Question 310
A BGP router has imported a route with an unexpected AS path. Observed: The next router drops it because its own AS is present in the path. What evidence would validate recovery from this precise failure mode?
Explanation
Correct Answer
The intended result is An authorized loop-free path is accepted and no repeated AS numbers cause rejection. It specifically verifies recovery from as-loop prevention correctly rejects a path containing the local autonomous system, which produced the original symptom: The next router drops it because its own AS is present in the path. It is stronger evidence than a generic interface-up indicator.
Incorrect Answers
This result is useful in another case with evidence Policy unexpectedly modifies MED for every customer route. It does not test recovery from the next router drops it because its own as is present in the path. Check instead whether an authorized loop-free path is accepted and no repeated AS numbers cause rejection.
That observation would verify a separate fault involving bgp export policy is too broad for the neighbor's contractual prefix set. Its symptom is The transit edge begins advertising an infrastructure loopback to an external customer. For this case the actual issue is as-loop prevention correctly rejects a path containing the local autonomous system, and the relevant success signal is An authorized loop-free path is accepted and no repeated AS numbers cause rejection.
It confirms an unrelated service correction: Standard communities do not provide the three-field large-community semantics. The present case reports The next router drops it because its own AS is present in the path. Its completion test is An authorized loop-free path is accepted and no repeated AS numbers cause rejection.