Date: Wed, 11 Feb 2015 18:51:42 +0800 From: Julian Elischer <julian@freebsd.org> To: Matt Churchyard <matt.churchyard@userve.net>, "freebsd-net@freebsd.org" <freebsd-net@freebsd.org> Subject: Re: Invalid subnet masks Message-ID: <54DB343E.7090008@freebsd.org> In-Reply-To: <ecc9027578ce45d7a0436e345aadc249@SERVER.ad.usd-group.com> References: <7e069c1946454793b1c7e0be988877c4@SERVER.ad.usd-group.com> <DE405399-70FE-48A3-B550-992EDEB5C468@netapp.com> <ecc9027578ce45d7a0436e345aadc249@SERVER.ad.usd-group.com>
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On 2/11/15 5:55 PM, Matt Churchyard wrote: > > I appreciate that it might be 'valid' as a binary mask, but I'm struggling to find any documentation anywhere that actually suggests that it's valid as a network configuration. The entire modern CIDR notation, and all the routing system & hardware built around it (that shows networks in CIDR form and will collapse routes) has no way of dealing with these subnets. most can deal with it, just not optimally > > 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 middle two quarters were separate nets. Sure, it made my skin crawl, but I was in a pinch to get more machines onto that /26. all four were served by the same router so only one router needed to know.. I have however at times though we could think about making ifconfig at give a warning. (but not an error). > I'm learning towards the opinion that they should be rejected unless the user specifically overrides it (with something like an ifconfig flag or sysctl). Although having said that, it's not really doing any damage letting people get their netmasks wrong. However, as I mentioned in my first email, Windows 8.1 (and I've now tested Server 2012 which is fairly common in enterprise globally...) will not allow them. > _______________________________________________ > freebsd-net@freebsd.org mailing list > http://lists.freebsd.org/mailman/listinfo/freebsd-net > To unsubscribe, send any mail to "freebsd-net-unsubscribe@freebsd.org" >
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