you have to remember that Tor is a PROXY. proxies act on behalf of another, and therefore, theoretically you would only need to "resolve" the address of the first node of the circuit, but you don't have to do that, because Tor already has that information in its configuration files. What happens is that the exit node "handles" everything, including DNS, for the nodes behind it, because of the nature of being a proxy server. It then transmits the DNS information backwards through a Tor circuit. Given that Tor circuits for a specific machine change every few minutes, This is what makes it difficult and next to impossible for anyone to track a machine through the nodes, because ALL of the traffic though Tor is encrypted, with the exception of the exit node's handling of the original request which it will then encrypt on its way backwards through the Tor. This is because it takes, even in a simple hypothetical case, at least several attempts and a good few minutes to decrypt anything without having direct knowledge of BOTH keys required for decyrption, and this depends largely on the encryption method. The exception to this is the .onion domain, i.e. the hidden service, wherein Tor itself handles the DNS issue in a manner that, while is in fact DNS request in CONCEPT, tor does not follow the conventional "Rules" for DNS when it comes to hidden services, because of the rendevous server, where a random Tor server, in a way "fakes" being the real host of the .onion site, for the purposes of concealing the IP of the machine the .onion server is running on.

You have to remember, that Tor is a PROXY. Proxies act on behalf of another, and therefore, theoretically you would only need to "resolve" the address of the first node of the circuit. But you don't have to do that, because Tor already has that information in its configuration files. 

What happens is that the exit node "handles" everything, including DNS, for the nodes behind it, because of the nature of being a proxy server. It then transmits the DNS information backwards through a Tor circuit. Given that Tor circuits for a specific machine change every few minutes, this is what makes it difficult and next to impossible for anyone to track a machine through the nodes, because ALL of the traffic though Tor is encrypted, with the exception of the exit node's handling of the original request which it will then encrypt on its way backwards through the Tor. This is because it takes, even in a simple hypothetical case, at least several attempts and a good few minutes to decrypt anything without having direct knowledge of BOTH keys required for decyrption, and this depends largely on the encryption method. 

The exception to this is the .onion domain, i.e. the hidden services. Wherein Tor itself handles the DNS issue in a manner that, while is in fact DNS request in CONCEPT, tor does not follow the conventional "Rules" for DNS when it comes to hidden services. Because of the rendezvous server, which is a random Tor server, in a way "fakes" being the real host of the .onion site, for the purposes of concealing the IP of the machine the .onion server is running on.