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質問 # 21
Which two statements are correct regarding Layer 2 network switches? (Choose two.)
- A. Switches flood broadcast traffic.
- B. Switches are susceptible to traffic loops.
- C. Switches create a single collision domain.
- D. Switches do not learn MAC addresses.
正解：A、B
解説：
Layer 2 network switches are crucial components in local area networks (LANs), providing multiple functions for data packet forwarding and network segmentation. One inherent characteristic of switches is their susceptibility to traffic loops, especially in networks with redundant paths. Without proper loop prevention protocols like Spanning Tree Protocol (STP), loops can cause broadcast storms and network instability.
Additionally, switches inherently flood broadcast traffic to all ports within the broadcast domain, except the port on which the broadcast was received. This is because broadcast frames are meant to be delivered to all devices within the VLAN, and the switch ensures this by flooding these frames to all ports in the VLAN, except the source port.
質問 # 22
What are two examples of exception traffic? (Choose two.)
- A. log messages
- B. routing updates
- C. transit packets
- D. ping to the local device
正解：A、B
解説：
Exception traffic includes traffic that is not simply forwarded by the router but requires special handling, such as routing updates (B) and log messages (C). These types of traffic are processed by the router's control plane rather than just being forwarded through the data plane.
質問 # 23
Which command displays all IPv6 routes in the default routing instance?
- A. showroute table inet.0
- B. showroute table inet6.1
- C. showroute table inet6.0
- D. showroute table inet.1
正解：C
解説：
The show route table inet6.0 command displays all IPv6 routes in the default routing instance. In Junos OS, the routing table for IPv6 addresses is referred to as inet6.0, whereas inet.0 is used for IPv4 unicast routes.
The other options do not correspond to the correct IPv6 routing table.
References:
* Juniper official documentation: Junos OS Routing Tables Overview.
質問 # 24
Which type of device uses the destination IP address to forward packets?
- A. Layer 2 switch
- B. hub
- C. repeater
- D. Layer 3 router
正解：D
解説：
A Layer 3 router uses the destination IP address to forward packets. The correct answer is A. Routers operate at Layer 3 of the OSI model and make forwarding decisions based on IP addresses. They are responsible for routing packets across different networks by examining the destination IP address contained in the packet's header.
質問 # 25
You issue the monitor traffic interface ge-0/0/0 command.
What will this command accomplish?
- A. It displays real-time statistics for interface ge-0/0/0.
- B. It displays an operational summary of ge-0/0/0.
- C. It displays the MTU and MAC address for ge-0/0/0.
- D. It displays a packet capture on interface ge-0/0/0.
正解：D
解説：
The command "monitor traffic interface ge-0/0/0" (D) initiates a packet capture on the specified interface, allowing you to view the actual packets being transmitted and received. This is useful for troubleshooting and analyzing the traffic passing through the interface in real time.
質問 # 26
Which service does RADIUS provide?
- A. time synchronization
- B. authentication
- C. routing
- D. DNS resolution
正解：B
解説：
RADIUS, which stands for Remote Authentication Dial-In User Service, provides authentication services for users trying to access a network. It is a networking protocol that provides centralized Authentication, Authorization, and Accounting (AAA) management for users who connect and use a network service.
質問 # 27
What are two functions of the routing protocol daemon (rpd)? (Choose two.)
- A. It creates forwarding tables.
- B. It maintains routing tables.
- C. It generates chassis alarms.
- D. It provides access to the CLI.
正解：A、B
解説：
The Routing Protocol Daemon (rpd) is a critical component in Juniper Networks devices, responsible for all routing operations. It maintains routing tables, which hold information about network paths and destinations derived from various routing protocols. These tables are used to make decisions about where to send packets. Additionally, rpd generates forwarding tables based on the information in the routing tables. The forwarding tables are then used by the Packet Forwarding Engine (PFE) to actually forward packets to their next hop or final destination.
質問 # 28
Which two external authentication methods does Junos support for administrative access? (Choose two.)
