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Question 261

Which Junos command displays the routing table entries for a specific destination?

1. show route forwarding
2. show route <destination>
3. show routing destination
4. show ip route detail

Correct Answer: 2

Explanation

The show route <destination> command can be used to examine routing information for a particular destination prefix. This is useful when an administrator wants to determine which route Junos has selected for a specific network. The output can provide information about the protocol that installed the route, route preference, next hop, and other attributes depending on the command form used. Troubleshooting a routing problem often requires checking the route for the exact destination rather than reviewing the entire routing table. This command helps narrow the investigation and understand how Junos is handling traffic toward a particular network.

Question 262

Which Junos command displays information about the physical hardware installed in the device?

1. show system hardware
2. show chassis hardware
3. show platform hardware
4. show device inventory

Correct Answer: 2

Explanation

The show chassis hardware command displays information about the hardware components installed in a Junos device. Depending on the platform, the output can include the chassis, routing engines, line cards, power supplies, fan modules, and other hardware components. This command is useful when verifying installed hardware or troubleshooting hardware-related issues. It provides a quick overview of the physical components recognized by the operating system. Other commands may provide operational details about individual components, but show chassis hardware is the standard Junos command used for obtaining a general hardware inventory.

Question 263

Which protocol is used to synchronize the system clock of network devices?

1. SNMP
2. DHCP
3. NTP
4. SCP

Correct Answer: 3

Explanation

Network Time Protocol, or NTP, is used to synchronize the clocks of network devices with a reliable time source. Accurate time is important for logging, troubleshooting, authentication, security mechanisms, and event correlation. Junos devices can be configured to obtain time from one or more NTP servers. When multiple network devices have synchronized clocks, administrators can more easily compare log entries and determine the sequence of events during an incident. SNMP is primarily used for monitoring and management, DHCP provides network configuration information, and SCP is used for secure file transfer.

Question 264

Which Junos configuration command is used to remove an existing configuration statement?

1. erase
2. delete
3. remove
4. clear

Correct Answer: 2

Explanation

The delete command is used in Junos configuration mode to remove an existing configuration statement or hierarchy. For example, an administrator can navigate to the appropriate configuration hierarchy and use delete to remove a configured interface setting, user, route, or service. The change is applied to the candidate configuration and does not become active until the configuration is committed. This separation allows administrators to review their changes before applying them. Commands such as commit, rollback, and show | compare can then be used to manage and verify the configuration process.

Question 265

Which IPv4 subnet mask corresponds to a /24 prefix length?

1. 255.255.0.0
2. 255.255.255.0
3. 255.0.0.0
4. 255.255.255.252

Correct Answer: 2

Explanation

An IPv4 /24 prefix contains 24 network bits and 8 host bits. Its corresponding subnet mask is 255.255.255.0. This addressing scheme provides 256 total IPv4 addresses within the subnet, although traditional subnetting reserves addresses for the network and broadcast identifiers. A /16 uses the mask 255.255.0.0, while /8 uses 255.0.0.0. The /30 prefix corresponds to 255.255.255.252 and is commonly used for small point-to-point networks. Understanding prefix lengths and subnet masks is fundamental when configuring IPv4 interfaces and troubleshooting routing.

Question 266

Which Junos command displays the configured interfaces and their IP addresses in a compact view?

1. show interfaces terse
2. show interfaces compact
3. show interface summary
4. show ip interface

Correct Answer: 1

Explanation

The show interfaces terse command provides a compact overview of interfaces on a Junos device. It can display interface names, administrative state, operational state, and addressing information. Because the output is concise, it is especially useful when an administrator needs to quickly determine which interfaces are configured and whether they are operational. If more detailed information is required, commands such as show interfaces detail or show interfaces extensive can be used. Starting with the terse output is often an efficient troubleshooting approach because it quickly identifies interfaces that may be administratively disabled or operationally down.

Question 267

What is the primary purpose of an access interface on a Layer 2 Junos switch?

1. Carry multiple tagged VLANs
2. Carry traffic for a single VLAN
3. Perform BGP routing
4. Synchronize NTP

Correct Answer: 2

Explanation

An access interface is generally associated with a single VLAN and is commonly used to connect end devices such as computers, printers, or servers to a switching network. Traffic arriving from the connected endpoint is associated with the configured VLAN. In contrast, a trunk interface is designed to carry traffic for multiple VLANs and normally uses VLAN tagging to distinguish them. Correctly configuring access and trunk interfaces is important for maintaining VLAN separation and ensuring that devices communicate within the intended broadcast domain. Administrators often verify the VLAN membership and interface mode when troubleshooting Layer 2 connectivity.

