From: Darek Kuzma (darekk@xxxxxxxxxxxxx)
Date: Tue Jul 16 2002 - 22:37:20 GMT-3
It is apparently not a XOR as defined on the website you provided.
However it has sth to do with XOR. I would call it multivariable or
multidimensional XOR: XOR(x1,x2,x3,...,xN),
where we simply compare all variables at one step, not one by one --> XOR[
XOR(( XOR(x1,x2),x3 ), ... xN) ]
I don't now if there is any name for this function in Logic Gate theory.
But anyway it is way OT.
Darek
Brian McGahan wrote:
> Now that I'm thinking about this a bit more, I'm starting to confuse
> myself. When you have two addresses and you're trying to figure out the
> most specific wildcard to match them, the operation is XOR. For
> example:
>
> 10000000 <-- 128
> 00000001 <-- 1
> --------
> 10000001 <-- 129 wildcard
>
> 10000000 <-- 128
> 10000001 <-- 129
> --------
> 00000001 <-- 1 wildcard
>
> The truth table for XOR is:
>
> __XOR__
> 0 0 | 0
> 0 1 | 1
> 1 0 | 1
> 1 1 | 0
>
> However, if you extend XOR to a 3 digit comparison, you get:
>
> ___XOR___
> 0 0 0 | 0
> 0 1 0 | 1
> 1 0 0 | 1
> 1 1 0 | 0
> 0 0 1 | 1
> 0 1 1 | 0
> 1 0 1 | 0
> 1 1 1 | 1
>
> and this is not the wildcard operation.
>
> So what is the wildcard operation? A pseudo extended XOR? For more
> info on logic gates:
>
> http://www.shef.ac.uk/uni/academic/N-Q/phys/teaching/phy107/othergates.h
> tml
>
> Brian McGahan, CCIE #8593
> Director of Design and Implementation
> brian@cyscoexpert.com
>
> CyscoExpert Corporation
> Internetwork Consulting & Training
> http://www.cyscoexpert.com
> Voice: 847.674.3392
> Fax: 847.674.2625
>
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
> Hemant_Kumar@BERLEX.COM
> Sent: Tuesday, July 16, 2002 6:39 PM
> To: Darek Kuzma
> Cc: ccielab@groupstudy.com; nobody@groupstudy.com
> Subject: Re: ACL fewest numbers of lines
>
> Darek,
> Very good explaination. Can you direct me where i can get more
> information
> on this. I have been looking for such explaination but never found any
> document that would explain it.
>
> Thanks
> HK
>
>
>
> Darek Kuzma
>
> <darekk@opton
>
> line.net> To: ccielab@groupstudy.com
>
> Sent by: cc:
>
> nobody@groups Subject:
>
> tudy.com Re: ACL fewest numbers of lines
>
>
>
>
>
> 07/17/2002
>
> 12:41 AM
>
> Please
>
> respond to
>
> Darek Kuzma
>
>
>
>
>
> Alex,
> We can write one line ACL which will deny networks you specified but it
> will also deny the whole bunch of other IPs.
>
> Assuming that listed networks are /24s ACL is:
>
> deny ip 128.3.1.0 109.252.56.255
>
> Formula is:
> write all adresses in binary one under another
>
> 10001100.11000111.00111001.00000000
> 10100001.11000111.00111001.00000000
> 11001001.00111011.00000001.00000000
> 11001001.00111111.00000001.00000000
>
> if in a column we have all "0" or all "1" it means that wildcard mask
> must be 0 - care; 1 otherwise:
>
> 01101101.11111100.00111001.11111111 (last octet is 255 because of
> assumtion of /24 networks)
>
> if mask bit=0 network bit is 0 or 1 depending whether bit was all "0" or
> all "1" (because we "care")
> if mask bit=1 network bit is 0 or 1 (anyway mask is "don't care). I'm
> putting all "0"
>
> 10000000.00000011.00000001.00000000
>
> result is: 128.3.1.0 109.252.56.255
>
> Thanks,
> Darek Kuzma
>
> Alex wrote:
>
> > Requirement:
> >
> > Create an access list with the fewest numbers of lines to deny.
> >
> > 140.199.57.0
> > 161.199.57.0
> > 201.59.1.0
> > 201.63.1.0
> >
> > I can do it in 3 lines but I believe that there is a way to do it in 1
> >
> > line? any body know?
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