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質問 # 17
What are two characteristics of RSTP alternate ports? (Choose two.)
- A. RSTP alternate ports provide an alternate lower cost path to the root bridge.
- B. RSTP alternate ports block traffic while receiving superior BPDUs from a neighboring switch.
- C. RSTP alternate ports are active ports used to forward frames toward the root bridge.
- D. RSTP alternate ports provide an alternate higher cost path to the root bridge.
正解：B、D
解説：
A is correct because RSTP alternate ports block traffic while receiving superior BPDUs from a neighboring switch. An alternate port is a backup port for a root port, which means it receives better BPDUs from another bridge than the current root port1. However, an alternate port does not forward any traffic, as it is in a discarding state2. It only listens to BPDUs and waits for the root port to fail. If the root port fails, the alternate port can immediately transition to a forwarding state and become the new root port1.
C is correct because RSTP alternate ports provide an alternate higher cost path to the root bridge. An alternate port is selected based on the same criteria as the root port, which are the lowest bridge ID, the lowest path cost, the lowest sender port ID, and the lowest receiver port ID3. However, an alternate port receives a higher cost BPDU than the root port, otherwise it would be the root port itself1. Therefore, an alternate port provides an alternate higher cost path to the root bridge than the root port.
質問 # 18
Exhibit.
What is the management IP address of the device shown in the exhibit?
- A. 172.23.11.10
- B. 172.23.12.100
- C. 10.210.20.233
- D. 128.0.0.1
正解：B
解説：
Explanation
The management IP address of a device is the IP address that is used to access the device for configuration and monitoring purposes. It is usually assigned to a dedicatedmanagement interface that is separate from the data interfaces. The management interface can be accessed via SSH, Telnet, HTTP, or other protocols.
In the exhibit, the list of interfaces and their statuses shows that the management interface isme0. This interface has an admin status ofup, a protocol status ofinet, a local address of172.23.12.100/24, and a remote address ofunspecified. This means that the me0 interface is active, has an IPv4 address assigned, and is not connected to another device.
Therefore, the management IP address of the device shown in the exhibit is172.23.12.100.
References:
[Management Interfaces Overview] : [Displaying Interface Status Information]
質問 # 19
Exhibit
You have configured a GRE tunnel. To reduce the risk of dropping traffic, you have configured a keepalive OAM probe to monitor the state of the tunnel; however, traffic drops are still occurring.
Referring to the exhibit, what is the problem?
- A. For GRE tunnels, the OAM protocol requires that the BFD protocols also be used.
- B. LLDP needs to be removed from the gr-1/1/10.1 interface.
- C. The "event link-adjacency-loss" option must be set.
- D. The hold-time value must be two times the keepalive-time value
正解：D
解説：
Explanation
A keepalive OAM probe is a mechanism that can be used to monitor the state of a GRE tunnel and detect any failures in the tunnel path. A keepalive OAM probe consists of sending periodic packets from one end of the tunnel to the other and expecting a reply. If no reply is received within a specified time, the tunnel is considered down and the line protocol of the tunnel interface is changed to down1.
To configure a keepalive OAM probe for a GRE tunnel, you need to specify two parameters: the keepalive-time and the hold-time. The keepalive-time is the interval between each keepalive packet sent by the local router. The hold-time is the maximum time that the local router waits for a reply from the remote router before declaring the tunnel down2.
According to the Juniper Networks documentation, the hold-time value must be two times the keepalive-time value for a GRE tunnel2. This is because the hold-time value must account for both the round-trip time of the keepalive packet and the processing time of the remote router. If the hold-time value is too small, it may cause false positives and unnecessary tunnel flaps.
In the exhibit, the configuration shows that the keepalive-time is set to 10 seconds and the hold-time is set to
15 seconds for the gr-1/1/10.1 interface. This means that the local router will send a keepalive packet every 10 seconds and will wait for 15 seconds for a reply from the remote router. However, this hold-time value is not two times the keepalive-time value, which violates the recommended configuration. This may cause traffic drops if the remote router takes longer than 15 seconds to reply.
Therefore, option D is correct, because the hold-time value must be two times the keepalive-time value for a GRE tunnel. Option A is incorrect, because BFD is not required for GRE tunnels; BFD is another protocol that can be used to monitor tunnels, but it is not compatible with GRE keepalives3. Option B is incorrect, because the "event link-adjacency-loss" option is not related to GRE tunnels; it is an option that can be used to trigger an action when a link goes down4. Option C is incorrect, because LLDP does not need to be removed from the gr-1/1/10.1 interface; LLDP is a protocol that can be used to discover neighboring devices and their capabilities, but it does not interfere with GRE tunnels5.
