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TCP
Unknown
631 IPP / CUPS
IPP manages print jobs and printer capabilities on Unix, macOS, and many office networks.
Security Context
Port 631 is context-dependent. Its risk depends on the daemon behind it, whether the traffic is encrypted, and how tightly the listener is scoped to trusted networks.
Nmap Check
Use a version probe first so you confirm whether the expected service is really what is listening on this port.
nmap -sV -p 631 <host>Firewall Commands
UFW
sudo ufw allow 631/tcpiptables
sudo iptables -A INPUT -p tcp --dport 631 -j ACCEPT