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I mean, if someone is downloading a file from me, doesn't that means that I'm the host and he is connecting to me? Or am I connecting to him? Either way one of us need an open port, no? I don't have any open port routing to my computer in my router, so how is that I'm accepting connections?
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If your router supports UPnP, it is possible that the p2p application that you are using is opening ports on the router without you needing to manually configuring open ports. Otherwise, it is possible that your application is using a process called NAT traversal, which is common in p2p applications and remote desktop applications such as GoToMyPC or Hamachi. This technology is designed to work through Network Address Translation, which is considered a firewall, but is also a means for having a private network sharing a single IP address on the internet (what your router uses). | |||||
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In protocols like BitTorrent as long one one of the two sides of the connection has port forwarding turned on the open side will always act as the host. If both sides are open either end could be the "host". If both sides are closed you need a 3rd party who has a open connection to negotiate the connection, this is how things like skype does it (the 3rd party is called a Supernode) Here is a good blog post explaining how skype uses Supernodes and how it uses it to get around firewalls. | |||
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