From owner-freebsd-net@FreeBSD.ORG Wed Feb 11 14:56:10 2015 Return-Path: Delivered-To: freebsd-net@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by hub.freebsd.org (Postfix) with ESMTPS id 77F6A389 for ; Wed, 11 Feb 2015 14:56:10 +0000 (UTC) Received: from mail-oi0-f48.google.com (mail-oi0-f48.google.com [209.85.218.48]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (Client CN "smtp.gmail.com", Issuer "Google Internet Authority G2" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id 38237B2D for ; Wed, 11 Feb 2015 14:56:09 +0000 (UTC) Received: by mail-oi0-f48.google.com with SMTP id a3so15905080oib.7 for ; Wed, 11 Feb 2015 06:56:03 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:content-type:mime-version:subject:from :in-reply-to:date:cc:content-transfer-encoding:message-id:references :to; bh=/TuT1tb/dLERFHtKst+jNFwSMCDlL5Qwkpg/7WYxhgk=; b=FTCkESFHlHKhLE1xeDofn9Y9Auo6FSrgJGW7bPvZcqduW3oscm5QV0kQEmrVqTO5nZ WtBLxzvgHlV0H6wvl7h2jyIttHsbwLYO/PyxX0JVT4kRC9OZILuWOS5x1WTfloyRUUyn xif4qzmjN11JHdO4ebMF3Z4A4fSb/0fHfhc0yEJ8sbTMNx/BNV0Q5M170y7U9uIPr3Q/ Py5ZjpalOtnHcZow84soe2DZmXKYa7yr5tiPUa7NiQnPannYHGa8EE0+JV1GG3gj9946 ipHa1p2twggaZbg+mk1cP8QAAHydCAFJeVq5SmA+HJI2Glk8bj8+JCoShEzsheTaU/Y8 3AoA== X-Gm-Message-State: ALoCoQmhZ8BXlICFbxa2RLc0UaNv2yy/gempKk2yO4jUnbrFrZaPjRE9BacacP9nJAaYVGqafFwY X-Received: by 10.202.227.11 with SMTP id a11mr18663289oih.9.1423665031386; Wed, 11 Feb 2015 06:30:31 -0800 (PST) Received: from [172.21.0.96] (65-36-83-120.static.grandenetworks.net. [65.36.83.120]) by mx.google.com with ESMTPSA id km8sm405049oeb.11.2015.02.11.06.30.30 (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Wed, 11 Feb 2015 06:30:30 -0800 (PST) Mime-Version: 1.0 (1.0) Subject: Re: Invalid subnet masks From: Jim Thompson X-Mailer: iPad Mail (12B466) In-Reply-To: <54DB343E.7090008@freebsd.org> Date: Wed, 11 Feb 2015 08:30:28 -0600 Message-Id: <580B0DA4-05B3-45B8-ACB9-27B9174D76A8@netgate.com> References: <7e069c1946454793b1c7e0be988877c4@SERVER.ad.usd-group.com> <54DB343E.7090008@freebsd.org> To: Julian Elischer Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: quoted-printable X-Content-Filtered-By: Mailman/MimeDel 2.1.18-1 Cc: "freebsd-net@freebsd.org" , Matt Churchyard X-BeenThere: freebsd-net@freebsd.org X-Mailman-Version: 2.1.18-1 Precedence: list List-Id: Networking and TCP/IP with FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 11 Feb 2015 14:56:10 -0000 > On Feb 11, 2015, at 4:51 AM, Julian Elischer wrote: >=20 >> On 2/11/15 5:55 PM, Matt Churchyard wrote: >>=20 >> I appreciate that it might be 'valid' as a binary mask, but I'm strugglin= g to find any documentation anywhere that actually suggests that it's valid a= s a network configuration. The entire modern CIDR notation, and all the rout= ing system & hardware built around it (that shows networks in CIDR form and w= ill collapse routes) has no way of dealing with these subnets. > most can deal with it, just not optimally >>=20 >> Are there actually valid use cases for these types of network? > yes. > I've had networks that were the first and last quarter of a /24, and the m= iddle two quarters were separate nets. >=20 > Sure, it made my skin crawl, but I was in a pinch to get more machines ont= o that /26. > all four were served by the same router so only one router needed to know.= . >=20 > I have however at times though we could think about making ifconfig at giv= e a warning. > (but not an error). https://lists.freebsd.org/pipermail/freebsd-hackers/2011-April/034997.html Subject came up on -hackers in 2011 Quoting RFC-1219: "While RFC-950 allows the "ones" in the subnet mask to be non-contiguous, RFC= -950 recommends that 1) they be contiguous, and 2) that they occupy the most= significant bits of the "host" part of the internet address." Jim