From owner-freebsd-hackers Wed Aug 7 10:43:30 2002 Delivered-To: freebsd-hackers@freebsd.org Received: from mx1.FreeBSD.org (mx1.FreeBSD.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id 8A18537B400 for ; Wed, 7 Aug 2002 10:43:27 -0700 (PDT) Received: from rwcrmhc51.attbi.com (rwcrmhc51.attbi.com [204.127.198.38]) by mx1.FreeBSD.org (Postfix) with ESMTP id E55D443E70 for ; Wed, 7 Aug 2002 10:43:26 -0700 (PDT) (envelope-from crist.clark@attbi.com) Received: from blossom.cjclark.org ([12.234.91.48]) by rwcrmhc51.attbi.com (InterMail vM.4.01.03.27 201-229-121-127-20010626) with ESMTP id <20020807174326.UQKT19356.rwcrmhc51.attbi.com@blossom.cjclark.org>; Wed, 7 Aug 2002 17:43:26 +0000 Received: from blossom.cjclark.org (localhost. [127.0.0.1]) by blossom.cjclark.org (8.12.3/8.12.3) with ESMTP id g77HhPJK072646; Wed, 7 Aug 2002 10:43:25 -0700 (PDT) (envelope-from crist.clark@attbi.com) Received: (from cjc@localhost) by blossom.cjclark.org (8.12.3/8.12.3/Submit) id g77HhPpt072645; Wed, 7 Aug 2002 10:43:25 -0700 (PDT) X-Authentication-Warning: blossom.cjclark.org: cjc set sender to crist.clark@attbi.com using -f Date: Wed, 7 Aug 2002 10:43:24 -0700 From: "Crist J. Clark" To: Terry Lambert Cc: Brad Laue , freebsd-hackers@FreeBSD.ORG Subject: Re: ifconfig alias and the 0xffffffff netmask Message-ID: <20020807174324.GB71991@blossom.cjclark.org> Reply-To: "Crist J. Clark" References: <3D4F7539.2090201@brad-x.com> <3D4F7F4F.97609D75@mindspring.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <3D4F7F4F.97609D75@mindspring.com> User-Agent: Mutt/1.4i X-URL: http://people.freebsd.org/~cjc/ Sender: owner-freebsd-hackers@FreeBSD.ORG Precedence: bulk List-ID: List-Archive: (Web Archive) List-Help: (List Instructions) List-Subscribe: List-Unsubscribe: X-Loop: FreeBSD.ORG On Tue, Aug 06, 2002 at 12:48:31AM -0700, Terry Lambert wrote: > Brad Laue wrote: > > Minor question regarding this; to recap: > > > > Creating an IP alias on the same subnet as the original seems under > > FreeBSD to require setting the netmask of the alias to 255.255.255.255, > > or at least a subnet of the original. > > > > What impact, if any, will having a /32 netmask on an aliased IP have? > > > > It seems inconsistent with networking practice regarding interface > > aliases, which typically view the aliased IP's simply as distinct hosts > > on the same physical network, allowing them to have the same netmask. > > This method is used with Cisco IOS and other Unix-like operating > > systems. Is it incorrect? > > 255.255.255.255 means "This is an alias IP address". > > The actual netmask in effect is the same netmask as the real > IP address. > > The thing that's broken is that you can't have a different > netmask from that of the real IP address. I've seen you say this before, Terry, and I'm not sure I understand exactly what you are saying is broken. This, ep0: flags=8843 mtu 1500 inet 172.16.0.1 netmask 0xffff0000 broadcast 172.16.255.255 inet 172.16.255.254 netmask 0xffffffff broadcast 172.16.255.254 inet 172.16.2.128 netmask 0xffffff00 broadcast 172.16.2.255 ether 00:20:af:17:0f:11 media: Ethernet 10baseT/UTP Works fine for me. What do you mean by, "you can't have a different netmask from that of the real IP address?" In the case of a 255.255.255.255 netmask, you have a different netmask from the "real" IP address. That's the whole point of using the all-ones mask after all. -- 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-hackers" in the body of the message