About TCP Port 721
Port 721 is not assigned to any service in the IANA Service Names and Port Numbers Registry. While most ports below 1024 are assigned to canonical services, this specific port has no current IANA registration. It does not currently appear in the IDS rulesets or malware activity indicators in our data sources. Unregistered ports are still commonly repurposed by local software, games, and occasionally malware, so verify what is listening before allowing traffic.
Browse other ports: the port numbers list, starting with the well-known ports 0 to 1023.