JN0-106 Practice Test 3 — 10 Questions

Question 1

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 2

Refer to the exhibit. Which interface has a physical layer connectivity problem?

Accepted Answer

ge-0/0/1. Interface ge-0/0/1 shows 'Physical link is Down' in the output, which directly indicates a physical layer connectivity problem. The 'Device present' field is also 'No', confirming that no transceiver or cable is detected, which is a Layer 1 issue.

Answer

ge-0/0/2

Answer

ge-0/0/0

Answer

ge-0/0/3

Question 3

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.

Question 4

A network is experiencing intermittent routing loops. The engineer discovers that routes are being redistributed from OSPF into BGP and then from BGP back into OSPF on different routers. What is the most effective way to prevent this?

Accepted Answer

Configure route filters to prevent mutual redistribution.. Mutual redistribution between OSPF and BGP creates routing loops when routes are exported from OSPF into BGP on one router and then re-injected back into OSPF on another router. The most effective way to prevent this is to use route filters (e.g., prefix lists, route-maps, or policy-statement in Junos) to control which routes are redistributed, ensuring that routes learned from one protocol are not re-advertised back into the same protocol. This breaks the redistribution cycle without altering protocol preference or metrics.

Answer

Use a higher preference for BGP routes.

Answer

Set a lower metric on OSPF routes.

Answer

Increase the OSPF cost on interfaces.

Question 5

A switch receives a unicast frame with a destination MAC address that is present in its MAC address table. How does the switch process the frame?

Accepted Answer

It forwards the frame only out of the port associated with that MAC address. When a switch receives a unicast frame and the destination MAC address is already in its MAC address table, it performs a lookup and forwards the frame only out of the specific port associated with that MAC address. This is the fundamental switching behavior known as 'unicast forwarding' or 'filtering,' which avoids unnecessary flooding and preserves bandwidth.

Answer

It sends the frame back to the source port

Answer

It floods the frame to all ports except the receiving port

Answer

It drops the frame

Question 6

Scenario: Your company has a Juniper MX Series router at a branch office running Junos 18.4. The device has been in production for two years with a stable configuration. Yesterday, a senior engineer made several changes to the OSPF configuration to optimize routing for a new link. They committed the changes and left for the day. This morning, the branch office experiences intermittent connectivity, and the OSPF neighbor relationships are flapping. You suspect the recent OSPF changes caused the issue. You have remote console access to the router. The goal is to restore network stability as quickly as possible while preserving the ability to re-apply the changes after troubleshooting. Which course of action should you take?

Accepted Answer

Use 'rollback 1' to revert to the configuration before the changes, then 'commit confirmed 10' to verify stability.. 'rollback 1' reverts the active configuration to the previous committed version (before the problematic OSPF changes), and 'commit confirmed 10' applies that rollback with a 10-minute confirmation timer. If connectivity stabilizes, the rollback becomes permanent; if not, the router automatically reverts to the previous configuration, ensuring no prolonged outage. This approach restores stability quickly while preserving the ability to later re-apply and test the OSPF changes in a controlled manner.

Answer

Use 'deactivate protocols ospf' to disable OSPF entirely and then manually re-enable pieces.

Answer

Immediately delete the OSPF configuration sections that were changed and re-add the original settings manually.

Answer

Perform a 'load factory-default' and 'commit' to reset the device to base settings, then reconfigure from backup.

Question 7

Which TWO commands can be used to view the current routing table entries for IPv4 unicast routes?

Accepted Answer

show route table inet.0. `show route table inet.0` explicitly displays the IPv4 unicast routing table (inet.0) in Junos. Option D is correct because `show route` without any filter defaults to showing all routes in the inet.0 table, which is the primary IPv4 unicast routing table.

Answer

show route protocol static

Answer

show forwarding-table

Answer

show route table inet6.0

Question 8

A company wants to implement best practice for password recovery on Juniper devices to avoid service disruption. Which of the following is the recommended method?

Accepted Answer

Boot the device into single-user mode from the console and reset the root password. Booting the device into single-user mode from the console is the standard, secure method for password recovery on Juniper devices. This process allows an administrator with physical console access to reset the root password without affecting the running configuration or causing service disruption, as the device boots with a minimal kernel and does not load the full configuration.

Answer

Perform a factory reset to default configuration

Answer

Use SNMP to modify the password field in the configuration

Answer

Contact JTAC to remotely reset the password

Question 9

You are a junior network engineer at a company that uses Juniper MX routers. You are troubleshooting a connectivity issue on a branch router. The branch router has two upstream links to the corporate network: ge-0/0/0 (10.1.1.1/30, connected to core router A) and ge-0/0/1 (10.1.1.5/30, connected to core router B). The branch router runs OSPF and has a default route learned from both upstream routers. The routing table shows two equal-cost default routes via both next hops. However, traffic from the branch to the corporate network is experiencing intermittent high latency and some packet loss. You suspect that asymmetric routing is causing issues because the return traffic is not following the same path. You want to influence the router to prefer one upstream link for all traffic to the corporate network. You have decided to adjust the OSPF metric on the branch router to make the link to core router A more preferred. You are in configuration mode on the branch router. Which single configuration change will accomplish this goal?

Accepted Answer

set protocols ospf area 0 interface ge-0/0/1 metric 200. Setting the OSPF metric on interface ge-0/0/1 to a higher value (200) increases the cost of that link, making the default route via ge-0/0/0 (which retains the default OSPF metric of 1 on a Gigabit Ethernet interface) more preferred. This influences the branch router to use the lower-cost path through core router A for all traffic to the corporate network, resolving asymmetric routing issues.

Answer

set interfaces ge-0/0/1 unit 0 family inet cost 200

Answer

set protocols ospf area 0 interface ge-0/0/1 passive

Answer

set interfaces lo0 unit 0 family inet address 10.0.0.1/32 metric 100

Question 10

An engineer enables Spanning Tree PortFast on a switch port connected to a host. Later, another switch is connected to that same port, causing a loop. What feature could have prevented this?

Accepted Answer

BPDU guard. BPDU guard is the correct answer because it disables a port configured with PortFast if a BPDU is received, preventing loops when a switch is accidentally connected. In this scenario, PortFast was enabled for a host, but connecting another switch caused BPDUs to be sent, which BPDU guard detects and shuts down the port to break the loop.

Answer

Loop guard

Answer

Root guard

Answer

UplinkFast