https://www.youtube.com/watch?v=kWhIwlNkZm4

https://www.patreon.com/cloudtutorials

https://stackoverflow.com/questions/51734945/cidr-address-is-not-within-cidr-address-from-vpc

An IPv4 address consists of 32 bits.

1. /32 in CIDR x.x.x.x/32 means use all 32 bits to form a range of addresses. In this case just one IP address is possible.

2. /24 in CIDR x.x.x.0/24 means fix the first 24 bits and use last 8 bits to form a range of addresses. In this case, there can be 2^8 IP addresses i.e. from x.x.x.0 to x.x.x.255.

3. /16 in CIDR x.x.0.0/16 means fix the first 16 bits and use the last 16 bits to form a range of addresses. In this case, there can be 2^16 IP addresses i.e. from x.x.0.0 to x.x.255.255.

4. /8 in CIDR x.0.0.0/8 means fix the first 8 bits and use the last 24 bits to form a range of addresses. In this case, there can be 2^24 IP addresses i.e. from x.0.0.0 to x.255.255.255.

5. /0 in CIDR 0.0.0.0/0 means fix the first 0 bits and use the last 32 bits to form a range of addresses. In this case, all the possible IP addresses are included in the range.

https://en.wikipedia.org/wiki/Classless_Inter-Domain_Routing#CIDR_notation