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Question 301

Which Junos command is used to display the configuration in a hierarchical format?

1. show configuration
2. show configuration hierarchy
3. display hierarchy
4. show config tree

Correct Answer: 1

Explanation

The show configuration command displays the Junos configuration in its hierarchical structure. Junos organizes configuration statements into logical levels, such as system, interfaces, protocols, and routing options. This hierarchical organization makes it easier to understand how different settings relate to one another. Administrators can navigate through this hierarchy using commands such as edit, up, and top. The command can be used from configuration mode to inspect the current candidate configuration. Reviewing the configuration hierarchy is an important part of verifying settings before making additional changes or committing a new configuration.

Question 302

Which Junos command is used to display information about the Routing Engine and system processes?

1. show chassis routing-engine
2. show routing-engine status
3. show system routing
4. show engine information

Correct Answer: 1

Explanation

The show chassis routing-engine command displays information about the Routing Engine. Depending on the platform, the output can include CPU utilization, memory utilization, uptime, temperature, and other operational details. This information is useful when troubleshooting control-plane performance or determining whether the Routing Engine is experiencing unusually high resource utilization. The Routing Engine handles important control-plane tasks such as routing protocols and system management. Administrators can use this command together with system process and log information when investigating performance issues or unexpected behavior on a Junos device.

Question 303

Which protocol is used by routers to exchange routing information within an autonomous system using a link-state approach?

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

Correct Answer: 2

Explanation

OSPF is a link-state routing protocol commonly used to exchange routing information within an autonomous system. OSPF routers exchange link-state advertisements and build a link-state database representing the network topology. Each router then uses the Shortest Path First algorithm to calculate appropriate routes. BGP is a path-vector protocol generally used for interdomain routing, while DHCP provides host configuration information and SNMP supports network management. OSPF is useful in enterprise networks and other environments that require dynamic internal routing. Understanding its link-state operation helps administrators troubleshoot neighbors, routes, and topology changes.

Question 304

Which Junos command can be used to verify whether a configuration can be committed successfully?

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

Correct Answer: 2

Explanation

The commit check command validates the candidate configuration without activating it. This allows administrators to identify syntax or configuration-related problems before performing a normal commit. It is particularly useful after making several changes across different configuration hierarchies. A successful commit check indicates that the configuration passes the relevant validation checks, but administrators should still review the intended changes before activating them. The show | compare command can be used to inspect differences between the candidate and active configurations. Together, these commands support a safer and more controlled Junos configuration workflow.

Question 305

Which IPv4 prefix represents a network with 30 network bits?

1. /8
2. /16
3. /30
4. /24

Correct Answer: 3

Explanation

An IPv4 /30 prefix contains 30 network bits and leaves 2 bits for host addressing. This results in four total addresses within the subnet. Traditionally, one address identifies the network and another identifies the broadcast address, leaving two addresses commonly available for hosts. /30 networks have historically been useful for point-to-point IPv4 links. A /24 leaves eight host bits, while /16 leaves sixteen and /8 leaves twenty-four. Understanding prefix lengths helps administrators calculate subnet sizes and configure appropriate addressing for interfaces and network links.

Question 306

Which Junos command displays the MAC addresses learned by a switch?

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

Correct Answer: 1

Explanation

The show ethernet-switching table command displays MAC addresses learned by a Junos switching device. The Ethernet switching table associates learned MAC addresses with interfaces and VLAN information. Switches learn source MAC addresses from incoming Ethernet frames and use the learned information to make forwarding decisions. Administrators can inspect this table when troubleshooting Layer 2 connectivity, VLAN membership, or unexpected traffic behavior. If a MAC address is not present, possible causes include a disconnected endpoint, incorrect VLAN configuration, or traffic not yet being received from the device. The command is therefore an important Layer 2 troubleshooting tool.

Question 307

Which BGP attribute records the autonomous systems that a route advertisement has traversed?

1. Local Preference
2. MED
3. Origin
4. AS Path

Correct Answer: 4

Explanation

The AS Path attribute records the sequence of autonomous systems through which a BGP route advertisement has passed. It is an important part of BGP route selection and also helps prevent routing loops between autonomous systems. When a BGP speaker advertises a route to another autonomous system, its AS number is added to the AS Path. Routers can inspect this attribute when selecting among multiple available routes. A route with a shorter AS Path may be preferred when other applicable selection criteria do not result in a different choice. AS Path information is therefore fundamental to BGP operation.

