Question 340
Two neighboring eBGP routers have a mixed 16-bit and 32-bit AS numbering design. Observed: A monitoring system reports AS_TRANS unexpectedly in the legacy view. Which change-acceptance control is most relevant to preventing this exact failure?
Explanation
Correct Answer
The control is specific to the initial failure. It requires the result Both peers display the intended full AS numbers and routes retain valid AS paths. and treats A monitoring system reports AS_TRANS unexpectedly in the legacy view. as a failure signal. The causal concern is four-octet as capability handling is being read as an actual unexpected transit asn.
Incorrect Answers
This gate monitors a different failure, peers see the advertised prefix but cannot install it in their ribs. It would not detect the current problem: A monitoring system reports AS_TRANS unexpectedly in the legacy view. The appropriate check requires both peers display the intended full AS numbers and routes retain valid AS paths.
The proposed control is tied to the reflector has no alternate path because add-path or path-diversity strategy is absent, typically observed when another iBGP router receives the path but loses it when the originating client flaps. Here the target is four-octet as capability handling is being read as an actual unexpected transit asn; monitor both peers display the intended full AS numbers and routes retain valid AS paths.
It is valid for another service scenario but checks a route arrives with the right community but enters the wrong routing instance. This case instead needs a gate for a monitoring system reports as_trans unexpectedly in the legacy view and evidence that both peers display the intended full AS numbers and routes retain valid AS paths.