From: Victor Cappuccio (cvictor@protokolgroup.com)
Date: Fri Jul 28 2006 - 13:00:43 ART
Hi Brian, I do not see any problem with that at all
Xor is only 1 (true) if 1 Xor 0; 0 Xor 1
http://mathworld.wolfram.com/XOR.html
http://www.vipan.com/htdocs/bitwisehelp.html
http://en.wikipedia.org/wiki/Xor_swap_algorithm
http://en.wiktionary.org/wiki/XOR
From the Internetwork Link:
10.0.0.0/16
10.4.0.0/16
10.32.0.0/16
10.36.0.0/16
128 64 32 16 8 4 2 1
0 0 0 0 0 0 0 0 0
4 0 0 0 0 0 1 0 0
32 0 0 1 0 0 0 0 0
36 0 0 1 0 0 1 0 0
=================================================
AND 0 0 0 0 0 0 0 0 == 0
XOR 0 0 1 0 0 1 0 0 == 36
So the access-list should be something like 10.0.0.0 0.36.0.0
You can test this also in the router using
R6#show ip route 10.0.0.0 255.219.0.0 long | b Gate
Gateway of last resort is not set
10.0.0.0/16 is subnetted, 4 subnets
C 10.0.0.0 is directly connected, Loopback101
C 10.4.0.0 is directly connected, Loopback101
C 10.32.0.0 is directly connected, Loopback101
C 10.36.0.0 is directly connected, Loopback101
HTH
Victor.-
-----Mensaje original-----
De: nobody@groupstudy.com [mailto:nobody@groupstudy.com] En nombre de Brian
Enviado el: Viernes, 28 de Julio de 2006 11:32 a.m.
Para: ccielab@groupstudy.com
Asunto: XOR for Computing ACL Masks
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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