Ok, working off the binary math posted By Brian McGahan.
http://www.internetworkexpert.com/resources/01700370.htm
I've converted the method to work in decimal format on the windows calc.
The advantage here is that windows calc is useable in the lab!
This method has a simple sequence of operations, keeping down to
possibility of human error under stress. :)
Note - Logical operations work in any number base.
I've checked and it seems to work every time.
Also have had other people check it.
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Instructions for using Windows Calc in decimal for accesslist
generation.
Operations are done per octet. Processed in columns.
Let`s do 10.55.0.0; 10.33.0.0; 10.36.0.0;
The Network value is defined as octets `AND`-ed together.
Example 55 & 33 & 36 = 32 ; Keep result.
The Wildcard value is defined (in binary) as all ones = false, all
zeros=false anything else=true
But we will use the windows calc so you don`t have to worry about
binary.
Our next operation is to `Or` the same numbers.
55 | 33 | 36 = 55 ; Keep result
Now for the wildcard, take result of `&` operation and result of `|`
operation use the `XOR` operation on the two previous results.
32 xor 55 = 23
So the answer `10.32.0.0 0.23.0.0` should match 55,33,36
Checking with the boson wildcard util. It checks.
In summary,
Using windows calc, in decimal numbers.
`AND` all the numbers of the octet column together.
Keep this result, this your network number for that octet.
`OR` the same column, keep result.
`XOR` the two previous values, that`s the wildcard mask.
Simple Enough, and you can`t make binary mistake using method in the
lab.
Note - don`t discard zero results, it will be used later in method.
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Please feel free to check method,
I believe it works in all cases.
Michael Snyder
Lead Network Engineer
CCSP, CCDP, MCSE
Revolution Computer Systems
(270) 443-7400
-----Original Message-----
From: Cristian Henry H [mailto:chenry@xxxxxxxx]
Sent: Tuesday, September 30, 2003 7:03 AM
To: Casey, Paul (6822)
Cc: ccielab@xxxxxxxxxxxxxx
Subject: Re: Access list filter in the shortest lines possible.
I got the following one:
access-list 10 permit 100.0.33.0 27.55.94.0
"Casey, Paul (6822)" ha escrito:
>
> > Hello,
> >
> > For example, say we are asked to filter the following routes using
the
> > shortest nuber of lines possible
> >
> > 102.17.63.0
> > 126.22.61.0
> > 111.22.57.0
> > 125.33.101.0
> >
> > Can someone tell me the best access list to use to filter these
networks.
> >
> > Thanks in advance.
> > Kind regards.
> >
> >
> >
> >
>
>
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