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I have always been curious about how do, say two computers, connect over the Internet.

For example, using the IP address from whatismyip service, I can only see the config page of my router, but pure p2p services like Bitcoin connect two computers directly, if they use IP address. the would have connected to my router/wireless AP. Do they really use IP or other methods? I do not need to do even port-forwarding in order to get p2p software working.

Keltari
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Alexander Ho
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2 Answers2

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I know what exactly you are struggling with. Yes, the P2P network does use some kind of technology like "automatically port forwarding " called Hole punching (networking) or NAT traversal. VoIP products, online gaming applications, and P2P networking software all use hole punching.

Jack
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If you are interested in how P2P applications communicate over the internet, it really depends on which P2P application you are talking about. All of the P2P applications I am aware of transmit over TCP/IP considering it is the foundation that the Internet works on top of.

Each application communicates over a network protocol which is usually specifically tailored by whomever developed the application in question. For example, BitTorrent usually transmits over a range of ports (6881-6889) and the functionality of BitTorrent in regard to how it communicates over the internet is best summed up by the following (taken from WikiPedia)

A BitTorrent client is any program that implements the BitTorrent protocol. Each client is capable of preparing, requesting, and transmitting any type of computer file over a network, using the protocol. A peer is any computer running an instance of a client.

The same can be said for any application, be it server-client based or P2P or whatever other type of topology it uses. All communication happens via network protocols that both computers understand.

Richie086
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