- A. RADIUS
- B. NIS
- C. TACACS+
- D. ACE
正解：C
解説：
Junos OS supports several external authentication methods for administrative access, with TACACS+ (Terminal Access Controller Access-Control System Plus) and RADIUS (Remote Authentication Dial-In User Service) being among the most commonly used. Both TACACS+ and RADIUS are protocols that allow network devices to communicate with a central authentication server, enabling centralized control over user authentication and authorization. This centralization simplifies the management of user credentials and access policies, especially in larger networks with multiple devices.
質問 # 29
Click the Exhibit button.
Referring to the exhibit, what should be configured on R1 to advertise a default static route into OSPF?
- A. a loopback interface
- B. a management interface
- C. a routing policy
- D. a firewall filter
正解：C
解説：
To advertise a default static route into OSPF on router R1, a routing policy should be configured. This policy would typically include a statement to match the default route (0.0.0.0/0) and then apply an action to set the route as an OSPF external type, which would then be redistributed into the OSPF domain. The routing policy is a set of conditions and actions that determine how routes are imported into or exported from the routing table and how routes are shared between routing instances or routing protocols. After defining the policy, it must be applied to OSPF under the export section of the OSPF configuration on R1. This process will allow R1 to announce the default route to other OSPF routers in the network, which then can use it as a gateway of last resort to reach the Internet or other networks not explicitly known to the OSPF domain.
質問 # 30
What is the primary system log file that is present in the default configuration of a Junos device?
- A. messages
- B. vrrp
- C. jsrpd
- D. kmd
正解：A
解説：
In the default configuration of a Junos device, the primary system log file is "messages" (B). This log file contains a wide range of system messages, including operational status changes, system errors, and other critical information, making it a key resource for troubleshooting and monitoring the system's health.
質問 # 31
A network administrator is attempting to route traffic on a Juniper switch to one of three different VLANs: Prod, Test, and Dev. Each VLAN has been assigned a numerical value.
In this scenario, what are these numerical values called?
- A. defaults
- B. tags
- C. names
- D. interfaces
正解：B
解説：
In the context of VLANs (Virtual Local Area Networks) on a Juniper switch, the numerical values assigned to each VLAN, such as those for Prod, Test, and Dev, are known as VLAN tags. These tags are part of the 802.1Q VLAN standard, which allows multiple VLANs to coexist on a single physical network. Each tag uniquely identifies the VLAN to which a frame belongs, enabling the switch to segregate and manage traffic based on VLAN membership. This tagging mechanism allows for efficient traffic separation and management, ensuring that devices within one VLAN do not receive traffic intended for another, thus maintaining network security and efficiency.
質問 # 32
Which character is used to filter the command output in the Junos CLI?
- A. >
- B. ?
- C. |
- D. <
正解：C
解説：
In the Junos CLI, the pipe character | is used as a filter operator to refine command output. This operator can be combined with various filtering commands like match, except, count, etc., to display only the relevant portions of the command output. For example, using | match <pattern> filters the output to show only the lines that contain the specified pattern, making it easier to find specific information within extensive command output. This functionality is especially useful in managing and troubleshooting complex configurations and network states, allowing for more efficient analysis of the device's operational status and configuration details.
質問 # 33
What are two link-state routing protocols? (Choose two.)
- A. OSPF
- B. RIP
- C. BGP
- D. IS-IS
正解：A、D
解説：
Link-state routing protocols are a type of routing protocol used in packet-switching networks for finding the best path between source and destination. OSPF (Open Shortest Path First) and IS-IS (Intermediate System to Intermediate System) are both examples of link-state routing protocols. They work by maintaining a complete map or topology of the network, allowing routers to independently calculate the best path to each destination. Unlike distance-vector protocols like RIP, link-state protocols are more efficient and scalable, making them suitable for larger networks.
質問 # 34
Which two statements are correct about Junos traceoptions? (Choose two.)
- A. Traceoptions are enabled through configuration.
- B. Traceoption output, by default, is stored in /var/iog/<fiie-name>.
- C. Traceoptions are enabled by default.
- D. Traceoptions cannot be enabled in a production environment.
