From: Brian McGahan (bmcgahan@internetworkexpert.com)
Date: Sun Jul 02 2006 - 17:56:37 ART
Assuming the BGP topology looks like:
AS_100 --X-- AS_400 --Y-- AS_54
and you are trying to affect how traffic goes from AS 54 to AS
100 you can either change the Weight or Local-Preference as AS 400
learns the routes from AS 100 via peering(s) X or do AS-Path prepending
or change the MED value as the routing advertisement goes from AS 400 to
AS 54 via peering(s) Y. Technically you could perform other operations
as well like prepending inbound on peering X or setting the origin
inbound on X or outbound on Y, but changing Local-Preference inbound on
X and AS-Path outbound on Y would be the most common in practical
application. Within the context of the lab exam it ultimately depends
on what the restrictions of the question are and what the exact traffic
engineering path is that you are trying to achieve.
HTH,
Brian McGahan, CCIE #8593
bmcgahan@internetworkexpert.com
Internetwork Expert, Inc.
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> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
Of
> forwardtruth@yahoo.com
> Sent: Sunday, July 02, 2006 12:56 PM
> To: ccielab@groupstudy.com
> Subject: BGP attributes and traffic flow passes transit AS
>
> As a general rule, these attributes should be applied in the following
> manner to
> affect the following traffic flow :
> (( Weight and Local-Preference are used to affect how traffic leaves
the
> autonomous system. AS-Path and MED are used to affect how traffic
enters
> the
> AS. Since Weight and Local-Preference are higher in the decision
process
> than
> AS-Path and MED, you (generally) have control of how traffic leaves
your
> AS )).
>
> Does the same rule applied to a traffic that passes transit AS in the
> following scenarios :
>
> Lab 2 V3 Task 5.4
> "Parts of the acquisition agreement between AS400 and AS 100
stipulates
> that AS 400 will not provide transit for traffic coming from AS 54 and
its
> customers that is destined for AS 254. Configure AS 400 to reflect
this
> policy".
>
> Lab 4 V3 Task 6.2
> "AS 100s corporate policy dictates that it should not provide transit
> service to get to any of ASs 54s customers. However, AS100 should
still
> be able to reach the prefixes of AS 54s customers,,,,,,etc".
>
> Now my query if I want to control traffics that originate in AS54
towards
> AS 100 (destination) via AS 400 (transit AS) , do I need to control
the
> AS 54s traffics, when it enters AS 400 (Traffic flow affected
inbound)
> or when It leaves AS 400 (Traffic flow affected outbound) towards AS
100
> (destination) ??
>
>
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