Which of the following statements regarding BGP control plane convergence is FALSE?

Question

Options

• ACore and edge node failure recovery depends on IGP convergence.
• BLosing neighbor failure is detected by the eBGP session timeout.
• CBGP control plane convergence is independent of number of affected prefixes.
• DUpon BGP control plane convergence, an optimal path is installed in the FIB.

• A
  20% (5)
• B
  12% (3)
• C
  64% (16)
• D
  4% (1)

Explanation

Option C is false because BGP control plane convergence is actually dependent on the number of affected prefixes - each prefix requires individual best-path recalculation and update propagation, so a larger routing table change (e.g., a provider withdrawing thousands of prefixes) takes significantly longer to converge than a single-prefix change.

Why the distractors are true (and not the answer):

• A is true: BGP relies on the IGP (OSPF, IS-IS) to resolve next-hops; a node failure cannot trigger BGP re-convergence until the IGP has already converged and updated reachability.
• B is true: Without BFD, eBGP peer loss is detected via hold-timer expiry (default 90s), which is the session timeout mechanism - not an instantaneous signal.
• D is true: Control plane convergence culminates in the BGP best-path selection process updating the RIB, which then pushes the optimal route down into the FIB for hardware forwarding.

Memory tip: BGP convergence scales with prefixes - picture a stack of mail: delivering 1 letter is fast, delivering 10,000 takes much longer. Any claim that BGP "doesn't care" how many prefixes are affected should immediately raise a red flag.

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