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Date:      Thu, 27 May 1999 13:25:17 -0700
From:      "David Schwartz" <davids@webmaster.com>
To:        "Jasper O'Malley" <jooji@webnology.com>, "Dan Langille" <junkmale@xtra.co.nz>
Cc:        <freebsd-chat@freebsd.org>
Subject:   RE: Mickey Mouse networking...
Message-ID:  <000201bea87f$08a86840$021d85d1@whenever.youwant.to>
In-Reply-To: <Pine.LNX.4.02.9905271359260.30337-100000@mercury.webnology.com>

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	And even if you assume that Microsoft is trying to remain compatible with
older classful implementations, this is class B space. So even under the old
rules, forgetting about VLSM and CIDR, this address would _still_ be valid.

	It's clearly valid under classless rules, as already pointed out.

	DS

> On Fri, 28 May 1999, Dan Langille wrote:
>
> > I understood that ip addresses ending in either 0 or 255 were not to be
> > used.  They are both used as broadcast addresses.  Is that correct?
>
> An IP address with all zeros in the node bits is a network address, and an
> IP address with all ones in the node bits is a broadcast address. The
> trick is determining what the node bits are, and that's what subnet masks
> are for. They're contiguous bitmasks that specify the network bits of a
> given IP address.
>
> For instance, 255.255.255.0.0 in binary is
>
>    11111111 11111111 00000000 00000000
>
> The ones bits in the mask are network bits, the zeros are node bits. If
> I've got the address 10.4.100.255 with a netmask of 255.255.0.0, it looks
> like this:
>
>    00001010 00000100 01100100 11111111
>    ^---------------^ ^---------------^
>         network             node
>
> The node portion is not all ones or zeros, so it's a valid node address.
>
> Cheers,
> Mick



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