JNCIS-ENT IS IS Practice Test 3 — 15 Questions

Question 1

Which command allows you to view the IS-IS database summary?

Accepted Answer

show isis database. The 'show isis database' command shows the LSPs currently in the database.

Answer

show isis statistics

Answer

show isis route

Answer

show isis summary

Question 2

What is the function of the DIS in an IS-IS broadcast network?

Accepted Answer

To generate pseudonode LSPs.. The DIS (Designated Intermediate System) is responsible for generating pseudonode LSPs to represent the broadcast network.

Answer

To authenticate all neighbors.

Answer

To perform path calculation for all routers.

Answer

To act as the routing controller for the area.

Question 3

What happens if you have an area address mismatch in a Level 1 adjacency?

Accepted Answer

The adjacency will fail to form.. Level 1 adjacencies require the routers to share at least one area address.

Answer

The DIS will override the mismatch.

Answer

The adjacency will form but no routes will be exchanged.

Answer

The router will automatically adopt the neighbor's area address.

Question 4

You need to redistribute OSPF routes into IS-IS. Where do you configure this?

Accepted Answer

Under the 'protocols isis export' hierarchy.. Redistribution is configured under the 'policy-options' and applied under 'protocols isis export'.

Answer

Under the OSPF configuration only.

Answer

It is not possible to redistribute OSPF into IS-IS.

Answer

Under the interface level.

Question 5

What is the purpose of the 'lsp-generation-interval'?

Accepted Answer

To limit the frequency of LSP updates.. This command controls how frequently the router generates a new LSP following a topology change.

Answer

To set the hello interval.

Answer

To define the authentication key rotation.

Answer

To set the time for database aging.

Question 6

Which TLV is used to carry IP prefixes in IS-IS?

Accepted Answer

TLV 128. TLV 128 and 135 are used for IP reachability information.

Answer

TLV 10

Answer

TLV 22

Answer

TLV 1

Question 7

How does an IS-IS router identify the DIS in its hello packets?

Accepted Answer

By the router's System ID followed by a non-zero pseudonode ID.. The DIS is identified by the System ID and a pseudonode number (the 7th byte of the LSP ID).

Answer

By a special flag in the header.

Answer

By the area address.

Answer

By the MAC address only.

Question 8

What does the 'show isis statistics' command reveal?

Accepted Answer

The number of received and transmitted PDUs.. This command displays the number of PDUs sent and received by the IS-IS process.

Answer

The current SPF calculation time.

Answer

The database size in bytes.

Answer

The adjacency hold-time.

Question 9

When should you consider increasing the 'csnp-interval'?

Accepted Answer

To reduce control traffic overhead on slow links.. Increasing the interval is useful on slow or congested links to reduce the frequency of full database synchronization traffic.

Answer

To improve convergence time.

Answer

To increase the maximum LSP size.

Answer

To fix adjacency flapping.

Question 10

Which command displays the IS-IS interface parameters?

Accepted Answer

show isis interface. 'show isis interface' shows the configuration and state of IS-IS interfaces.

Answer

show isis configuration

Answer

show interfaces isis

Answer

show protocols isis interface

Question 11

Which of the following are true regarding IS-IS Level 1/Level 2 routers? (Choose TWO)

Accepted Answer

They maintain both a Level 1 and a Level 2 database.. L1/L2 routers act as bridges between areas and must maintain both databases.

Answer

They are always the DIS for the segment.

Answer

They only form Level 1 adjacencies.

Answer

They do not perform SPF calculations.

Question 12

What is the default behavior when an IS-IS router receives an LSP it already has?

Accepted Answer

It discards the LSP if the sequence number is lower.. If the sequence number is the same, the router discards it. If newer, it updates; if older, it sends a copy of the newer one back to the sender.

Answer

It always floods it to all neighbors.

Answer

It restarts the SPF calculation immediately.

Answer

It requests the LSP from the source again.

Question 13

Which of the following are valid IS-IS PDU types? (Choose THREE)

Accepted Answer

IIH PDU. The four PDU types are IIH, LSP, CSNP, and PSNP.

Answer

Hello ACK PDU

Answer

Routing Update PDU

Question 14

Which factors influence the DIS election on a broadcast link? (Choose TWO)

Accepted Answer

SNPA (MAC) address. The DIS is determined by the configured priority and, as a tie-breaker, the SNPA (MAC) address.

Answer

System ID

Answer

Area Address

Answer

LSP sequence number

Question 15

Which of the following are true regarding IS-IS authentication? (Choose TWO)

Accepted Answer

It secures the PDUs exchanged between neighbors.. Authentication can be applied to PDUs (Hello/LSP/SNP) and can be configured globally or per interface.

Answer

It is mandatory for all IS-IS deployments.

Answer

It can only be configured for the entire area.

Answer

It encrypts the entire link traffic.