Notes on Home Network Documentation
Last month my router died. Not a graceful decline with warnings and degraded performance — it just stopped working. One evening everything was fine, the next morning the power light was off and nothing I did would bring it back. I drove to the store, bought a replacement, brought it home, and had the whole network back up within about forty minutes. This would not have been possible a year ago.
A year ago, I had the same network but no documentation. Same modem, same router, same switch, same collection of devices. But if you'd asked me what IP address the printer was on, or which port on the switch went to the office, or what the DNS settings were, I would have shrugged. I set it all up at various times over several years, making decisions I didn't record and then promptly forgetting them. It worked, and as long as it worked, the details didn't matter.
What prompted me to document everything was not foresight but embarrassment. I was helping a friend troubleshoot a networking issue at his place and found myself saying things like "you should really write down your configuration" and "do you know what's on each port of that switch?" He did not. Neither did I, for my own network. The hypocrisy was hard to ignore.
So I spent a Saturday afternoon doing it properly. The process was straightforward, if tedious. I started with a physical diagram — just a hand-drawn sketch on graph paper showing every device, how they're connected, and what cable runs where. The modem from the ISP connects to the router. The router connects to an eight-port switch. The switch connects to my desktop, the printer, a Raspberry Pi I use for a small project, and a few Ethernet runs to other rooms. Not complicated. But having it drawn out revealed a couple of things I'd forgotten, including an Ethernet cable running to the guest room that wasn't plugged into anything on either end. I have no memory of installing it.
After the diagram, I made a spreadsheet. Each row is a device. The columns are: device name, MAC address, IP address (static or DHCP-reserved), location in the house, what it connects to, and any notes. The notes column turned out to be the most useful part. That's where I put things like "printer needs static IP or the scanning feature breaks" and "Pi is on port 5, don't move it, the cable on port 6 is flaky." The kind of information that exists only in your head until you write it down, and then ceases to exist entirely when you forget it.
I also labeled the cables. This is the part that might push this from "reasonable precaution" into "possibly excessive" territory. I bought a label maker — one of those Brother P-Touch devices that I'd been looking for an excuse to purchase anyway — and put a small label on each end of each Ethernet cable. "SW-P1 to DESKTOP," "SW-P3 to OFFICE-WALL," that sort of thing. It took about twenty minutes and used a trivial amount of label tape. If you have ever stared at a tangle of identical blue cables behind a piece of furniture, trying to figure out which one to unplug, you understand why I did this.
I'll admit that for a home network of this size, all of this is overkill. There are maybe a dozen devices total, counting the wireless ones. A person with a good memory could keep the whole thing in their head. I kept it in my head for years. The problem with keeping it in your head is that you don't notice the information degrading. You think you know which cable goes where, but you're actually remembering the configuration from two routers ago. You think you know the printer's IP, but that was before you changed the subnet that one time.
When the router died, the documentation paid for itself immediately. I pulled out the spreadsheet, confirmed the settings I needed to replicate on the new router, and typed them in. Static IPs, DHCP range, DNS servers, port forwarding rules for the one service I run. Without the spreadsheet, I would have spent the afternoon rediscovering all of this by trial and error, probably breaking the printer's scanning feature at least once in the process.
I keep the diagram and the spreadsheet in a folder on my desktop, with a printed copy in the filing cabinet. The printed copy might seem redundant, but consider: if your network is down and your documentation is only on a network-attached device, you have a problem. Paper doesn't need a working router to be readable.
This is, I recognize, the archivist's impulse applied to household infrastructure. The same instinct that makes me want to catalog and label and preserve things at work follows me home and asks why the cable behind the bookshelf doesn't have a tag on it. I don't think this is a personality trait that everyone needs or should cultivate. But if you're the kind of person who ends up being the one to fix things when they break — and in my household that's me, by default and by temperament — having documentation turns an emergency into an inconvenience. That seems worthwhile.
The new router, by the way, is already in the spreadsheet. Row one, column A.
— K. Vadala