Question : Network Address Range - CIDR Notation - Explaination Please?

Hello All;

  We are fixing to correct a lot of bad Entries from our SMTP BLOCK LIST in our Mail Server.
The following information we are needing to find out.
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IP Address
172.16.0.0 - 172.31.255.255  /12

If I was to enter the:   172.16.0.0        into our IP Field. And then Enter   172.31.255.255   into our MASK field.
Would that mean that it will look at and BLOCK out everything from    172.16.0.0 - 172.31.255.255

I am understanding that correctly?

10.0.0.0 - 10.255.255.255 /8   --> I add this in, and it BLOCKS everything in that range.
172.16.0.0 - 172.31.255.255 /12  --> This I am not sure about?
192.168.0.0 - 192.168.255.255 /16  --> This block everything in that range

Thanks all;
Carrzkiss

Answer : Network Address Range - CIDR Notation - Explaination Please?

You  might just want to get an IP subnet calculator
http://lantricks.com/lancalculator/
Easier to just work with the calculator than try to understand it all.
Took me a loooonnnnnggggg time to understand that subnet mask is nothing more than a binary string of 1's ... where the 1's stop, that determines the network ID and where the 0's start determines the host ID

255.0.0.0 = 11111111.00000000.00000000.00000000
255.255.0.0 = 11111111.11111111.00000000.00000000
255.255.255.0 = 11111111.11111111.11111111.00000000

255.255.254.0 = 11111111.11111111.11111110.00000000


http://www.learntosubnet.com/