What is the correct EBGP path attribute list, ordered from most preferred to least preferred, that the BGP best-path algorithm uses?
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A. B. C. D.B.
The correct EBGP (External Border Gateway Protocol) path attribute list, ordered from most preferred to least preferred, that the BGP (Border Gateway Protocol) best-path algorithm uses is:
C. weight, AS path, local preference, MED
Here's a detailed explanation of each path attribute and why it is ordered the way it is:
Weight: The weight attribute is a Cisco proprietary attribute that is local to the router. It is used to influence the path selection process within the same AS (Autonomous System). A higher weight value is preferred over a lower weight value. Since it is a Cisco proprietary attribute, it is not passed on to other BGP routers outside the AS. This attribute is the first in the path attribute list because it is the most preferred attribute and is only used locally within the router.
AS path: The AS path attribute is used to prevent routing loops and to provide information about the path a packet takes to reach a destination. The AS path is a list of AS numbers that the route has passed through to reach the destination. The BGP best-path algorithm prefers the path with the shortest AS path. Therefore, the shorter AS path is preferred over a longer AS path.
Local preference: The local preference attribute is used to indicate the preferred egress point for a BGP route within the AS. It is used to influence the path selection process within the AS. A higher local preference value is preferred over a lower local preference value. This attribute is third in the path attribute list because it is used within the AS and is more important than the next attribute, MED.
MED (Multi-Exit Discriminator): The MED attribute is used to influence the path selection process when there are multiple entry points into an AS. It is used to indicate the preferred egress point for a BGP route to a neighboring AS. A lower MED value is preferred over a higher MED value. This attribute is last in the path attribute list because it is less important than the other attributes and is only used when there are multiple entry points into an AS.
In summary, the correct EBGP path attribute list, ordered from most preferred to least preferred, that the BGP best-path algorithm uses is: