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Question 241

Which Junos command displays detailed information about a specific route in the routing table?

1. show route extensive
2. show route detail
3. show route brief
4. show route summary

Correct Answer: 4

Explanation

The show route detail command provides detailed information about routes installed in the Junos routing table. It can display information such as route preference, the protocol that learned the route, next hop, interface, and other route attributes. This is particularly useful when troubleshooting routing decisions or determining why a specific path was selected. The show route command provides a more general routing-table view, while summary-related commands provide higher-level information. Administrators commonly use detailed route information when investigating connectivity problems, verifying route selection, or checking protocol-specific attributes associated with a particular destination.

Question 242

Which Junos command is used to enter configuration mode from operational mode?

1. configure
2. edit
3. set
4. commit

Correct Answer: 1

Explanation

The configure command is used to move from Junos operational mode into configuration mode. In operational mode, administrators can monitor the device, inspect interfaces, view routing information, and perform troubleshooting tasks. Configuration mode provides access to the candidate configuration, where changes can be made before they are committed to the active configuration. The edit command is generally used within configuration mode to navigate the configuration hierarchy. The set command adds or modifies configuration statements, while commit activates the candidate configuration. Understanding the distinction between operational and configuration modes is fundamental when working with Junos devices.

Question 243

Which routing protocol uses a link-state database to calculate the shortest path?

1. BGP
2. RIP
3. OSPF
4. DHCP

Correct Answer: 3

Explanation

OSPF is a link-state routing protocol that maintains a link-state database containing information about the topology of the OSPF area. Routers exchange link-state advertisements so that each router can build a consistent view of the network topology. OSPF then uses the Shortest Path First algorithm to calculate the best paths. BGP is a path-vector protocol, while DHCP is used for address configuration rather than routing. RIP is a distance-vector routing protocol that uses hop count as its primary metric. Understanding OSPF’s link-state operation is important for troubleshooting neighbor relationships, route calculation, and convergence behavior.

Question 244

Which Junos command displays the status of interfaces in a concise format?

1. show interfaces extensive
2. show interfaces detail
3. show interfaces terse
4. show interface status

Correct Answer: 2

Explanation

The show interfaces terse command is designed to provide a concise overview of interface status. It commonly displays interface names, administrative status, link status, and addressing information in a compact format. This makes it useful for quickly checking whether interfaces are operational without displaying a large amount of diagnostic information. More detailed commands such as show interfaces detail or show interfaces extensive provide substantially more information about individual interfaces. When troubleshooting a Junos device, administrators often start with the terse interface output and then use more detailed commands when a specific interface requires further investigation.

Question 245

What is the primary purpose of the Junos commit operation?

1. To reboot the router
2. To activate candidate configuration changes
3. To display the routing table
4. To clear interface counters

Correct Answer: 2

Explanation

The Junos commit operation activates configuration changes that have been made in the candidate configuration. Junos separates the candidate configuration from the active configuration, allowing administrators to review and validate changes before applying them. Once the configuration is committed successfully, the changes become active on the device. This approach reduces the risk of immediately applying incomplete or incorrect changes. Commands such as commit check can be used to validate configuration syntax before committing. Other operational commands are used for rebooting devices, displaying routes, or clearing counters. The commit process is therefore a central part of Junos configuration management.

Question 246

Which IPv4 prefix represents the default route?

1. 192.168.0.0/16
2. 10.0.0.0/8
3. 172.16.0.0/12
4. 0.0.0.0/0

Correct Answer: 4

Explanation

The IPv4 default route is represented by 0.0.0.0/0. It matches destinations for which no more specific route exists in the routing table. A router can use the default route to forward traffic toward an upstream router or another designated next hop. The /0 prefix means that zero network bits are fixed, so the route can match any IPv4 destination. The other prefixes represent private IPv4 address ranges. Default routes are commonly used in enterprise networks, branch offices, and connections to service providers where traffic destined for unknown networks should be forwarded toward a specific gateway.

Question 247

Which Junos command can be used to display the current system uptime?

1. show system uptime
2. show chassis uptime
3. show uptime system
4. show system time

Correct Answer: 1

Explanation

The show system uptime command displays information about how long the Junos device has been running. The output can include the current time, system boot time, uptime duration, and load information depending on the Junos version and platform. System uptime is useful during troubleshooting because it helps administrators determine whether a device has recently rebooted. Unexpected reboots can affect routing protocols, interface states, and system services. The command is different from commands that display the current clock or detailed chassis hardware information. Checking uptime is often one of the first steps when investigating a recently reported network interruption.

