JN0-106 Hard Questions — 25 Difficult Questions

Question 1

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?

Choose an answer to begin — your selection is scored in the full session.

Accepted Answer

The next-hop address is not reachable.. The exhibit shows that the route's next-hop type is 'Unreachable', indicating that the next-hop address 192.168.1.1 is not reachable. Since the next-hop is unreachable, the static route cannot be installed in the active routing table. Option B is incorrect because a reject route would show 'Reject' or 'Discard'. Option C is incorrect: even if an OSPF route existed with lower preference (higher priority), the static route would still appear as a backup; the problem here is next-hop unreachability. Option D is incorrect: a static route with preference 5 is low, meaning it is highly preferred; high preference would make it less preferred, but the route is not active due to unreachable next-hop, not preference.

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 2

While in configuration mode, an administrator wants to see the difference between the candidate configuration and the active configuration. Which command accomplishes this?

Accepted Answer

show | compare. The 'show | compare' command, when executed in configuration mode, displays the differences between the candidate configuration and the active (committed) configuration. This pipe filter compares the current candidate configuration against the last committed configuration, highlighting additions, deletions, and changes, which is the exact requirement for seeing the difference.

Answer

show configuration

Answer

run show configuration

Answer

show system commit

Question 3

Which THREE commands are valid in Junos operational mode? (Choose three.)

Accepted Answer

show interfaces terse. 'show interfaces terse' is a valid operational mode command that displays a concise summary of interface status and configuration. Operational mode in Junos is used for monitoring, troubleshooting, and viewing the current state of the device, and 'show' commands are the primary tools for this purpose.

Answer

set interfaces ge-0/0/0 unit 0 family inet address 10.0.0.1/24

Answer

commit and-quit

Question 4

A network engineer needs to analyze NTP synchronization status and offset. Which command provides detailed NTP peer information including delay, offset, and jitter?

Accepted Answer

show ntp associations. The 'show ntp associations' command displays detailed NTP peer information, including delay, offset, and jitter, which are essential for analyzing synchronization status. This command lists all configured NTP peers and their current state, providing the specific metrics needed to assess clock accuracy and stability.

Answer

show ntp statistics

Answer

show ntp status

Answer

show ntp peer

Question 5

Which THREE statements are true about commit operations in Junos OS?

Accepted Answer

Multiple users can make configuration changes simultaneously, but only one can commit at a time.. Junos OS allows multiple users to enter configuration mode and make changes simultaneously, but the commit operation is serialized: only one user can commit at a time. This prevents conflicting changes from being applied concurrently, ensuring configuration consistency.

Answer

The 'commit confirmed' command immediately discards changes if not confirmed.

Answer

The 'commit' command always requires 'commit synchronize' when using dual Routing Engines.

Question 6

A service provider operates a Juniper MX router that receives a default route from two different ISPs via EBGP. Both ISPs advertise 0.0.0.0/0 with the same local preference (100), same AS path length, and same metric. The network administrator wants to load balance outgoing traffic across both ISPs for redundancy and bandwidth utilization. After applying the configuration, the administrator checks the routing table and sees that only one default route is active, the one from ISP-A. The other route from ISP-B is present but not active. The administrator verifies that both routes have the same preference (170) and same BGP attributes. The ISP links are different: ISP-A is connected via interface ge-0/0/0.0 with next-hop 10.1.1.2, and ISP-B via interface ge-0/0/1.0 with next-hop 10.2.2.2. What is the most likely reason that both routes are not active and load-balanced?

Accepted Answer

The BGP routes are from different autonomous systems.. By default, Junos BGP does not load balance routes from different autonomous systems. To enable multipath across different ASes, the 'multipath multiple-as' command must be configured under BGP. Option A is irrelevant. Option B is not a cause because different next-hops can be load-balanced under multipath. Option D is the solution, not the cause. Therefore, the most likely cause is that the routes are from different ASes.

Answer

The router has 'no-policy-statistics' enabled on the BGP sessions.

Answer

The BGP routes have different next-hop addresses.

Answer

The router is configured with 'multipath multiple-as' under BGP.

Question 7

Which TWO statements correctly describe the behavior of the 'commit confirmed' command in Junos?

Accepted Answer

The confirmation timeout can be modified by specifying a number of minutes.. The `commit confirmed` command in Junos accepts an optional numeric argument (in minutes) to override the default confirmation timeout. For example, `commit confirmed 10` sets a 10-minute window during which the administrator must issue a `commit` to make the changes permanent; otherwise, the system automatically rolls back to the previous active configuration.

Answer

The default confirmation timeout is 5 minutes.

Answer

It requires a reboot to revert to the previous configuration.

Answer

It stages the configuration in the candidate configuration but does not apply it until confirmed.