Question 308

Which Junos command is commonly used to test the path packets take toward a destination?

1. tracepath
2. traceroute
3. path-test
4. show route-path

Correct Answer: 2

Explanation

The traceroute command is used to examine the path toward a destination by identifying intermediate Layer 3 hops. It is useful when a destination is reachable but administrators need to determine where traffic is traveling or where delays or failures may occur. Each responding hop can provide information about the path between the source device and the destination. Traceroute is often used together with ping and routing-table commands during troubleshooting. While ping primarily tests reachability, traceroute provides additional path information that can help identify routing problems or unexpected network paths.

Question 309

What is the primary purpose of a firewall filter in Junos?

1. Assign IP addresses
2. Synchronize clocks
3. Control packets based on defined criteria
4. Establish BGP sessions

Correct Answer: 3

Explanation

A Junos firewall filter is used to examine and control packets based on configured matching criteria and actions. A filter can match characteristics such as source address, destination address, protocol, ports, or other packet properties. Depending on the configuration, actions can include accepting, discarding, counting, or logging matching traffic. Firewall filters are useful for implementing traffic-control policies and protecting network resources. They are different from routing protocols, which determine paths, and from services such as NTP, which synchronize time. Administrators should carefully verify filter terms because an incorrect filter can unintentionally block legitimate traffic.

Question 310

Which Junos command displays system log messages stored in the messages log file?

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

Correct Answer: 2

Explanation

The show log messages command displays entries from the Junos messages log file. These logs can contain information about system events, interface changes, authentication activity, routing protocols, configuration operations, and other events depending on the device configuration. Reviewing log messages is an important troubleshooting technique because timestamps and event details can help establish what happened before or during a network problem. Administrators often combine log analysis with interface, routing, and system commands. Understanding the available logs helps identify whether a problem is caused by configuration, hardware, connectivity, or another operational condition.

Question 311

Which IPv6 address prefix is associated with unique local addresses?

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

Correct Answer: 3

Explanation

The FC00::/7 IPv6 prefix is associated with unique local addresses. These addresses are intended for private IPv6 communication within organizations and are not designed for direct routing across the public Internet. They provide functionality similar in purpose to private IPv4 addressing, although the addressing mechanisms are different. The FE80::/10 range is used for link-local addresses, while FF00::/8 is reserved for multicast. The 2000::/3 range is commonly associated with global unicast addressing. Recognizing these address ranges helps administrators identify the intended scope of IPv6 traffic.

Question 312

Which Junos command can display the current system uptime and load information?

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

Correct Answer: 1

Explanation

The show system uptime command displays system uptime information and can include load-related information. It can help administrators determine when the device last booted and assess whether the system has recently restarted. This is useful when investigating unexpected outages, software restarts, or system instability. Uptime information can also be helpful when correlating system events with log timestamps. If the device has recently rebooted, administrators can investigate system logs and hardware information for additional clues. The command provides a quick operational overview without requiring detailed inspection of individual system processes.

Question 313

Which command is used to enter a specific configuration hierarchy in Junos?

1. move
2. edit
3. enter
4. navigate

Correct Answer: 2

Explanation

The edit command is used in Junos configuration mode to move into a specific configuration hierarchy. For example, an administrator can use edit interfaces to enter the interfaces hierarchy and then navigate to a specific interface. This hierarchical approach allows configuration changes to be organized logically. Commands such as up move one level higher, while top returns to the top of the configuration hierarchy. Using edit effectively helps administrators locate the correct configuration section before adding, modifying, or deleting statements. It is a fundamental command for working interactively in Junos configuration mode.

Question 314

Which protocol provides secure remote command-line access to a Junos device?

1. Telnet
2. FTP
3. SSH
4. TFTP

Correct Answer: 3

Explanation

Secure Shell, or SSH, provides encrypted remote command-line access to Junos devices. SSH protects authentication information and interactive management traffic by encrypting the communication between the administrator and the device. It is commonly preferred for secure network administration. Telnet provides remote terminal access but does not offer the same encryption protections. FTP and TFTP are primarily file-transfer protocols rather than interactive device-management protocols. Administrators can configure SSH under the appropriate Junos system services hierarchy and use authentication mechanisms such as local accounts or external authentication services.

