JNCIA-JUNOS Practice Test 21 — 15 Questions

Question 1

Based on the exhibit, the interface appears to be up and has an IP address, but the 'monitor traffic' output shows no packets. What is the most likely cause?

Accepted Answer

The interface is not in promiscuous mode, and 'monitor traffic' requires that mode to capture packets.. Option B is correct because the interface is in forwarding mode, and 'monitor traffic' only captures packets when the interface is in promiscuous mode. Option A is wrong because the interface is administratively up. Option C is wrong because there is no firewall filter configured in the exhibit. Option D is wrong because the interface has an IP address and is not unnumbered.

Answer

The interface is administratively down.

Answer

The interface is an unnumbered Ethernet interface.

Answer

A firewall filter is blocking all inbound traffic.

Question 2

An engineer needs to check for packet errors on an interface. Which two commands provide error counter information? (Choose two.)

Accepted Answer

show interfaces extensive. Option B, 'show interfaces errors', provides a concise view of error counters per interface. Option C, 'show interfaces extensive', includes detailed error statistics. Option A shows a brief summary without errors. Option D is invalid syntax (singular 'interface'). Option E shows optical diagnostics, not packet errors.

Answer

show interfaces diagnostics

Answer

show interface errors

Answer

show interfaces terse

Question 3

Refer to the exhibit. A network administrator notices intermittent connectivity issues. Based on the log messages, what is the most likely cause?

Accepted Answer

The interface ge-0/0/0 is experiencing a physical layer issue causing it to flap.. The log shows rapid down/up events (flapping) on interface ge-0/0/0. This pattern typically indicates a physical layer problem such as a faulty cable or transceiver. Option B is plausible but the traps are symptoms, not the cause. Option C is less likely because the adjacency recovers quickly. Option D is unsupported by the logs.

Answer

The ISIS protocol has a configuration error that prevents adjacency.

Answer

An SNMP trap is causing a loop in the network.

Answer

The router's MIB is corrupted causing false logs.

Question 4

Which TWO statements about the Junos CLI are correct?

Accepted Answer

The pipe character (|) can be used to filter command output.. Option A is correct because the pipe character filters output in operational mode. Option D is correct because the `run` command allows executing operational commands from configuration mode. Option B is wrong because `commit confirmed` requires a subsequent commit to make changes permanent. Option C is wrong because `rollback 0` reverts to the current active configuration, not the previous one. Option E is wrong because `set cli screen-length 0` disables paging, not command-line editing.

Answer

The `commit confirmed` command saves the configuration permanently.

Answer

The `set cli screen-length 0` command disables command-line editing features.

Answer

The `rollback 0` command reverts to the previous committed configuration.

Question 5

A network engineer is configuring a new Juniper MX router to replace an existing core router. The engineer has applied several configuration changes and wants to ensure that the new configuration can be tested safely. If the test fails (e.g., loss of management connectivity), the router should automatically revert to the previous configuration after a 5-minute period. The engineer performs a commit confirmed with a timeout of 5 minutes. After 4 minutes, the engineer verifies that the change is successful and wants to make it permanent. Which action should the engineer take to ensure the configuration persists?

Accepted Answer

Issue a standard 'commit' command to confirm the configuration.. Option C is correct because issuing 'commit check' does not make the configuration permanent; it only validates syntax. The engineer must explicitly commit the candidate configuration to confirm it. Option A is wrong because 'rollback 0' reverts to the previous configuration, undoing the change. Option B is wrong because 'request system reboot' would interrupt operations and is unnecessary. Option D is wrong because 'commit confirmed' with a new timeout would restart the timer but does not finalize; a standard commit is needed.

Answer

Issue the 'rollback 0' command, then commit.

Answer

Issue the 'commit confirmed 5' command again to reset the timer.

Answer

Issue the 'request system reboot' command to reload the router.

Question 6

Refer to the exhibit. The interface ge-0/0/0 is configured as shown, but the interface is operationally down. Which command would provide the most detailed information about the interface status and errors?

Accepted Answer

show interfaces ge-0/0/0 extensive. Option C is correct because `show interfaces extensive` provides detailed operational status, including error counters, physical state, and protocol information. Option A only shows a brief summary. Option B shows basic information but not as detailed as extensive. Option D shows the configuration, not operational status.

Answer

show interfaces ge-0/0/0

Answer

show configuration interfaces ge-0/0/0

Answer

show interfaces ge-0/0/0 terse

Question 7

Which TWO statements about IPv4 addressing are correct?

Accepted Answer

The network 169.254.0.0/16 is used for link-local addressing.. Options A and B are correct. 127.0.0.1 is the loopback address, and 169.254.0.0/16 is used for link-local addressing (APIPA). Option C is false because 192.168.0.0/16 is a private address. Option D is false because 10.0.0.0/8 is private. Option E is false because a /24 subnet mask provides 254 usable host addresses, not 256.

Answer

A /24 subnet mask provides 256 usable host addresses.

Answer

The address 192.168.0.0/16 is a public address.

Answer

The address 10.0.0.0/8 is a public address.

Question 8

Refer to the exhibit. The administrator has verified that the remote router's interface uses PPP encapsulation. What is the most likely cause of the link not passing traffic?

Accepted Answer

The encapsulation type is mismatched.. Option C is correct. The exhibit shows the local interface is configured with HDLC encapsulation, while the remote uses PPP. This encapsulation mismatch prevents Layer 2 communication. Options A and B are incorrect because the physical link is up and enabled. Option D is incorrect because an IP address mismatch would allow Layer 2 connectivity but prevent Layer 3 routing.