Question 8

Which THREE are valid methods to exit configuration mode in Junos? (Choose three.)

Accepted Answer

exit configuration-mode. 'exit configuration-mode' is a valid operational mode command that explicitly exits from configuration mode back to operational mode. This command is used when you are at the top of the configuration hierarchy and want to leave the configuration CLI session.

Answer

commit check

Answer

quit

Question 9

During a network traffic storm, a Juniper EX switch's CPU utilization spikes to 100%. Which command would best help identify the cause?

Accepted Answer

monitor traffic interface ge-0/0/0. The 'monitor traffic interface' command captures live packet headers on the specified interface, allowing you to see the type and source of traffic causing the CPU spike. During a traffic storm (e.g., broadcast storm), this command reveals excessive broadcast, multicast, or unknown unicast frames, which are typically the root cause of high CPU utilization on Juniper EX switches.

Answer

show spanning-tree bridge

Answer

show ethernet-switching table

Answer

show interfaces extensive ge-0/0/0

Question 10

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

Accepted Answer

The rescue configuration is designed to provide a method of last-resort recovery.. The rescue configuration is explicitly designed to provide a method of last-resort recovery. It allows an administrator to save a known-good configuration that can be loaded even if the active configuration becomes corrupted or inaccessible, ensuring the device can be brought back to a functional state.

Answer

The rescue configuration is automatically saved after every commit.

Answer

The 'rollback rescue' command loads the factory-default configuration.

Answer

The rescue configuration can be used to restore only a subset of the configuration.

Question 11

Which THREE route types are considered protocol-independent in Junos?

Accepted Answer

Direct routes. Direct, local, and static routes are considered protocol-independent because they are not learned or installed by any dynamic routing protocol. Direct routes are automatically created for directly connected interfaces, local routes represent the interface's own IP address, and static routes are manually configured by an administrator. These routes exist in the routing table regardless of whether any routing protocol is running, hence the term 'protocol-independent'.

Answer

BGP routes

Answer

OSPF routes

Question 12

An engineer is implementing VLAN trunking between two Juniper EX switches. Which statement about native VLANs on a trunk is correct?

Accepted Answer

Untagged frames arriving on a trunk port are assigned to the native VLAN.. On Juniper EX switches, a trunk port can accept both tagged and untagged frames. Untagged frames received on a trunk port are automatically assigned to the native VLAN, which by default is VLAN 1. This behavior is defined by the IEEE 802.1Q standard, where the native VLAN is the only VLAN that can carry untagged traffic on a trunk link.

Answer

The native VLAN cannot be changed after initial configuration.

Answer

Frames in the native VLAN are always tagged with the VLAN ID on the trunk.

Answer

The native VLAN must be the same as the management VLAN.

Question 13

You are responsible for a Juniper MX router that connects two customer sites over a Layer 3 VPN. The router is configured with BGP for VPN routes and uses MPLS to forward traffic. Recently, the customer reported that traffic from Site A (10.0.1.0/24) to Site B (10.0.2.0/24) is intermittently failing. You check the routing table on the router and see that both routes are present with valid next-hops. However, when you ping from the router's loopback to the remote site's loopback, the ping succeeds. MPLS labels are being assigned and the LSP is up. You also notice that when the failure occurs, the router's BGP session to the remote PE is still established. The failure seems random and lasts a few seconds before recovering. Which troubleshooting step is most likely to identify the root cause?

Accepted Answer

Review the forwarding table for the affected prefixes and check for any discrepancies.. The issue is intermittent packet loss with valid routes in the routing table but successful pings from the loopback. This points to a forwarding table (FIB) inconsistency, where the control plane (routing table) has the correct next-hop, but the forwarding plane (PFE) may have a stale or incorrect entry for the specific prefixes. Checking the forwarding table with 'show route forwarding-table' will reveal if the next-hop or label information differs from the routing table, which is a classic symptom of a hardware programming issue or a transient PFE problem.

Answer

Check the interface error counters for CRC errors or drops.

Answer

Verify the BGP session state and check for route flapping.

Answer

Check the MPLS label switching table to ensure labels are correctly assigned.

Question 14

Refer to the exhibit. An administrator wants to ensure that log messages are stored even if the remote syslog server becomes unavailable. What additional configuration is required?

Accepted Answer

set system syslog file messages any any. Configuring a local log file with `set system syslog file messages any any` ensures that log messages are stored locally on the device, even if the remote syslog server becomes unavailable. This provides a persistent local copy of logs that can be reviewed later, independent of the remote server's reachability.

Answer

set system syslog archive world-readable

Answer

set system syslog host 10.10.10.1 facility-override

Answer

set system syslog rate-limit 1000

Question 15

During a network outage, a router is unresponsive via SSH. You have console access but the console displays 'Amnesiac (ttyd0)' prompt. What is the most likely cause and recovery action?

