From: Brian (briane@surewest.net)
Date: Sat Jul 29 2006 - 19:42:06 ART
Brian,
Thank you for the clarification.
-----Original Message-----
From: Brian McGahan [mailto:bmcgahan@internetworkexpert.com]
Sent: Saturday, July 29, 2006 3:35 PM
To: Brian; Ricardo AF Silva
Cc: ccielab@groupstudy.com
Subject: RE: XOR for Computing ACL Masks
You are correct, XOR does not hold true for an odd number of
inputs. I believe the actual logic gate should be:
AND(OR(A1,A2, ...An),NOT(AND(A1,A2, ...An)))
Where A1 through An are the inputs. The result is that if all
inputs are TRUE the result is FALSE, and if all inputs are FALSE the
result is FALSE, regardless if there are an even or odd number of
inputs. Any other combination results in TRUE. I'll have to revise my
document to make this a little clearer; for an odd number of inputs I
don't think there is a name for this gate.
Thanks for the feedback,
Brian McGahan, CCIE #8593
bmcgahan@internetworkexpert.com
Internetwork Expert, Inc.
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> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
Of
> Brian
> Sent: Friday, July 28, 2006 11:06 PM
> To: 'Ricardo AF Silva'
> Cc: ccielab@groupstudy.com
> Subject: RE: XOR for Computing ACL Masks
>
> I agree with what you have stated and I understand. However this is
not
> an XOR.
>
> Brian
>
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
Of
> Ricardo AF Silva
> Sent: Friday, July 28, 2006 10:53 AM
> To: Brian
> Cc: ccielab@groupstudy.com
> Subject: Re: XOR for Computing ACL Masks
>
> Brian,
> I think I got your point so,
>
> Given two inputs A & B, Xor'ed, the output Y is:
>
> A B Y
> 0 0 0
> 0 1 1
> 1 0 1
> 1 1 0
>
> For three inputs A, B and C, the output Y is:
>
> A B C Y
> 0 0 0 0
> 0 0 1 1
> 0 1 0 1
> 0 1 1 1
> 1 0 0 1
> 1 0 1 1
> 1 1 0 1
> 1 1 1 0
>
> Conclusion:
> the inputs are different ( no matter how many inputs) Y is 1)
> the inputs are the same, Y is 0...
> That is the logic behind XOR... Look at the inputs and just check if
are
> equal
> or not....
>
> HTH
> Ricardo
>
> As you can see in the example you have
> On Friday 28 July 2006 13:17, Brian wrote:
> > I was using http://mathworld.wolfram.com/XOR.html as a reference. I
> am
> > interested in the specific process (steps) that were used in the
> > example.
> >
> > Brian
> >
> > -----Original Message-----
> > From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
> Of
> > Mienbaikebi Patani
> > Sent: Friday, July 28, 2006 9:00 AM
> > To: Brian
> > Cc: ccielab@groupstudy.com
> > Subject: Re: XOR for Computing ACL Masks
> >
> > I think the XOR works such that u need to have equal number of 0 and
1
> > for
> > the result to be equal to 1. Anything other than equal number of 0
and
> 1
> > results in a value equal to 0.
> >
> > Hope that was informative brother.
> >
> > On 7/28/06, Brian <briane@surewest.net> wrote:
> > > I have been looking at the following example on how to calculate
an
> > > appropriate mask.
> > > http://www.internetworkexpert.com/resources/01700370.htm. While I
> > > understand the process that was use (and it works well) I cannot
> >
> > figure
> >
> > > out how the mask was calculated using XOR in example 2. If I
> >
> > understand
> >
> > > XOR correctly anytime there are an even number of 1's in a
> computation
> > > the result of XOR will be 0. When there are an odd number of 1's
> the
> > > result will be 1. This does not seem to hold true in the example.
> > >
> > > Can someone please help me understand how XOR was applied to come
up
> > > with the mask in example 2. Specifically the second octet is
where
> >
> > the
> >
> > > confusion comes in. The only conclusions I can draw are that this
> is
> > > not truly an XOR or I do not understand XOR.
> > >
> > > By the way I tried to XOR 0011 in the MS calculator and the result
> is
> >
> > 0.
> >
> > > Thanks!
> >
> >
>
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