Re: ip prefix-list calculator or any short cut tips?

Now sure how to provide a short cut. There are some excellent resources
available.

Here's an idea for a quick lab to learn them better:

R1 - Create a lot of loopbacks for various masks - say /1 - /32 for example.
Then advertise into a routing protocol like RIP for example.

R2 - Create a neighbor for R1 and then create a distribute-list with various
combinations and then check the results. Using some of the combinations
I've listed below or better yet experiment a bit till you feel more
comfortable.

Gotta admit Prefix-lists seem tough at first until you do them a few times.

1. Understand le (less than or equal to), ge (greater than or equal to) and
what /xx (the binary bit count notation) means.

2. Understand that 0.0.0.0/0 = 0.0.0.0 0.0.0.0 and that's it.

Example if you were to create a distribute-list in and specify 0.0.0.0/0 -
that is all you will be allowing and not the whole world.

3. Understand that 0.0.0.0/0 ge 32 = Everything

4. Understand that 192.168.121.0/24 le 32 would match all specific addresses
in the given /24... Take the same example 192.168.121.0/17 le 24 ge 24 and
now we just want to match the specific /24.... Take 192.168.0.0/16 le 17 ge
24 means we want to match the subnets including /17 and in between /24 with
/24 too.

5. Hmm... You can change the bit-representation under the various line
interfaces and change the representation of the mask to a bit count if you
need to to see it in decimal.

 SUMMARY STEPS

*1. **enable*

*2. **configure* *terminal*

*3. **line* *vty* *first* *last*

*4. **term* *ip* *netmask-format* {*bitcount* | *decimal* | *hexadecimal*}

*5. **end*

On Fri, Sep 4, 2009 at 6:14 PM, CCIE League <ccieleague_at_ymail.com> wrote:

> Experts,
>
> Is there any on-line calculator to practise & verify your results quickly
> or any short cuts or tips 4 ip prefix calculations?
>
> I have seen fantastic explanation by Scott that explains ip prefix in
> details :
> http://blog.internetworkexpert.com/2008/11/03/binary-math-part-ii/
>
>
> Ta,
>
>
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-- 
Darby Weaver
Network Engineer
407-802-7394
darbyweaver_at_yahoo.com
Blogs and organic groups at http://www.ccie.net