The IP address 172.21.243.250 : Class B networks
Secure IP address This IP is only local, it is not accessible from outside the network
Rating: 5
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 (172.16.0.0 - 172.31.255.255).
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 172.21.243.250 detail
The IP address 172.21.243.250 (IPv4 Class B networks) belonging to the network 172.16.0.0 - 172.31.255.255 is written in long version -1407847430.
Color obtained mathematically from the IP address: Bright violet
Addresses on the same network : 172.21.243.0 172.21.243.1 172.21.243.2 172.21.243.3 172.21.243.4 172.21.243.5 172.21.243.6 172.21.243.7 172.21.243.8 172.21.243.9 172.21.243.10 172.21.243.20 172.21.243.30 172.21.243.40 172.21.243.50 172.21.243.60 172.21.243.70 172.21.243.80 172.21.243.90 172.21.243.100 172.21.243.200 172.21.243.254 172.21.243.255