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Re: [vox-tech] question about ip addresses and netmasks
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Re: [vox-tech] question about ip addresses and netmasks



Thanks dale, that made sense

Jay Strauss
jjstrauss@yahoo.com

----- Original Message -----
From: "Dale Bewley" <dale@bewley.net>
To: <vox-tech@franz.mother.com>
Sent: Tuesday, February 20, 2001 4:21 PM
Subject: Re: [vox-tech] question about ip addresses and netmasks


> I have a hard time explaining it to other people, but
> you have to picture the binary number in your head and after a while you
> memorize most of these.
>
>
> To convert /30 to the mask I say to myself:
> 32-30=2 bits
> 2 bits can create a maximum of 4 in decimal
> 256-4=252
> so the netmask is 255.255.255.252.
>
>
> Once you do enough of that, you quickly see 252 and think /30.
> Or see 240 and think /28. (256-240=16 which is 2^4 and 32-4=28)
>
> 255.255.254.0 would be /23 meaning 23 bits in the netmask.
> If you subtract 254 from 256 you'll get 2. That tells you you have two
> /24 subnetworks.
>
>
> It gets more complicated when you are peeling off a /29 or something in
> the middle of the range from 0-255. You have to make sure you network
> starts on a boundary divisible by 8. (32-29=3bits = max of 8)
>
> i.e. For the address 1.2.3.74/28 what is the broadcast address and what
> is the subnet?
> It's 1.2.3.79 and 1.2.3.72. The next subnet starts at .80 so the
> broadcast is one below that.
>
> Sorry if that wasn't much help.
> If anyone has a easier way to explain that, please do.
> I probably should have just kept my mouth shut. :)
>
>
>
> On Tue, 20 Feb 2001, Peter Jay Salzman wrote:
> > is there a way to see, without converting numbers to binary and performing a
> > a bitwise and, that:
> >
> > 131.155.72.0/255.255.254.0
> >
> > means all addresses from 131.155.72.0 through 131.155.73.255?  is there
> > short cut for this?
> >
> > something like "255 means that quad is firm, 254 means you can go one
> > higher, and 0 means the quad can be anything"?  i know that's "loose talk",
> > but is it generally true?
> >
> > pete
> >
> > --
> > "It's better to be safe than assimilated."                   p@dirac.org
> >                       -- Chakotay                            www.dirac.org/p
> >
>
> --
> Dale Bewley - Bewley Internet Solutions Inc. http://bewley.net/


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