CIDR block 10.0.96.32/18 overlaps with pre-existing CIDR block 10.0.96.0/28 from subnet

Question

Wondering how does this overlap, it seems like it comes afterward.

CIDR block 10.0.96.32/18 overlaps with pre-existing CIDR block 10.0.96.0/28 from subnet-3fa92058.

Answer 1

Convert each quad to binary...

$ dc -e '2o 10p 0p 96p 32p' | xargs printf '%08d\n'
00001010
00000000
01100000
00100000

Now you've got the IP address as a binary number:

00001010000000000110000000100000
|       |       |       |

The first 18 bits of that represent the network for this IP address...

00001010000000000100000000000000
******************--------------

Which, if you convert back to dotted quad notation, look like this:

$ dc -e '2i 00001010 p 00000000 p 01000000 p 00000000 p'
10
0
64
0

So, 10.0.64.0/18. You can also calculate your broadcast:

$ dc -e '2i 00001010 p 00000000 p 01111111 p 11111111 p'
10
0
127
255

Or, 10.0.127.255/18.

And the network 10.0.96.0/28 is certainly within this range.