350-501 Question #122: Real Exam Question with Answer & Explanation

Question

Refer to the exhibit. If the SP network is configuring RTBH filtering to protect hosts on the 152.68.19.0/24 network, which router should be configured as the black hole activating router?

Options

• AF
• BC
• CD
• DL
• EA
• FK

Explanation

In a Remotely Triggered Black Hole (RTBH) filtering scenario, the 'black hole activating router' is the router that receives the trigger (e.g., a specific BGP community) and then injects a blackhole route for the target network into the IGP or BGP.

Common mistakes.

• A. Router F, without context, is unlikely to be the sole activating router if it's an internal or core device not handling ingress traffic and blackhole route injection.
• B. Router C, presumably an internal or core router, is typically a blackhole router that receives the blackhole route, not the one activating or originating it.
• C. Router D, similar to Router C, is likely a core or transit router that would receive and apply the blackhole route, rather than being the activating router.
• E. Router A, without context, is unlikely to be the sole activating router if it's an internal or core device not handling ingress traffic and blackhole route injection.
• F. Router K, without context, is unlikely to be the sole activating router if it's an internal or core device not handling ingress traffic and blackhole route injection.

Concept tested. Remotely Triggered Black Hole (RTBH)

Reference. https://www.cisco.com/c/en/us/td/docs/ios/12_0s/feature/guide/s_rtbh.html

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