Internet-Security.com TCP port 9993 details

ZeroTier One (virtual networking/SD-WAN software) uses port 9993 for its control-plane; while UDP is the primary transport, it also uses TCP 9993 to contact its public root/supernode infrastructure when UDP is unavailable or filtered.
In real deployments, the ZeroTier service (zerotier-one) on Windows/macOS/Linux initiates outbound connections to TCP 9993 to join and maintain virtual networks, and many enterprise firewall guides explicitly allow TCP 9993 for ZeroTier connectivity.
Example: endpoints that use ZeroTier to access a company’s private network require egress to TCP 9993 on the Internet so they can reach ZeroTier supernodes/controllers when UDP is blocked.
Security note: several threat actors have abused ZeroTier for covert remote access/C2, so unexpected outbound traffic on 9993 (TCP or UDP) is sometimes flagged by defenders.

TCP 9993