Q:

Why do DNS queries use loopback interface?

Sniffing (using Wireshark), for didactical purpose, my loopback interface on Ubuntu 12.04, I noticed that a lot of DNS queries (maybe ALL of them) have 127.0.0.1 as source and destination address. 
Why?
P.S. I can find the same DNS queries, obviously, on the interface connected to the Internet.

A:

Applications are querying a local resolver cache, which is then querying a remote resolver. Most likely, the local resolver is implementing a cross-application cache. That way, if two programs both resolve google.com, there won't be two remote requests.

