Squid: The Definitive Guide

Squid normally checks that DNS replies come from the same IP address to which the query was sent. If the addresses don't match, Squid writes a warning to cache.log and ignores the reply. Some installations use an /etc/resolv.conf trick to query any local name server. If the name server IP address is 0.0.0.0 , DNS queries are broadcast on the local area network. The replies, however, come from specific addresses. If you want to use this trick, you must disable the ignore_unknown_nameservers directive.