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質問 # 32
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 # 33
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 must be configured on the BGP neighbor.
- C. The BFD liveness must be configured on the BGP group.
- D. The BFD liveness is set too low.
正解：B
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 # 34
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 # 35
You are receiving multiple BGP routes from an upstream neighbor and only want to advertise a single summarized prefix to your internal OSPF neighbors. This route should only be advertised when you are receiving these BGP routes from this neighbor.
In this scenario, which type of route should you create?
- A. static route using the resolve feature
- B. static route using qualified next hops
- C. generate route
- D. aggregate route
正解：D
解説：
Explanation
In this scenario, you should create an 1. Aggregate routes are used for advertising summarized network prefixes1. They help minimize the number of routing tables in an IP network by consolidating selected multiple routes into a single route advertisement1. This approach is in contrast to non-aggregation routing, in which every routing table contains a unique entry for each route1.
Therefore, option A is correct. Options B, C, and D are not correct because:
Static route using the resolve feature: This type of route uses the resolve feature to install a static route in the routing table only if a specific condition is met1. However, it does not provide the capability to summarize multiple routes into a single prefix.
Generate route: This type of route generates a route that is always present in the routing table and can be used to summarize routes. However, it does not have the capability to only advertise the route when specific BGP routes are being received from a neighbor1.
Static route using qualified next hops: This type of route allows for the specification of multiple next-hop addresses for a static route1. However, it does not provide the capability to summarize multiple routes into a single prefix.
質問 # 36
Which statement is correct about IP-IP tunnels?
- A. There are 24 bytes of overhead with IP-IP encapsulation.
- B. IP-IP tunnels only support encapsulating IP traffic.
- C. IP-IP tunnels only support encapsulating non-IP traffic.
- D. The TTL in the inner packet is decremented during transit to the tunnel endpoint.
正解：B
解説：
Explanation
IP-IP tunnels are a type of tunnels that use IP as both the encapsulating and encapsulated protocol. IP-IP tunnels are simple and easy to configure, but they do not provide any security or authentication features. IP-IP tunnels only support encapsulating IP traffic, which means that the payload of the inner packet must be an IP packet. IP-IP tunnels cannot encapsulate non-IP traffic, such as Ethernet frames or MPLS labels1.
Option A is correct, because IP-IP tunnels only support encapsulating IP traffic. Option B is incorrect, because IP-IP tunnels only support encapsulating non-IP traffic. Option C is incorrect, because the TTL in the inner packet is not decremented during transit to the tunnel endpoint. The TTL in the outer packet is decremented by each router along the path, but the TTL in the inner packet is preserved until it reaches the tunnel endpoint2.
Option D is incorrect, because there are 20 bytes of overhead with IP-IP encapsulation. The overhead consists of the header of the outer packet, which has a fixed size of 20 bytes for IPv43.
References:
1: IP-IP Tunneling 2: What is tunneling? | Tunneling in networking 3: IPv4 - Header
質問 # 37
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 hello-time must be increased.
- B. The force-version must be removed.
- C. The max-age must be increased to 20
- D. The bridge priority for EX-4 must be set at 4000.
正解：B
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 # 38
Exhibit.
Which router will become the OSPF BDR if all routers are powered on at the same time?
- A. R3
- B. R4
- C. R1
- D. R2
正解：B
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 # 39
Which statement is correct about graceful Routing Engine switchover (GRES)?
- A. When combined with NSR, routing is preserved and the new master RE does not restart rpd.
- B. GRES has a helper mode and a restarting mode.
- C. The PFE restarts and the kernel and interface information is lost.
- D. With no other high availability features enabled, routing is preserved and the new master RE does not restart rpd.
正解：A
解説：
Explanation
The Graceful Routing Engine Switchover (GRES) feature in Junos OS enables a router with redundant Routing Engines to continue forwarding packets, even if one Routing Engine fails1. GRES preserves interface and kernel information, ensuring that traffic is not interrupted1. However, GRES does not preserve the control plane1.
To preserve routing during a switchover, GRES must be combined with either Graceful Restart protocol extensions or Nonstop Active Routing (NSR)1. When GRES is combined with NSR, nearly 75 percent of line rate worth of traffic per Packet Forwarding Engine remains uninterrupted during GRES1. Any updates to the primary Routing Engine are replicated to the backup Routing Engine as soon as they occur1.
Therefore, when GRES is combined with NSR, routing is preserved and the new master RE does not restart rpd1.
質問 # 40
Which statement is correct about the IS-IS ISO NET address?
- A. You can only define a single ISO NET address per device.
- B. The Area ID must match on all devices within a L2 area.
- C. An ISO NET address must be unique for each device in the network.
- D. An ISO NET address defined with a system ID of 0000.0000.0000 must be selected as the DIS.
正解：C
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 # 41
You are asked to create a new firewall filter to evaluate Layer 3 traffic that is being sent between VLANs. In this scenario, which two statements are correct? (Choose two.)
- A. You should create a family inet firewall filter with the appropriate match criteria and actions.
- B. You should apply the firewall filter to the appropriate VLAN.
