NetTest

NetTest is my first hardware project as a network engineer: a pocket-sized device you plug into any Ethernet port to find out, in seconds, whether that drop actually works and how it's configured.

Tools like the NetAlly LinkSprinter do this well, but they cost hundreds of dollars, which puts them out of reach for students, hobbyists, and small IT shops. NetTest aims to do everything the LinkSprinter can do, and a little more, for under $100 in parts, with the hardware, firmware, and documentation fully open source so anyone can build one themselves.

Microcontroller

ESP32 with onboard PoE Ethernet

Power

PoE, with a rechargeable or AA battery option for unpowered ports

Display

Small onboard screen for live results

Enclosure

Custom 3D-printed case

Storage

Last few test results saved on-device, oldest rotated out

Target cost

Under $100 in parts

License

Open source: hardware, firmware, and docs

Everything the LinkSprinter checks, run in order from the physical layer up. More tests are still being scoped.

1. 01

   Power

   Detect whether the device is being powered over PoE

2. 02

   Link

   Confirm a physical link is up and report the negotiated speed and duplex

3. 03

   Switch & Port

   Listen for LLDP/CDP to identify the upstream switch, port number, and VLAN

4. 04

   DHCP

   Request an address and report the IP, subnet mask, gateway, and DNS servers handed out

5. 05

   Gateway

   Ping the default gateway to confirm local reachability

6. 06

   DNS

   Resolve a known hostname against the assigned DNS servers

7. 07

   Internet

   Reach an outside host to confirm the drop has a working path to the internet

More than pass / fail lights: the display shows the details you'd normally have to log into a switch to find.

• ●Pass / fail for each test
• ●Assigned IP address and subnet
• ●Default gateway and DNS servers
• ●Switch name and port number
• ●VLAN
• ●Link speed and duplex

When NetTest is plugged into a PoE port, the port powers it on and it starts a full test run automatically, with no buttons needed. On a port without PoE, you turn it on with the battery first, then plug it in.

Each run steps through the checks in order, from the physical link up to the internet, so the first failure tells you exactly where the problem is. Results show on the screen as they come in, and the last few runs are saved on the device so you can walk a building testing drops and review them afterward.

Building on a sub-$100 ESP32 comes with tradeoffs. These are the ones I know about so far.

• Link speed tops out at 100 Mbps

  The ESP32's built-in Ethernet supports 10/100 Mbps only, so NetTest can confirm a link and its duplex but can't negotiate or verify gigabit like the LinkSprinter can. Gigabit support would need a different Ethernet chip, which is a job for the custom PCB.

• PoE details need extra circuitry

  The board can tell when it's running on PoE, but reporting details like PoE class or supplied voltage requires measurement hardware beyond an off-the-shelf board. I'm still deciding whether that's worth adding to the first version.

1. Research & parts sourcing

   In Progress

   Finding an ESP32 board with PoE Ethernet built in, plus the right screen and battery setup

2. First prototype

   Up Next

   Order parts and get a breadboard build running the core tests

3. Firmware

   Planned

   Build out the full test sequence, the on-screen results, and on-device history

4. 3D-printed case

   Planned

   Design an enclosure that fits the board, screen, and battery

5. Build guide

   Planned

   Write documentation good enough for anyone to source parts and build their own

6. Custom PCB

   Planned

   Eventually move everything onto a single custom board

I work on campus networks every day, and a tester like this is one of the most useful tools you can have. Plug it in and you know right away whether a drop is live, which switch port it lands on, and what VLAN it's on.

What bothers me is how much these tools cost. NetTest is my answer to that: powerful network testing at the lowest possible cost, by giving people everything they need to build it themselves.