Date: Tue, 23 Jul 2013 16:10:39 +0100 From: Frank Leonhardt <frank2@fjl.co.uk> To: J.McKeown@ru.ac.za Cc: freebsd-questions@freebsd.org Subject: Re: dhcp server returns core dump when i define network with mask 8 Message-ID: <51EE9CEF.6030105@fjl.co.uk> In-Reply-To: <20130723143522.818353lrdr4lo5u2@webmail.ru.ac.za> References: <CAA_1SgGFpBCnxWf4tKa3--nZiYhDgyiEcwvrfsUodxiOwMNfdg@mail.gmail.com> <loom.20130723T095802-729@post.gmane.org> <51EE3E2C.2090203@fjl.co.uk> <CAA_1SgGtZzVJscEsR5GADRH_o-3t2u_1YRmckP%2BYe7Qt74w_xg@mail.gmail.com> <51EE4A63.9040909@fjl.co.uk> <20130723143522.818353lrdr4lo5u2@webmail.ru.ac.za>
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On 23/07/2013 13:35, J.McKeown@ru.ac.za wrote: > Quoting Frank Leonhardt <frank2@fjl.co.uk>: > >> >> There are two common ways of defining a subnet mask - one is a dotted >> quad (e.g. 255.255.255.0) and the other is with a slash and the >> number of low-order bits - e.g. 192.168.1.0/8. Eight bits here means >> you get 2^8 addresses (i.e. 256). Don't use the first and last >> address in the range - the first is "complicated" (the network >> address) and the last is for broadcast packets. This doesn't always >> hold true but you're unlikely to come across exceptions. > > This is the wrong way round. the number after the slash indicates the > number of bits in the network address - the high-order bits. > >> So, when you say you want to define a "network with mask 8" I don't >> really know what you mean from your example. Do you mean a /8? >> >> 192.168.1.0/8 = range 192.168.1.1 192.168.1.254 with a subnet mask >> of 255.255.255.0 (0xFFFFFF00) > > Nope. 192.168.1.0/24 = 192.168.1.1-255 mask 255.255.255.0. > 192.168.1.0/8 doesn't start where you think it does (and is arguably > the wrong way to specify that network) because all but the first 8 > bits are masked out - it's 192.0.0.0 - 192.255.255.255. Quite correct - for some reason I got that bit backwards when I'm using it every day the right way around. It's ludicrously hot and humid in London at the moment, lack of sleep caused thereby &c...
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