Question 268

Which BGP attribute is used to indicate the sequence of autonomous systems through which a route has passed?

1. Local Preference
2. MED
3. AS Path
4. Next Hop

Correct Answer: 3

Explanation

The BGP AS Path attribute records the sequence of autonomous systems associated with a route advertisement. It is an important component of BGP path selection and also helps prevent routing loops between autonomous systems. When a BGP route is advertised across an autonomous system boundary, the originating AS is added to the path information. A route with a shorter AS path may be preferred when other relevant path-selection criteria do not result in a different decision. Local preference is used primarily for outbound path selection within an autonomous system, while MED can provide information about preferred entry points.

Question 269

Which Junos command can be used to test IP connectivity to another device?

1. ping
2. test ip
3. check connectivity
4. trace ip

Correct Answer: 1

Explanation

The ping command is commonly used to test IP connectivity between a Junos device and another network destination. It sends ICMP echo requests and waits for corresponding replies. Successful responses generally indicate that the destination is reachable and that the relevant forwarding path is functioning. However, a failed ping does not always mean that routing is completely broken because firewalls or security policies may block ICMP traffic. Administrators can combine ping testing with route-table inspection, interface status, and traceroute to identify where connectivity problems may exist. Ping is therefore a basic but valuable troubleshooting tool.

Question 270

Which protocol does the ping utility commonly use for IPv4 connectivity testing?

1. TCP
2. UDP
3. ICMP
4. ARP

Correct Answer: 3

Explanation

The traditional IPv4 ping utility uses Internet Control Message Protocol, or ICMP, to test reachability. It sends ICMP Echo Request messages to a destination, which normally responds with ICMP Echo Reply messages when permitted. Ping does not establish a TCP connection and does not use ARP as its primary end-to-end testing protocol. ARP can still be involved locally when a device needs to resolve an IPv4 address to a MAC address. ICMP is also used for other network-control and diagnostic functions. Understanding this distinction helps administrators interpret ping results and troubleshoot connectivity issues correctly.

Question 271

What is the main function of the Routing Engine in a Junos device?

1. Forward every packet in hardware
2. Perform control-plane and routing functions
3. Provide electrical power
4. Act as a Layer 2 access port

Correct Answer: 2

Explanation

The Routing Engine performs the control-plane functions of a Junos device. It runs Junos software and is responsible for tasks such as maintaining routing protocols, calculating routes, managing configuration, and handling system processes. The Packet Forwarding Engine is responsible for high-speed packet forwarding based on forwarding information supplied by the control plane. Separating control and forwarding functions allows the device to maintain routing intelligence while forwarding traffic efficiently. Understanding the role of the Routing Engine is especially important when troubleshooting routing protocols, configuration operations, system processes, and control-plane issues.

Question 272

Which Junos feature allows an administrator to automatically revert to the previous configuration if a change is not confirmed?

1. commit confirmed
2. commit automatic
3. rollback timer
4. save confirmed

Correct Answer: 1

Explanation

The Junos commit confirmed feature provides a safety mechanism for remote configuration changes. When an administrator commits a configuration using this feature, the change remains temporary until another confirmation commit is performed within the specified period. If confirmation does not occur, Junos automatically rolls back to the previous committed configuration. This is particularly useful when making changes to remote devices because an incorrect configuration could otherwise interrupt management connectivity. The feature reduces the risk of being locked out after a configuration change. Administrators should confirm the configuration after verifying that the new settings operate as expected.

Question 273

Which IPv6 prefix is reserved for multicast addresses?

1. FE80::/10
2. FC00::/7
3. FF00::/8
4. 2001::/16

Correct Answer: 3

Explanation

The IPv6 prefix FF00::/8 is reserved for multicast addresses. IPv6 multicast allows a packet to be delivered to multiple interested receivers without requiring separate unicast transmissions to each destination. Multicast is used by several IPv6 functions and network protocols, including aspects of neighbor and router discovery. The FE80::/10 range is used for link-local addresses, while FC00::/7 is associated with unique local addresses. Recognizing IPv6 address categories helps administrators understand traffic behavior and troubleshoot addressing or neighbor-discovery issues on Junos devices.

Question 274

Which command can display the IPv6 neighbor discovery table on a Junos device?

