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
An access network oversubscribes the uplink because not everyone transmits at once. The calculators estimate that ratio, a CGNAT port block, and a PPPoE MTU. They do not configure a router. 100.64.0.0/10 is carrier space. It is not a LAN you assign to desks, and it is not a prefix you advertise.
Write the subscriber count, the uplink, and the ratio you accept. A port block that is too small breaks a subscriber's many connections. One access router you administer, or a paper design.
Do not open the router to the internet to test the ratio. Do not apply CGNAT during the reading.
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.
- Write subscribers and uplink.
- Read the ratio.
- If you use CGNAT, size the port block and keep 100.64.0.0/10 off the LAN.
- Note the PPPoE MTU.
- Do not configure the router.
- Stop.
Mistakes that outlive the command
ISP Network Design Basics goes wrong in a small set of ways. The list is here so the ticket can forbid them before the window.
- 100.64.0.0/10 used as office space.
- Advertising carrier space.
- A port block too small to say.
- Opening the router to test.
- Applying CGNAT during the reading.
Decisions to write down
One decision for ISP Network Design Basics: The ratio is a choice you wrote. Carrier space is not a LAN. Nothing was advertised. Nothing was configured. And the MTU is noted if PPPoE is in the design.
Checks before you call it done
Confirm this before you call the change done: Subscribers and uplink are written. The ratio is written. CGNAT is in or out on purpose. No prefix was advertised. And no router was changed. If one of those fails, stop.
Before you leave the device
ISP Network Design Basics 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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