RE: Class "A" prefix-list

ip prefix-list YOU-NAME-IT seq 5 permit 0.0.0.0/1 ge 8 le 8

translated in English, you would say,

"the first 1 bit of a given network address must match the first 1 bit of my
prefix-list", hence the /1 AND
"the subnet mask can have the length ge 8 AND le 8, hence =8" (i.e. only
255.0.0.0)

In other words words /N refers to the number of bits that will match in the
specified prefix-list
AND
"ge M le M" states how many bits (M) of the subnet mask are 1s (ones)
So if Subnet mask is 255.0.0.0, then M=8 ---> match
 

Furthermore,
If Route is 10.0.0.0 AND Subnet mask is 254.0.0.0 ---> prefix-list
0.0.0.0/1 ge 8 le 8 will NOT match
--- first 1 bit is 0 AND
--- the length of the Subnet mask is 7
However, this is a valid Class A summarized network address

On the other hand, prefix-list 0.0.0.0/1 le 32 will match
(Which says, first 1 bit must be zero AND the Subnet mask must have a length
-- the number of 1s in the subnet mask -- less than or equal to 32)

-
Daniel

-----Original Message-----
From: nobody_at_groupstudy.com [mailto:nobody_at_groupstudy.com] On Behalf Of
Hammer cisco
Sent: Mittwoch, 1. Juni 2011 23:56
To: Narbik Kocharians
Cc: Daniel Kutchin; Cisco certification
Subject: Re: Class "A" prefix-list

Hi Narbrik,

thanks for your illustrations , but i have 2 comments :

1- i think 0.0.0.0/1 ge 8 is enough instead of saying "ge 8 le 32 " as
mentioned in your example below

2- if the the required in a certain routing protocol to deny all Class A
network address routes :
         what do u recommend ?

On 2 June 2011 00:21, Narbik Kocharians <narbikk_at_gmail.com> wrote:

> *
>
> Class A networks that are NOT subnetted:
>
>
>
> R2(config)#ip prefix-list Class-A seq 5 permit 0.0.0.0/1 ge 8 le 8
>
>
>
> Class A networks are identified as follows:
>
>
>
> Where n identifies the network bits and h identifies the host bits.
>
> 0nnnnnnn hhhhhhhh hhhhhhhh hhhhhhhh
>
> 7 First bit is set to 0; Therefore there
> are 7 network bits; 24 host bits
>
> 7 First octet: 0 - 127
>
> 7 126 Class As exist (0 and 127 are
> reserved)
>
> 7 16,777,214 hosts on each Class A
>
> Note the most significant bit of the first octet is set to a binary
> 0, the rest of the bits in the first octet can be zeros or ones,
> therefore, if the most significant bit of the first octet is 0 it
> must be class A. The prefix-list picks on the first bit by using a /1
prefix-length.
>
>
>
> Class A networks that are or are not subnetted:
>
>
>
> R2(config)#ip prefix-list Class-A seq 5 permit 0.0.0.0/1 ge 8 le 32
>
>
>
> Note in this case the prefix-list picks on class A, with a
> prefix-length of greater than or equal 8 and less than or equal 32,
> which means that all major class A networks, plus all class A networks
that are subnetted.
>
>
>
> *
> On Wed, Jun 1, 2011 at 1:45 PM, Hammer cisco <cisco.iers_at_gmail.com>wrote:
>
>> thanks danel ,
>>
>> but still i need to know exactly what's the difference between
>> 0.0.0.0/1ge
>> 8 and 0.0.0.0/1 le 32
>>
>> as i think all class A networks starting from mask 8 and greater , i
>> have not seen a network with mask less 8
>>
>> On 1 June 2011 23:35, Daniel Kutchin <daniel_at_kutchin.com> wrote:
>>
>> > If you just want to match Class A's with 8 bit masks, Class B's
>> > with 16
>> bit
>> > masks, and class C's with 24 bit masks.
>> >
>> > 0.0.0.0/1 ge 8 le 8
>> > 128.0.0.0/2 ge 16 le 16
>> > 192.0.0.0/3 ge 24 le 24
>> >
>> > If you want to match anything in the individual address spaces for
>> > class A,B, C
>> > 0.0.0.0/1 le 32
>> > 128.0.0.0/2 le 32
>> > 192.0.0.0/3 le 32
>> >
>> >
>> > Class A- binary first bit 0.
>> > Class B - binary first two bits 10.
>> > Class C - binary first three bits 110.
>> >
>> > -
>> > Daniel
>> >
>> >
>> > -----Original Message-----
>> > From: nobody_at_groupstudy.com [mailto:nobody_at_groupstudy.com] On
>> > Behalf Of Hammer cisco
>> > Sent: Mittwoch, 1. Juni 2011 21:38
>> > To: ccielab_at_groupstudy.com
>> > Subject: Class "A" prefix-list
>> >
>> > Hi experts,
>> >
>> > i am a little bit confused about the exact prefix-list we can use
>> > to
>> match
>> > all class A network address routes :
>> >
>> > ip prefix-list 0.0.0.0/1 ge 8
>> >
>> > or
>> >
>> > ip prefix-list 0.0.0.0/1 le 32
>> >
>> >
>> > Blogs and organic groups at http://www.ccie.net
>> >
>> > ___________________________________________________________________
>> > ____ Subscription information may be found at:
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>>
>>
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>>
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>>
>>
>>
>>
>>
>>
>>
>
>
> --
> *Narbik Kocharians
> *CCSI#30832, CCIE# 12410 (R&S, SP, Security) www.MicronicsTraining.com
> <http://www.micronicstraining.com/>
> Sr. Technical Instructor
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Received on Thu Jun 02 2011 - 00:53:55 ART