Question 120
A new IS-IS site is added to an existing common core. Observed: Neighbors remain Down even though interface transport and timers match. Which ongoing validation gate would best detect a recurrence of this problem?
Explanation
Correct Answer
A useful regression gate tests whether neighbor adjacency forms at the intended level and LSDB distribution is correct and alerts when neighbors remain Down even though interface transport and timers match. This directly checks the technical weakness: NET area identifiers disagree for intended Level 1 adjacency. The gate is derived from the fictional incident and is not an independent Juniper engineer signoff.
Incorrect Answers
It is valid for another service scenario but checks one neighbor reports only a level 2 adjacency despite the access level being required. This case instead needs a gate for neighbors remain down even though interface transport and timers match and evidence that neighbor adjacency forms at the intended level and LSDB distribution is correct.
This gate monitors a different failure, the route repeatedly returns to the protocol it came from. It would not detect the current problem: Neighbors remain Down even though interface transport and timers match. The appropriate check requires neighbor adjacency forms at the intended level and LSDB distribution is correct.
The proposed control is tied to dis priority and tie-break criteria were not considered in interface design, typically observed when a maintenance router unexpectedly controls pseudonode LSP generation. Here the target is net area identifiers disagree for intended level 1 adjacency; monitor neighbor adjacency forms at the intended level and LSDB distribution is correct.