2023年最新ののJuniper JN0-351リアル試験問題集PDF
JN0-351試験問題集、JN0-351練習テスト問題
質問 # 11
What is a purpose of using a spanning tree protocol?
- A. to route IP packets
- B. to eliminate broadcast storms
- C. to tunnel Ethernet frames
- D. to look up MAC addresses
正解：B
解説：
A broadcast storm is a network condition where a large number of broadcast packets are sent and received by multiple devices, causing congestion and performance degradation1. A broadcast storm can occur when there are loops in the network topology, meaning that there are multiple paths between two devices2.
A spanning tree protocol is a network protocol that prevents loops from being formed when switches or bridges are interconnected via multiple paths. It does this by creating a logical tree structure that spans all the devices in the network, and disabling or blocking the links that are not part of the tree, leaving a single active path between any two devices3.
By eliminating loops, a spanning tree protocol also eliminates broadcast storms, as broadcast packets will not be forwarded endlessly along the looped paths. Instead, broadcast packets will be sent only along the tree structure, reaching each device once and avoiding congestion3.
質問 # 12
Exhibit.
You are using OSPF to advertise the subnets that are used by the Denver and Dallas offices. The routers that are directly connected to the Dallas and Denver subnets are not advertising the connected subnets.
Referring to the exhibit, which two statements are correct? (Choose two.)
- A. Create static routes on the switches using the local vMX router's loopback interface for the next hop.
- B. Configure and apply a routing policy that redistributes the Dallas and Denver subnets using Type 5 LSAs.
- C. Configure and apply a routing policy that redistributes the connected Dallas and Denver subnets.
- D. Enable the passive option on the OSPF interfaces that are connected to the Dallas and Denver subnets.
正解：C、D
解説：
Explanation
The routers that are directly connected to the Dallas and Denver subnets are not advertising the connected subnets. This can be resolved by redistributing the connected subnets into OSPF1.
Option C suggests to configure and apply a routing policy that redistributes the connected Dallas and Denver subnets. This is correct because redistribution allows routes from one routing protocol to be communicated to another, and in this case, it allows the connected subnets to be advertised through OSPF1.
Option D suggests enabling the passive option on the OSPF interfaces that are connected to the Dallas and Denver subnets. This is also correct because in OSPF, a passive interface is an interface that belongs to the OSPF router, but does not send OSPF Hello packets1. It's typically used on an interface that you don't want to use for OSPF adjacencies, but you still want to advertise its IP address1. Therefore, enabling passive interface can help in advertising the Dallas and Denver subnets.
質問 # 13
You have two OSPF routers forming an adjacency. R1 has a priority of 32 and a router ID of 192.168.1.2. R2 has a priority of 64 and a router ID of 192.168.1.1. The routers were started at the same time and all other OSPF settings are the default settings.
Which statement is correct in this scenario?
- A. R2 will be the BDR.
- B. Router IDs must match for an adjacency to form.
- C. R1 will be the BDR.
- D. At least three routers are required for a DR/BDR election
正解：C
解説：
Explanation
In OSPF, the Designated Router (DR) and Backup Designated Router (BDR) are elected based on the priority of the routers1. The router with the highest priority becomes the DR, and the router with the second highest priority becomes the BDR1. If there is a tie in priority, then the router with the highest Router ID is chosen1.
In this scenario, R2 has a higher priority (64) than R1 (32), so R2 will become the DR1. Since R1 has the second highest priority, it will become the BDR1. Therefore, option D is correct.
質問 # 14
Which two statements are true about the default VLAN on Juniper switches? (Choose two.)
- A. The default VLAN is set to a VLAN ID of 1 by default
- B. The default VLAN ID can be changed.
- C. The default VLAN ID is not visible.
- D. The default VLAN ID is not assigned to any interface.
正解：A、B
解説：
Explanation
On Juniper switches, the default VLAN is set to a VLAN ID of 1 by default12. This means that all interfaces on the switch are members of VLAN 1 until they are specifically assigned to another VLAN12. Therefore, option A is correct.
The default VLAN ID can be changed12. This allows network administrators to configure the switch to use a different VLAN as the default, if necessary12. Therefore, option D is correct.
質問 # 15
Exhibit.
You have configured the four EX Series switches with RSTP, as shown in the exhibit. You discover that whenever a link between switches goes up or down, the switches take longer than expected for RSTP to converge, using the default settings.
In this scenario, which action would solve the delay in RSTP convergence?
- A. The force-version must be removed.
- B. The hello-time must be increased.
- C. The bridge priority for EX-4 must be set at 4000.