正解：A、B
解説：
Traceoptions in Junos OS are used for detailed debugging and troubleshooting of protocols and processes within the system. They are not enabled by default due to the potential performance impact and volume of data generated. Instead, traceoptions are enabled through specific configuration settings under the relevant protocol or process hierarchy. This allows administrators to target their troubleshooting efforts and control the scope of logging. By default, the output generated by traceoptions is stored in files located in the /var/log directory, with the file name typically specified in the traceoptions configuration. This structured approach to logging and debugging helps in diagnosing complex issues without overwhelming the system or the administrator with irrelevant data.
質問 # 35
Exhibit
[edit]
user@routerl set interfaces ge-0/1/2 unit 0 family inet address 172.16.101.1/24 [edit] user@router# commit check configuration check succeeds
[edit]
user@router#
You need to configure interface ge-0/1/2 with an IP address of 172.16.100.1/24. You have accidentally entered
172.16.101.1/24 as shown in the exhibit.
Which command should you issue to solve the problem?
- A. [edit] user@router# rollback 2
- B. (edit] user@router# rollback 1
- C. [edit] user@routeri rollback rescue
- D. [edit] userOrouter# rollback 0
正解：B
解説：
If you've committed a configuration and then need to revert to the previous configuration, therollback command is used. Since the incorrect IP address has not been committed, as indicated by thecommit check command being successful, issuingrollback 1will undo the changes made in the current session, which includes the accidental entry of the IP address.
質問 # 36
Which protocol is responsible for learning an IPv4 neighbor's MAC address?
- A. Address Resolution Protocol (ARP)
- B. Media Access Control Security (MACsec)
- C. Neighbor Discovery Protocol (NDP)
- D. Network Address Translation (NAT)
正解：A
解説：
The Address Resolution Protocol (ARP) is responsible for mapping an IPv4 address to a machine's MAC address. ARP operates at Layer 2 of the OSI model and is used to find the MAC address of a host given its IPv4 address. When a device wants to communicate with another device on the same local network, it uses ARP to discover the recipient's MAC address.
Reference:
Juniper official documentation: ARP.
Networking standards: RFC 826.
質問 # 37
How many rescue configuration files are supported on a Junos device?
- A. 0
- B. 1
- C. 2
- D. 3
正解：C
解説：
Junos OS supports only 1 rescue configuration file on a device. This rescue configuration is a safeguard feature that allows network administrators to revert to a known good configuration in case of a configuration error or issue, ensuring network stability.
In Junos OS, each device supports only one rescue configuration file. The rescue configuration is a specific configuration that can be saved and later retrieved if needed. This is used as a fallback configuration that you know works and can be applied in case of an emergency or if the current configuration has issues.
Reference:
"You can create a rescue configuration file by using the request system configuration rescue save operational mode command. Each Junos OS device can have only one rescue configuration file."
質問 # 38
You have configured some interfaces on a Junos device; however, you have not yet committed the configuration.
What happens if you issue the rollback 0 command in this scenario?
- A. The messages.log file is deleted.
- B. The interface changes you made are discarded.
- C. The factory default configuration is loaded.
- D. The Junos device is rebooted.
正解：B
解説：
Issuing the rollback 0 command in Junos OS will discard any uncommitted changes and revert to the last committed configuration. This command effectively cancels any configuration changes that have been made but not yet committed, ensuring that the device returns to its previous stable state.
Reference:
"rollback 0 ...................................(rolls back the changes just made )" from Useful Juniper Commands.txt.
Juniper official documentation: Rolling Back a Configuration.
質問 # 39
Which prompt indicates that you are using configuration mode?
- A. >
- B. $
- C. #
- D. %
正解：C
解説：
In Junos OS, the # prompt indicates that you are in configuration mode. This mode is used for making changes to the configuration of the device.
Reference:
"The # prompt indicates that you are in configuration mode."
質問 # 40
You want to find out the chassis serial number of a Junos device.
Which command would display this information?