Answer

The interface has a speed mismatch.

Answer

The interface is using the wrong IP address.

Answer

The interface is administratively down.

Question 9

Which two statements about static routes in Junos OS are correct?

Accepted Answer

Static routes have a default preference of 5.. Option A is correct: static routes have a default preference of 5. Option B is correct: when a static route uses an interface as the next-hop, the router uses ARP to resolve the MAC address of the next-hop. Option C is incorrect: a next-hop of 0.0.0.0 is used for a default route, not a discard route; a discard route uses the 'discard' keyword. Option D is incorrect: static routes cannot have a preference of 0; preference 0 is reserved for directly connected routes. Option E is incorrect: 127.0.0.1 is a loopback address, but as a next-hop it would require the loopback interface to be specified and is not typically used for unreachable routes.

Answer

A static route with a next-hop of 127.0.0.1 is an unreachable route.

Answer

A static route with a next-hop of 0.0.0.0 is a discard route.

Answer

Static routes can have a preference value of 0.

Question 10

Refer to the exhibit. A network administrator configured a static route to 10.0.0.0/24 with next-hop 192.168.1.1. The route is not appearing in the active routing table. What is the most likely reason?

Accepted Answer

The next-hop address is not reachable.. The exhibit shows the route's next-hop type as 'Unreachable', indicating that 192.168.1.1 is not reachable. Option B is correct. Option A is incorrect because the preference of 5 is low, and a higher preference would make it less preferred, but the route is not active due to next-hop unreachability. Option C is incorrect: if an OSPF route with lower preference (higher priority) existed, it would be active, but the static route would still be present as a backup; the exhibit shows the route is not active because the next-hop is unreachable. Option D is incorrect: a reject route would show a next-hop of 'Reject' or 'Discard'.

Answer

The route is a reject route.

Answer

The route is being overridden by an OSPF route with lower preference.

Answer

The static route preference is too high.

Question 11

An administrator is troubleshooting a configuration issue where a route filter is unexpectedly dropping traffic. The filter uses an 'exact' match type. Which statement correctly describes the behavior of the 'exact' match type in a prefix list?

Accepted Answer

The route must match the prefix and prefix length exactly.. Option B is correct because the 'exact' match type in a Junos prefix list requires the route's prefix and prefix length to match the specified prefix and length identically. This is defined in the Junos routing policy framework, where 'exact' is used for precise route filtering, such as matching a specific network like 192.168.1.0/24 without allowing any subnets or supernets.

Answer

The route mask must be equal to or greater than the specified prefix length.

Answer

The prefix 0.0.0.0/0 is never matched by 'exact' filters.

Answer

The route mask must be greater than the specified prefix length.

Question 12

Which TWO statements about configuration groups are correct? (Choose two.)

Accepted Answer

Multiple groups can be applied, and the order of application determines priority.. Option D is correct because when multiple configuration groups are applied, the order of the 'apply-groups' statements determines the priority: the last group listed has the highest priority and overrides conflicting settings from earlier groups. This allows administrators to layer configuration changes predictably, with more specific groups overriding more general ones.

Answer

The 'apply-groups' statement is only valid at the top level of the configuration.

Answer

Configuration groups can only contain interface-related configuration.

Answer

The 'apply-groups' statement can be used to apply only specific statements from a group.

Question 13

Refer to the exhibit. A route policy named DENY-RFC1918 is configured. What is the final action of this policy for a route matching 172.20.0.0/16?

Accepted Answer

The route is rejected because it matches the prefix list.. The route policy DENY-RFC1918 uses a prefix list that matches RFC 1918 private addresses, including 172.20.0.0/16 (which falls within the 172.16.0.0/12 range). Since the route matches the prefix list, term 1 applies a 'reject' action, and because no subsequent term explicitly accepts the route, the final action is reject.

Answer

The route is accepted because it does not match the prefix list.

Answer

The route is accepted because term 2 accepts all routes.

Answer

The route is rejected only if the prefix is exactly 172.16.0.0/12.

Question 14

An administrator makes changes to the candidate configuration and wants to automatically revert to the previous configuration if the changes cause a loss of connectivity. Which method should be used?

Accepted Answer

Use the 'commit confirmed' command.. The 'commit confirmed' command is the correct method because it allows an administrator to commit a candidate configuration with a confirmation timeout (default 10 minutes). If connectivity is lost and the commit is not confirmed within the timeout, Junos automatically reverts to the previous configuration, ensuring the device remains reachable.

Answer

Use the 'commit check' command.

Answer

Use the 'commit synchronize' command.

Answer

Use the 'rollback' command.

Question 15

Which THREE statements about the commit operation are correct? (Choose three.)

Accepted Answer

The 'commit check' command validates the syntax of the candidate configuration without activating it.. Option A is correct because the 'commit check' command validates the syntax and semantics of the candidate configuration without activating it. This allows an administrator to verify that the configuration is error-free before making it active, preventing potential misconfigurations from disrupting network operations.

Answer

The candidate configuration is stored in a file named 'juniper.conf' on the flash drive.

Answer

A commit operation automatically saves the rescue configuration.

JNCIA-JUNOS Practice Test 21 — 15 Questions

Exhibit

JNCIA-JUNOS Practice Test 21 — 15 Questions

Exhibit