Question 248

Which protocol is commonly used by Junos devices to exchange routing information between autonomous systems?

1. OSPF
2. STP
3. BGP
4. NTP

Correct Answer: 3

Explanation

BGP, or Border Gateway Protocol, is commonly used to exchange routing information between autonomous systems. It is a path-vector routing protocol and is widely used by service providers, large enterprises, and organizations that require policy-based control over route advertisement and selection. BGP uses attributes such as AS path and local preference to influence routing decisions. OSPF is primarily an interior gateway protocol used within an autonomous system, while STP prevents Layer 2 loops and NTP synchronizes system clocks. Understanding BGP is important when working with external routing relationships, Internet connectivity, and large-scale network architectures.

Question 249

What does the rollback command primarily allow a Junos administrator to do?

1. Change the device hostname
2. Restore a previous configuration
3. Display interface statistics
4. Restart a routing protocol

Correct Answer: 2

Explanation

The Junos rollback command allows an administrator to load a previously committed configuration into the candidate configuration. This is useful when recent configuration changes need to be removed or when an administrator wants to return to an earlier known configuration state. After loading the desired rollback configuration, the administrator can review the changes and commit them if appropriate. Junos maintains several previous committed configurations, making rollback an important recovery and change-management feature. The command does not directly restart routing protocols or display interface statistics. It is primarily associated with configuration recovery and controlled restoration of previous settings.

Question 250

Which protocol is used by IPv6 routers to discover neighboring devices and resolve Layer 2 addresses?

1. ARP
2. NDP
3. FTP
4. DHCP

Correct Answer: 2

Explanation

IPv6 uses Neighbor Discovery Protocol, or NDP, to perform functions that include discovering neighboring devices and resolving IPv6 addresses to link-layer addresses. NDP operates through ICMPv6 messages and provides several capabilities, including neighbor discovery, router discovery, and address resolution. IPv4 commonly uses ARP for address resolution, but IPv6 does not use ARP. DHCP can provide addressing information and other network parameters, but it does not replace NDP for neighbor discovery. Understanding NDP is important when troubleshooting IPv6 connectivity, neighbor relationships, router advertisements, and link-local communication on Junos devices.

Question 251

Which command displays the Ethernet switching table on a Junos switch?

1. show ethernet-switching table
2. show switching mac
3. show ethernet mac-table
4. show layer2 table

Correct Answer: 1

Explanation

The show ethernet-switching table command displays the Ethernet switching table on Junos switching platforms. The table contains learned Layer 2 information, including MAC addresses and the interfaces or VLANs associated with those addresses. Switches learn MAC addresses by examining the source MAC address of incoming Ethernet frames. When forwarding traffic, the switch uses the learned information to determine where frames should be sent. If a destination MAC address is unknown, the switch may flood the frame within the appropriate broadcast domain. Administrators use the switching table command when troubleshooting Layer 2 connectivity and MAC-learning behavior.

Question 252

What is the purpose of a trunk interface in an Ethernet switching environment?

1. To carry traffic for multiple VLANs
2. To disable VLAN tagging
3. To provide only management traffic
4. To prevent all broadcast traffic

Correct Answer: 1

Explanation

A trunk interface is used to carry traffic for multiple VLANs across a single physical or logical link. VLAN identification is normally preserved using tagging, such as IEEE 802.1Q tagging, allowing the receiving device to determine which VLAN each frame belongs to. Trunk links are commonly used between switches, between switches and routers, and between switching devices and other network infrastructure. An access interface generally carries traffic for a single VLAN. Trunking therefore provides an efficient way to transport multiple Layer 2 broadcast domains over shared network infrastructure while maintaining VLAN separation.

Question 253

Which BGP attribute is commonly used to prefer one outbound path within an autonomous system?

1. MED
2. Origin
3. Local Preference
4. Community

Correct Answer: 3

Explanation

BGP local preference is commonly used to influence the preferred outbound path from an autonomous system. A higher local preference value is generally preferred when selecting among available BGP routes. The attribute is propagated within the autonomous system and can therefore influence outbound routing decisions across multiple routers. Local preference is different from the AS path, which is commonly considered during BGP path selection and is also used for loop prevention. MED can influence path selection between neighboring autonomous systems in certain situations. Understanding local preference is important when designing or troubleshooting multiple external connectivity paths.

Question 254

Which Junos command displays the configured hostname of a device as part of the system configuration?

