Date: Thu, 28 Aug 2003 08:49:57 -0300 From: "Daniel C. Sobral" <dcs@tcoip.com.br> To: Olivier Nicole <on@cs.ait.ac.th> Cc: freebsd-net@freebsd.org Subject: Re: subnetting C class into /26 /25 /26, why can this be done? Message-ID: <3F4DEC65.3080808@tcoip.com.br> In-Reply-To: <200308280245.JAA19927@banyan.cs.ait.ac.th> References: <3F4CBA6A.5AA7DEB0@cvt.dk> <3F4D0968.5050800@tcoip.com.br> <200308280245.JAA19927@banyan.cs.ait.ac.th>
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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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Daniel.Sobral@tcoip.com.br
dcs@tcoip.com.br
Outros:
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capo@notorious.bsdconspiracy.net
For there are moments when one can neither think nor feel. And if one can
neither think nor feel, she thought, where is one?
-- Virginia Woolf, "To the Lighthouse"
[Quoted in "VMS Internals and Data Structures", V4.4, when
referring to powerfail recovery.]
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