11.91.209.181.in-addr.arpa has no NS records.
NS records for this zone are defined at 91.209.181.in-addr.arpa.
NS records for this zone are defined at 91.209.181.in-addr.arpa.
Question and response
Question
dig 11.91.209.181.in-addr.arpa. NS
Answer
The response has no answer records.
Authority
91.209.181.in-addr.arpa. 38400 SOA ns1.dcarsat.com.ar. nsadmin.dcarsat.com.ar. 2015050201 10800 3600 604800 38400
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0