I noticed when trying to create a vpc with a cidr range of 10.200.113.0/20 that this is not a valid range. I can either do a range of 10.200.112.0/20 or 10.200.128.0/20.
I haven’t come across this limitation before and would like to educate myself more on this subject. Why is this the case and what rules govern the starting points of cidr blocks. Are there specific sections within RFC which may address this particular situation?
>Solution :
I highly recommend the use of a CIDR Calculator such as: https://cidr.xyz/
- A CIDR of
10.200.112.0/20goes from10.200.112.0to10.200.127.255 - A CIDR of
10.200.128.0/20goes from10.200.128.0to10.200.143.255
The /20 is saying that the first 20 bits are ‘fixed’ and the remaining 12 bits can change. The CIDR range of 10.200.113.0 does not start on a /20 boundary (with the first 20 bits unchanging) and is therefore invalid.
See also: Classless Inter-Domain Routing – Wikipedia