350-401 Question #821: Real Exam Question with Answer & Explanation

Question

Refer to the exhibit. An engineer is reaching network 172.16.10.0/24 via the R1-R2-R4 path. Which configuration forces the traffic to take a path of R1-R3-R4?

Options

• AR1(config)#route-map RM_LOCAL_PREF permit 10
• BR1(config)#route-map RM_AS_PATH_PREPEND
• CR1(config)#router bgp 100
• DR2(config)#route-map RM_MED permit 10

Explanation

BGP Local Preference Path Manipulation

Option A is correct because Local Preference is a BGP attribute used within an Autonomous System (AS) to influence outbound path selection - a higher Local Preference value wins, so configuring a route-map on R1 that sets a higher Local Preference for paths learned via R3 will steer traffic along the R1-R3-R4 path instead of R1-R2-R4.

• Option B is wrong because AS Path Prepending is used to influence inbound traffic from external ASes by making a path appear longer/less desirable - it doesn't control internal path selection between R2 and R3.
• Option C is wrong because simply entering BGP router configuration mode on R1 (router bgp 100) performs no path manipulation on its own - no attribute is being set.
• Option D is wrong because MED (Multi-Exit Discriminator) is sent to external BGP neighbors to influence how traffic enters your AS from outside, not how internal routers forward traffic; additionally, configuring it on R2 rather than the ingress router R1 would not achieve the desired effect.

🧠 Memory Tip: Think "Local Preference = Local Control" - it's the go-to tool for controlling which exit path routers inside your own AS prefer. Higher value = preferred path.

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