350-501 Question #327: Real Exam Question with Answer & Explanation

Question

Refer to the exhibit. The network engineer who manages ASN 65001 is troubleshooting suboptimal routing to the 198.18.15.0/24 prefix. According to the network requirements: - Routing to IP destinations in the 198.18.15.0/25 block must be preferred via the EDGE-1 PE. - Routing to IP destinations in the 198.18.15.128/25 block must be preferred via the EDGE-2 PE. - More specific prefixes of the 198.18.15.0/24 block must not be advertised beyond the boundaries of ASN 64611. - Routing to 198.18.15.0/24 must be redundant in case one of the uplinks on INT-R1 fails. Which configuration must the network engineer implement on INT-R1 to correct the suboptimal routing and fix the issue?

Options

• Aconfigure terminal
• Bconfigure terminal
• Cconfigure terminal
• Dconfigure terminal

Explanation

The engineer must configure BGP Local Preference on INT-R1 to influence routing within ASN 65001. Local Preference, applied at the point of route origination, ensures that specific prefixes are routed optimally via the designated PEs.

Common mistakes.

• A. This option uses AS-path prepending with the local AS (65001) which is not typically used for influencing internal path selection or specific egress points as Local Preference does, and it also sets the Local Preference values in a way that doesn't align with the requirement for 198.18.15.128/25.
• C. This option incorrectly assigns Local Preference values; it sets a lower preference (100) for 198.18.15.0/25, which is supposed to be preferred via EDGE-1, and a higher preference (200) for 198.18.15.128/25, contradicting the desired routing outcome where EDGE-1 is primary for 0/25 and EDGE-2 for 128/25.
• D. This option incorrectly uses AS-path prepending with the local AS (65001) which is generally unsuitable for the stated requirements. Additionally, while the LP values for 198.18.15.0/25 are consistent, the use of AS-path prepend and the LP for 198.18.15.128/25 doesn't meet the requirement for preferred routing via EDGE-2.

Concept tested. BGP Local Preference for path selection

Reference. https://www.cisco.com/c/en/us/support/docs/ip/border-gateway-protocol-bgp/13761-40.html#local_preference

No community discussion yet for this question.