Finding what's after the slash

[Barry Margolin]

In article <00051114144601.00395 at sparc1.np.rbp.com.br>,
augusto bott  <augusto.bott at via-rs.net> wrote:
>I've seen lots of messages, texts and pages around and was trying to figure
>out how one can know what to write after a slash ("/") on a subnet...
>
>like, for instance, 10.1.1.0/26 meaning ip's from 10.1.1.1 untill 10.1.1.50
>(is this statement correct?)

No.  It goes from 10.1.1.0 to 10.1.1.63.

Subnets are always a power of 2 in size.

>i.e., for a net like 192.168.2.45 untill 192.168.2.221 it would be what?
>Thanks...

The smallest block that encompasses that range is 192.168.2.0/24, i.e. the
whole class C.

The number after the slash is the number of 1-bits in the corresponding
subnet mask.  If you're looking for a simple formula, for subnets of a
class C (i.e. only the last byte varies), subtract the last byte of the
mask from 256, determine what power of 2 that is, and then add that to 24.

-- 
Barry Margolin, barmar at genuity.net
Genuity, Burlington, MA
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