20+ practice questions focused on IS IS — one of the most tested topics on the Juniper Networks Enterprise Routing and Switching, Specialist (JNCIS-ENT, JN0-352) (JNCIS-ENT) exam. Each question includes a detailed explanation so you learn why the right answer is correct.
Start IS IS PracticeAn engineer needs to influence the DIS election on a multi-access broadcast segment running IS-IS on Junos devices. Which configuration parameter and hierarchy should the engineer modify to guarantee a specific router wins the DIS election?
Explanation: The DIS election in IS-IS is influenced by the interface priority. Configuring 'set protocols isis interface <name> priority <value>' with a higher value increases the likelihood of winning the DIS election. The default priority is 64, and the highest priority wins; if tied, the highest MAC address wins.
An engineer needs to configure a Junos device to operate in an IS-IS routing domain where the router should connect both Level 1 and Level 2 areas, forming a boundary between them. Which configuration command under the [edit protocols isis interface] hierarchy correctly enables dual-level operations on the interface?
Explanation: On Junos, dual-level IS-IS operation on an interface is enabled by setting the interface's level to '1-2' under [edit protocols isis interface]. The 'wide-metrics-only' keyword is a valid modifier that tells the interface to advertise only wide (TLV 22) metrics for both levels, which is the modern recommended style. Together, 'set level 1-2 wide-metrics-only' both enables L1/L2 adjacency formation on the interface and constrains metric advertisement to wide metrics.
A network administrator troubleshooting an IS-IS adjacency issue notices that two routers are failing to form an adjacency over a point-to-point link. One router has wide metrics enabled globally, while the other router has wide metrics disabled and only supports narrow metrics. Which parameter or feature must be matching or handled for IS-IS link-state PDUs to be successfully processed between these neighbors?
Explanation: IS-IS supports narrow metrics (default in older implementations, max weight 63 per link) and wide metrics (supporting up to 2^24-1). If metric styles do not match or if compatibility modes (such as traffic-engineering metrics or metric-style transition settings) are not configured, routers may experience issues exchanging reachability, although point-to-point adjacencies can technically form, routing tables will not converge correctly without metric style alignment or wide-metrics configuration.
Which THREE statements are true regarding the Designated Intermediate System (DIS) election and its operational differences compared to OSPF's Designated Router (DR) election? (Choose three)
Explanation: Option A is correct because IS-IS DIS election is non-preemptive: once a DIS is elected, a newly arriving router with a higher priority will not displace it until the DIS fails or the interface/adjacency is reset, unlike OSPF DR election which can be influenced by priority and re-election events. Option B is correct because IS-IS breaks priority ties by comparing the highest interface MAC address on broadcast media (or the highest System ID on point-to-point/non-broadcast media), which is a deterministic tie-breaker. Option D is correct because IS-IS has no Backup DIS role analogous to OSPF's BDR; instead, other routers on the segment maintain awareness of priorities and can assume the DIS role if the current DIS fails. Option C is not correct because DIS election is per-level and does not require all routers on the segment to share identical area addresses regardless of Level 1 or Level 2 status. Option E is not correct because the DIS floods LSPs using multicast (and on point-to-point links uses specific mechanisms), not exclusively unicast to all neighbors.
You have two routers connected via a point-to-point link. You need to ensure they form an IS-IS adjacency. Which configuration is required?
Explanation: On point-to-point links, IS-IS will form an adjacency regardless of the level match, provided the interface is enabled in the correct protocol hierarchy.
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Practice all IS IS questions1. Baseline your knowledge
Start with 10 questions to gauge your current understanding of IS IS. This tells you whether you need a concept refresher or just practice.
2. Review every explanation
For each question — right or wrong — read the full explanation. Understanding why an answer is correct is more valuable than knowing the answer itself.
3. Focus on exam traps
IS IS questions on the JNCIS-ENT frequently use trap wording. Look for subtle differences in answers that test your precision, not just general knowledge.
4. Reach 80% consistently
Do repeated sessions until you score 80%+ three times in a row. Then move to mixed-mode practice to test cross-topic recall under realistic conditions.
The exact number varies per candidate. IS IS is tested as part of the Juniper Networks Enterprise Routing and Switching, Specialist (JNCIS-ENT, JN0-352) (JNCIS-ENT) blueprint. Practicing with targeted IS IS questions ensures you can handle any format or difficulty that appears.
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Difficulty is subjective, but IS IS is a high-priority exam concept tested in multiple ways — direct recall, scenario analysis, and command-output interpretation. Consistent practice is the best way to build confidence.
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