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

[Daniel C. Sobral]

Olivier Nicole wrote:
> Christoffer Pio wrote:
> 
>>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?
> 
> 
> I think you got explanations on the why.
> 
> Now it should still be possible to subnet the way you want I think.
> 
> While I would never recommend it, think routing should go with the
> most significant mask for a given address.
> 
> So if you subnet:
> 
> 1) x.x.x.0/26
> 2) x.x.x.192/26
> 3) x.x.x.0/24
> 
> you should be able to do the trick.
> 
> An address in the range 0-63 will match both mask 1) and 3) but mask
> 1) is most significant (more bits, higer value) so the packet will be
> routed to subnet 1).
> 
> Same thing for a packet in the range 192-255, with subnet 2) and 3),
> it will be router to subnet 2).
> 
> And a packet in the range 64-191 will only match the subnet 3) so it
> will go to the subnet 3).
> 
> IF I AM NOT WRONG, this should work, but it is definitely nasty.
> 
> If you absolutely need 2 subnets of 64 addresses and one of 128,
> doing:
> 
> 1) x.x.x.0/26
> 2) x.x.x.64/26
> 3) x.x.x.128/25
> 
> is nicer and will result in the ranges 0-64, 64-127 and 128-255.

Yes, but any host in the 64-191 range will need to be configured with a 
/24 net mask *and* have static routes for 0-63 and 192-255. And I'm not 
even completely sure that will work.

-- 
Daniel C. Sobral                   (8-DCS)
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