RE: BGP inbound/outbound filter preference

Emir,

It is important to understand the logic because all can be applied to the
same neighbor statements. Because it is logic that you need to understand
it could always be a question on a lab or the actual exam. As an example

Let's say for one task you are asked to control inbound prefix's using
prefix lists. Then later another task asks you to attach communities to a
network that you filtered with your prefix list. If you were not aware of
this logic you wouldn't realize that the previous task needs to be appended
to include the additional prefix that you need to add to your prefix list
and make sure your last route-map statement is a permit as the route-map is
not being used as your filtering policy.

Regards,
 
Tyson Scott - CCIE #13513 R&S, Security, and SP
Managing Partner / Sr. Instructor - IPexpert, Inc.
Mailto: tscott_at_ipexpert.com
Telephone: +1.810.326.1444, ext. 208
Live Assistance, Please visit: www.ipexpert.com/chat
eFax: +1.810.454.0130

IPexpert is a premier provider of Self-Study Workbooks, Video on Demand,
Audio Tools, Online Hardware Rental and Classroom Training for the Cisco
CCIE (R&S, Voice, Security & Service Provider) certification(s) with
training locations throughout the United States, Europe, South Asia and
Australia. Be sure to visit our online communities at
www.ipexpert.com/communities and our public website at www.ipexpert.com

-----Original Message-----
From: nobody_at_groupstudy.com [mailto:nobody_at_groupstudy.com] On Behalf Of emir
d souza
Sent: Tuesday, November 02, 2010 5:54 PM
To: alexeim73_at_gmail.com
Cc: Cisco certification
Subject: Re: BGP inbound/outbound filter preference

Hi Alex,

Yup, that's true, but why then would we need the prefix list in the same
config if the route-map is good enough to do everything else. I've seen this
config on some SP routers, but fail to understand the logic of having both
inbound.

neighbor yadayada route-map CISCO in
neighbor yadayada prefix-list CISCO in

Does anyone know?

Cheers.

On Tue, Nov 2, 2010 at 6:52 PM, Alexei Monastyrnyi
<alexeim73_at_gmail.com>wrote:

> Hi.
>
> With route-map you can match things other than prefixes, and also
> manipulate attributes. Also with route-maps you can impose more
> sophisticated logic upon your peers.
>
> HTH
> A.
>
> On 11/2/2010 9:45 AM, emir d souza wrote:
>
> Hi Guys,
>
> I'm a bit confused, from what I understand is that for filtering traffic,
> BGP will look at filtering in this order:-
>
> Inbound: route-map > filter-list > prefix-list
> Outbound: prefix-list > filter-list > route-map
>
> Question is: For example. why bother having both route-map and prefix-list
> filtering on the inbound when you can just use a single route-map to
filter
> in traffic. I've seen this being done on some SP routers, and I'm
wondering
> if there good explanation as to why they are doing this.
>
> Route-map will filter out community tags and prefix-list will filter out
> specific routes, can't we do both on route-maps alone??
>
> Cheers.
>
> Emir
>
>
> Blogs and organic groups at http://www.ccie.net
>
> _______________________________________________________________________
> Subscription information may be found at:
http://www.groupstudy.com/list/CCIELab.html

Blogs and organic groups at http://www.ccie.net
Received on Tue Nov 02 2010 - 22:42:05 ART