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List:       suse-linux-uk-schools
Subject:    Re: [suse-linux-uk-schools] Some showstopping network issues..
From:       Bill Antonia <at () beacon ! e-sussex ! sch ! uk>
Date:       2002-06-27 9:24:00
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> > I may be trying to teach Granny to suck eggs here but you cannot flout the
> > rules.
> > 
> > Subnet masks must always be a series of 1's then 0's. You cannot mix and
> > match. The mask is used to separate the host and network portions ie the
> > last non-zero octet must always be one of 192, 224, 240, 248 or 252 (254 is
> > allowed in Class A in the second or third octet or Class B in the third
> > octet but not in either case the fourth octet). 128 is also not allowed to
> > be the next octet from the standard netmask for each class in subnetting.
> > 
> > All the following netmasks allow no hosts
> > Class A netmasks 255.255.255.254 or 255.128.0.0.0
> > Class B netmasks 255.255.255.254 or 255.255.128.0
> > Class C netmasks 255.255.255.254 or 255.255.255.128
> 
> The idea of classes A, B and C is something like a decade out of date,
> the original idea was that the subnet mask could be worked out by
> looking at the first octet of the IP address.

Classes are still linked to the first octet
A 0xxxxxxx
B 10xxxxxx
C 110xxxxx
D 1110xxxx
E 1111xxxx

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