From: Brian McGahan (bmcgahan@internetworkexpert.com)
Date: Fri Dec 23 2005 - 12:56:11 GMT-3
Venkatesh,
You are still doing the same binary logic whether you say 17 is "16+1" or 10001. Also it's much faster just to use Windows calculator to convert 214 into 11010110 than it is to convert it to 128+64+16+4+2 in your head.
Brian McGahan, CCIE #8593
bmcgahan@internetworkexpert.com
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________________________________________
From: Venkatesh Palani [mailto:kvpalani@gmail.com]
Sent: Friday, December 23, 2005 1:35 AM
To: swm@emanon.com
Cc: Farrukh Haroon; Khurana, Sameer; Emil Patel; Nawaz, Ajaz; nenad pudar; Brian McGahan; ccielab@groupstudy.com
Subject: Re: Question for Brian McGahan and others
HI Scot,
Thanks for your insight explanation, but I am afraid If I have not explained it in the right way.
My concept is
the same digits will form the network part
and the rest will be taken to for the mask part (not the common ones)
so I am not using the same digits to form the masks this goes with ur XOR logic.
let me try again
[8+2].[16+4+].[16+4+8++2].[32+8] ----> 1
[32+8].[16+4+8+2].[16+4].[8+2] ------> 2
I am taking the common stuff form 1 and 2 to form the network part not for the mask
so in this case
it will be 8.[16+4].[16+4].8
and the left overs are the remaiing stuffs are used for the mask in this it can be translated as non identical ones
so it will be
[32+2].[8+2].[8+2].[32+2]
which is 34.10.10.34 and I do accept this is not a perfect match though my intention was to use a single ACL. My appologies for not mentioning it directly but I refrenced IE in previous mail actually what I was refrencing was http://www.internetworkexpert.com/resources/01700370.htm.
Thank you,
On 12/23/05, Scott Morris <swm@emanon.com> wrote:
So you're saying the mask would be 8.20.20.8???
First, that's mathematically incorrect but we'll worry about that in a
moment.
Second, look at the mask in binary:
00001000.00010100.00010100.00001000... There are 6 one-bits in there. 2^6
= 64 matches to that mask alone. You only listed two things to match.
If you are FORCED to come up with a one-line ACL that may be acceptable,
otherwise I would advise against it. If you don't care how many extra
things you're permitting or denying just use "any any" to save the brain
power.
So on the math side, I think you're looking at it wrong for what bits go
where. If your two values have a bit in common you do NOT put a one-bit in
the mask. The XOR would be 0. So your 8-bit-position value, since they
both have it would yeild a 0 in that position whereas the 32 and 4 bit
positions would have a 1 in the mask.
So to get them in one line:
00100010.00001010.00001010.00100010 which is worse because it gives 8 bits
of 1's in the mask and 2^8 = 256 matches.
34.10.10.34 would be your mask if your were FORCED to come up with a
one-line ACL. IMHO this is rare and not incredibly bright. If your lab
tells you to do it, well... Just do it. ;)
Scott
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Venkatesh Palani
Sent: Thursday, December 22, 2005 9:28 PM
To: Scott Morris
Cc: Farrukh Haroon; Khurana, Sameer; Emil Patel; Nawaz, Ajaz; nenad pudar;
bmcgahan@internetworkexpert.com; ccielab@groupstudy.com
Subject: Re: Question for Brian McGahan and others
sorry I just realized there is a TYPO
vlaue for 30 is 16+8+4+2 and not 16+4+2.
ThanX
On 12/23/05, Venkatesh Palani < kvpalani@gmail.com> wrote:
>
>
> Hi All,
>
> Thanks Scott, I personllay dont use binary rather I use Decimal.
>
> below is the technique
>
> for instance lets take the same example from IE
>
> 10.20.30.40
> 40.30.20.10
>
> to find a access list for these address with overlapping networks I
> wld write the aboves address as shown below
>
> [8+2].[16+4].[16+4+2].[32+8]
> [32+8].[16+4+2].[16+4].[8+2]
>
> and the common vlaues in two colums shld represent the network
> address and the remaining shld fall back as wild cad mask
>
>
> in this case it will be
>
> 8.[16+4].[16+4].[8] = 8.20.20.8
>
> and the wild card mask is the sum of the left overs(the vlaues that
> were not used in the network address) in each octects from all the
> rows(in this case only two rows)
>
> [32+2].[8+2].[8+2].[32+2] = 34.10.10.34
>
>
> This shld work for any no of rows , this works better for me rather
> than those AND and XOR operations. Any comments are welcome.
>
>
> Thanx,
>
> Venkatesh
>
>
> On 12/23/05, Scott Morris <swm@emanon.com > wrote:
> >
> > From: http://en.wikipedia.org/wiki/Xor
> >
> > The case of a three, or more, input XOR operation tends to be an
> > ill-considered case. An XOR operation with three simultaneous inputs
> > is not so easily expressed in most popular programming languages.
> > When expressed as successive binary operations the result is a
> > simple parity, giving a TRUE result for any odd number of TRUE
> > inputs.