- D. The max-age must be increased to 20
正解：A
解説：
The exhibit shows the configuration of RSTP on EX-4, which has the command force-version stp. This command forces the switch to use the legacy STP protocol instead of RSTP, even though the switch supports RSTP1. This means that EX-4 will not be able to take advantage of the faster convergence and enhanced features of RSTP, such as edge ports, link type, and proposal/agreement sequence2.
The other switches in the network are likely to be running RSTP, as it is the default protocol for EX Series switches3. Therefore, there will be a compatibility issue between EX-4 and the other switches, which will result in longer convergence times and suboptimal performance. The switch will also generate a warning message that says "Warning: STP version mismatch with neighbor" when it receives a BPDU from a RSTP neighbor1.
To solve this problem, the force-version command must be removed from EX-4, so that it can run RSTP natively and interoperate with the other switches in the network. This will enable faster convergence and better stability for the network topology. To remove the command, you can use the delete protocols rstp force-version command in configuration mode1.
質問 # 16
What is the default MAC age-out timer on an EX Series switch?
- A. 300 seconds
- B. 30 seconds
- C. 30 minutes
- D. 300 minutes
正解：A
解説：
Explanation
The default MAC age-out timer on an EX Series switch is 300 seconds12. The MAC age-out timer is the maximum time that an entry can remain in the MAC table before it "ages out," or is removed31. This configuration can influence efficiency of network resource use by affecting the amount of traffic that is flooded to all interfaces1. When traffic is received for MAC addresses no longer in the Ethernet routing table, the router floods the traffic to all interfaces1.
質問 # 17
Which two mechanisms are part of building and maintaining a Layer 2 bridge table? (Choose two.)
- A. blocking
- B. listening
- C. learning
- D. flooding
正解：C、D
解説：
Option B is correct. Flooding is a mechanism used in Layer 2 bridging where the switch sends incoming packets to all its ports except for the port where the packet originated1. This is done when the switch doesn't know the destination MAC address or when the packet is a broadcast or multicast1.
Option C is correct. Learning is another mechanism used in Layer 2 bridging where the switch learns the source MAC addresses of incoming packets and associates them with the port on which they were received23. This information is stored in a MAC address table, also known as a bridge table23.
Option A is incorrect. Blocking is a state in Spanning Tree Protocol (STP) used to prevent loops in a network2. It's not a mechanism used in building and maintaining a Layer 2 bridge table2.
Option D is incorrect. Listening is also a state in Spanning Tree Protocol (STP) where the switch listens for BPDUs to make sure no loops occur in the network before transitioning to the learning state2. It's not a mechanism used in building and maintaining a Layer 2 bridge table2.
質問 # 18
Which two statements about redundant trunk groups on EX Series switches are correct? (Choose two.)
- A. Redundant trunk groups must be connected to the same aggregation switch.
- B. Layer 2 control traffic is permitted on the secondary link
- C. If the active link fails, then the secondary link automatically takes over.
- D. Redundant trunk groups load-balance traffic across two designated uplink interfaces.
正解：A、C
解説：
Explanation
Redundant Trunk Groups (RTGs) on EX Series switches provide a simple solution for network recovery when a trunk port on a switch goes down1. They are configured on the access switch and contain two links: a primary or active link, and a secondary link1. Therefore, option B is correct because if the active link fails, the secondary link automatically starts forwarding data traffic without waiting for normal spanning-tree protocol convergence1.
Option D is also correct. In a typical enterprise network composed of distribution and access layers, RTGs are used where one Access switch is connected to two different uplink switches2. This implies that RTGs must be connected to the same aggregation switch2.
質問 # 19
Exhibit
You are a network operator troubleshooting BGP connectivity.
Which two statements are correct about the output shown in the exhibit? (Choose two.)
- A. The BGP session is not established.
- B. The R1 is configured for AS 65400.
- C. The routers are exchanging IPv4 routes.
- D. Peer 10.32.1.2 is configured for AS 63645.
正解：A、B
解説：
Explanation
Option B suggests that the BGP session is not established. This is correct because in the output, the state of the BGP session is shown as "Idle". In BGP, an "Idle" state means that the BGP session is not currently established1.
Option C suggests that R1 is configured for AS 65400. This is also correct because in the output, it's shown that the local AS number is 654001. The local AS number represents the Autonomous System (AS) number of the router on which you're checking the BGP session1.
質問 # 20
You are asked to connect an IP phone and a user computer using the same interface on an EX Series switch.
The traffic from the computer does not use a VLAN tag, whereas the traffic from the IP phone uses a VLAN tag.
Which feature enables the interface to receive both types of traffic?
