The PortQry.exe utility is a convenient tool to check the response of TCP/UDP ports on hosts to diagnose issues related to the operation of various network services and firewalls in TCP/IP networks.

Using the –b, -o, -an, interval, and tasklist commands, you can find IP addresses, port numbers, connections, process IDs and associated DLLs that are using the TCP and UDP ports.

Test if Firewall is blocking a Port. Check which Ports are being used. Also learn how to check which process or service is using the open port.

According to this group, starting with February 1, 2020, DNS servers that can't handle DNS queries over both UDP and TCP may be pushed out of the DNS ecosystem and stop working.