subnetting C class into /26 /25 /26, why can this be done?

[Clark Gaylord]

When in doubt, do it in binary:
   0 = 00000000
  64 = 01000000
 128 = 10000000
 192 = 11000000
As a /26 (taking as given the 24 x's not shown for the other three octets):
       xxyyyyyy - y's are the host
                  xx doesn't have the same value from 64-191
As a /25:
       xyyyyyy - y's are the host
                 x doesn't have the same value from 64-191

A /26 means there are 26 bits of network and 6 bits of host; a /25 means 25
bits of network and 7 for host.

As /26's xx = {00, 01, 10, 11} for the four distinct values, with the other
six bits signifying the host address.  As /25s x = {0, 1} are the two
distinct values.  Now, you could use 0/25 (as 0-127 all have same first bit)
and 128/26 and 192/26 as each of these network address bits (10 and 11) stay
the same through the respective block of addresses.

Hopefully this helps.
Clark

> -----Original Message-----
> From: owner-freebsd-net at freebsd.org 
> [mailto:owner-freebsd-net at freebsd.org] On Behalf Of Christoffer Pio
> Sent: Wednesday, August 27, 2003 10:04 AM
> To: freebsd-net at freebsd.org
> Subject: subnetting C class into /26 /25 /26, why can this be done?
> 
> 
> Is it not possible to subnet a C class into 3 nets, like
> 
> 0-63
> 64-191  <-- Offending network (?)
> 192-255
> 
> If so, why is this?
> 
> Christoffer
> _______________________________________________
> freebsd-net at freebsd.org mailing list 
> http://lists.freebsd.org/mailman/listinfo/f> reebsd-net
> To 
> unsubscribe, send any mail to 
> "freebsd-net-unsubscribe at freebsd.org"
>