知名端口查找

What the Well-Known Port Lookup does

Network ports are the numbered doors a computer uses to keep dozens of simultaneous conversations apart, and remembering which service lives behind which number is a constant small friction. This tool lets you search a built-in table of well-known TCP and UDP ports by number or by service name: type 443 and it tells you HTTPS, type ssh and it points you to port 22, type dns and it shows 53 on both TCP and UDP. It is the reference you reach for when you are writing or reading a firewall rule, scanning a log line full of bare port numbers, opening a NAT mapping on a router, or trying to work out what a service on a strange port is likely to be. Because the whole table ships with the page, results appear instantly as you type, with no round trip.

How it works technically

The full port space runs from 0 to 65535, and IANA splits it into three bands worth knowing. Ports 0–1023 are the well-known ports assigned to core services (HTTP on 80, HTTPS on 443, SSH on 22, SMTP on 25, DNS on 53); ports 1024–49151 are registered to specific applications; and ports 49152–65535 are dynamic or ephemeral, the temporary source ports your operating system hands out for outgoing connections. This tool holds a curated table of the most common entries, each tagged with its transport — TCP, UDP, or both — because a port number only has meaning together with its protocol: TCP 53 and UDP 53 are technically different endpoints even though both are DNS. When you type, the tool matches your text against port numbers and against service names, so either a number or a keyword finds the row you want.

Concrete examples and use cases

• Reading firewall logs — a dropped packet to port 3389 (RDP) or 445 (SMB) instantly tells you what someone was probing.
• Opening the right door — forwarding a game or app port on your router without accidentally exposing 22 or 3389 to the whole internet.
• Mail troubleshooting — distinguishing 25 (server-to-server SMTP), 587 (mail submission) and 465 (SMTP over TLS), or 143 (IMAP) versus 993 (IMAP over TLS).
• VPN setup — recognizing that WireGuard commonly runs on UDP 51820 and OpenVPN on 1194, so you open the correct protocol.

Practical tips and gotchas

A port number is a convention, not a guarantee. Nothing stops an administrator from running SSH on 2222 or a web server on 8080, so treat the well-known assignment as the likely default rather than proof of what is actually listening. Pay attention to the protocol column: opening a firewall for TCP when the service is UDP (as with many VPNs and DNS) is a classic reason a connection silently fails. Note the security difference between plaintext and encrypted twins — 80 vs 443, 21 vs 22, 23 (Telnet) vs SSH — and prefer the encrypted port wherever you have the choice. And remember this tool tells you what a port usually means, not whether it is open on a given host; to test reachability you need an actual connection attempt.

Privacy: the entire port table is embedded in the page, so every lookup runs 100% locally in your browser — nothing you type is uploaded, sent to a server, or logged. That makes it safe to research ports from internal diagrams or security notes without leaking anything. If you want to go beyond definitions and actually check whether a port is reachable on a public host, or see how your own connection is exposed, explore the live checks in our network tools.