netdiag

netdiag is a small home-network diagnostic tool for this path:

PC -> WiFi/router -> optical modem/ONT -> ISP -> public internet

It samples each layer with ping, writes CSV, then prints a diagnosis based on packet loss, p95 latency, jitter, and latency increase between layers.

It also writes a self-contained HTML report next to the CSV. The report includes the diagnosis, target list, summary table, p95 bars, and per-sample details.

Build

cd ~/netdiag
go build -o netdiag .

Quick run

cd ~/netdiag
./netdiag -duration 5m

By default it automatically detects your default gateway as the PC -> WiFi/router target and also pings several public DNS IPs.

Better run with modem and ISP targets

If your router can reach the optical modem management IP, add it:

./netdiag -duration 10m -modem 192.168.1.1

If you know the ISP first-hop gateway, add it too:

./netdiag -duration 10m -modem 192.168.1.1 -isp 10.4.32.1

You can usually find the ISP hop with traceroute, mtr, or from your router status page.

How to read the result

• Bad router: likely PC WiFi signal, WiFi interference, PC wireless card, or router LAN/WiFi side.
• Good router but bad modem: likely router-to-optical-modem link, router WAN port/cable, or optical modem LAN side.
• Good router/modem but bad isp: likely optical line, PPPoE/access network, or ISP first hop.
• Good local hops but bad public targets: likely ISP backbone, peering, DNS/public route, or remote network.

CSV output is written to result/netdiag-<timestamp>.csv unless -out is provided. HTML output is written to result/netdiag-<timestamp>.html unless -html is provided.