Network Segmentation for Security

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

Network Segmentation for Security names the two networks, what may cross, and what stays on its own side. 192.0.2.10/24 and 198.51.100.0/24 are documentation until you replace them with networks you run. You do not change a rule during the reading. 0.0.0.0/0 is not the allowed path.

Write the system you administer, the name of this change, and the time. A second change waits until this line has been read back.

The browser tool drafts text or reads a paste you already hold. It does not log in, it does not scan, and it does not apply.

192.0.2.10/24, gateway 192.0.2.1, 198.51.100.0/24, 203.0.113.0/24, and 2001:db8::/32 are documentation. example.com is a documentation name. A sample password is replaced.

The change you can finish

Apply nothing while you are writing the note. When the lab window opens, it is one change on the system named in the ticket. Read the draft, then the system, then decide.

Rollback is the file, the record, or the snapshot you saved first. You do not invent a rollback after the only copy is gone.

Write the two networks you administer.
Write what may cross.
Write what must not cross.
Do not change a firewall rule.
Stop.

Mistakes that outlive the statement

Network Segmentation for Security goes wrong in a small set of ways. The list is here so the ticket can forbid them before the window.

A firewall rule changed during the reading.
0.0.0.0/0 left as the allowed path.
A network you do not administer included as if it were linked.
Two boundaries in one note.

Decisions to write down

One decision for Network Segmentation for Security: Both networks are yours, or the far side is only a name. Nothing is changed. The allowed path is narrow. One boundary is the window. And documentation prefixes stay labelled.

Checks before you call it done

Confirm this before you call the change done: Both sides are written. Nothing was changed. 0.0.0.0/0 is not the design. The allowed path is one sentence. And a second person can say what must not cross. If one of those fails, stop.

# Segmentation plan. Do not change a firewall. Do not allow every address.

Before you leave the system

Network Segmentation for Security ends when the system in the note is the system in the ticket. If it is not, stop.

The draft stays a draft until a person has read the names in it. A generator does not log in, does not scan, and does not send mail.

192.0.2.10/24, gateway 192.0.2.1, 198.51.100.0/24, 203.0.113.0/24, and 2001:db8::/32 are documentation. example.com is a documentation name. They belong in the note. They are not values you publish because a draft included them.

prompt-for-this is a reminder that a secret is missing. It is not a password, a key, or a token you save. A sample password is replaced. It is not a password you keep.

One change is the window. If two things move and the result is wrong, you will not know which one did it.

If the same step fails twice, stop for the day. Restore the copy you took first.

A second person reads the scope aloud. If they cannot find it in the ticket, the note is not done.

This page is a planning guide. It is not legal advice, not an audit opinion, not a vendor manual, and not the text of a standard. You do not disable a security control to make a check pass. You do not use the page against a system you do not administer.

Tools for this guide

These tools run in the browser on this site. They do not log into your machines.

Network Segmentation Planner

Server Hardening Guide

More in this cluster

The pillar for this page, and the next published pages filed with it.

Companion: Network: Microsegmentation Explained.