References:
1: Configuring Keepalive Time and Hold time for a GRE Tunnel Interface 2: keepalive | Junos OS | Juniper Networks 3: Configuring Bidirectional Forwarding Detection 4: event link-adjacency-loss | Junos OS | Juniper Networks 5: Understanding Link Layer Discovery Protocol
質問 # 20
Which two BGP attributes must be supported by all BGP implementations and must be included in every update? (Choose two.)
- A. MED
- B. AS path
- C. next hop
- D. community
正解：B、C
解説：
Explanation
BGP attributes are properties that BGP uses for route advertisement, path selection, and loop prevention1. There are four categories of BGP attributes123:
Well-known mandatory: Must be recognized by all BGP routers, present in all BGP updates, and passed on to other BGP routers123.
Well-known discretionary: Supported by all BGP implementations, and are optionally included in BGP updates1.
Optional transitive: May not be supported by all implementations of BGP1.
Optional non-transitive: May not be supported by all implementations of BGP1.
The well-known mandatory attributes must be supported by all BGP implementations and must be included in every update123. These include the AS path and next hop attributes23. Therefore, options A and C are correct.
質問 # 21
An update to your organization's network security requirements document requires management traffic to be isolated in a non-default routing-instance. You want to implement this requirement on your Junos-based devices.
Which two commands enable this behavior? (Choose two.)
- A. set routing-instances mgmtjunoa interface ge-0/0/0.0
- B. set routing-instances mgmt_junos interface em1
- C. set system management-instance
- D. set routing-instances mgmt_junos
正解：C、D
解説：
Explanation
To isolate management traffic in a non-default routing-instance on Junos-based devices, you can use the set system management-instance and set routing-instances mgmt_junos commands12.
set system management-instance: This command associates the management interface (usually named fxp0 or em0 for Junos OS, or re0:mgmt-* or re1:mgmt-* for Junos OS Evolved) with the non-default virtual routing and forwarding (VRF) instance1. After you configure the non-default management VRF instance, management traffic no longer has to share a routing table with other control traffic or protocol traffic1.
set routing-instances mgmt_junos: This command creates a new routing instance named mgmt_junos. The name of the dedicated management VRF instance is reserved and hardcoded as mgmt_junos; you cannot configure any other routing instance by the name mgmt_junos1.
Therefore, options C and D are correct. Options A and B are not correct because they attempt to assign an interface to the mgmt_junos routing instance, which is not necessary for isolating management traffic1.
質問 # 22
Exhibit.
Which router will become the OSPF BDR if all routers are powered on at the same time?
- A. R4
- B. R3
- C. R1
- D. R2
正解：A
解説：
Explanation
OSPF DR/BDR election is a process that occurs on multi-access data links. It is intended to select two OSPF nodes: one to be acting as the Designated Router (DR), and another to be acting as the Backup Designated Router (BDR).The DR and BDR are responsible for generating network LSAs for the multi-access network and synchronizing the LSDB with other routers on the same network1.
The DR/BDR election is based on two criteria: the OSPF priority and the router ID. The OSPF priority is a value between 0 and 255 that can be configured on each interface participating in OSPF. The default priority is
1. A priority of 0 means that the router will not participate in the election and will never become a DR or BDR. The router with the highest priority will become the DR, and the router with the second highest priority will become the BDR. If there is a tie in priority, then the router ID is used as a tie-breaker. The router ID is a
32-bit number that uniquely identifies each router in an OSPF domain.It can be manually configured or automatically derived from the highest IP address on a loopback interface or any active interface2.
In this scenario, all routers have the same priority of 1, so the router ID will determine the outcome of the election. The router IDs are shown in the exhibit as RID values. The highest RID belongs to R4 (10.10.10.4), so R4 will become the DR. The second highest RID belongs to R3 (10.10.10.3), so R3 will become the BDR.
References:
1:OSPF DR/BDR Election: Process, Configuration, and Tuning2:OSPF Designated Router (DR) and Backup Designated Router (BDR)
質問 # 23
Exhibit
You are receiving the BGP route shown in the exhibit from four different upstream ISPs.
Referring to the exhibit, which ISP will be selected as the active path?
