Apex domains cannot have CNAME records.
Question and response
Question
dig 0-255.0.179.136.in-addr.arpa. NS
Answer
0-255.0.179.136.in-addr.arpa. 5 NS ns4.active.com.
0-255.0.179.136.in-addr.arpa. 5 NS ns3.active.com.
0-255.0.179.136.in-addr.arpa. 5 NS ns1.active.com.
0-255.0.179.136.in-addr.arpa. 5 NS ns2.active.com.
Authority
The response has no authority records.
Additional
ns1.active.com. 5 A 156.154.64.28
ns2.active.com. 5 A 156.154.65.28
ns3.active.com. 5 A 156.154.66.28
ns4.active.com. 5 A 156.154.67.28
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0