f.dns.tds.net has no CNAME records.
Question and response
Question
dig f.dns.tds.net. NS
Answer
The response has no answer records.
Authority
dns.tds.net. 2648 SOA pv-dnsm.dns.tds.net. hostmaster.tds.net. 2025041703 10800 3600 604800 43200
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0