RE: Another Prefix list question

From: Scott Morris (smorris@ipexpert.com)
Date: Tue Apr 15 2008 - 02:53:04 ART

"ge 24" will permit subnetted Class C addresses as well, won't it? :)

On the other hand, the "le 32" will also permit SUPERnetted addresses in
that range. Just depends on what you are looking for.

HTH,

Scott Morris, CCIE4 (R&S/ISP-Dial/Security/Service Provider) #4713, JNCIE-M
#153, JNCIS-ER, CISSP, et al.
CCSI/JNCI-M/JNCI-ER
VP - Technical Training - IPexpert, Inc.
IPexpert Sr. Technical Instructor

smorris@ipexpert.com

 

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-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Tarun
Sent: Tuesday, April 15, 2008 1:40 AM
To: Athaide, Dwayne
Cc: groupstudy
Subject: Re: Another Prefix list question

That prefix 192.0.0.0/3 ge 24 means the following.

1) It will match only the first 3 bits of the IP '192.0.0.0' which means any
class C address because class C addresses are characterized by a '110' in
the beginning of there 1st octet.

2) The 'ge 24' part means that the subnets mask of the class C address just
matches has to be either equal to or greater than 24, i.e it will not match
192.168.2.3/16 for example.

If you want to permit all "Class C networks" then the prefix list ideally
should be

ip prefix CLASS_C_NETWORKS permit/deny 192.0.0.0/3 le 32 - this would
include all subnetted class C addresses as well.

This is a good link on prefix lists:
http://ccienotes.blogspot.com/2007/08/ip-prefix-list.html

On 4/15/08, Athaide, Dwayne <DAthaide@eprod.com> wrote:

> Please check
>
> If I want to permit only Class C networks
>
>
>
> Is this correct?
>
>
>
> 192.0.0.0/3 ge 24
>
>
>
> Thanks
>
>
> Pass the CCIE in six weeks, Guaranteed!
> http://www.certscience.com/CCIE
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