From: Michael Snyder (msnyder@revolutioncomputer.com)
Date: Mon Nov 03 2003 - 12:46:16 GMT-3
Thanks,
Dont think anyone else got it.
What I posted last week was the tutorial. :)
Thought I have asked Brian McGahan to update his paper with the decimal
method.
Lets do a quick one.
All even subnets of the third octet in the 10.0.0.0 to 10.10.0.0 range.
Laid out would look like this.
(0 & 2 & 4 & 6 & 8 & 10) XOR (0 | 2 | 4 | 6 | 8 | 10)
Network 10.0.0.0 Wildcard 0.14.0.0
Which checks on the boson wildcard checker.
BTW, be sure to sanity check your results.
The math works, but what you ask of it may have unintended results.
In this case networks 12 and 14 are also allowed.
-----Original Message-----
From: iwan [mailto:iwan@i-lusion.nl]
Sent: Monday, November 03, 2003 4:24 AM
To: Michael Snyder
Subject: RE: Instructions for using Windows Calc in decimal format for
access list generation.
Hi,
This is pretty cool what you found out...
DO you have more examples ...and are you planning to make a small
tutorial for this?
Thanks
Iwan Hoogendoorn
MCSA,MCSE, MCDBA, CCA, CCNA, CCIE (Written)
Tel : +31 6 45708325
E-mail : iwan@i-lusion.nl
From: nobody@groupstudy.com on behalf of Michael Snyder
Sent: Sat 11/1/2003 17:11
To: ccielab@groupstudy.com
Cc: 'Cristian Henry H'
Subject: Instructions for using Windows Calc in decimal format for
access list generation.
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.
------------------------------------------------------------------------
----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.
------------------------------------------------------------------------ ----
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@reuna.cl] Sent: Tuesday, September 30, 2003 7:03 AM To: Casey, Paul (6822) Cc: ccielab@groupstudy.com 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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