I notice on the Network tab that one of the host devices on my home network is not displayed. Scanning for devices simply doesn’t find it.
I’m referring to my cable modem’s local LAN-facing network interface, which has as IP address of 192.168.100.1. (it is pingable and there is even a web server running on that IP address for configuring the cable modem – an IP address I can reach directly from my PC that I’m running Glasswire on).
Glasswire can see my router (192.168.1.1) and all the other devices connected to my router, but just not the cable modem (192.168.100.1) which is also connected directly to my router.
Technically, being able to ping a device and access its web interface doesn’t make it a device on your LAN.
First, the cable modem normally functions as a bridge between your router and your ISP’s network. That’s why it doesn’t normally show up on a trace route to the Internet. It’s also on the other side of the router which denotes the boundary of your LAN.
Second, on a home network/LAN the normal subnet mask is 255.255.255.0 (called Class C). This means only devices with IP addresses that change the last number (byte/octet) are detected. Anything with the IP address 192.168.1.# is found but 192.168.#.# will not be unless the third number is the same as for the router. Note: # represents numbers 0 to 254, 255 is reserved for broadcasting.
To see the cable modem on the router subnet we normally have to use a static route. As in this diagrammatic example to give your cable modem an address in the same range as the router is assigning:
The IP address of the cable modem is hard-coded. I’ve added a static, persistent route on my PC to the subnet of the cable modem, specifying the router as the gateway. But Glasswire still can’t see that device.
C:\>tracert 192.168.100.1
Tracing route to 192.168.100.1 over a maximum of 30 hops
1 <1 ms <1 ms <1 ms 192.168.1.1
2 <1 ms <1 ms <1 ms 192.168.100.1
Trace complete.
I think, at the very least, Glasswire should be parsing my local routing table and taking that into account when deciding what subnets to scan (within the private IP address space).