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My question is, where does bitcoin-qt try to connect to when running for the first time? How does it know where to connect?
Is blockchain.info some domain that has discovery services? If yes, then what happens if this domain goes down? Would that mean that bitcoin is not really decentralized in the end?
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It only needs one node to connect to to discover the network. After that it has a cache of several thousand other nodes that were once on the network, and most of those will still be.
On initial startup that is not available yet though, so the reference client will try to either find it in the configuration file (seed), try to find it via DNS, or even IRC if configured to do that.
what one node? what does it try to find via DNS/IRC? – knocte – 2013-04-14T12:51:16.293
Via IRC it just joins a channel via a hardcoded server address and looks for other people in that channel. Via DNS there are several hardcoded DNS locations that resolve to multiple IP addresses, and those are used to discover the initial node. The initial node discovery is centralized to those DNS addresses and optionally the IRC channel. After that, Bitcoin is decentralized. – Tom van der Woerdt – 2013-04-14T12:54:45.653