From: Scott Morris (swm@emanon.com)
Date: Sun Dec 10 2006 - 12:45:08 ART
Well, given that the third octet is the only one that changes, one can
reasonably assume that's the octet being asked about! :) (Too much logic
this early in the morning!)
Binary:
81 01010001
83 01010011
85 01010101
87 01010111
Dif -----xx-
For those specific four routes, you have two bits different. Rememember, no
more, no less when doing these things.
Access-list permit 208.10.81.0 0.0.6.x
There's your list. The 'x' may vary depending on how we're applying this.
In a distribute list, where we're moving routes, that can be .0 because the
fourth octet should only be a '0' value as a /24 route. If it's a packet
filter for hosts, we may see a .255 there because an individual packet could
present any value in the 4th octet as hosts move things through.
HTH,
Scott Morris, CCIE4 (R&S/ISP-Dial/Security/Service Provider) #4713, JNCIE
#153, CISSP, et al.
CCSI/JNCI-M/JNCI-J
IPExpert VP - Curriculum Development
IPExpert Sr. Technical Instructor
smorris@ipexpert.com
http://www.ipexpert.com
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Heiko Liedtke
Sent: Sunday, December 10, 2006 5:33 AM
To: Tandou Mohamed
Cc: ccielab@groupstudy.com
Subject: Re: Access-List
Hi,
ODD in which octett? I guess there are talking about the 3rd octett...
If you write down some odd and some even networks in binary notation, you
can see, that there is always the least significant bit (the 2EXP0) which
makes the differens between ODD and EVEN.
Knowing this you can easily write an ACL to filter on this bit.
Heiko
Tandou Mohamed schrieb:
>Hello GS
> can someone explain to me the best way to filter access-list.
> The question asked to permit only ODD route without using distribute list
> When i do show ip route this is what i get
>
> 208.10.80.0/24
> 208.10.81.0/24
> 208.10.82.0/24
> 208.10.83.0/24
> 208.10.84.0/24
> 208.10.85.0/24
> 208.10.86.0/24
> 208.10.87.0/24
> How do i filter odd route from here?
>
> Thanks
>
> Mohamed
>
>
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