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Date: Tue, 23 Jul 2013 16:10:39 +0100
From: Frank Leonhardt <frank2@fjl.co.uk>
Organization: Frank Leonhardt
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To: J.McKeown@ru.ac.za
Subject: Re: dhcp server returns core dump when i define network with mask
 8
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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...