20FTP (data)File Transfer Protocol, data channel.
21FTP (control)File Transfer Protocol, command channel.
22SSHSecure Shell, remote login and tunneling.
23TelnetUnencrypted remote login, considered obsolete/insecure.
25SMTPSimple Mail Transfer Protocol, sending email between servers.
53DNSDomain Name System queries.
67DHCP (server)Dynamic Host Configuration Protocol, server side.
68DHCP (client)Dynamic Host Configuration Protocol, client side.
80HTTPUnencrypted web traffic.
110POP3Post Office Protocol, retrieving email.
123NTPNetwork Time Protocol, clock synchronization.
143IMAPInternet Message Access Protocol, retrieving email.
161SNMPSimple Network Management Protocol.
194IRCInternet Relay Chat.
389LDAPLightweight Directory Access Protocol.
443HTTPSEncrypted (TLS) web traffic.
445SMBWindows file/printer sharing (Server Message Block).
465SMTPSSMTP over TLS, implicit encryption.
514SyslogSystem logging protocol.
587SMTP (submission)Email submission from a client to its outgoing server.
636LDAPSLDAP over TLS.
993IMAPSIMAP over TLS.
995POP3SPOP3 over TLS.
1433Microsoft SQL ServerDefault SQL Server database port.
1521Oracle DBDefault Oracle database listener port.
3000Common dev serverFrequently used by Node.js/React/Next.js development servers.
3306MySQL / MariaDBDefault MySQL/MariaDB database port.
3389RDPWindows Remote Desktop Protocol.
5432PostgreSQLDefault PostgreSQL database port.
5672AMQPAdvanced Message Queuing Protocol (RabbitMQ default).
6379RedisDefault Redis database port.
8080HTTP (alternate)Common alternate web/proxy port.
8443HTTPS (alternate)Common alternate encrypted web port.
9200ElasticsearchDefault Elasticsearch REST API port.
27017MongoDBDefault MongoDB database port.
