This is an original planning guide. It is not a vendor manual, an official standard, or legal advice. Example addresses use documentation ranges. Review every command before you paste it.
What this hour is for
A port number is not an application, but a short list helps you recognise SSH, DNS, HTTP, HTTPS, and the few others you actually use. The lookup drafts a name from a number you type. Confirm it. Overlapping uses exist.
Allowing a port because it is common is how a firewall grows. The rule still needs a source and a destination. The security desk's rule generator is a neighbour. This sheet does not open a port.
Do not scan to see which of these are open on a network you do not run. The port-check page is one host you administer.
One port is the lookup.
The change you can finish
Apply nothing during the writing of the note. When the lab window opens, it is one change on the device named in the ticket. Read the draft, then the device, then decide.
Rollback is the file or the revision you saved first. You do not invent a rollback after the only copy is gone.
- Type the number you mean.
- Read the name.
- Write the application you actually run.
- If they disagree, believe your application and note the disagreement.
- Do not open the port here.
- Do not scan.
Mistakes that outlive the command
Common Ports Cheat Sheet goes wrong in a small set of ways. The list is here so the ticket can forbid them before the window.
- A port opened because the sheet listed it.
- A scan of a foreign network.
- The application left unnamed.
- Several ports added from the common list.
Decisions to write down
One decision for Common Ports Cheat Sheet: The number and your application are written. A disagreement is noted. Nothing was opened. And no scan ran.
Checks before you call it done
Confirm this before you call the change done: The port is in the ticket. The application is a word. No rule was added. No scan ran. And the firewall change waits for its own page. If one of those fails, stop.
| Port | Often | Still write |
|---|---|---|
| 22/tcp | SSH | The admin prefix |
| 53/udp | DNS | The resolver you mean |
| 443/tcp | HTTPS | The server name |
One port. Name your application.
Do not scan from the sheet.Before you leave the device
Common Ports Cheat Sheet ends when the hostname on the device matches the hostname in the ticket. If it does not, you are on the wrong box. Stop. A command that succeeded on the wrong box is not progress.
The draft stays a draft until a person has read the names in it. A generator does not log into the device and does not know which interface is the uplink. You delete a line that names a device, a zone, or a prefix you did not write down.
0.0.0.0/0 is not kept because a sample included it. A source you can say is the source you keep. 192.0.2.0/24, 198.51.100.0/24, 203.0.113.0/24, and 2001:db8::/32 are documentation. They belong in the note. They are not prefixes you type onto a production device because they appeared in a draft.
prompt-for-this is a reminder that a secret is missing. It is not a password, a key, a community string, or a pre-shared key you save in the ticket or in git. The real secret stays in the store.
One change is the window. A VLAN and a routing protocol and a VPN do not share it. If two things move and the result is wrong, you will not know which one did it. The next feature waits for its own page.
If the same step fails twice, stop for the day. The failure is the result. Adding a forum command beside a half-applied config produces a device nobody can rebuild. Restore the copy you took first.
A second person reads the device name and the change aloud. If they cannot find them in the ticket, the note is not done. Silence is not agreement. Then leave the device alone.
This page is a planning guide. It is not a vendor manual, not an official standard, and not a permission to touch a network you do not administer. The pillar guide owns the wider design. This page owns one lab proof.
Tools for this guide
These tools run in the browser on this site. They do not log into your machines.
Related pillar guides
More in this cluster
The pillar for this page, and the next published pages filed with it.
- Pillar: Network Security & VPN Guide
- Explainer: Access Control Lists (ACLs) Explained
- Checklist: Firewall Rule Cleanup Best Practices
- Explainer: Port Forwarding Explained
Companion: Security: Firewall Rule Generator.