Question 130
An L1/L2 IS-IS PE imports customer prefixes from Level 2. Observed: A Level 1 access router never learns a required remote subnet. What evidence would validate recovery from this precise failure mode?
Explanation
Correct Answer
The intended result is The allowed prefix reaches Level 1 without route feedback into Level 2. It specifically verifies recovery from controlled l2-to-l1 route leaking is not configured for the permitted destination, which produced the original symptom: A Level 1 access router never learns a required remote subnet. It is stronger evidence than a generic interface-up indicator.
Incorrect Answers
It confirms an unrelated service correction: Authentication method and key match do not agree between adjacent peers. The present case reports A Level 1 access router never learns a required remote subnet. Its completion test is The allowed prefix reaches Level 1 without route feedback into Level 2.
This result is useful in another case with evidence The LSDB shows a second device's LSP under an existing system ID. It does not test recovery from a level 1 access router never learns a required remote subnet. Check instead whether the allowed prefix reaches Level 1 without route feedback into Level 2.
That observation would verify a separate fault involving attached-bit and default-cost selection ignore intended internal metric planning. Its symptom is Traffic consistently uses the farther gateway despite the closer one being healthy. For this case the actual issue is controlled l2-to-l1 route leaking is not configured for the permitted destination, and the relevant success signal is The allowed prefix reaches Level 1 without route feedback into Level 2.