f.nic.is has no CNAME records.
Question and response
Question
dig f.nic.is. NS
Answer
The response has no answer records.
Authority
nic.is. 1263 SOA ht-secondary01.isnic.is. hostmaster.isnic.is. 1772290912 21600 7200 2419200 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0