What is the difference between well-known ports and registered ports?

Well-known ports (0–1023) are assigned by IANA to fundamental internet services — HTTP uses port 80, HTTPS uses 443, SSH uses 22, DNS uses 53. They typically require root/admin privileges to bind. Registered ports (1024–49151) are assigned to specific applications by IANA request — MySQL uses 3306, PostgreSQL uses 5432, Redis uses 6379 — and can be bound by any user.

What are ephemeral or dynamic ports?

Ephemeral ports (49152–65535) are temporary ports automatically assigned by the operating system to client-side connections. When your browser makes an HTTP request, the OS assigns an ephemeral port for the client side of the connection. These ports are not assigned to specific services and are recycled after each connection closes.

Why do some services use both TCP and UDP on the same port?

Some protocols are designed to run over both transport layers. DNS uses UDP port 53 for fast query/response (queries fit in a single datagram) and TCP port 53 for large responses (zone transfers, DNSSEC). The same port number is used in both cases but they are separate sockets — the OS distinguishes them by protocol.

TCP & UDP Port Numbers Reference

Well-known and registered ports with the service on each and its transport protocol.

61 ports

Port	Protocol	Service	Category	Description
20	TCP	FTP	Well-known	File Transfer Protocol — data transfer
21	TCP	FTP	Well-known	File Transfer Protocol — control
22	TCP	SSH	Well-known	Secure Shell — encrypted remote login and tunneling
23	TCP	Telnet	Well-known	Telnet — unencrypted remote terminal (legacy)
25	TCP	SMTP	Well-known	Simple Mail Transfer Protocol — email sending
53	TCP/UDP	DNS	Well-known	Domain Name System — hostname to IP resolution
67	UDP	DHCP	Well-known	Dynamic Host Configuration Protocol — server
68	UDP	DHCP	Well-known	Dynamic Host Configuration Protocol — client
69	UDP	TFTP	Well-known	Trivial File Transfer Protocol
80	TCP	HTTP	Well-known	Hypertext Transfer Protocol — unencrypted web traffic
110	TCP	POP3	Well-known	Post Office Protocol v3 — email retrieval
119	TCP	NNTP	Well-known	Network News Transfer Protocol
123	UDP	NTP	Well-known	Network Time Protocol — clock synchronization
143	TCP	IMAP	Well-known	Internet Message Access Protocol — email retrieval
161	UDP	SNMP	Well-known	Simple Network Management Protocol
194	TCP	IRC	Well-known	Internet Relay Chat
389	TCP/UDP	LDAP	Well-known	Lightweight Directory Access Protocol
443	TCP	HTTPS	Well-known	HTTP Secure — encrypted web traffic (TLS)
445	TCP	SMB	Well-known	Server Message Block — Windows file sharing
465	TCP	SMTPS	Well-known	SMTP over TLS — secure email sending
514	UDP	Syslog	Well-known	System Logging Protocol
587	TCP	SMTP	Well-known	SMTP submission — email sending (STARTTLS)
636	TCP	LDAPS	Well-known	LDAP over TLS
993	TCP	IMAPS	Well-known	IMAP over TLS — secure email retrieval
995	TCP	POP3S	Well-known	POP3 over TLS
1080	TCP	SOCKS	Registered	SOCKS proxy protocol
1194	TCP/UDP	OpenVPN	Registered	OpenVPN
1433	TCP	MSSQL	Registered	Microsoft SQL Server database
1521	TCP	Oracle DB	Registered	Oracle Database default listener
1883	TCP	MQTT	Registered	Message Queuing Telemetry Transport (IoT)
2181	TCP	ZooKeeper	Registered	Apache ZooKeeper client port
2375	TCP	Docker	Registered	Docker daemon API (unencrypted)
2376	TCP	Docker	Registered	Docker daemon API (TLS)
3000	TCP	Dev Server	Registered	Common dev server port (React, Next.js, etc.)
3306	TCP	MySQL	Registered	MySQL and MariaDB database
3389	TCP	RDP	Registered	Remote Desktop Protocol — Windows
4200	TCP	Angular	Registered	Angular CLI dev server default
4443	TCP	HTTPS Alt	Registered	Alternate HTTPS port
5000	TCP	Flask / UPnP	Registered	Flask dev server / UPnP
5432	TCP	PostgreSQL	Registered	PostgreSQL database
5601	TCP	Kibana	Registered	Kibana web interface (ELK stack)
5672	TCP	RabbitMQ	Registered	RabbitMQ AMQP messaging
5900	TCP	VNC	Registered	Virtual Network Computing remote desktop
6379	TCP	Redis	Registered	Redis key-value data store
6443	TCP	Kubernetes	Registered	Kubernetes API server
7700	TCP	Meilisearch	Registered	Meilisearch search engine
8000	TCP	HTTP Alt	Registered	Common alternative HTTP / Django dev server
8080	TCP	HTTP Alt	Registered	Common HTTP proxy / Tomcat / Spring Boot
8086	TCP	InfluxDB	Registered	InfluxDB time-series database HTTP API
8443	TCP	HTTPS Alt	Registered	Common alternative HTTPS port
8888	TCP	Jupyter	Registered	Jupyter Notebook web interface
9000	TCP	PHP-FPM	Registered	PHP-FPM / SonarQube / MinIO API
9090	TCP	Prometheus	Registered	Prometheus metrics server
9092	TCP	Kafka	Registered	Apache Kafka broker
9200	TCP	Elasticsearch	Registered	Elasticsearch REST API
9300	TCP	Elasticsearch	Registered	Elasticsearch inter-node communication
9418	TCP	Git	Registered	Git protocol
10250	TCP	Kubelet	Registered	Kubernetes Kubelet API
15672	TCP	RabbitMQ	Registered	RabbitMQ management web UI
27017	TCP	MongoDB	Registered	MongoDB document database
50051	TCP	gRPC	Registered	gRPC default port

