Which of the following descriptions of problems caused by the mutual introduction of BGP and IGP is wrong?

Question

Options

• AIf a certain route is unstable, it may cause route flapping in the entire AS and affect the stability of the network.
• BPossible loop risks
• CWhen the number of EGP routes is large, the low-end devices within the AS may not be able to load such a large number of routes, causing route loss.
• DIt may cause the BGP neighbor relationship to be disconnected

• A
  4% (2)
• B
  8% (4)
• C
  4% (2)
• D
  84% (42)

Explanation

Option D is the wrong description because mutual redistribution between BGP and IGP does not inherently disconnect BGP neighbor relationships - BGP sessions are maintained over TCP and depend on TCP connectivity and peer configuration, not on what routes are being redistributed between protocols. The session stays up regardless of route redistribution activity.

Why the other options describe real problems (and are therefore not the wrong answer):

• A is correct: An unstable route redistributed from BGP into an IGP (like OSPF) causes repeated IGP recalculations, spreading route flapping across the entire AS and destabilizing the network.
• B is correct: Mutual redistribution creates loop risk - a route learned via BGP can be redistributed into the IGP, then potentially redistributed back into BGP, forming a routing loop if not carefully filtered.
• C is correct: The global BGP table can contain hundreds of thousands of routes; injecting all of them into an IGP forces every router in the AS to hold that full table, which can exceed the memory or processing capacity of low-end devices, causing routes to be dropped.

Memory tip: Remember "BGP sessions survive on TCP" - redistribution problems hurt the routing table (loops, flapping, memory overflow), but they don't pull down the neighbor session itself. If you see an answer claiming redistribution breaks the BGP peering, that's the distractor.

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