- A. ISP 3
- B. ISP 2
- C. ISP 4
- D. ISP1
正解：C
解説：
Explanation
In BGP, the path selection process is based on a set of attributes1. The process starts by preferring the path with the highest weight, then the highest local preference, then the locally originated routes, and so on1. If all these attributes are the same, then it prefers the path with the shortest AS path1.
Referring to the exhibit, all four ISPs have the same weight, local preference, and origin1. However, ISP 4 has the shortest AS path1. Therefore, ISP 4 will be selected as the active path. So, option C is correct.
質問 # 24
Which statement is correct about the storm control feature?
- A. The storm control feature is enabled in the factory-default configuration on EX Series switches.
- B. The storm control feature is not supported on aggregate Ethernet interfaces.
- C. The storm control configuration only applies to traffic being sent between the forwarding and control plane.
- D. The storm control feature requires a special license on EX Series switches.
正解：A
解説：
Option A is correct. The storm control feature is enabled in the factory-default configuration on EX Series switches12. On EX2200, EX3200, EX3300, EX4200, and EX6200 switches, the factory default configuration enables storm control for broadcast and unknown unicast traffic on all switch interfaces2. On EX4300 switches, the factory default configuration enables storm control on all Layer 2 switch interfaces1.
Option B is incorrect. The storm control feature does not require a special license on EX Series switches34.
Option C is incorrect. There's no information available that suggests the storm control feature is not supported on aggregate Ethernet interfaces.
Option D is incorrect. The storm control configuration applies to traffic at the ingress of an interface5, not just between the forwarding and control plane.
質問 # 25
What are two characteristics of RSTP alternate ports? (Choose two.)
- A. RSTP alternate ports provide an alternate lower cost path to the root bridge.
- B. RSTP alternate ports block traffic while receiving superior BPDUs from a neighboring switch.
- C. RSTP alternate ports are active ports used to forward frames toward the root bridge.
- D. RSTP alternate ports provide an alternate higher cost path to the root bridge.
正解：B、D
解説：
A is correct because RSTP alternate ports block traffic while receiving superior BPDUs from a neighboring switch. An alternate port is a backup port for a root port, which means it receives better BPDUs from another bridge than the current root port1. However, an alternate port does not forward any traffic, as it is in a discarding state2. It only listens to BPDUs and waits for the root port to fail. If the root port fails, the alternate port can immediately transition to a forwarding state and become the new root port1.
C is correct because RSTP alternate ports provide an alternate higher cost path to the root bridge. An alternate port is selected based on the same criteria as the root port, which are the lowest bridge ID, the lowest path cost, the lowest sender port ID, and the lowest receiver port ID3. However, an alternate port receives a higher cost BPDU than the root port, otherwise it would be the root port itself1. Therefore, an alternate port provides an alternate higher cost path to the root bridge than the root port.
質問 # 26
Exhibit
You are a network operator troubleshooting BGP connectivity.
Which two statements are correct about the output shown in the exhibit? (Choose two.)
- A. Peer 10.32.1.2 is configured for AS 63645.
- B. The BGP session is not established.
- C. The routers are exchanging IPv4 routes.
- D. The R1 is configured for AS 65400.
正解：B、D
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 # 27
Exhibit
Your BGP neighbors, one in the USA and one in France, are not establishing a connection with each other.
Referring to the exhibit, which statement is correct?
- A. The BFD liveness is set too high.
- B. The BFD liveness is set too low.
- C. The BFD liveness must be configured on the BGP group.
- D. The BFD liveness must be configured on the BGP neighbor.
正解：D
解説：
Explanation
The exhibit shows the configuration of BFD liveness detection for BGP at the global level, which applies to all BGP neighbors by default1. However, this configuration does not specify the session mode, which determines whether BFD uses single-hop or multihop mode to communicate with a neighbor2.
For single-hop BGP neighbors, which are directly connected on the same subnet, the session mode can be either automatic or single-hop. For multihop BGPneighbors, which are not directly connected and require multiple hops to reach, the session mode must be multihop2.
