_netblocks2.talktalkplc.com has no CNAME records.
Question and response
Question
dig _netblocks2.talktalkplc.com. NS
Answer
The response has no answer records.
Authority
talktalkplc.com. 1084 SOA ds0.opaltelecom.net. noc.opaltelecom.net. 2025110500 1200 3600 1728000 1200
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0