Cisco
352-001 · Question #587
352-001 Question #587: Real Exam Question with Answer & Explanation
The correct answer is A: Use traffic engineering by injecting a preferred LOCAL_PREF attribute to routes advertised from. BGP LOCAL_PREF is the correct attribute to influence outbound path preference within an AS, making the Paris peering the preferred exit for traffic to Big ISP.
Question
Refer to the exhibit. Service provider ACME Internet just added a 100 GB/s peering in Paris that it wants to use by default for outbound traffic to Big ISP. Which routing policy achieves the desired outcomes?
Exhibit
Options
- AUse traffic engineering by injecting a preferred LOCAL_PREF attribute to routes advertised from
- BApply an import policy in New York that adds a Weight attribute to routes learned from Very Big
- CApply an export policy in Paris by applying a MED or community attribute with a preference that
- DApply an import policy hat filters longer prefixes than /24 in Brussels and zurich
Explanation
BGP LOCAL_PREF is the correct attribute to influence outbound path preference within an AS, making the Paris peering the preferred exit for traffic to Big ISP.
Common mistakes.
- B. Weight is a Cisco-proprietary attribute that is local to a single router and is not propagated via iBGP, so it cannot coordinate outbound path preference across the entire ACME network.
- C. MED (Multi-Exit Discriminator) is advertised to neighboring ASes to influence how they send inbound traffic into your AS, not a mechanism to control your own outbound traffic preference.
- D. Filtering prefixes longer than /24 in Brussels and Zurich would limit reachability by discarding more-specific routes but would not establish a preference for the Paris peering for outbound traffic.
Concept tested. BGP LOCAL_PREF for outbound path preference
Reference. https://www.cisco.com/c/en/us/support/docs/ip/border-gateway-protocol-bgp/13753-25.html
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