- A. DHCP snooping
- B. voice VLAN
- C. native VLAN
- D. MAC limiting
正解：B
解説：
Explanation
The feature that enables an interface on an EX Series switch to receive both untagged traffic (from the computer) and tagged traffic (from the IP phone) is the voice VLAN12.
The voice VLAN feature in EX-series switches enables access ports to accept both data (untagged) and voice (tagged) traffic and separate that traffic into different VLANs12. This allows the switch to differentiate between voice and data traffic, ensuring that voice traffic can be treated with a higher priority12. Therefore, option D is correct.
質問 # 21
You implemented the MAC address limit feature with the shutdown action on all interfaces on your switch.
In this scenario, which statement is correct when a violation occurs?
- A. By default, you must manually clear the violation for the interface to send and receive traffic again.
- B. By default, devices that are learned before the violation occurs are still allowed to send and receive traffic through the specific interface.
- C. By default, the violation will automatically be cleared after 300 seconds and the interface will resume sending and receiving traffic for all learned devices.
- D. By default, the interface will continue to send and receive traffic for all connected devices after a violation has occurred.
正解：A
解説：
Explanation
When the MAC address limit feature with the shutdown action is implemented on a switch, if a violation occurs, the interface is disabled and a system log entry is generated1. If the switch has been configured with the port-error-disable statement, the disabled interface recovers automatically upon expiration of the specified disable timeout1. However, if the switch has not been configured for auto-recovery from port error disabled conditions, you must manually clearthe violation by running the clear ethernet-switching port-error command for the interface to send and receive traffic again1. This explanation is based on the Enterprise Routing and Switching Specialist (JNCIS-ENT) documents and learning resources available at Juniper Networks1.
質問 # 22
You have DHCP snooping enabled but no entries are automatically created in the snooping database for an interface on your EX Series switch. What are two reasons for the problem? (Choose two.)
- A. Dynamic ARP inspection is enabled on the interface.
- B. The device that is connected to the interface has performed a DHCPRELEASE.
- C. The device that is connected to the interface has a static IP address.
- D. MAC limiting is enabled on the interface.
正解：C、D
解説：
Explanation
The DHCP snooping feature in Juniper Networks' EX Series switches works by building a binding database that maps the IP address, MAC address, lease time, binding type, VLAN number, and interface information1. This database is used to filter and validate DHCP messages from untrusted sources1.
However, there are certain conditions that could prevent entries from being automatically created in the snooping database for an interface:
MAC limiting: If MAC limiting is enabled on the interface, it could potentially interfere with the operation of DHCP snooping. MAC limiting restricts the number of MAC addresses that can be learned on a physical interface to prevent MAC flooding attacks1. This could inadvertently limit the number of DHCP clients that can be learned on an interface, thus preventing new entries from being added to the DHCP snooping database.
Static IP address: If the device connected to the interface is configured with a static IP address, it will not go through the DHCP process and therefore will not have an entry in the DHCP snooping database1. The DHCP snooping feature relies on monitoring DHCP messages to build its database1, so devices with static IP addresses that do not send DHCP messages will not have their information added.
Therefore, options B and C are correct. Options A and D are not correct because performing a DHCPRELEASE would simply remove an existing entry from the database1, and Dynamic ARP inspection (DAI) uses the information stored in the DHCP snooping binding database but does not prevent entries from being created1.
質問 # 23
Which statement is correct about the IS-IS ISO NET address?
- A. An ISO NET address defined with a system ID of 0000.0000.0000 must be selected as the DIS.
- B. An ISO NET address must be unique for each device in the network.
- C. The Area ID must match on all devices within a L2 area.
- D. You can only define a single ISO NET address per device.
正解：B
解説：
An ISO NET address is a type of network address used by the IS-IS routing protocol. It identifies a point of connection to the network, such as a router interface, and is also called a Network Service Access Point (NSAP)1.
An ISO NET address consists of three parts: an area ID, a system ID, and a selector2. The area ID identifies the IS-IS area to which the device belongs. The system ID uniquely identifies the device within the area. The selector identifies a specific service or function on the device, such as routing or management2.
An ISO NET address must be unique for each device in the network, because it is used by IS-IS to establish adjacencies, exchange routing information, and compute shortest paths2. If two devices have the same ISO NET address, they will not be able to communicate with each other or with other devices in the network. Therefore, it is important to assign different ISO NET addresses to each device in the network.
質問 # 24
You are troubleshooting a BGP routing issue between your network and a customer router and are reviewing the BGP routing policies. Which two statements are correct in this scenario? (Choose two.)
- A. Export policies are applied after the RIB-Local table.
