Hello,

The MongoDB cluster does not resolve using standard dig requests to the hostname provided in the connection string, since the MongoDB cluster is hosted in multiple nodes and each has its own hostnames. To retrieve the node hostnames of a cluster using dig, you must specify the SRV record type in the request and prepend mongodb.tcp. to the hostname in the connection string.

dig srv _mongodb._tcp.<cluster-hostname>

Also for nslookup you can try the below command

nslookup -type=SRV _mongodb._tcp.<cluster-hostname>

For more details: https://docs.digitalocean.com/products/databases/mongodb/how-to/connect/

Regards,
Rajkishore