RE: Subnetting question

4 0100
5 0101
6 0110
7 0111

12 1100
13 1101
14 1110
15 1111

4, 0100, exists in all or does not change
These all change 1011

So, there's your answer 200.200.4.0 0.0.11.0. 0.0.11.255 is actually less correct, particularly when matching networks, 255 at the end would imply match all hosts or networks with the first 3 matching octets.

Another quick and dirty way to do it, which works a lot is if the number of networks are a power of 2 (a requirement for creating a single with no overlap). Just take the first network in question, use it for your starting network and derive the mask by subtracting the first network from the last.

200.200.4.0 first network
200.200.15.0 last network

15 - 4 = 11. Not saying this works everytime... you can usually spot them pretty easily though.

-ryan

-----Original Message-----
From: nobody_at_groupstudy.com [mailto:nobody_at_groupstudy.com] On Behalf Of Nishant Aggarwal
Sent: Sunday, August 23, 2009 6:24 AM
To: ccielab_at_groupstudy.com
Subject: Re: Subnetting question

Hi All,

Corrected question on subnetting. We are getting routes:

200.200.0.0 /24
200.200.1.0 /24
200.200.2.0 /24
         -
         -
         -
         -
         -
200.200.19.0 /24
200.200.20.0 /24

Now only routes given below are required with only one statements in your
ACL:

200.200.4.0 /24
200.200.5.0 /24
200.200.6.0 /24
200.200.7.0 /24

and

200.200.12.0 /24
200.200.13.0 /24
200.200.14.0 /24
200.200.15.0 /24

*Answer is : 200.200.4.0 0.0.11.255*

But we are unable to understand the math behind it. Can anyone suggest, how
to find out wil card mast of *0.0.11.255 ??*

Thanks,

Nishant.

On 8/23/09, Federico Cossu <federico.cossu_at_gmail.com> wrote:

> i know the answer! and the answer is:
>
> http://blog.internetworkexpert.com/2008/09/15/binary-math-part-i/
>
>
>
> /R
>
>
>
> 2009/8/23 Naufal Jamal <naufalccie_at_yahoo.in>
>
> > Hi experts,
> >
> > I am receiving the following routes in my router.
> >
> > 192.168.1.0/24
> > 192.168.2.0/24
> > .
> > .
> > .
> > 192.168.20.0/24
> >
> > I want to filter the routes 192.168.4.0/24 - 192.168.9.0/24 and the acl
> > should
> > use the minimum stmts possible.
> >
> > can anyone help??
> >
> > naufal
> >
> >
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Received on Sun Aug 23 2009 - 08:16:21 ART