BGP Attribute for Choosing Preferred BGP Speakers in Customer AS
Question
A customer of an ISP requests support to setup a BGP routing policy.
Which BGP attribute should be configured to choose specific BGP speakers as preferred points for the customer AS?
Answers
Explanations
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A. B. C. D.B.
When an ISP provides BGP routing services to a customer, the customer can use BGP attributes to influence the routing of traffic between its AS and other networks. One of the attributes that can be used to influence BGP route selection is the local preference.
The local preference attribute is a non-transitive attribute that is used to indicate the degree of preference for an advertised BGP route within the local AS. It is a numeric value that can be set by the local AS on incoming BGP routes. The higher the local preference value, the more preferred the route is considered to be.
In this scenario, the customer is requesting support to set up a BGP routing policy that would allow them to choose specific BGP speakers as preferred points for their AS. Therefore, the BGP attribute that should be configured is the local preference attribute.
Option A, the lowest multi-exit discriminator, is an optional non-transitive attribute that is used to identify the preferred egress point for traffic leaving an AS with multiple exit points. This attribute is used by the receiving AS to choose the best path to reach the advertised network.
Option B, the highest local preference outbound, is not a valid BGP attribute. The local preference attribute is only set on incoming BGP routes and is not used for outbound routing decisions.
Option C, the lowest local preference inbound, is not the correct answer in this scenario because the customer wants to choose specific BGP speakers as preferred points for their AS. Lowering the local preference on incoming routes would not achieve this goal.
Option D, the highest local preference inbound, is the correct answer because it would allow the customer to set a high local preference value on incoming BGP routes from specific BGP speakers. This would cause those routes to be preferred over other routes with lower local preference values when making routing decisions within the local AS.
Therefore, the correct answer is D - the highest local preference inbound.
