mx1.sco.cisco.com has no NS records.
NS records for this zone are defined at sco.cisco.com.
NS records for this zone are defined at sco.cisco.com.
Question and response
Question
dig mx1.sco.cisco.com. NS
Answer
The response has no answer records.
Authority
sco.cisco.com. 300 SOA use1.akam.net. stbu-hostmaster.cisco.com. 2026021203 1200 300 1209600 3600
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0