mx51.codetel.com.do has no NS records.
NS records for this zone are defined at codetel.com.do.
NS records for this zone are defined at codetel.com.do.
Question and response
Question
dig mx51.codetel.com.do. NS
Answer
The response has no answer records.
Authority
codetel.com.do. 86400 SOA ns1.claro.net.do. hostmaster.claro.net.do. 2017030953 21600 900 604800 86400
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0