Accepted Answer

The router lost its configuration; load the rescue configuration using 'rollback rescue-config' or 'load override /config/rescue.conf.gz' then commit. The 'Amnesiac (ttyd0)' prompt indicates the router has booted without a valid configuration file in the /config directory. This typically occurs after a 'request system zeroize' command, a failed commit that corrupted the configuration, or a storage issue that prevented the configuration from loading. The recovery action is to load a previously saved rescue configuration using 'rollback rescue' or 'load override /config/rescue.conf.gz' and then commit, which restores the router to a known working state.

Answer

The router's boot device failed; need to replace hardware

Answer

The router booted from backup media; run 'request system software add' to reinstall Junos

Answer

The router's flash memory is corrupted; perform a full reinstall via USB

Question 16

An enterprise uses OSPF across multiple areas. To reduce routing table size in the backbone area, the engineer wants to advertise a single summary route for all subnets in area 2. Which configuration is appropriate?

Accepted Answer

Configure 'area 2 area-range 10.0.0.0/16' on the ABR. The 'area-range' command on an Area Border Router (ABR) allows you to summarize a set of routes from a specific area into the backbone (area 0) by advertising a single aggregate route (e.g., 10.0.0.0/16) instead of all individual subnets. This reduces the routing table size in area 0 while still providing reachability to all subnets in area 2.

Answer

Configure a virtual-link between area 2 and area 0

Answer

Configure a default route from area 2 using 'default-metric'

Answer

Use a static route for the summary and redistribute it into OSPF

Question 17

A host in VLAN 10 can ping a host in VLAN 20 without a default gateway configured. What feature is likely enabled on the router that interconnects the VLANs?

Accepted Answer

Proxy ARP. Proxy ARP allows a router to respond to ARP requests on behalf of hosts in different subnets. When a host in VLAN 10 sends an ARP request for a host in VLAN 20, the router responds with its own MAC address if it has a route to the destination. This enables the host to send traffic to the router, which then forwards it to the destination VLAN, even without a default gateway configured on the host.

Answer

VLAN translation is configured on the trunk

Answer

IP routing is enabled on the router

Answer

Dynamic ARP Inspection

Question 18

Which THREE steps are typically part of a Junos OS upgrade process?

Accepted Answer

Add the image using the request system software add command.. The correct steps for a Junos OS upgrade are: B: Use `request system software add` to stage and install the new image; D: Validate the new image (though the add command often performs validation, a separate validation step is also typical); E: Reboot the device to load the new image. Option A is not needed because Junos automatically handles the old image, and option C is unrelated to the software upgrade process—commit applies to configuration changes, not software installation.

Answer

Remove the previous image.

Answer

Commit the configuration.

Question 19

An operator wants to monitor the temperature and voltage sensors on a Juniper chassis. Which command displays current sensor readings?

Accepted Answer

show chassis environment. The 'show chassis environment' command displays real-time sensor readings for temperature, voltage, and fan status on Juniper devices. It is the standard operational command for monitoring chassis environmental health, directly matching the operator's requirement to check temperature and voltage sensors.

Answer

show chassis hardware

Answer

show system health

Answer

show log messages | match temperature

Question 20

Your company operates a dual-homed network with two Juniper MX routers (R1 and R2) each connected to a different ISP. R1 uses BGP to receive a default route from ISP-A (preference 170), and R2 uses BGP to receive a default route from ISP-B (preference 170). Additionally, both routers have a static default route pointing to a local next-hop (192.0.2.1) with preference 5 for backup. R1 and R2 are connected via an internal link (10.0.0.0/30) and run OSPF to exchange internal routes. You notice that traffic from internal hosts is always exiting via R1's ISP-A link, even when R1's BGP session to ISP-A goes down. The OSPF routes are preferred. You want traffic to fail over to R2's ISP-B link when R1 loses its BGP default. Which configuration change should you make?

Accepted Answer

Configure the static default route with a preference of 180 so that the BGP default routes (pref 170) are preferred when available.. The static default route currently has a preference of 5, making it preferred over the BGP default (preference 170) even when the BGP route is available. By raising the static default's preference to 180 (higher than BGP's 170), the BGP default will be chosen when present, and the static default will only be used as a backup when BGP is unavailable. This ensures traffic fails over to R2's ISP-B link when R1 loses its BGP default, as OSPF will propagate the default from R2.

Answer

Increase the preference of the BGP default routes to 180 so that the static default is always preferred.

Answer

Configure a routing policy on R2 to reject the default route from ISP-B, forcing all traffic through R1.

Answer

Remove the static default route and rely on OSPF to propagate a default route from the router with the active BGP session.