# How I check common port numbers when debugging a service

A beginner-friendly guide to TCP and UDP ports, common services, port lookup, and avoiding assumptions during network debugging.

- Date: 2026-09-27
- URL: https://ilham.dev/posts/how-to-check-common-port-numbers/
- Markdown: https://ilham.dev/posts/how-to-check-common-port-numbers/index.md
- Tags: ports, networking, devops, tools
- Reading time: 2 min


Port numbers are labels for network services, but a port number alone does not guarantee what is actually running there.

The [Port Reference](/tools/port-reference/) tool helps me inspect the input and output without writing a one-off script first.

## The simple idea

Port numbers are labels for network services, but a port number alone does not guarantee what is actually running there.

I use it to answer one focused question at a time, then I review the result before using it anywhere important.

## Step 1: Search the port number or service name

Search the port number or service name.

## Step 2: Check whether the service normally uses TCP, UDP, or both

Check whether the service normally uses TCP, UDP, or both.

## Step 3: Use the result as a clue, not proof

Use the result as a clue, not proof.

## Step 4: Confirm with server config or a scan when appropriate

Confirm with server config or a scan when appropriate.

## Step 5: Watch for custom ports used by internal apps

Watch for custom ports used by internal apps.

## Step 6: Document non-standard port choices

Document non-standard port choices.

## Step 7: Avoid exposing admin ports publicly unless intentionally secured

Avoid exposing admin ports publicly unless intentionally secured.

## My checklist

Before I trust the result, I check:

- Search the port number or service name.
- Check whether the service normally uses TCP, UDP, or both.
- Use the result as a clue, not proof.
- Confirm with server config or a scan when appropriate.
- Watch for custom ports used by internal apps.
- Document non-standard port choices.
- Avoid exposing admin ports publicly unless intentionally secured.

The tool makes the mechanical part faster. The decision still belongs to me: is this result correct, safe, and appropriate for the real task?