On Tue, 10 Sep 2002, Paul Hess wrote:
> Could someone point me towards a simple resource or a calculator program to
>understand the *.*.*.*/XX notation and how to convert it to an address range?
The yy in x.x.x.x/yy is the number of bits in the netmask.
192.168.1.0/24 has 24 set bits (ones), counting from left to right, in the
netmask:
11111111 11111111 11111111 00000000
So that's basically the same as 255.255.255.0
10.0.0.0/8 has eight:
11111111 00000000 00000000 00000000
or 255.0.0.0.
Now the 'mask' part of the netmask comes in. If you've got a network like
192.168.1.0/24, those ones 'mask' the part of the address that doesn't
change.
address: 11000000 10101000 00000001 00000000 = 192.168.1.0
netmask: 11111111 11111111 11111111 00000000 = 255.255.255.0
The bits that aren't 'masked' by ones can change.
Another example: 172.16.0.0/20
address: 10101100 00001000 00000000 00000000 = 172.16.0.0
netmask: 11111111 11111111 11110000 00000000 = 255.255.240.0
That's the low end of the range. If you set the 'unmasked' bits to all
ones, you'll get the high end of it:
address: 10101100 00001000 00001111 11111111 = 172.16.31.255
netmask: 11111111 11111111 11110000 00000000 = 255.255.240.0
these bits don't change ^^^^ 'cause they're masked
So, for a address range specified as 172.16.0.0/20, the low end (all zeros
in the unmasked portion) it 172.16.0.0. The high end (all ones in the
unmasked portion) is 172.16.31.255.
-jrs
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