[tor-relays] How does Tor use nameservers?

[Steve Snyder]

I am attempting to load-balance DNS resolution requests.

Suppose, in Linux, you have a /etc/resolv.conf with this contents:

 nameserver aaa.bbb.ccc.ddd
 nameserver eee.fff.000.111
 nameserver 222.333.444.555

How does a Tor exit node use these 3 nameservers?

Are they used in a round-robin fashion with the next name resolution request being handled by the next nameserver in rotation?

Is the first nameserver ("aaa.bbb.ccc.ddd" above) always used first, with the second being used if the first exceeds some time-out threshold, and the third used only if the first 2 fail?

Does a middle node use name resolution at all, or is the relaying based purely on IP addresses?

Thanks.