mx4.switch.ch has no NS records.
NS records for this zone are defined at switch.ch.
NS records for this zone are defined at switch.ch.
Question and response
Question
dig mx4.switch.ch. NS
Answer
The response has no answer records.
Authority
switch.ch. 180 SOA scsnms.switch.ch. dns-operation.switch.ch. 2026022201 900 600 604800 180
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0