- A. show chassis location
- B. show chassis hardware
- C. show chassis environment
- D. show chassis routing-engine
正解：B
解説：
Theshow chassis hardwarecommand in Junos OS displays detailed information about the hardware installed in the device, including the chassis itself. This command provides a list of all hardware components, their serial numbers, part numbers, and version information. When looking for the chassis serial number specifically, this command is the most direct and comprehensive way to retrieve that information, as it includes the serial number of the chassis among the details provided.
質問 # 41
A network administrator is attempting to route traffic on a Juniper switch to one of three different VLANs:
Prod, Test, and Dev. Each VLAN has been assigned a numerical value.
In this scenario, what are these numerical values called?
- A. defaults
- B. tags
- C. names
- D. interfaces
正解：B
解説：
In the context of VLANs (Virtual Local Area Networks) on a Juniper switch, the numerical values assigned to each VLAN, such as those for Prod, Test, and Dev, are known as VLAN tags. These tags are part of the 802.1 Q VLAN standard, which allows multiple VLANs to coexist on a single physical network. Each tag uniquely identifies the VLAN to which a frame belongs, enabling the switch to segregate and manage traffic based on VLAN membership. This tagging mechanism allows for efficient traffic separation and management, ensuring that devices within one VLAN do not receive traffic intended for another, thus maintaining network security and efficiency.
質問 # 42
Which protocol would you configure to synchronize the time and date on a Junos device?
- A. NMP
- B. NTP
- C. SNMP
- D. RIP
正解：B
解説：
The Network Time Protocol (NTP) is designed to synchronize the clocks of computers over a network. Configuring NTP on a Junos device ensures that its clock is set accurately, which is crucial for logging, troubleshooting, and maintaining the integrity of time-sensitive operations and security protocols. NTP allows devices to use a hierarchy of time sources, from primary servers synchronized to a reference clock (such as an atomic clock or GPS time) to secondary servers that distribute the time to other devices on the network.
質問 # 43
You configured your system authentication order using the set authentication-order tacplus radius password command.
Which statement is correct in this scenario?
- A. All authentication methods are used with the most restrictive permission set used.
- B. A rejection by TACACS+ will prevent a login and bypass the other two authentication methods.
- C. The password authentication will only be used if the TACACS+ and RADIUS servers fail to respond.
- D. The password authentication method is evaluated if the TACACS+ and RADIUS servers respond with a reject message.
正解：C
解説：
In the scenario where the system authentication order is set to "tacplus radius password," the correct statement is (B). If the TACACS+ and RADIUS servers are unreachable or fail to respond, the system will fall back to using password authentication. This ensures that users can still authenticate using locally stored passwords if external authentication servers are unavailable.
質問 # 44
What are two benefits when implementing class of service? (Choose two.)
- A. Traffic congestion will be eliminated.
- B. Latency-sensitive traffic can be prioritized.
- C. Traffic congestion can be managed.
- D. The network will be faster.
正解：C
解説：
Class of Service (CoS) in Junos OS provides tools for managing traffic congestion and ensuring that latency-sensitive traffic is given priority over less time-critical data. By implementing CoS, network administrators can classify traffic into different priority levels, apply scheduling policies to ensure that high-priority traffic is transmitted first, and use congestion management techniques such as queue buffers and drop profiles. This helps in maintaining the quality of service for critical applications, especially during periods of high network congestion. However, CoS does not eliminate congestion entirely nor does it inherently make the network faster; it provides a mechanism for better managing and controlling traffic flows according to their importance and time sensitivity.
質問 # 45
You are logged in to a Junos OS device with SSH and issued the show protocols | compare command in the configuration, but no output is shown.
Which statement is correct in this scenario?
- A. You must commit the configuration before any output will be shown.
- B. The command only works for interface configuration differences.
- C. There are no changes to the candidate configuration.
- D. Someone accidentally deleted the active configuration.
正解：C
解説：
If issuing the "show | compare" command in configuration mode yields no output, it indicates that there are no changes to the candidate configuration (B). This command is used to compare the current candidate configuration with the active configuration, and a lack of output suggests that the candidate configuration matches the active one, meaning no changes have been made or the changes have already been committed.
質問 # 46
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