A certain enterprise's network is as shown in the figure. Which of the following is a suitable reinjection method?

Question

Options

• APolicy routing back injection
• BStatic routing back injection
• CSecond level reinjection
• DGRE VPN backnote

• A
  10% (3)
• B
  3% (1)
• C
  83% (24)
• D
  3% (1)

Explanation

Second-level reinjection is correct for the topology shown because it avoids the routing loops that arise when the cleaning/scrubbing center sits in a position where simpler reinjection methods would send cleaned traffic back through the same path it came from - the two-stage design breaks the loop by injecting traffic at a different routing tier.

Policy routing reinjection (A) is ruled out because in this specific topology the policy routing would still create a loop or require complex per-packet matching that the diagram's architecture doesn't support cleanly. Static routing reinjection (B) introduces permanent route entries that conflict with the existing routing table in this layout, leading to black-holing or loops without additional workarounds. GRE VPN (D) is an encapsulation/tunneling mechanism used for site-to-site connectivity, not a native reinjection technique for traffic-cleaning architectures - using it here adds unnecessary overhead and complexity without solving the loop problem.

Memory tip: Think "two-stage = two-loop-break." Whenever the cleaning center's position in the topology would cause cleaned traffic to re-enter the dirty path, you need a second level to steer it elsewhere - a single-level method (static or policy) will just circle back.

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