The three port ranges

Range	Name	Assignment	Notes
0–1023	Well-known	IANA	Binding requires root on Unix — the origin of privilege-dropping in daemons
1024–49151	Registered	IANA on request	Where most application services live
49152–65535	Dynamic / ephemeral	Unassigned	Source ports for outbound connections, allocated by the OS

Linux defaults its ephemeral range to 32768–60999 rather than the IANA range, which is why a service bound to 40000 can intermittently conflict with an outbound connection. Check /proc/sys/net/ipv4/ip_local_port_range before choosing a fixed port in that region.

Ports worth knowing by heart

Port	Service	Note
22	SSH	Also used by SFTP and git over SSH
53	DNS	UDP for queries, TCP for large responses and zone transfers
80 / 443	HTTP / HTTPS	443 also carries HTTP/3 over QUIC, which is UDP
3306	MySQL / MariaDB	Should never be exposed publicly
5432	PostgreSQL	Should never be exposed publicly
6379	Redis	Historically no authentication by default — a long-running source of breaches
27017	MongoDB	Same history as Redis; bind to localhost
9200 / 9300	Elasticsearch	HTTP API and transport. Frequently found exposed
3000 / 5173 / 8080	Dev servers	Node, Vite, and the common alternate HTTP port
25 / 587 / 465	SMTP	25 for server-to-server, 587 for submission with STARTTLS, 465 for implicit TLS

Port problems

EADDRINUSE — address already in use

Cause:Another process holds the port, or a previous instance did not release it.

Fix:Find it with `lsof -i :3000` on macOS/Linux or `netstat -ano | findstr :3000` on Windows. If the old process is gone but the port is held, it is in TIME_WAIT; SO_REUSEADDR lets you rebind immediately.

EACCES binding to port 80 or 443

Cause:Ports below 1024 require elevated privileges on Unix.

Fix:Do not run the application as root. Put a reverse proxy in front, use setcap to grant CAP_NET_BIND_SERVICE, or bind high and redirect with a firewall rule.

Service works locally but not from another machine

Cause:Bound to 127.0.0.1 rather than 0.0.0.0, so it only accepts loopback connections.

Fix:Bind to 0.0.0.0 to listen on all interfaces — and make sure a firewall is in front, because this exposes it to the whole network.

Intermittent connection failures under load

Cause:Ephemeral port exhaustion. Each outbound connection consumes a source port, and ports in TIME_WAIT are held for up to two minutes.

Fix:Use connection pooling and keep-alive so connections are reused rather than reopened. Widening the ephemeral range treats the symptom.

About

The Port Numbers Reference lists well-known (0–1023) and registered (1024–49151) TCP and UDP ports used by common network services and protocols. It covers HTTP (80), HTTPS (443), SSH (22), FTP (21), DNS (53), SMTP (25), MySQL (3306), PostgreSQL (5432), Redis (6379), and many more — useful for firewall rules, server configuration, and network debugging.

How to use

1 Browse the list or search by service name or port number.
2 Filter between Well-known (0–1023) and Registered (1024–49151) ports.
3 Click any row to copy the port number.

What is the difference between well-known ports and registered ports?: Well-known ports (0–1023) are assigned by IANA to fundamental internet services — HTTP uses port 80, HTTPS uses 443, SSH uses 22, DNS uses 53. They typically require root/admin privileges to bind. Registered ports (1024–49151) are assigned to specific applications by IANA request — MySQL uses 3306, PostgreSQL uses 5432, Redis uses 6379 — and can be bound by any user.
What are ephemeral or dynamic ports?: Ephemeral ports (49152–65535) are temporary ports automatically assigned by the operating system to client-side connections. When your browser makes an HTTP request, the OS assigns an ephemeral port for the client side of the connection. These ports are not assigned to specific services and are recycled after each connection closes.
Why do some services use both TCP and UDP on the same port?: Some protocols are designed to run over both transport layers. DNS uses UDP port 53 for fast query/response (queries fit in a single datagram) and TCP port 53 for large responses (zone transfers, DNSSEC). The same port number is used in both cases but they are separate sockets — the OS distinguishes them by protocol.

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