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
If 192.0.2.0/25 and 192.0.2.0/24 both exist, the /25 wins for the addresses it covers. The simulator shows that. It does not install routes. A shorter prefix does not erase a longer one.
Use documentation prefixes or prefixes you originate. A more specific you do not hold is not a trick you announce. A summary that covers a foreign network is the same mistake as on the summarization page.
One pair of prefixes. Write which one wins for one address inside the longer block.
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.
- Pick two prefixes you may use.
- Pick one address inside the longer one.
- Read which route wins.
- Reject a foreign more-specific.
- Do not advertise either prefix.
- Stop.
Mistakes that outlive the command
Longest Prefix Match Explained goes wrong in a small set of ways. The list is here so the ticket can forbid them before the window.
- Announcing a more specific you do not hold.
- Assuming the shorter route erases the longer one.
- A pair from someone else's table.
- Installing the routes.
Decisions to write down
One decision for Longest Prefix Match Explained: The prefixes are yours or documentation. The longer one wins inside itself. Nothing was advertised. Nothing was installed. And one address was the example.
Checks before you call it done
Confirm this before you call the change done: Both prefixes are written. The test address is written. The winner is written. No foreign prefix was added. And no router was changed. If one of those fails, stop.
Before you leave the device
Longest Prefix Match Explained 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.
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