Network Scanner

"What's on my network?" - discovers devices on your own local network using two complementary, entirely local techniques. No root required, no cloud dependency.

Usage

"scan the network"
"can you see my Sony TV"
"is my printer on the network"
"scan netværket"                (Danish)
"kan du se min printer"         (Danish)

How it finds devices

1. mDNS/Bonjour (via zeroconf) - most consumer smart devices (Chromecast, HomeKit accessories, printers, many smart speakers) announce themselves on the network. Gives a clean, self-reported name, but only for devices that participate in mDNS - plenty of devices (including many robot vacuums, which talk only to a cloud service) never announce themselves at all, no matter how good the scanner is.

2. Ping sweep + ARP + MAC vendor lookup - catches devices that don't announce themselves. Pings every address in the local /24 subnet (parallelized, a few seconds), reads the OS's own ARP cache to get each responder's MAC address, looks up the MAC's manufacturer via mac-vendor-lookup's bundled offline IEEE database, and tries a reverse-DNS lookup for a hostname. Needs no special privileges - sending a ping via the system binary and reading the ARP cache are both unprivileged operations; only actively rewriting the ARP table would need root, and this skill never does that.

Why both

They catch different, only-partially-overlapping devices:

• mDNS gives a clean name, but only for announcing devices.
• Ping+ARP+vendor catches almost anything with an IP, but only gives a manufacturer guess ("a Sony Corporation device") - never a specific model, and even that guess can be missing entirely, since many modern phones/tablets randomize their MAC address by default for privacy, which breaks vendor lookup completely for those devices.

A real, honest limit: you only see what announces itself

If a device is genuinely silent on both fronts - no mDNS, doesn't respond to ping, or (rarer) has no reverse-DNS entry and an unrecognized/randomized MAC - it won't show up, no matter how the scanning is done. A robot vacuum that only talks to its manufacturer's cloud service is invisible to this skill, and there's no way around that from the local network side.

Local-subnet-only - a protocol property, not a policy

mDNS multicast and ARP do not cross routers by design - both techniques are physically incapable of seeing anything outside this device's own local subnet, regardless of any code here. This is not a restriction imposed by this skill; it's just what these protocols do.

Known rough edge

A single physical device can advertise several different mDNS names for different services on the same IP (observed during real testing: one machine advertised both a caching-service name and a separate KDE Connect ID on the same address). Since each IP here only keeps one name, whichever service happens to be processed last wins - not a stable, deterministic choice. Not fixed in this release.

Install

pip install ovos-skill-network-scanner

Development

See DEVELOPMENT.md.

Category

Utility

Tags

#network #scanner #mdns #discovery #lan