- B. Import policies are applied to routes in the RIB-Local table.
- C. Import policies are applied after the RIB-ln table.
- D. Export policies are applied to routes in the RIB-ln table.
正解：A、C
解説：
Explanation
In BGP, routing policies are used to control the flow of routing information between BGP peers1.
Option C suggests that import policies are applied after the RIB-In table. This is correct because import policies in BGP are applied to routes that are received from a BGP peer, before they are installed in the local BGP Routing Information Base (RIB-In)1. The RIB-In is a database that stores all the routes that are received from all peers1.
Option D suggests that export policies are applied after the RIB-Local table. This is correct because export policies in BGP are applied to routes that are being advertised to a BGP peer, after they have been selected from the local BGP Routing Information Base (RIB-Local)1. The RIB-Local is a database that stores all the routes that the local router is using1.
Therefore, options C and D are correct.
質問 # 25
Which two statements about redundant trunk groups on EX Series switches are correct? (Choose two.)
- A. Layer 2 control traffic is permitted on the secondary link.
- B. Redundant trunk groups use spanning tree to provide loop-free redundant uplinks.
- C. Redundant trunk groups load balance traffic across two designated uplink interfaces.
- D. If the active link fails, then the secondary link automatically takes over.
正解：A、D
解説：
C is correct because Layer 2 control traffic is permitted on the secondary link of a redundant trunk group (RTG) on EX Series switches. Layer 2 control traffic includes protocols such as LLDP, LACP, and STP, which are used to exchange information and coordinate actions between switches1. According to the Juniper Networks documentation2, Layer 2 control traffic is allowed to pass through both the active and the secondary links of an RTG, but data traffic is only forwarded through the active link. This allows the switches to maintain their Layer 2 adjacencies and monitor the link status on both links.
D is correct because if the active link fails, then the secondary link automatically takes over in an RTG on EX Series switches. An RTG consists of two trunk links: an active or primary link, and a secondary or backup link2. The active link is used to forward data traffic, while the secondary link is in standby mode. If the active link fails or becomes unavailable, the secondary link immediately transitions to a forwarding state and takes over the data traffic without waiting for normal STP convergence2. This provides fast recovery and redundancy for the network.
質問 # 26
Exhibit
Referring to the exhibit, which statement is correct?
- A. The root bridge is using a bridge priority of 4k.
- B. The local device is using a bridge priority of 4k.
- C. The local device is the root bridge for this RSTP topology.
- D. The root bridge has not been elected for this RSTP topology.
正解：C
解説：
Explanation
In a Rapid Spanning Tree Protocol (RSTP) topology, the root bridge is determined by the switch with the lowest bridge priority value12. If all switches have the same priority, then the root bridge is assigned to the switch whose MAC address's hex value is the lowest2. The default bridge priority value is 3276832. However, without the actual exhibit, it's difficult to definitively determine which device is the root bridge. But based on the options provided, if we assume that the local device has a lower bridge priority or a lower MAC address than other devices in the network, then it could be considered as the root bridge for this RSTP topology45.
質問 # 27
Exhibit.
Why is this OSPF adjacency remaining in this state?
- A. A hello interval mismatch exists between the OSPF neighbors.
- B. An MTU mismatch exists between the OSPF neighbors.
- C. An area ID mismatch exists between the OSPF neighbors
- D. A subnet mask mismatch exists between the OSPF neighbors.
正解：B
解説：
The exhibit shows the output of the command , which displays information about the OSPF neighbors on a router1.
The output shows that the OSPF neighbor with the address 172.26.1.1 and the interface ge-0/0/3.0 is in the Exstart state1.
The Exstart state is the fourth state in the OSPF neighbor formation process, after Down, Init, and
2-Way states2. In this state, the OSPF neighbors establish a master-slave relationship and exchange database description (DBD) packets, which contain summaries of their link-state databases2.
The most common reason for OSPF neighbors to be stuck in the Exstart state is an MTU mismatch between the interfaces3. MTU stands for maximum transmission unit, which is the largest size of a packet that can be transmitted on a network segment4. If the MTU values of two OSPF neighbors are different, theymay not be able to exchange DBD packets successfully, as some packets may be dropped or fragmented due to their size exceeding the MTU limit3.
To solve this problem, you need to ensure that the MTU values of both OSPF neighbors are the same or compatible. You can use the command show interfaces to display the MTU value of an interface5. You can also use the command ping with the do-not-fragment option to test the MTU size between two routers. You can change the MTU value of an interface by using the command set interfaces interface-name mtu mtu-value in configuration mode5.
質問 # 28
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