Since your BGP neighbors are in different countries, they are likely to be multihop neighbors. Therefore, you need to configure the session mode as multihop for each neighbor individually at the [edit protocols bgp group group-name neighbor address bfd-liveness-detection] hierarchy level2. For example:
protocols { bgp { group usa { neighbor 192.0.2.1 { bfd-liveness-detection { session-mode multihop; } } } group france { neighbor 198.51.100.1 { bfd-liveness-detection { session-mode multihop; } } } } } If you do not configure the session mode for multihop neighbors, BFD will use the default mode of automatic, which will try to use single-hop mode and fail to establish a BFD session with the remote neighbor2. This will prevent BGP from using BFD to detect liveliness and failover.
Therefore, the answer B is correct, as you need to configure the BFD liveness detection on the BGP neighbor level with the appropriate session mode for multihop neighbors.
質問 # 28
What is the default MAC age-out timer on an EX Series switch?
- A. 30 seconds
- B. 30 minutes
- C. 300 minutes
- D. 300 seconds
正解：D
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 # 29
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. Router IDs must match for an adjacency to form.
- B. R2 will be the BDR.
- 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 # 30
Which statement is correct about controlling the routes installed by a RIB group?
- A. Only routes in the last table are installed.
- B. An import policy is applied to the RIB group.
- C. An export policy is applied to the RIB group.
- D. A firewall filter must be configured to install routes in the RIB groups.
正解：B
解説：
Explanation
A RIB group is a configuration that allows a routing protocol to install routes into multiple routing tables in Junos OS. A RIB group consists of an import-rib statement,which specifies the source routing table, and an export-rib statement, which specifies the destination routing table or group. A RIB group can also include an import-policy statement, which specifies one or more policies to control which routes are imported into the destination routing table or group1.
An import policy is a policy statement that defines the criteria for accepting or rejecting routes from the source routing table. An import policy can also modify the attributes of the imported routes, such as preference, metric, or community. An import policy can be applied to a RIB group by using the import-policy statement under the [edit routing-options rib-groups] hierarchy level1.
Therefore, option A is correct, because an import policy is applied to the RIB group to control which routes are installed in the destination routing table or group. Option B is incorrect, because all routes in the source routing table are imported into the destination routing table or group, unless filtered by an import policy.
Option C is incorrect, because a firewall filter is not used to install routes in the RIB groups; a firewall filter is used to filter packets based on various criteria. Option D is incorrect, because an export policy is not applied to the RIB group; an export policy is applied to a routing protocol to control which routes are advertised to other devices.
References:
1: rib-groups | Junos OS | Juniper Networks
質問 # 31
Exhibit
Referring to the exhibit, which two configuration changes must you apply for packets to reach from R1 to R3 using IS-IS? (Choose two.)
- A. On R3 enable Level 1 on the ge-0/0/4 interface
- B. On R1, enable Level 1 on the ge-0/0/1 interface.
- C. On R3 disable Level 2 on the ge-0/0/4 interface.
- D. On R1, disable Level 2 on the ge-0/0/1 interface.
正解：A、B
解説：
Explanation
A: On R1, enable Level 1 on the ge-0/0/1 interface. In IS-IS, both levels (Level 1 and Level 2) are enabled by default when you enable IS-IS on an interface1. Level 1 systems route within an area2. If the destination is outside an area, Level 1 systems route toward a Level 2 system2. Therefore, enabling Level 1 on the ge-0/0/1 interface on R1 would allow packets to reach from R1 to R3.
D: On R3 enable Level 1 on the ge-0/0/4 interface Similarly, enabling Level 1 on the ge-0/0/4 interface on R3 would allow packets to reach from R1 to R3.
These explanations are based on the IS-IS configuration documents and learning resources available at Juniper Networks1 and Cisco34.
質問 # 32
Which two mechanisms are part of building and maintaining a Layer 2 bridge table? (Choose two.)
- A. listening
- B. learning
- C. blocking
- D. flooding
正解：B、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 # 33
What are two reasons for creating multiple areas in OSPF? (Choose two.)
- A. to reduce the convergence time
- B. to reduce LSA flooding across the network
- C. to increase the size of the LSDB
- D. to increase the number of adjacencies in the backbone
正解：A、B
解説：
Explanation
Option A is correct. Creating multiple areas in OSPF can help to reduce the convergence time . This is because changes in one area do not affect other areas, so fewer routers need to run the SPF algorithm in response to a change.
Option D is correct. Creating multiple areas in OSPF can help to reduce Link State Advertisement (LSA) flooding across the network. This is because LSAs are not flooded out of their area of origin.
質問 # 34
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. voice VLAN
- B. DHCP snooping
- C. native VLAN
- D. MAC limiting
正解：A
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 # 35
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