The IP address 192.168.3.129 : Class C Networks
Secure IP address This IP is only local, it is not accessible from outside the network
This means that the IP address is not accessible from the Internet, it is local and only accessible within the network. Everyone has the same local address (192.168.0.0 - 192.168.255.255).
Each device (laptop, printer, scanner, phone, surveillance camera, tablet, ...) has a unique local IP address assigned by the adsl box that allows the box to identify the different devices to within a local network and send the right product at the right flow.
Specifically, the adsl box has a public IP address in your case, which connects to the Internet and the box assigns a local address to all devices to identify them.
The IP address 192.168.3.129 detail
The IP address 192.168.3.129 (IPv4 Class C Networks) belonging to the network 192.168.0.0 - 192.168.255.255 is written in long version -1062730879.
Addresses on the same network : 192.168.3.0 192.168.3.1 192.168.3.2 192.168.3.3 192.168.3.4 192.168.3.5 192.168.3.6 192.168.3.7 192.168.3.8 192.168.3.9 192.168.3.10 192.168.3.20 192.168.3.30 192.168.3.40 192.168.3.50 192.168.3.60 192.168.3.70 192.168.3.80 192.168.3.90 192.168.3.100 192.168.3.200 192.168.3.254 192.168.3.255