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From: brian@shift.utell.net (Brian Somers)
Newsgroups: comp.unix.bsd.freebsd.misc
Subject: Re: User PPP
Date: 23 May 1997 09:47:03 GMT
Organization: Awfulhak Ltd.
Message-ID: <5m3p2n$ic4@ui-gate.utell.co.uk>
References: <Pine.BSI.3.95.970519184616.5906A-100000@gold.interlog.com>
<86yb97tiis.fsf@bitbox.follo.net> <EALotq.1Bw@sphynx.fdn.fr>
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In article <EALotq.1Bw@sphynx.fdn.fr>,
causse@sphynx.fdn.fr (Philippe Causse) writes:
> BTW, I never heard about non-continuous netmasks... What are they ?
> TIA.
It's one where the netmask isn't all contiguous 'one's. ie. if
you have a netmask of 255.255.255.184.
11111111.11111111.11111111.10111000
And an IP number of 1.2.3.4
00000001.00000010.00000011.00000100
then my net address is 1.2.3.0 and my broadcast is 1.2.3.71.
*BUT* my network doesn't encompass all 72 values. It just
covers 1.2.3.0-1.2.3.7 and 1.2.3.64-1.2.3.71 - 16 addresses
in all. This 16 addresses can easily be deduced by
counting the bits in the netmask - same as usual. Just
shuffle them all to the left and see how big a number you
can fit in the zeros.
This phenomena is a result of a changing network that has
very little unused space (or probably a school exercise).
You end up with a chunk of IP numbers allocated in the middle
of a bigger chunk, and you need to offer the free bits on either
side of the used bit as one network.
Best avoided if you ask me. It takes too long to figure
out what the hell is going on :I
>: Eivind.
> Philippe.
--
Brian <brian@awfulhak.org> <brian@freebsd.org>
<http://www.awfulhak.org>
Don't _EVER_ lose your sense of humour !