Port 631 — TCP
Internet Printing Protocol uses port 631 to submit and manage network print jobs. Distinguish IPP traffic from printer discovery before changing firewall rules.
What is port 631 used for?
TCP 631 is the standard port for IPP and IPPS, including CUPS deployments. Print requests, job status and IPP replies use HTTP or HTTPS connections. Discovery is separate and may use DNS-SD/mDNS on UDP 5353.
Diagnose printer discovery, TCP 631 access, print-queue state and job processing separately.
Transport protocol
TCP
Security precautions
Restrict access to trusted networks and keep printers and print servers updated.
Should we open this port in the firewall?
Allow TCP 631 only between the workstations, print servers and printers that need it. Protect CUPS and printer administration interfaces from public exposure. IPPS can also use 631 with TLS, so validate certificates and access policies as well as the port.
How do I check this port?
Test TCP 631, then check whether the printer or server responds to HTTP/IPP requests. On a CUPS server, lpstat -v identifies queue URIs and ss -lntp shows TCP listeners.
- Identify the actual printer URI and queue.
- Test TCP 631 connectivity to the destination.
- Check queue state, document format, driver and spooler logs.
- If discovery fails, investigate DNS-SD/mDNS and the local network separately.
FAQ — port 631 / IPP
Does IPP use TCP or UDP on port 631?
IPP uses TCP 631. Discovery can use other protocols, such as mDNS on UDP 5353, but those are separate from IPP transport.
Why is port 631 reachable while the document does not print?
The queue may be paused, the job rejected, the format unsupported or the spooler faulty even when network connectivity is working.
Does IPPS use a different port?
IPP and IPPS can both use port 631; IPPS protects the connection with TLS.