Identify the listener
Record the process, software version, service owner, transport protocol, and local address bound to the port.
TCP and UDP Port Reference
A port number is only a clue. Confirm the process, protocol, listening address, and firewall rule on the actual system before changing exposure.
The IANA registry is downloaded to your browser. Searches are not submitted to FirewallGuide.
443
TCPHTTPS
A registered use, not proof of the software that is listening.
Look up a registered port or service
Search the complete IANA service-name registry by an exact number or part of a service name.
Loading the current IANA service-name registry.
Common checks
Choose a port or service to see its registered transports, descriptions, exposure context, and the evidence needed to identify the live service.
Turn a registry match into a service decision
Review common exposure risks and verification steps after the lookup. A registry entry does not answer what is running on your computer or whether internet access is appropriate.
Trace the reachable path
Check host rules, router forwarding, cloud security groups, proxies, VPNs, and every trust boundary between source and service.
Decide from the requirement
Keep access only when the service has a named purpose, approved sources, maintained software, useful logs, and a review date.
Example: deciding whether port 445 belongs at the internet boundary
The lookup identifies TCP port 445 with SMB file sharing. That registry clue does not prove which process is listening, but it is enough to stop and investigate before allowing public access. On a typical home or office network, file sharing should remain limited to explicitly trusted networks or a controlled remote-access path.
Why this result deserves investigation
Confirm the listening process and address on the destination system, then inspect the gateway and host rules that make it reachable. If remote file access is needed, use a supported authenticated design rather than exposing the service directly because a port number appears in a registry.
If a public service is suspected, use the limited public port scanner to test selected TCP ports from an external network position.
To summarize a bounded event sample before investigating a service, use the local firewall log analyzer and preserve the original device and time window.
Before exposing an internal listener, document the source, mapping, owner, and removal plan with the port forwarding planner .
Before changing access, follow the firewall testing method so a port lookup becomes part of an authorized allow-and-deny test.
Why a port number cannot identify the running software
Use the result for
- Finding the registry records for a number or service label.
- Checking whether TCP and UDP have different assignments.
- Starting a documented service and exposure review.
Do not use it as
- A registered name does not identify the live process.
- An open port does not prove the application is secure or correctly authenticated.
- A closed or timed-out result can be caused by service state, routing, filtering, or the test vantage point.
Combine registry, host, and path evidence
| Evidence source | Question it answers | What it cannot prove alone |
|---|---|---|
| IANA registry | Which services are registered for this number and transport? | Which application is listening now |
| Host process and socket data | Which process owns the local listener and address? | Whether an external source can reach it |
| Firewall, route, and scan evidence | Which tested source can cross the network path? | Whether authentication and application behavior are safe |
Port lookup questions
Why can TCP and UDP share a port number?
They are separate transport-protocol namespaces. A service can use one, both, or neither on a particular system.
What are dynamic ports?
Higher-numbered ports can be assigned temporarily for client connections or applications. Interpret them with process and connection evidence rather than a static name alone.
Registry source: IANA Service Name and Transport Protocol Port Number Registry. FirewallGuide adds the exposure and verification guidance; it does not alter the registry records.