auth3.opendns.com has no CNAME records.
Question and response
Question
dig auth3.opendns.com. NS
Answer
The response has no answer records.
Authority
opendns.com. 9607 SOA auth1.opendns.com. noc.opendns.com. 1771892912 16384 2048 1048576 2560
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0