350-501 Question #425: Real Exam Question with Answer & Explanation

Question

Refer to the exhibit. Routers R1 through R5 are being deployed within the core of a service provider running BGP. The core supports distribution of VPNv4 routes using MPLS. R3 currently has multiple paths to reach R4. A network engineer must implement BGP attributes so that R3 can reach R4 via R1. Which action must the engineer take to meet the requirement?

Options

• AConfigure R3 so the route to R4 through R1 will have a higher weight than the route from R2 or
• BConfigure R2 to send the route from R4 to R1 using a higher metric than what is advertised to R3.
• CConfigure R3 so the route to R4 through R1 will have a lower local preference than the route from
• DConfigure R5 to send the route from R4 to R1 using a longer AS path than the AS path that it

Explanation

To ensure R3 prefers the path to R4 via R1, the BGP path selection process on R3 must be influenced by configuring a higher BGP weight for the route learned through R1.

Common mistakes.

• B. A higher MED or IGP metric would generally make a path less preferred, and the phrasing implies R2 influencing a path to R1, which is incorrect; R2 advertises paths to R3.
• C. A lower local preference would make the route through R1 less preferred by R3, which is the opposite of the desired outcome.
• D. A longer AS path makes a route less preferred in BGP path selection, which is contrary to the goal of making the path via R1 preferred.

Concept tested. BGP Path Selection - Weight Attribute

Reference. https://www.cisco.com/c/en/us/support/docs/ip/border-gateway-protocol-bgp/13753-3.html

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