Port Number Lookup

About the Port Number Lookup

Type a port number, a range or a service name to see what the IANA Service Name and Transport Protocol Port Number Registry — the official list behind “port 443 is HTTPS” — says about it, for TCP, UDP, SCTP and DCCP. The search runs on a copy of the registry in your browser (it is loaded the first time you search and then works offline), including registered ranges, reserved and unassigned ports, references and the unauthorized uses IANA has recorded.

For more than 100 commonly seen ports there are practical notes: what actually uses the port today (which is not always what IANA registered), whether it is normal to open it to the internet, and the attacks it is known for. The tool never scans or contacts anything — it is a reference.

Common uses

• Finding out what an unfamiliar port in a firewall log, netstat output or scan report is used for.
• Choosing which ports to open on a server — and which to keep closed — when writing firewall rules or cloud security groups.
• Picking a free port number for a new service without colliding with a registered one.
• Looking up the port of a protocol while configuring a client, proxy or SRV record.

The three port ranges

TCP, UDP, SCTP and DCCP each have 65,536 port numbers, divided by RFC 6335 into:

• System (well-known) ports, 0–1023: assigned by IANA only through IETF review or IESG approval. On Linux, binding to one needs root or the CAP_NET_BIND_SERVICE capability by default (Linux kernel ip-sysctl documentation).
• User (registered) ports, 1024–49151: assigned by IANA on request, so applications can use a fixed number.
• Dynamic (private or ephemeral) ports, 49152–65535: never assigned. Software may use them freely, and operating systems pick the source port of outgoing connections from an ephemeral range: Linux uses 32768–60999 by default (ip_local_port_range), and Windows has used 49152–65535 since Windows Vista (Microsoft). RFC 6056 recommends choosing from the whole 1024–65535 range, for better randomisation.

An assignment is a convention, not a rule: any program can listen on any free port, and malware often uses well-known ports to blend in.

Reading an IANA entry

• Service name: the registered short name, also used in DNS SRV records (_sip._tcp) — you can search for those too.
• Protocols: a service is often registered on TCP and UDP even when it uses only one of them.
• Reference: the RFC or contact that requested the assignment; RFCs are linked.
• Notes and unauthorized use: IANA records de-assignments, aliases and reports of software using a port it was not assigned.

The snapshot was downloaded from the IANA registry.

Should this port be open to the internet?

The notes use four labels: Public service (normal to expose if you deliberately run it — web, mail, DNS, VPN endpoints), Limit access (built for remote use, but restrict who can connect — SSH, RDP, admin consoles), Internal only (databases, file sharing, directory services, industrial controllers) and Avoid (insecure or obsolete protocols such as Telnet, FTP and PPTP).

A safe default for any internet-facing firewall is to block everything inbound and open only the ports of services you actually publish. To check what is reachable on your own systems, run a port scanner such as Nmap against them from outside your network — only on systems you are authorised to test.

Limitations

• A reference, not a scanner: it cannot tell you whether a port is open on any machine.
• Registry data is a snapshot; assignments made since are missing.
• The notes describe typical use and risk, simplified. Your own software may use a port differently.
• The full registry (about 150 KB compressed) is downloaded the first time you search.

Privacy

Everything happens in your browser. What you enter or open here is not uploaded or stored by MySmartCoPilot.