Question 315

Which Junos routing table is primarily used to determine the best route for IP packet forwarding?

1. Forwarding table
2. Ethernet table
3. ARP table
4. MAC table

Correct Answer: 1

Explanation

The forwarding table contains the information used by the Packet Forwarding Engine to make packet-forwarding decisions. It is derived from routing information and contains the forwarding information necessary to send packets toward their destinations. The routing table is maintained as part of the control plane, while forwarding information is installed for high-speed packet processing. The ARP table maps IPv4 addresses to Layer 2 addresses, and the MAC table is primarily associated with Ethernet switching. Understanding the distinction between routing and forwarding tables is important when troubleshooting cases where routes appear correct but packet forwarding is not functioning as expected.

Question 316

Which command can display the OSPF link-state database on a Junos device?

1. show ospf database
2. show ospf lsdb
3. show ospf topology
4. show ospf links

Correct Answer: 1

Explanation

The show ospf database command displays information from the OSPF link-state database. The database contains link-state advertisements that describe the topology information known by an OSPF router. Examining the database can help administrators troubleshoot missing routes, incorrect adjacencies, or unexpected topology information. The OSPF database works together with the SPF calculation process to determine available paths. When diagnosing an OSPF problem, administrators commonly inspect neighbor status, interfaces, the link-state database, and the resulting routing table to identify where the problem occurs.

Question 317

Which protocol is used by IPv6 Neighbor Discovery to exchange control messages?

1. ICMPv4
2. TCP
3. UDP
4. ICMPv6

Correct Answer: 4

Explanation

IPv6 Neighbor Discovery uses ICMPv6 messages for functions such as neighbor discovery, router discovery, address resolution, and duplicate address detection. ICMPv6 provides the control-message framework required for these IPv6 operations. This differs from IPv4, where ARP is used for address resolution and ICMP provides other control functions. Blocking required ICMPv6 traffic can therefore cause important IPv6 features to fail. When troubleshooting IPv6 connectivity, administrators should consider both addressing and the appropriate ICMPv6 messages. Understanding NDP and ICMPv6 is especially important for diagnosing local IPv6 neighbor and router-discovery problems.

Question 318

What is the main purpose of a default route?

1. To identify every directly connected network
2. To provide a path when no more specific route exists
3. To disable dynamic routing
4. To assign addresses to hosts

Correct Answer: 2

Explanation

A default route provides a forwarding path for destinations that do not have a more specific matching route in the routing table. In IPv4, the default route is represented by 0.0.0.0/0. It is commonly used to forward unknown destinations toward an upstream router or Internet gateway. Routers use longest-prefix matching, so a more specific route is preferred over the default route when one exists. Default routing is particularly useful at branch locations and edge networks where most external traffic should be sent toward a single upstream connection.

Question 319

Which Junos command can display detailed information about a particular interface?

1. show interfaces <interface-name> detail
2. show interface-info <interface-name>
3. show port <interface-name>
4. display interface <interface-name>

Correct Answer: 1

Explanation

The show interfaces <interface-name> detail command provides detailed operational information about a specific interface. It can include interface status, addressing information, traffic statistics, errors, protocol information, and other relevant details. Specifying an individual interface is useful when troubleshooting because it limits the output to the device component being investigated. Administrators often begin with show interfaces terse to identify a problem and then use a detailed interface command for deeper analysis. Reviewing interface statistics can help identify physical connectivity problems, configuration issues, packet errors, or unexpected traffic conditions.

Question 320

Which Junos feature allows multiple logical units to be configured on a single physical interface?

1. Routing policy
2. Interface units
3. Firewall terms
4. Routing instances

Correct Answer: 2

Explanation

Junos interfaces can be divided into logical units, allowing multiple logical interfaces to operate over a single physical interface. Each logical unit can have its own configuration, including addressing and other properties appropriate to the interface type. Logical units are useful in situations where multiple logical connections or services need to share one physical interface. The physical interface provides the underlying connectivity, while the logical units provide separate logical interfaces for configuration purposes. This concept is fundamental to Junos interface configuration and is commonly encountered when configuring routed interfaces, VLAN-related services, and other network functions.