Apparently, blocks, which records every transaction, can also record the ip address of the sender and receiver.
Here's the raw data from a block:
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http://blockexplorer.com/rawblock/00000000000000fb84a13a76c4594f3aae4b1173e308887e961c9953031b4811There is no IP address recorded.
However Blockchain.info says that it believes Deepbit was the miner where that specific block came from:
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http://blockchain.info/block-index/266324/00000000000000fb84a13a76c4594f3aae4b1173e308887e961c9953031b4811Blockchain.info knows this only because it has a connection to Deepbit (and to most other pools and some miners). Because Deepbit was the first node where that block was seen, Blockchain.info themselves record that node's IP address and displays it as the "relayed by".
In other words, by listening to the network, some conclusions can be made and be semi-accurate.
The same thing happens for transactions. If your node was connected only to one node, let's say that node was Deepbit's, and Deepbit relayed your transaction, then Blockchain.info would think that Deepbit was the node where your transaction occurred. Your IP would not be revealed anywhere as a result.
I love being entirely anonymous, so I was wondering if there was a why to prevent a block from recording your ip address.
The bitcoin.org client can use tor.
Even without Tor, you can make sure your client does no listening, and only connects to a specific well connected node that isn't sharing your IP. Because there is no guarantee that this sharing occurs, if anonymity is important, then your better bet is to use Tor.
Another thing you can do is to use a hosted (shared) EWallet, such as Instawallet, or a hybrid EWallet (Bitcoin Spinner mobile app, Electrum, or Blockchain.info/wallet ) instead of running a node yourself. That way the IP address reported will not have any link to your IP. There is no guarantee that an EWallet isn't logging your IP address though, so again, the best answer there as well is Tor.
