From owner-freebsd-net Wed Nov 28 22:24:33 2001 Delivered-To: freebsd-net@freebsd.org Received: from femail17.sdc1.sfba.home.com (femail17.sdc1.sfba.home.com [24.0.95.144]) by hub.freebsd.org (Postfix) with ESMTP id A32E837B43F for ; Wed, 28 Nov 2001 22:24:29 -0800 (PST) Received: from lightnin ([65.11.111.111]) by femail17.sdc1.sfba.home.com (InterMail vM.4.01.03.20 201-229-121-120-20010223) with ESMTP id <20011129062429.OEHX5929.femail17.sdc1.sfba.home.com@lightnin> for ; Wed, 28 Nov 2001 22:24:29 -0800 Date: Wed, 28 Nov 2001 22:24:28 -0800 Subject: Re: netmask for aliased ip Content-Type: text/plain; charset=ISO-8859-1; format=flowed Mime-Version: 1.0 (Apple Message framework v475) From: justin@mac.com To: freebsd-net@FreeBSD.ORG Content-Transfer-Encoding: quoted-printable In-Reply-To: <20011128170815.G3985@blossom.cjclark.org> Message-Id: X-Mailer: Apple Mail (2.475) Sender: owner-freebsd-net@FreeBSD.ORG Precedence: bulk List-ID: List-Archive: (Web Archive) List-Help: (List Instructions) List-Subscribe: List-Unsubscribe: X-Loop: FreeBSD.org FWIW, the FreeBSD FAQ (10.9) sez this (it's a one-liner that shows the=20= netmask 0xffffffff). Regards, Justin On Wednesday, November 28, 2001, at 05:08 , Crist J. Clark wrote: > On Wed, Nov 28, 2001 at 08:37:42AM -0800, irado@nettaxi.com wrote: >> >> somebody told me that, when aliasing, the 2nd to =B4n=B4 ipaddress = netmask=20 >> must not be the regular one, but 0xffffffff instead. Example: >> >> rl0 =3D 200.200.200.200 netmask 255.255.0.0 >> rl0:0 (the aliased) 200.200.220.200 netmask 0xffffffff >> [lots more] >> rl0:3000 200.200.255.200 netmask 0xffffffff >> >> is it for real?? what is the reason for this? > > Somebody told you wrong. When adding an alias _which is on the same > logical network_ as other addresses, it should have an 0xffffffff > mask. That is, only one address on an interface should have the "real" > netmask for any one network. > > The simple explanation for this is that if you have, > > a.b.c.d/24 > a.b.c.e/24 > > On an interface and you try to initiate a connection to another > machine through this interface, should your connection use a.b.c.d or > a.b.c.e as the source address? It is ambiguous and can make problems. > > In your case, the addresses lie on different networks. Each address > should have the netmask of the network it is on. Note that you do not > have the above problem in this case. > -- > Crist J. Clark | cjclark@alum.mit.edu > | cjclark@jhu.edu > http://people.freebsd.org/~cjc/ | cjc@freebsd.org > > To Unsubscribe: send mail to majordomo@FreeBSD.org > with "unsubscribe freebsd-net" in the body of the message > > -- /~\ The ASCII Justin C. Walker, Curmudgeon-at-large \ / Ribbon Campaign X Against HTML / \ Email! To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-net" in the body of the message