151.124.253.145.in-addr.arpa has no NS records.
NS records for this zone are defined at 124.253.145.in-addr.arpa.
NS records for this zone are defined at 124.253.145.in-addr.arpa.
Question and response
Question
dig 151.sub128.124.253.145.in-addr.arpa. NS
Answer
The response has no answer records.
Authority
sub128.124.253.145.in-addr.arpa. 300 SOA ns4.sophos.com. hostmaster.sophos.com. 2013012202 7200 3600 604800 86400
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0