is because of routers that do.

The router has to know which of your computers to send the incoming connection to, so you give it a rule
for a specific port number for one computer and another port number for the second computer.

The router then routes the incoming connection to the right computer when the incoming connection for a certain port.

Make sure your Shareaza uses different ports on each computer so the router can serve both of them.

Networks will work, but you are limited. Not able to accept incoming connections = less available download sources for you. Simple...

There are routers doing UPnP and if you have turned on UPnP in your software then it will forward ports for you.

THANK YOU, aaron_walkhouse and brov

I didn't run the connection test after configuring my router for both PCs. So I didn't notice I couldn't accept incoming connections. What is intresting is I had acceptable search results and no special symptom to make me suspicious.

I port forwarded it right now with your help and its working fine.

Just another question. How is it that I cannot accept incoming connections but other computers can send packet to me? For instance how router knows incoming packets for a requested website are for which PC?

That's how NAT works. If connection is from the inside - it records source address and port, and dest address and port, then before packet is sent to the internet it rewrites source address to be your WAN address. Now if received some reply packet, nat looks up its table and send you the packet (it knows the destination now).

I hope I explained it clearly

Most likely it will reject any new connections.