1. show system hostname
2. show configuration system
3. show hostname configuration
4. display system name

Correct Answer: 2

Explanation

The show configuration system command displays the system portion of the active configuration, including configuration statements such as the device hostname when one has been configured. This command is useful when administrators need to inspect system-level settings without displaying the entire configuration. The hostname itself is configured under the system hierarchy in Junos. Configuration inspection commands are valuable for verifying what is currently configured before making changes. Administrators can also use configuration mode navigation to examine or modify individual hierarchy levels. Understanding Junos configuration hierarchy makes it easier to locate system settings such as hostname, users, services, and logging.

Question 255

Which IPv6 address range is used for link-local addresses?

1. 2000::/3
2. FC00::/7
3. FF00::/8
4. FE80::/10

Correct Answer: 4

Explanation

The IPv6 prefix FE80::/10 is reserved for link-local addresses. Link-local IPv6 addresses are automatically associated with interfaces and are intended for communication on the local network segment. Routers do not normally forward link-local traffic between different links. Link-local addresses are important for IPv6 neighbor discovery and routing protocols such as OSPFv3. The 2000::/3 range is associated with global unicast addressing, FC00::/7 is used for unique local addresses, and FF00::/8 is reserved for multicast. Recognizing these IPv6 address ranges is important when configuring and troubleshooting IPv6 networks.

Question 256

Which Junos command is commonly used to view system log messages?

1. show log messages
2. show system events
3. show messages system
4. show logging status

Correct Answer: 1

Explanation

The show log messages command is commonly used to display entries from the system messages log on a Junos device. System logs can contain information about interfaces, routing protocols, authentication, system services, configuration events, and other operational conditions. Reviewing log messages is an important troubleshooting technique because logs can provide timestamps and details about events that are not immediately visible through status commands. Depending on the platform and configuration, Junos can maintain multiple log files for different purposes. Administrators should examine relevant logs alongside interface, routing, and system status information when investigating network problems.

Question 257

What is the main function of the Packet Forwarding Engine (PFE) in a Junos device?

1. Manage user accounts
2. Forward packets
3. Store configuration files
4. Synchronize system time

Correct Answer: 2

Explanation

The Packet Forwarding Engine, or PFE, is responsible for high-speed packet forwarding on Junos platforms. It uses forwarding information to determine how packets should be handled and sent toward their destinations. The Routing Engine performs control-plane functions such as maintaining routing protocols and calculating routing information, while the PFE handles the actual forwarding of traffic. This separation allows the device to process packets efficiently while the control plane manages routing and system operations. Understanding the distinction between the Routing Engine and Packet Forwarding Engine is important when troubleshooting forwarding problems and overall Junos architecture.

Question 258

Which command can be used to display OSPF neighbor relationships?

1. show ospf routes
2. show ospf neighbors
3. show ospf links
4. show ospf sessions

Correct Answer: 2

Explanation

The show ospf neighbor command is used in Junos to display OSPF neighbor relationships. The output provides information about neighboring OSPF routers and their current adjacency states. Neighbor state is an important troubleshooting indicator because successful OSPF adjacency is required for routers to exchange link-state information. If a neighbor is not reaching the expected state, administrators may investigate interface configuration, area settings, authentication, network types, or connectivity. OSPF neighbor information should be considered together with the OSPF interface status and link-state database when diagnosing routing problems.

Question 259

Which protocol is primarily responsible for preventing Layer 2 switching loops?

1. BGP
2. OSPF
3. STP
4. NTP

Correct Answer: 3

Explanation

Spanning Tree Protocol, or STP, is designed to prevent Layer 2 switching loops. Ethernet networks can contain redundant physical paths for resiliency, but those paths can create loops that result in excessive frame forwarding and broadcast traffic. STP logically blocks certain redundant paths while maintaining them as potential alternatives if the active path fails. This allows network designers to maintain redundancy without creating persistent Layer 2 loops. BGP and OSPF are routing protocols that operate at higher network functions, while NTP is used for time synchronization. Understanding STP is important when troubleshooting switching loops and redundant Ethernet topologies.

Question 260

Which Junos command can be used to compare the candidate configuration with the currently active configuration?

1. show | compare
2. show | difference
3. compare configuration
4. show configuration changes

Correct Answer: 1

Explanation

The show | compare command is used in Junos configuration mode to display differences between the candidate configuration and the currently active configuration. This allows administrators to review pending changes before committing them. The comparison can reveal configuration statements that have been added, modified, or deleted. Reviewing the differences is an important change-management practice because it helps prevent unintended configuration changes from being committed. After reviewing the output, an administrator can make corrections, perform a commit check if needed, and then commit the configuration. This workflow provides greater control and visibility when modifying Junos devices.