How is the filter of IP Range calculated in the allow-backend-egress-to-vpc-fwr firewall rule at min 15:22 of Chapter 4 video Custom-Mode VPCs – Challenge Lab Solution – Firewall Rules?
I was looking to do something like that in my solution, but ended up just adding one by one the external IP address of my vms whenever it was necessary.
IP Range depends upon the CIDR block representation. In the video, filter is applied on IP Range: 192.168.0.0/16, this means within the network, all machines which have IP range from 192.168.0.0 to 192.168.255.555 (192.168.0.0, 192.168.0.1 …. 192.168.255.254, 192.168.255.255) will filtered. There are a total of 65536 IP addresses (2 power 16).
Here is the small online utility which will help you list the range of Ip address (First IP to Last IP) for a given IP CIDR Block
Hope this helps!