The Opener
Two weeks ago I posted a video of me pulling my whole home network out of a closet for the move. It’s past 64,000 views now, and the comments mostly say the same thing. “Documentation my dude.” “Some people document, others don’t.” One person asked how I’ve been in IT this long and never wrote any of it down.
Fair. Every one of them.
Here’s what actually happened. Networks you get paid to run get documented, because other people depend on them. My home network only had one person depending on it, so I skipped it. Then I became the other person. Future me showed up with a screwdriver and zero context, and past me had left him nothing.
That’s the whole lesson. Documentation isn’t for you today. It’s for whoever shows up next, and a lot of the time that’s you, tired, remembering less than you think you will.
The Deep Dive: Documentation is doing your work in public
My short this week was about doing your work in public. I’m not a CCIE and I’m not a big creator. I just talk about what I’m learning, and that’s put me in rooms I never would have gotten into otherwise. People notice work they can see.
Documentation is how your work becomes something other people can see. There are two kinds, and you need both.
Part one: the bare minimum that keeps it running
For a home network or a lab, this fits on one page:
A port map. Switch, port, what’s plugged in, VLAN. A spreadsheet is fine.
An IP and VLAN list. VLAN number, name, subnet, gateway, and what lives there.
A diagram. Boxes and lines. draw.io is free, and nobody’s grading it on looks.
Config backups. Copy the config off each device after every change, with the date in the filename.
Labels on both ends of every cable, matching the port map.
And one rule that costs nothing: before you unplug anything, take a picture of the back.
You can put labels on the switch itself, too. On Cisco gear, description Living-Room-AP on an interface shows up in show interfaces status, so the next person sees it without opening a single file.
Then let the network check your homework
Documentation drifts. Somebody moves a cable and doesn’t update the sheet. So check it against what the gear actually sees:
show interfaces status: every port, whether it’s up, and its VLAN.show vlan brief: which ports are in which VLAN.show cdp neighborsorshow lldp neighbors: what’s actually plugged into what. LLDP is off by default on a lot of Cisco switches, so you may needlldp runfirst.
If the doc and the switch disagree, the doc is wrong. Fix it.
This isn’t just good habit, either. The new CCNA v2.0 exam topics include “Validate the accuracy of network documentation using CDP and LLDP.” It’s on the test now.
Part two: the write-up that shows what you did
A viewer who’s studying networking quoted back a list I gave in an earlier video. When you build something, write down five things: what you built, why you built it, what broke, how you found it, and how you recovered it.
That’s documentation too. It’s just pointed at people instead of at a rack.
A hiring manager can’t walk into your closet. They can read a one-page write-up about the VLAN you misconfigured and how you tracked it down. Post it on LinkedIn, GitHub, or a simple blog. That’s how “who knows your work” stops being a question.
The takeaway: this weekend, write one page for whatever you’ve got: your home network, your lab, even a Packet Tracer topology. Port map, IP list, diagram. Then write up one thing that broke and how you fixed it, and post it. That’s two things you can show in an interview that most candidates won’t have.
The Week in Networking
A config value saved in a format the DNS software couldn’t read stopped DNS for every paid customer for about 54 minutes.
Why it matters: One of their fixes is to document the data formats their DNS software depends on. Even DNS providers learn this one the hard way.
My podcast with Alexis Bertholf. Dale went from driving forklifts to working in IT, and we get into degrees versus certs along the way.
Why it matters: If you’re in a non-IT job right now, this is your episode.
My free lab guide, no email gate. It includes starter connection diagrams and a list of what to document: port, VLAN, speed, and neighbor.
Why it matters: If you’re starting this weekend’s one-page doc from scratch, start here.
Reader Question
“In the Cisco Networking entry course they only teach that the switch saves the MAC address that is incoming, not the destination. Does the exception exist because the destination is creating a new frame to respond? Or is the Cisco course missing that info?”
From a YouTube comment on this week’s flood-or-drop video, lightly edited.
Cisco’s right, and so is your instinct. There’s no exception. A switch only ever learns from the source MAC address of frames it receives. It never learns from the destination.
Here’s the sequence:
PC-A sends a frame to PC-B. The switch learns PC-A’s MAC on the port it came in on, from the source field. It doesn’t know where PC-B is, so it floods the frame.
PC-B replies. That reply is a brand-new frame, and this time PC-B is the source.
The switch learns PC-B’s MAC from that source field. Same rule as always.
So when I said “the switch sees which port the answer came in on,” that’s just source learning doing its job on the reply.
One related thing a few people asked about: flooding isn’t the same as broadcasting. A broadcast is addressed to everyone (FF:FF:FF:FF:FF:FF). A flood is a frame addressed to one device that the switch sends out every port in the VLAN except the one it came in on, because it doesn’t know where that device lives yet. In an interview, call it “unknown unicast flooding.” That phrase alone tells them you know the difference.
The Close
Next week: real gear or Packet Tracer? A viewer asked whether you even need physical equipment to learn this. I’ll tell you what I’d actually buy, and when I wouldn’t buy anything.
Someone also asked this week if I’d start a course or a Discord. No course, still nothing to sell. But the Discord exists: The Network Node is free, and people bring the thing that broke.
Short versions all week on YouTube, TikTok, Instagram, and LinkedIn. Got a question for next week’s Reader Question? Hit reply.
The Weekly Packet by Kevin Nanns
Enterprise network architect. Content creator. adjacentnode.com