Question 320
A BGP customer edge receives an unexpected default-only route after peering work. Observed: Specific destination prefixes disappear from the customer route table. What operational check best guards against this problem returning?
Explanation
Correct Answer
This control asks for the same recovery evidence (The customer receives exactly the contracted specific prefixes and default behavior) and flags recurrence of the same failure (Specific destination prefixes disappear from the customer route table). It targets the underlying issue, a peer export policy was accidentally changed to advertise default only, rather than a different service problem. The exact cadence must be agreed with operations.
Incorrect Answers
The proposed control is tied to the remote neighbor ip or expected autonomous-system setting does not match the peering contract, typically observed when bGP remains Idle even though next-hop IPs respond to ping. Here the target is a peer export policy was accidentally changed to advertise default only; monitor the customer receives exactly the contracted specific prefixes and default behavior.
It is valid for another service scenario but checks the ipv4 bgp session is established but ipv6 route exchange never starts. This case instead needs a gate for specific destination prefixes disappear from the customer route table and evidence that the customer receives exactly the contracted specific prefixes and default behavior.
This gate monitors a different failure, backup path is preferred when an origin prefix first appears. It would not detect the current problem: Specific destination prefixes disappear from the customer route table. The appropriate check requires the customer receives exactly the contracted specific prefixes and default behavior.