From owner-freebsd-net@FreeBSD.ORG Thu Aug 28 04:50:15 2003 Return-Path: Delivered-To: freebsd-net@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id C511D16A4BF for ; Thu, 28 Aug 2003 04:50:15 -0700 (PDT) Received: from mail.tcoip.com.br (erato.tco.net.br [200.220.254.10]) by mx1.FreeBSD.org (Postfix) with ESMTP id C318E43FBD for ; Thu, 28 Aug 2003 04:50:11 -0700 (PDT) (envelope-from dcs@tcoip.com.br) Received: from tcoip.com.br ([10.0.2.6]) by mail.tcoip.com.br (8.11.6/8.11.6) with ESMTP id h7SBnwj01243; Thu, 28 Aug 2003 08:50:00 -0300 Message-ID: <3F4DEC65.3080808@tcoip.com.br> Date: Thu, 28 Aug 2003 08:49:57 -0300 From: "Daniel C. Sobral" User-Agent: Mozilla/5.0 (X11; U; FreeBSD i386; en-US; rv:1.4) Gecko/20030702 X-Accept-Language: en-us, en, pt-br, ja MIME-Version: 1.0 To: Olivier Nicole References: <3F4CBA6A.5AA7DEB0@cvt.dk> <3F4D0968.5050800@tcoip.com.br> <200308280245.JAA19927@banyan.cs.ait.ac.th> In-Reply-To: <200308280245.JAA19927@banyan.cs.ait.ac.th> Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit cc: freebsd-net@freebsd.org Subject: Re: subnetting C class into /26 /25 /26, why can this be done? X-BeenThere: freebsd-net@freebsd.org X-Mailman-Version: 2.1.1 Precedence: list List-Id: Networking and TCP/IP with FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 28 Aug 2003 11:50:15 -0000 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) Gerencia de Operacoes Divisao de Comunicacao de Dados Coordenacao de Seguranca VIVO Centro Oeste Norte Fones: 55-61-313-7654/Cel: 55-61-9618-0904 E-mail: Daniel.Capo@tco.net.br Daniel.Sobral@tcoip.com.br dcs@tcoip.com.br Outros: dcs@newsguy.com dcs@freebsd.org 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.]