JNCIA-Junos (JN0-105) Comprehensive Exam: Set 4 With Correct
Answers
1. Explain the "Shared" configuration database and describe what occurs if two administrators
issue a "commit" command simultaneously.
==CORRECT ANSWER:== The shared database allows multiple users to edit the candidate
configuration at once. If two users commit at the same time, the Junos OS processes them
sequentially; the first commit succeeds, and the second commit will include the changes
from the first user plus their own.
2. Describe the "Routing Engine" (RE) protection mechanism and identify the interface where a
"Loopback Filter" should be applied to secure the control plane.
==CORRECT ANSWER:== RE protection uses a stateless firewall filter to limit traffic destined
for the router's own CPU. This filter must be applied to the input side of the "lo0.0"
(loopback) interface.
3. Define "Transit Traffic" and identify which hardware component handles it without
intervention from the main CPU.
==CORRECT ANSWER:== Transit traffic is data passing through the router from one network
interface to another. It is handled exclusively by the Packet Forwarding Engine (PFE).
4. Explain the difference between "Operational Mode" and "Configuration Mode" prompts in
the CLI.
==CORRECT ANSWER:== Operational mode uses the ">" prompt and is for monitoring and
troubleshooting. Configuration mode uses the "#" prompt and is for modifying the device's
settings.
5. Describe the "commit check" command and explain its value in a production environment.
==CORRECT ANSWER:== The "commit check" command validates the syntax and logic of the
candidate configuration without actually applying it, allowing an admin to catch errors before
an outage occurs.
6. What is the "inet.0" routing table and which protocol family does it support?
==CORRECT ANSWER:== "inet.0" is the primary routing table for IPv4 unicast routes.
7. Explain the "show | compare" command and identify what the "minus" (-) sign indicates in
the output.
==CORRECT ANSWER:== The command compares the candidate configuration to the active
one; a minus sign indicates a line that exists in the active config but will be deleted upon the
next commit.
8. Define "Exception Traffic" and provide two examples.
==CORRECT ANSWER:== Exception traffic is data destined for the router itself or traffic the
PFE cannot handle. Examples include OSPF Hello packets and SSH management sessions.
9. Describe the "rollback 1" command and explain what it does to the candidate configuration.
==CORRECT ANSWER:== It replaces the current candidate configuration with the
configuration that was active just prior to the current one (the previous commit).
10. What is the "unit" statement in an interface configuration and why is it mandatory?
==CORRECT ANSWER:== The "unit" statement defines a logical interface; it is mandatory
, because all protocol parameters (like IP addresses) must be bound to a logical unit rather
than a physical port.
11. Explain the "Protocol Preference" for a "Direct" route in Junos.
==CORRECT ANSWER:== Direct routes (interfaces with IP addresses) have a preference of 0,
making them the most trusted routes in the table.
12. Describe the "configure private" command and how it helps in a multi-administrator
environment.
==CORRECT ANSWER:== It creates a private candidate configuration for the user. When that
user commits, only their specific changes are applied, preventing them from accidentally
committing another admin's half-finished work.
13. What is the "Forwarding Table" and how is it populated?
==CORRECT ANSWER:== The Forwarding Table (FIB) is the hardware-optimized list of next-
hops in the PFE. It is populated by the Routing Engine selecting the "active" routes from the
Routing Table (RIB).
14. Explain the "Help Reference" command.
==CORRECT ANSWER:== It provides the full CLI syntax, including all options and hierarchy
details, for a specific configuration statement.
15. Describe the "load set" command and identify the format of the data it expects.
==CORRECT ANSWER:== The "load set" command is used to paste configuration data that is
written in the "set" command format rather than the standard curly-brace hierarchy.
16. What is "Family Inet6" used for?
==CORRECT ANSWER:== It enables IPv6 protocol support on a logical interface.
17. Explain the "Default Policy" for BGP export in Junos.
==CORRECT ANSWER:== By default, Junos BGP will not export any routes to peers; a manual
export policy must be created and applied.
18. Describe the "request system halt" command.
==CORRECT ANSWER:== It gracefully shuts down the Junos OS so the hardware can be safely
powered off without corrupting the file system.
19. Define "Administrative Status" vs "Operational Status" for an interface.
==CORRECT ANSWER:== Administrative status (Up/Down) is whether the admin has enabled
the port; Operational status is whether the physical link is actually detecting a signal.
20. What is the "Rescue Configuration"?
==CORRECT ANSWER:== A user-saved "known-good" configuration that can be quickly
reloaded if the router becomes unmanageable.
21. Explain the "Term" in a Firewall Filter.
==CORRECT ANSWER:== A "term" is a specific rule within a filter that contains match criteria
(from) and actions (then).
22. Describe the "show route terse" command.
==CORRECT ANSWER:== It provides a condensed view of the routing table, showing only the
destination prefix, protocol, preference, and next-hop.
