Drag and Drop Question Drag and drop the BGP attributes from the left into the order of route selection preference on the right. Answer:

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Explanation

The question tests knowledge of the BGP best path selection algorithm by requiring the test-taker to order BGP attributes by their preference.

Approach. The correct interaction is to drag the BGP attributes from the left column into the right column, arranging them from 'step 1' (highest preference) to 'step 5' (lowest preference) based on the BGP best path selection algorithm. Following the widely accepted Cisco BGP best path selection process, the attributes should be ordered as follows:

1. weight: This is a Cisco-specific attribute and is the first to be evaluated. A higher weight is preferred.
2. local preference: This attribute is exchanged between IBGP peers within an autonomous system (AS). A higher local preference is preferred.
3. AS path: The path with the fewest AS numbers (shortest AS path) is preferred.
4. origin: The origin code indicates how a route entered BGP. The preference order is IGP (i) > EGP (e) > Incomplete (?).
5. multi-exit discriminator (MED): Also known as the 'metric', this attribute is used to influence the path taken into an AS from another AS. A lower MED value is preferred.

Therefore, the drag-and-drop interaction should result in 'weight' at 'step 1', 'local preference' at 'step 2', 'AS path' at 'step 3', 'origin' at 'step 4', and 'multi-exit discriminator' at 'step 5'.

Common mistakes.

• common_mistake. Common mistakes include incorrectly recalling the order of attributes, especially confusing local preference and AS path, or misunderstanding the precedence of 'weight' (which is often router-specific and highest preference) or 'MED' (which is lower preference and often used to influence inbound traffic). For example, placing 'AS path' before 'local preference' or 'origin' before 'AS path' would be incorrect. Some might also forget that 'weight' is the first attribute considered, especially in Cisco implementations, or might confuse it with other metrics.

Concept tested. BGP (Border Gateway Protocol) best path selection algorithm and the order of preference for its attributes.

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