I tried:

192.168.100.2 for windows PC
255.255.255.0 netmask.

The cable modem remains unaccessable from the local LAN.

So your knowledge of this is now completely useless, because of either:

1. It's locked by the ISP, these cable modems can only be accessed from the outside.

2. It's a bug/problem, modem was resetted.

Most likely cause is locking/updating of the cable modem bios/firmware.

There was a thread on the internet about people locating their public IPs of their cable modems, this is more difficult to do then it seems.

A tracert will probably not report it because the cable modem does not take part in the trace and does not reveal itself ? Or there is another reason for it.

If you know how to find my public IP address of my Cable modem I am all ears, cause this is interesting stuff.

And apperently it is something completely different than my Windows PC public IP address which I can tell you right now is simply:

85.25.113.203

mask

255.255.254.0

gateway

84.25.112.1

dhcp

10.255.235.1

Scan/do with it what you want

Bye,
Skybuck.