Answers
1. Explain the "Shared" configuration database and describe what occurs if two administrators
issue a "commit" command simultaneously.
==CORRECT ANSWER:== The shared database allows multiple users to edit the candidate
configuration at once. If two users commit at the same time, the Junos OS processes them
sequentially; the first commit succeeds, and the second commit will include the changes
from the first user plus their own.
2. Describe the "Routing Engine" (RE) protection mechanism and identify the interface where a
"Loopback Filter" should be applied to secure the control plane.
==CORRECT ANSWER:== RE protection uses a stateless firewall filter to limit traffic destined
for the router's own CPU. This filter must be applied to the input side of the "lo0.0"
(loopback) interface.
3. Define "Transit Traffic" and identify which hardware component handles it without
intervention from the main CPU.
==CORRECT ANSWER:== Transit traffic is data passing through the router from one network
interface to another. It is handled exclusively by the Packet Forwarding Engine (PFE).
4. Explain the difference between "Operational Mode" and "Configuration Mode" prompts in
the CLI.
==CORRECT ANSWER:== Operational mode uses the ">" prompt and is for monitoring and
troubleshooting. Configuration mode uses the "#" prompt and is for modifying the device's
settings.
5. Describe the "commit check" command and explain its value in a production environment.
==CORRECT ANSWER:== The "commit check" command validates the syntax and logic of the
candidate configuration without actually applying it, allowing an admin to catch errors before
an outage occurs.
6. What is the "inet.0" routing table and which protocol family does it support?
==CORRECT ANSWER:== "inet.0" is the primary routing table for IPv4 unicast routes.
7. Explain the "show | compare" command and identify what the "minus" (-) sign indicates in
the output.
==CORRECT ANSWER:== The command compares the candidate configuration to the active
one; a minus sign indicates a line that exists in the active config but will be deleted upon the
next commit.
8. Define "Exception Traffic" and provide two examples.
==CORRECT ANSWER:== Exception traffic is data destined for the router itself or traffic the
PFE cannot handle. Examples include OSPF Hello packets and SSH management sessions.
9. Describe the "rollback 1" command and explain what it does to the candidate configuration.
==CORRECT ANSWER:== It replaces the current candidate configuration with the
configuration that was active just prior to the current one (the previous commit).
10. What is the "unit" statement in an interface configuration and why is it mandatory?
==CORRECT ANSWER:== The "unit" statement defines a logical interface; it is mandatory
, because all protocol parameters (like IP addresses) must be bound to a logical unit rather
than a physical port.
11. Explain the "Protocol Preference" for a "Direct" route in Junos.
==CORRECT ANSWER:== Direct routes (interfaces with IP addresses) have a preference of 0,
making them the most trusted routes in the table.
12. Describe the "configure private" command and how it helps in a multi-administrator
environment.
==CORRECT ANSWER:== It creates a private candidate configuration for the user. When that
user commits, only their specific changes are applied, preventing them from accidentally
committing another admin's half-finished work.
13. What is the "Forwarding Table" and how is it populated?
==CORRECT ANSWER:== The Forwarding Table (FIB) is the hardware-optimized list of next-
hops in the PFE. It is populated by the Routing Engine selecting the "active" routes from the
Routing Table (RIB).
14. Explain the "Help Reference" command.
==CORRECT ANSWER:== It provides the full CLI syntax, including all options and hierarchy
details, for a specific configuration statement.
15. Describe the "load set" command and identify the format of the data it expects.
==CORRECT ANSWER:== The "load set" command is used to paste configuration data that is
written in the "set" command format rather than the standard curly-brace hierarchy.
16. What is "Family Inet6" used for?
==CORRECT ANSWER:== It enables IPv6 protocol support on a logical interface.
17. Explain the "Default Policy" for BGP export in Junos.
==CORRECT ANSWER:== By default, Junos BGP will not export any routes to peers; a manual
export policy must be created and applied.
18. Describe the "request system halt" command.
==CORRECT ANSWER:== It gracefully shuts down the Junos OS so the hardware can be safely
powered off without corrupting the file system.
19. Define "Administrative Status" vs "Operational Status" for an interface.
==CORRECT ANSWER:== Administrative status (Up/Down) is whether the admin has enabled
the port; Operational status is whether the physical link is actually detecting a signal.
20. What is the "Rescue Configuration"?
==CORRECT ANSWER:== A user-saved "known-good" configuration that can be quickly
reloaded if the router becomes unmanageable.
21. Explain the "Term" in a Firewall Filter.
==CORRECT ANSWER:== A "term" is a specific rule within a filter that contains match criteria
(from) and actions (then).
22. Describe the "show route terse" command.
==CORRECT ANSWER:== It provides a condensed view of the routing table, showing only the
destination prefix, protocol, preference, and next-hop.