> > three ones XORed simultaneously
> >
> > When taken as a multi-input black box whose operation follows the
> > formal
> >
> > definition and yields the result TRUE when one, and only one, of its
> > inputs is TRUE, the behaviour is inconsistent with the successive
> > binary mode.
> > For
> > example; in the case where three inputs are all TRUE (as shown on
> > the right, in the IEC symbology to emphasise the definition) the
> > result would have to be FALSE because it does not meet the condition
> > that "only one of its inputs is TRUE".
> > [edit]
> >
> >
> > -----Original Message-----
> > From: nobody@groupstudy.com [mailto: nobody@groupstudy.com] On
> > Behalf Of Farrukh Haroon
> > Sent: Thursday, December 22, 2005 3:54 PM
> > To: Khurana, Sameer
> > Cc: Emil Patel; Nawaz, Ajaz; nenad pudar;
> > bmcgahan@internetworkexpert.com; ccielab@groupstudy.com
> > Subject: Re: Question for Brian McGahan and others
> >
> > what happened to the definition of XOR I learnt in college....
> >
> > Odd Number of 1's in input Results in Output of 1, Output = 0
> > otherwise...
> >
> > ??
> >
> > On 12/22/05, Khurana, Sameer < SKHURANA@amfam.com> wrote:
> > >
> > > I think you meant by column ;)
> > >
> > > Concept remains the same if its 4 rows, 5 rows or 10 rows.
> > >
> > > -----Original Message-----
> > > From: nobody@groupstudy.com [mailto: nobody@groupstudy.com] On
> > > Behalf Of Emil Patel
> > > Sent: Thursday, December 22, 2005 11:37 AM
> > > To: 'Nawaz, Ajaz'; 'nenad pudar'; bmcgahan@internetworkexpert.com
> > > ; ccielab@groupstudy.com
> > > Subject: RE: Question for Brian McGahan and others
> > >
> > >
> > > If the row is dissimilar the end result is 1.
> > >
> > >
> > > -----Original Message-----
> > > From: nobody@groupstudy.com [mailto: nobody@groupstudy.com] On
> > > Behalf Of Nawaz, Ajaz
> > > Sent: Thursday, December 22, 2005 11:05 AM
> > > To: 'Emil Patel'; 'nenad pudar'; bmcgahan@internetworkexpert.com;
> > > ccielab@groupstudy.com
> > > Subject: RE: Question for Brian McGahan and others
> > >
> > > What happens when you increase the #vertical rows and apply
> > > various combinations of 1's and 0's.
> > >
> > > Let's try 5rows?
> > >
> > > Tia
> > > Ajaz Nawaz
> > >
> > >
> > > -----Original Message-----
> > > From: nobody@groupstudy.com [mailto: nobody@groupstudy.com ] On
> > > Behalf Of Emil Patel
> > > Sent: 22 December 2005 17:07
> > > To: 'nenad pudar'; bmcgahan@internetworkexpert.com;
> > > ccielab@groupstudy.com
> > > Subject: RE: Question for Brian McGahan and others
> > >
> > > In XOR , if bit in a column is dissimilar result is 1. You do not
> > > add bit row by row.
> > >
> > > -----Original Message-----
> > > From: nobody@groupstudy.com [mailto: nobody@groupstudy.com] On
> > > Behalf Of Emil Patel
> > > Sent: Thursday, December 22, 2005 10:49 AM
> > > To: 'nenad pudar'; bmcgahan@internetworkexpert.com ;
> > > ccielab@groupstudy.com
> > > Subject: RE: Question for Brian McGahan and others
> > >
> > > 128 64 32 16 8 4 2 1
> > >
> > > 0 0 0 0 0 0 0 0
> > > 0 0 0 0 0 1 0 0
> > > 0 0 1 0 0 0 0 0
> > > 0 0 1 0 0 1 0 0
> > > ___________________________________________
> > > 0 0 1 0 0 1 0 0 = 36
> > >
> > > All vertical bits are checked XOR and if they are:
> > > (0+0)=0
> > > (0+1)=1
> > > (1+1)=0
> > > (1+0)=1
> > >
> > >
> > > -----Original Message-----
> > > From: nobody@groupstudy.com [mailto: nobody@groupstudy.com ] On
> > > Behalf Of nenad pudar
> > > Sent: Wednesday, December 21, 2005 7:57 PM
> > > To: bmcgahan@internetworkexpert.com; ccielab@groupstudy.com
> > > Subject: Question for Brian McGahan and others
> > >
> > > Hi Brian
> > > I have the question regarding your paper on Computing Access-List
> > > and Wildcard Pairs
> > >
> > > There you have
> > >
> > > 00000000
> > > 00000100
> > > 00100000
> > > 00100100
> > > _________
> > > XOR
> > > 00100100=36****
> > >
> > > I cannot get this trying in any way (for third column)
> > >
> > > 1) (((0 XOR 0) XOR 1) XOR 1)= ((0 XOR 1) XOR 1)= 1 XOR 1 =0
> > >
> > > 2) (0 XOR 0) XOR (1 XOR 1) = 0 XOR 0 = 0
> > >
> > > I am doing something wrong or there is some other trick here ?
> > >
> > >
> > > thanks
> > > nenad
> > >
> > > __________________________________________________________________
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