Quote from: ScripterRon on December 04, 2013, 08:50:46 PM

Quote from: joecascio on December 04, 2013, 08:00:43 PM

Thanks for the replies. Well, I always thought that the miners served out the blockchain not the clients. And my client is behind a firewall, with no port forwarding, so how are other clients attaching to it?

Bitcoin-Qt establishes 8 outgoing connections to peer nodes when it starts up. It then listens for incoming connections and will accept connections until the maxconnections limit is reached. By default, Bitcoin-Qt will use uPnP to open the 8333 port on your router if it is supported. You can specify listen=0 if you do not want to accept incoming connections.

I use NetLimiter to limit the upload bandwidth used by Bitcoin-Qt and I specify maxconnections to limit the total number of connections to something that is manageable.

Thanks for all the replies. This has been very informative. I checked the Preferences on bitcoin-qt and found that it uses uPnp, which has the ability to open ports on routers that have it enabled. So I am trying, just as an experiment, shutting off uPNP on my router and see if anything else breaks.

The other interesting thing I discovered was that my supposition was correct about UDP. UPnP uses a UDP variant of http called httpu. You can do some pretty cool things with UDP because it doesn't require establishing a heavyweight connection like TCP.