Common Ports Lookup

What this tool is used for

• Finding which service conventionally uses a port number.
• Finding the port a service you are configuring expects.
• Checking whether a port is in the well-known range.
• Identifying an unexpected port seen in a connection list.
• Confirming a port before opening it in a firewall.

Frequently Asked Questions

What are the three port ranges?

0-1023 are well-known and need privilege to bind on Unix, 1024-49151 are registered for specific services, and 49152-65535 are ephemeral — assigned to outgoing connections rather than listeners.

Does a service have to use its assigned port?

No, the assignments are conventions. Moving SSH off 22 reduces automated scanning noise but is not security — a port scan finds it in seconds, so it is tidiness rather than protection.

How do I find what is using a port?

`lsof -i :PORT` or `ss -ltnp` on Linux, `netstat -ano` on Windows. The usual reason for an address-already-in-use error is a previous instance that did not exit, not another product.

Why do the same development ports keep recurring?

Because frameworks pick memorable defaults — 3000, 8000, 8080, 5173 — and they collide the moment two projects run at once. Assigning a project its own port in config avoids the daily conflict.

What is the difference between a TCP and a UDP port?

They are separate spaces, so the same number can be in use by both simultaneously for different services. DNS famously uses both — UDP for ordinary queries and TCP for large responses and zone transfers.

Common errors and gotchas

• Assuming a port implies the service, since anything can listen on any port.
• Treating a registered assignment as enforced, which it is not.
• Opening a port because a service conventionally uses it, without checking what is actually listening.
• Forgetting ports below 1024 need elevated privileges on most systems.
• Confusing TCP and UDP assignments, which are separate namespaces.