Common Port Numbers

A reference to the 43 TCP and UDP ports that come up most often — what each one is for, whether it is safe to leave open, and what to do if a scan finds it exposed.

There are 65,535 ports in total. Almost all of them are unassigned or used by a single application, so this covers the ones worth knowing rather than reproducing the full registry.

Email

PortServiceTransportNotes
25 SMTP Simple Mail Transfer Protocol TCP The port mail servers use to hand messages to one another.
110 POP3 Post Office Protocol v3 TCP Downloads mail from a server to a single client, traditionally deleting the server copy.
143 IMAP Internet Message Access Protocol TCP Reads mail while leaving it on the server, keeping folders and read state consistent across every device.
465 SMTPS SMTP over implicit TLS TCP Mail submission where TLS is established immediately, before any SMTP conversation.
587 Submission SMTP mail submission TCP Where an email client or application submits outgoing mail to its own server, with authentication.
993 IMAPS IMAP over TLS TCP Encrypted IMAP — mail reading over TLS, established before any credentials are sent.
995 POP3S POP3 over TLS TCP Encrypted POP3, for clients that download messages and store them locally rather than leaving them on the server.

Web

PortServiceTransportNotes
80 HTTP Hypertext Transfer Protocol TCP Unencrypted web traffic, and the original port of the web.
443 HTTPS HTTP over TLS TCP Encrypted web traffic, and now effectively the default for the entire web.
8080 HTTP Alt Alternate HTTP TCP The conventional second HTTP port.
8443 HTTPS Alt Alternate HTTPS TCP The TLS counterpart to 8080, and a very common choice for the management interface of a firewall, load balancer, appliance or application server — anything that needs an HTTPS admin panel without taking port 443 from the main site..

Remote access

PortServiceTransportNotes
22 SSH Secure Shell TCP Encrypted remote login and command execution, and the transport under SFTP and SCP.
23 Telnet Telnet remote login TCP Unencrypted remote terminal access.
1194 OpenVPN OpenVPN UDP The default port for OpenVPN tunnels, usually over UDP for performance, with TCP available for networks that block UDP or interfere with it.
1723 PPTP Point-to-Point Tunneling Protocol TCP An old Microsoft VPN protocol, still offered by some consumer routers and older firewalls because it is trivial to configure and supported out of the box by most operating systems.
3389 RDP Remote Desktop Protocol TCP Windows graphical remote access: the full desktop, keyboard and mouse of a remote machine delivered over the network.
5900 VNC Virtual Network Computing TCP Cross-platform graphical remote access, sharing the actual screen of the remote machine rather than starting a separate session.

File sharing

PortServiceTransportNotes
20 FTP Data File Transfer Protocol (data) TCP The data channel of classic FTP.
21 FTP File Transfer Protocol (control) TCP The command channel for FTP: login, directory listings, and instructions to transfer files.
69 TFTP Trivial File Transfer Protocol UDP A deliberately minimal file transfer protocol with no authentication at all.
137 NetBIOS Name NetBIOS name service UDP Legacy Windows name resolution on a local network, from the era before Windows relied on DNS.
139 NetBIOS Session NetBIOS session service TCP The older transport for Windows file and printer sharing, carrying SMB over a NetBIOS session layer.
445 SMB Server Message Block TCP Windows file and printer sharing, running directly over TCP without the older NetBIOS session layer.
873 rsync rsync daemon TCP The standalone rsync daemon, offering named modules of files for synchronisation without tunnelling over SSH.
2049 NFS Network File System TCP/UDP Unix network file sharing, mounting remote directories so they appear as ordinary local paths.

Databases and caches

PortServiceTransportNotes
1433 MSSQL Microsoft SQL Server TCP The default listener for Microsoft SQL Server.
1521 Oracle DB Oracle database listener TCP The Oracle TNS listener, which accepts client connections and hands them to the right database instance.
3306 MySQL MySQL / MariaDB TCP The default port for MySQL and MariaDB.
5432 PostgreSQL PostgreSQL TCP The default PostgreSQL listener.
6379 Redis Redis TCP An in-memory data store used for caching, session storage, job queues and rate limiting.
9200 Elasticsearch Elasticsearch HTTP API TCP The REST API for Elasticsearch and OpenSearch, used for search and for log analytics.
11211 Memcached Memcached TCP/UDP A simple in-memory cache with no authentication by design — it was built for a trusted network behind an application, where the only thing that can reach it is your own code.
27017 MongoDB MongoDB TCP The default MongoDB port, where the database listens for client connections.

Network infrastructure

PortServiceTransportNotes
53 DNS Domain Name System TCP/UDP Name resolution: turning example.com into an IP address.
67 DHCP Server Dynamic Host Configuration Protocol UDP Where a DHCP server listens for devices joining a network and hands them an IP address, a default gateway, DNS servers and a lease time.
68 DHCP Client DHCP client UDP The client side of DHCP.
123 NTP Network Time Protocol UDP Clock synchronisation.
135 MSRPC Microsoft RPC endpoint mapper TCP Where Windows clients ask which dynamic port a given RPC service is on.
161 SNMP Simple Network Management Protocol UDP Polls network devices for status: interface counters, error rates, temperatures, uptime, disk usage.
389 LDAP Lightweight Directory Access Protocol TCP/UDP Directory queries — users, groups, and the organisational structure they sit in.
636 LDAPS LDAP over TLS TCP Encrypted directory queries — LDAP wrapped in TLS from the first byte, in the same way HTTPS relates to HTTP.
1080 SOCKS SOCKS proxy TCP A general-purpose proxy protocol that forwards arbitrary TCP connections rather than just HTTP, which means it can carry anything — mail, SSH, game traffic.
5060 SIP Session Initiation Protocol TCP/UDP Call setup for VoIP — registering a phone, ringing, answering, transferring and hanging up.

How to check whether a port is open

Use the port scanner against a host you own. It connects from outside your network, which is the view that matters: a service can be listening on the machine while the firewall blocks every attempt to reach it from the internet, and that distinction is the whole point of scanning from somewhere else.

A port reported as open means something accepted the connection. Closed means the host answered but nothing is listening. Filtered means nothing answered at all, which usually means a firewall dropped the packet silently.

Only scan hosts you own or have explicit permission to test.