Be able to identify IS-IS PDU and TLV types, run the right Junos show command to read the link-state database, and predict how lsp-lifetime and reference bandwidth change behavior. The key is knowing which PDU or timer does what before touching configuration.
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Domain overview
This domain covers IS-IS on Juniper devices: adjacency formation and levels, PDU and TLV types, link-state database inspection, metric styles, and route leaking between L1 and L2. JNCIS-ENT questions are operational and configuration-based, asking you to identify valid PDU types, select the correct Junos show command, and predict the effect of timers and metric changes.
Exam objectives
Valid IS-IS PDU types: LSP, CSNP, PSNP, and IIH, including LAN versus point-to-point behavior.
Junos operational commands such as show isis database extensive to inspect TLVs and extended IP reachability.
LSP lifetime and refresh behavior configured with the lsp-lifetime statement and its effect on database aging.
Metric configuration including reference bandwidth, wide metrics, and route leaking between Level 1 and Level 2.
Confusing PSNP and CSNP roles, or forgetting that IIH PDUs exist separately for LAN and point-to-point links.
Assuming lsp-lifetime sets how long an adjacency stays up rather than how long the router's own LSP remains valid.
Changing reference bandwidth without realizing it only affects metrics on interfaces using the default metric style, not explicit values.
Click any question to see the full explanation and answer options, or start a focused practice session above.
An administrator is configuring a new point-to-point link between two Junos routers running IS-IS. By default, how does IS-IS handle adjacency establishment on a point-to-point link compared to a broadcast link?
2During the examination of IS-IS packet captures on a multi-access LAN interface, an engineer notices a specific PDU type being transmitted periodically by the Designated Intermediate System (DIS) to maintain synchronized link-state databases. Which PDU type performs this function?
3A network engineer wants to verify IS-IS link-state database entries, specifically checking for TLVs that carry extended IP reachability information with wide metrics. Which Junos operational command should be used?
4Which TWO characteristics describe the behavior and properties of Level 1 and Level 2 routing in IS-IS? (Choose two)
5During an audit of an IS-IS routing network, an engineer examines the Type-Length-Value (TLV) structures used in IS-IS PDUs. Which TLV is specifically responsible for carrying IPv4 internal and external reachability information when using wide metrics?
6Which command is used to verify the IS-IS adjacency state on a Junos device?
7An engineer is troubleshooting IS-IS adjacency formation failures on a Junos device. Which THREE parameters must match or be compatible between neighboring routers to successfully establish an IS-IS adjacency? (Choose three)
8You have a Level 1/Level 2 router connecting two areas. How does it advertise itself to Level 1 routers?
9In a multi-access network, which PDU is responsible for the DIS election?
10What is the effect of changing the reference bandwidth in IS-IS?
11When using authentication in IS-IS, where can you apply the password?
12What happens if you have an LSP with an expired lifetime?
13Why would you set an interface to 'passive' in IS-IS?
14Which of the following is required for two routers to form a Level 2 adjacency?
15What is the purpose of the 'lsp-lifetime' command?
16Which level is enabled by default in Junos when configuring IS-IS on an interface?
17You are configuring multi-topology IS-IS. What does this allow?
18What is the function of the DIS in an IS-IS broadcast network?
19What happens if you have an area address mismatch in a Level 1 adjacency?
20What is the purpose of the 'lsp-generation-interval'?
21How does an IS-IS router identify the DIS in its hello packets?
22What does the 'show isis statistics' command reveal?
23When should you consider increasing the 'csnp-interval'?
24Which command displays the IS-IS interface parameters?
25Which of the following are valid IS-IS PDU types? (Choose THREE)
26Which of the following are true regarding IS-IS authentication? (Choose TWO)
27Which of the following are valid IS-IS interface types? (Choose TWO)
28Which actions occur during an IS-IS SPF calculation? (Choose THREE)
29Which of the following are true about IS-IS Level-1 and Level-2 areas? (Choose TWO)
30Which of the following are true regarding the IS-IS 'hello-interval'? (Choose TWO)
31A network administrator is configuring IS-IS on a Juniper router. They want to ensure that the router participates in both Level 1 and Level 2 routing. Which configuration statement is correct?
32You are configuring IS-IS on a Juniper router and want to verify the adjacency state with a neighbor. You issue the command 'show isis adjacency'. The output shows the neighbor's system ID, interface, and state as 'Up'. However, you notice that the 'Holdtime' field is decreasing. What does this indicate?
Be able to identify IS-IS PDU and TLV types, run the right Junos show command to read the link-state database, and predict how lsp-lifetime and reference bandwidth change behavior. The key is knowing which PDU or timer does what before touching configuration.
The Courseiva JNCIS-ENT question bank contains 32 questions in the IS IS domain. Click any question to see the full explanation and answer breakdown.
Start with a 10-question focused session to identify your baseline accuracy in this domain. Read every explanation — even for questions you answer correctly — to understand the reasoning. Once you score consistently above 80%, move to a 20–30 question session to confirm depth before moving to the next domain.
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