Bill wrote:
Hello Debian,
I want to block all ip's ending in 224 to 255 but not 220 and others
searching the net I found I need to add "/27" to end of the ip.
I understand /8 /16 /24 /32 somewhat but...
My question: what makes /27 significant
X.Y.Z.224 - X.Y.Z.255
deny from 63.148.99.224/27
Thanks
P.s. for example, how would I block only X.Y.Z.23 - X.Y.Z.55 ???
that is <network-address>/<bits-of-subnetmask>
for example if you have a class c network: x.y.z.0-x.y.z.255 you have
the following:
network-address: x.y.z.0
broadcast-address: x.y.z.255
host-addresses: x.y.z.1-254
subnet-mask: 255.255.255.0 - that is 11111111.11111111.11111111.00000000
- 24 ones.
taking your example from above:
x.y.z.224 - x.y.z.255: 255-224=31
that is 1111 (that are 4 bits and the subnet-mask you need is the
complement to the full 32 bits: 28 bits) => x.y.z.224/28
speaking of x.y.z.23 - x.y.z.55: there you have a problem because 23
is no network-address, you can do 16-32+32-64 ord 32-64:
x.y.z.16 - x.y.z.31: 31-16 = 15 => 111 => 3 bits: x.y.z.16/29
x.y.z.32 - x.y.z.63: 63-32 = 31 => 1111 => 4 bits: x.y.z.32/28
you can try google and "subnet calculator" and probably you will find
some helpful javascript or cgi-sites which calculate the numbers above.
regards
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