_netblocks.eloqua.com has no CNAME records.
Question and response
Question
dig _netblocks.eloqua.com. NS
Answer
The response has no answer records.
Authority
eloqua.com. 108 SOA ns1.p201.dns.oraclecloud.net. hostmaster.eloqua.com. 503 3600 600 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0