Designing AS100 for Prefixes from AS200
Question
AS100 and AS200 each have two peering points in different parts of their network.
AS100 would like to use one of the links and keep the other link as backup.
What should be changed for the design inside AS100 for prefixes received from AS200?
Answers
Explanations
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A. B. C. D.D.
To achieve the desired outcome of using one link while keeping the other as a backup, AS100 needs to implement some form of traffic engineering in their network. In this scenario, AS100 wants to influence the inbound traffic received from AS200, so the focus is on inbound routing policies.
Out of the four options provided, the most suitable one for this scenario would be D. local preference.
Local preference is an attribute used to influence the inbound traffic within a single AS. It is a well-known discretionary attribute, which means that it is not propagated to other ASes.
By setting a higher local preference value for prefixes received on the preferred link and a lower local preference value for prefixes received on the backup link, AS100 can influence the inbound traffic to use the preferred link.
In contrast, MED (A) is an attribute used to influence the outbound traffic to another AS, and it is only used when there are multiple exit points from the same AS. AS-PATH (C) is used to prevent routing loops and influence outbound traffic when advertising prefixes to other ASes. Neither MED nor AS-PATH is appropriate for influencing inbound traffic from another AS.
Weight (B) is a Cisco-specific attribute that is local to a router and not propagated to other routers. It is used to influence the preferred path to a destination within the same routing protocol. Therefore, weight is not appropriate for influencing inbound traffic from another AS.
In summary, the most appropriate attribute to use in this scenario would be local preference, as it is designed for influencing inbound traffic within a single AS.
