ポート番号一覧リファレンス

このツールについて

A port number identifies a specific process or service on a device, allowing a single IP address to handle many simultaneous network connections—web traffic on 443, email on 25, SSH on 22, and so on. IANA (the Internet Assigned Numbers Authority) divides the full 0–65535 range into three bands: well-known ports (0–1023), reserved for core, long-established services and requiring administrative privileges on most operating systems; registered ports (1024–49151), used by specific applications and vendors but not requiring special privileges; and dynamic or private ports (49152–65535), assigned temporarily by the operating system for outgoing client connections. This page is a searchable reference for the ports developers and sysadmins encounter most often.

使い方

1. 1Use the search box to filter by port number, protocol name, or keyword (e.g. "database", "mail").
2. 2Click a range filter (Well-Known, Registered, Dynamic) to narrow the list to that band.
3. 3Check the TCP/UDP column to see which transport protocol a service uses—some, like DNS, use both.

よくある質問 (FAQ)

What is the difference between TCP and UDP?

TCP (Transmission Control Protocol) is connection-oriented and guarantees ordered, reliable delivery—used for HTTP, SSH, and databases. UDP (User Datagram Protocol) is connectionless with no delivery guarantee, but has lower overhead—used for DNS lookups, video streaming, and online gaming, where speed matters more than guaranteed delivery.

Why do some services need administrator/root privileges to use their port?

On Linux and macOS, binding to a well-known port (0–1023) requires elevated privileges, a security convention that prevents ordinary users from impersonating standard services like HTTP (80) or SSH (22). Ports 1024 and above can be used by any user process.

What are ephemeral (dynamic) ports?

When your computer initiates an outgoing connection—like a browser connecting to a website—the operating system assigns it a temporary port from the dynamic range (49152–65535) for the duration of that connection. This is why you never have to configure a port for outgoing requests; it's chosen automatically and released when the connection closes.

Can two applications use the same port number?

Not for the same protocol and IP address at the same time—the OS will refuse to bind a second listener to a port that's already in use (a 'port already in use' error). However, a TCP service and a UDP service can share the same port number, since they are tracked independently.