Date: Thu, 28 Aug 2003 09:45:09 +0700 (ICT) From: Olivier Nicole <on@cs.ait.ac.th> To: freebsd-net@freebsd.org Subject: Re: subnetting C class into /26 /25 /26, why can this be done? Message-ID: <200308280245.JAA19927@banyan.cs.ait.ac.th> In-Reply-To: <3F4D0968.5050800@tcoip.com.br> (dcs@tcoip.com.br) References: <3F4CBA6A.5AA7DEB0@cvt.dk> <3F4D0968.5050800@tcoip.com.br>
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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. Olivier
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