Common Ports List Explained
What each well-known port does, and why it matters
Every TCP connection is addressed to a specific port number, and over decades of internet history certain port numbers have become strongly associated with specific services by convention. Knowing what typically runs on a given port helps you interpret a port check result correctly — an open port 3306 on a public-facing server, for example, is a very different situation from an open port 443. This guide goes beyond a simple lookup table and explains the practical implications of each common port.
Port Ranges at a Glance
Port numbers run from 0 to 65535 and are divided into three conventional ranges. Ports 0–1023 are well-known ports, registered with IANA and reserved for standard services such as HTTP and SSH. Ports 1024–49151 are registered ports, used by a huge range of applications but not formally reserved to the same degree. Ports 49152–65535 are dynamic or ephemeral ports, typically assigned automatically by an operating system to the client side of an outgoing connection rather than being associated with any particular service.
Port-by-Port Reference
21FTP (File Transfer Protocol)
Used to transfer files between a client and server. FTP sends credentials in plain text by default, so it is increasingly replaced by SFTP (port 22) or FTPS. If you see port 21 open on a public server, verify it is intentional and, if possible, migrate to an encrypted alternative.
22SSH (Secure Shell)
Provides encrypted remote command-line access and is also used as a transport for SFTP and Git over SSH. Because it is a prime target for automated brute-force attacks, many administrators move it to a non-standard port, enforce key-based authentication, and rate-limit login attempts.
25SMTP (Mail Transfer)
Used by mail servers to relay outgoing email between servers. Many residential ISPs block outbound port 25 to reduce spam originating from compromised home devices — if you are trying to run a mail server from home and this port never opens, that is usually the reason.
53DNS (Domain Name System)
Resolves domain names to IP addresses. DNS servers use both TCP and UDP on port 53 — UDP for typical lookups and TCP for larger responses such as zone transfers. This port only needs to be open if you are running your own authoritative or recursive DNS server.
80HTTP (Web Traffic)
The standard port for unencrypted web traffic. Modern best practice is to redirect all port 80 traffic to port 443 (HTTPS) rather than serving content over plain HTTP, since unencrypted traffic can be intercepted or modified in transit.
110 / 143POP3 / IMAP (Mail Retrieval)
Used by email clients to download or sync messages from a mail server. Like FTP, the unencrypted versions of these protocols are being phased out in favour of their encrypted counterparts, POP3S (995) and IMAPS (993).
443HTTPS (Secure Web Traffic)
Encrypted web traffic using TLS. This is the port almost every public-facing website and API should expose. If you are hosting a website, confirming port 443 is reachable is one of the first things to check after deployment.
3306MySQL / MariaDB
The default port for MySQL-compatible databases. This port should almost never be exposed directly to the public internet — database servers are typically kept on a private network or behind a VPN, with applications connecting internally rather than over the open internet.
3389RDP (Remote Desktop Protocol)
Used for Windows remote desktop access. RDP is a frequent target for credential-stuffing and ransomware campaigns when exposed directly to the internet. If remote access is required, most security guidance recommends placing RDP behind a VPN rather than forwarding the port directly.
5432PostgreSQL
The default port for PostgreSQL databases. As with MySQL, this port should generally stay on a private network rather than being reachable from the public internet.
6379Redis
Redis historically shipped with no authentication by default, and public-facing Redis instances on port 6379 have been a common source of data breaches and cryptomining malware. Always require authentication and firewall this port if Redis must be reachable remotely.
8080HTTP Alternate / Proxy
Commonly used for development servers, proxies, and some self-hosted applications as an alternative to port 80. It carries no special security guarantees of its own — treat it the same as any other HTTP port.
27017MongoDB
The default MongoDB port. Similar to Redis and MySQL, MongoDB instances left open on the public internet without authentication have historically been targeted by automated scanners looking for exposed data.
A Port Number Alone Does Not Guarantee a Service
Convention is not enforcement — nothing stops an administrator from running a web server on port 9999 or a game server on port 443. When checking an unfamiliar host, treat these port associations as a strong hint rather than a certainty, and where possible confirm what is actually listening by connecting to the service directly (for example with curl for an HTTP-like port).
Once you know what a port is supposed to do, use PortCheck to confirm whether it is actually reachable from the internet, and see our guide to the security risks of open ports before exposing anything beyond 80 and 443 publicly.