1. show ipv6 neighbors
2. show ndp
3. show neighbor ipv6
4. show ipv6 nd

Correct Answer: 2

Explanation

The show ndp command is used on Junos devices to display information learned through IPv6 Neighbor Discovery Protocol. The NDP table can contain information about neighboring IPv6 devices, including their IPv6 addresses, link-layer addresses, interfaces, and neighbor states. This information is useful when troubleshooting IPv6 connectivity on a local network segment. IPv6 does not use ARP in the same way as IPv4; instead, NDP provides address resolution and several other neighbor-related functions through ICMPv6. Checking the NDP table can help determine whether the local device has successfully discovered the expected neighboring systems.

Question 275

Which Junos command checks whether a candidate configuration is syntactically valid without activating it?

1. commit check
2. check commit
3. validate configuration
4. test configuration

Correct Answer: 1

Explanation

The commit check command validates the candidate configuration without activating the configuration changes. It is useful for identifying configuration errors before performing an actual commit. This can be particularly valuable when making multiple changes across different configuration hierarchies. A successful check does not mean that every operational behavior will be correct, but it confirms that the configuration passes the relevant commit validation checks. Administrators can use show | compare to review differences and then use commit after validation. This workflow helps reduce configuration mistakes and provides a safer approach to managing Junos devices.

Question 276

Which Layer 2 protocol is commonly used to provide loop prevention in redundant Ethernet topologies?

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

Correct Answer: 3

Explanation

Spanning Tree Protocol, or STP, provides Layer 2 loop prevention in Ethernet switching environments. Redundant physical connections can improve network availability, but they can also create loops if all paths forward traffic simultaneously. STP builds a logical tree and places selected redundant links into a non-forwarding state to prevent loops. If the active path fails, STP can allow an alternate path to become active depending on the STP implementation and configuration. Routing protocols such as OSPF and BGP solve different problems at Layer 3, while NTP is used for time synchronization.

Question 277

What does a routing instance provide in Junos?

1. A separate routing environment
2. A physical replacement for the Routing Engine
3. A new power supply
4. A Layer 1 cable connection

Correct Answer: 1

Explanation

A routing instance provides a separate routing environment within a Junos device. Routing instances can maintain separate routing tables and allow different interfaces and routing information to be logically separated. They are useful in scenarios such as virtualization, service provider networks, and environments where multiple independent routing domains must coexist on the same physical device. The exact behavior depends on the routing-instance type and configuration. Routing instances do not represent physical hardware components. They are a logical feature that provides greater flexibility in managing routing information and separating traffic within a Junos device.

Question 278

Which command displays the currently configured configuration hierarchy in Junos configuration mode?

1. show configuration
2. display active
3. show hierarchy
4. view configuration

Correct Answer: 1

Explanation

The show configuration command displays configuration statements within Junos configuration mode. Depending on the current hierarchy level, the output can show the configuration associated with that hierarchy or its relevant subordinate sections. This command is useful for reviewing settings before making additional changes. Administrators can also use commands such as show | compare to identify differences between the candidate and active configurations. Configuration-mode navigation commands such as top, up, and edit help move through the hierarchy. Reviewing configuration carefully before committing changes is an important part of Junos administration.

Question 279

Which routing protocol is commonly used as an interior gateway protocol for link-state routing?

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

Correct Answer: 2

Explanation

OSPF is an Interior Gateway Protocol that uses a link-state routing model. It is designed to exchange topology information within an autonomous system and calculate shortest paths using the SPF algorithm. OSPF routers form neighbor relationships and exchange link-state information to maintain a synchronized view of the network topology. BGP is primarily used for interdomain routing and uses a path-vector model. FTP is a file-transfer protocol, while NTP provides time synchronization. OSPF is therefore commonly selected when an organization needs dynamic internal routing with topology-aware path calculation and relatively fast convergence.

Question 280

Which Junos command can display the configuration in set-style statements?

1. show configuration | display set
2. show set configuration
3. display configuration set
4. show configuration | set

Correct Answer: 1

Explanation

The show configuration | display set command displays the Junos configuration as individual set commands. This format is useful because each configuration statement is presented as a command that can be entered directly in configuration mode. Administrators often use this output when documenting configurations, reproducing settings, or transferring configuration statements between devices. The standard hierarchical configuration format is useful for understanding the structure of the configuration, while set-style output provides a more command-oriented representation. Using display options with the Junos pipe syntax gives administrators flexible ways to inspect and work with configuration information.