Re: Prefix-list

A prefix-list matches on prefix lengths and ACL's matches on subnets.
With a standard ACL the wildcard mask says nothing about the prefix the
route must have to match.

ACL permit 10.0.0.0 0.255.255.255 matches all routes with 10.0.0.0 but the
prefix could be /8 /16 /32 etc.
ACL permit 10.0.0.0 255.255.255.255 matches the same as above , same as host
10.0.0.0

With a standard ACL you have no control in matching prefix lengths. With an
extended ACL with (in believe only BGP) you have more control, but a
prefixlist is easier.

To match routes with a certain prefix , a prefixlist is the best option.
It not only matches on subnet but you also have control on the prefix of
that subnet.

So you can permit a 10.0.0.0/8 but not a 10.0.0.0/16 route.

Prefix list permit 10.0.0.0/8 only matches 10.0.0.0/8 and not /16 etc.

On Thu, May 7, 2009 at 8:53 AM, Khurram Noor <
engr.khurramnoor_at_googlemail.com> wrote:

> Hello everyone,
> I am having a hard time in understanding mechanism of prefix-list and how
> can it be related to acls. Is there any good resource/exercise/article
> which
> can help me understand prefix-list and show me how to convert ACL into
> Prefix-list.
>
> I will be thankful if anyone can help or just define how prefix-list work
> with some examples.
>
> --
> Khurram Noor
> Internetwork Professional
>
>
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Received on Thu May 07 2009 - 09:38:38 ART