- C. You should create a family Ethernet-switching firewall filter with the appropriate match criteria and actions.
- D. You should apply the firewall filter to the appropriate IRB interface.
正解：A、D
解説：
Explanation
A firewall filter is a configuration that defines the rules that determine whether to forward or discard packets at specific processing points in the packet flow. A firewall filter can also modify the attributes of the packets, such as priority, marking, or logging. A firewall filter can be applied to various interfaces, protocols, or routing instances on a Juniper device1.
A firewall filter has a family attribute, which specifies the type of traffic that the filter can evaluate. The family attribute can be one of the following: inet, inet6, mpls, vpls, iso, or ethernet-switching2. The family inet firewall filter is used to evaluate IPv4 traffic, which is the most common type of Layer 3 traffic on a network.
To create a family inet firewall filter, you need to specify the appropriate match criteria and actions for each term in the filter. The match criteria can include various fields in the IPv4 header, such as source address, destination address, protocol, port number, or DSCP value. The actions can include accept, discard, reject, count, log, policer, or next term3.
To apply a firewall filter to Layer 3 traffic that is being sent between VLANs, you need to apply the filter to the appropriate IRB interface. An IRB interface is an integrated routing and bridging interface that provides Layer 3 functionality for a VLAN on a Juniper device. An IRB interface has an IP address that acts as the default gateway for the hosts in the VLAN. An IRB interface can also participate in routing protocols and forward packets to other VLANs or networks4.
Therefore, option C is correct, because you should create a family inet firewall filter with the appropriate match criteria and actions. Option D is correct, because you should apply the firewall filter to the appropriate IRB interface.
Option A is incorrect, because you should not create a family ethernet-switching firewall filter with the appropriate match criteria and actions. A family ethernet-switching firewall filter is used to evaluate Layer 2 traffic on a Juniper device. A family ethernet-switching firewall filter can only match on MAC addresses or VLAN IDs, not on IP addresses or protocols5.
Option B is incorrect, because you should not apply the firewall filter to the appropriate VLAN. A VLAN is a logical grouping of hosts that share the same broadcast domain on a Layer 2 network. A VLAN does not have an IP address or routing capability. A firewall filter cannot be applied directly to a VLAN; it must be applied to an interface that belongs to or connects to the VLAN6.
References:
1: Firewall Filters Overview 2: Configuring Firewall Filters 3: Configuring Firewall Filter Match Conditions and Actions 4: Understanding Integrated Routing and Bridging Interfaces 5: Configuring Ethernet-Switching Firewall Filters 6: Understanding VLANs
質問 # 42
A new network requires multiple topology support. You decide to use IS-IS in this situation. Which three protocol topologies are supported in this scenario? (Choose three.)
- A. IPv6
- B. IPv4
- C. IPsec
- D. anycast
- E. multicast
正解：A、B、E
解説：
Explanation
IS-IS (Intermediate System to Intermediate System) is a routing protocol that is designed to move information efficiently within a computer network12. It supports multiple protocol topologies, including IPv4, IPv6, and multicast12. Therefore, options C, E, and D are correct.
質問 # 43
Exhibit
What does the * indicate in the output shown in the exhibit?
- A. The switch ports have a router attached.
- B. All interfaces have elected a root bridge.
- C. The interface is down.
- D. The interface is active.
正解：D
解説：
The exhibit shows the output of the command show vlans brief, which displays brief information about VLANs and their associated interfaces1.
The output has four columns: Routing instance, VLAN name, Interfaces, and Tagging.
The * symbol indicates that the interface is active, meaning that it is up and forwarding traffic1. This can be verified by the command , which displays the status of the interfaces2.
質問 # 44
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 load balance traffic across two designated uplink interfaces.
- C. Redundant trunk groups use spanning tree to provide loop-free redundant uplinks.
- 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 # 45
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 4
- B. ISP 3
- C. ISP1
- D. ISP 2
正解：A
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 # 46
Refer to the exhibit.
Referring to the output shown in the exhibit, which statement is correct?
- A. An area ID mismatch exists between the OSPF neighbors
- B. The state is normal for a DR neighbor.
- C. The state is normal for a DRother neighbor
- D. An MTU mismatch exists between the OSPF neighbors.
正解：C
解説：
Explanation
In OSPF, the state of the neighbor relationship is determined by the exchange of OSPF packets between routers1. The state "2Way" as shown in the exhibit indicates that bi-directional communication has been established between the two OSPF routers1. This is the normal state for a neighbor that is not the Designated Router (DR) or Backup Designated Router (BDR) on a broadcast, non-broadcast multi-access (NBMA), or point-to-multipoint network1. These neighbors are often referred to as "DRothers"1. Therefore, option B is correct.
質問 # 47
What are two reasons for creating multiple areas in OSPF? (Choose two.)
- A. to increase the number of adjacencies in the backbone
- B. to reduce the convergence time
- C. to reduce LSA flooding across the network
- D. to increase the size of the LSDB
正解：B、C
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 # 48
You are configuring an IS-IS IGP network and do not see the IS-IS adjacencies established. In this scenario, what are two reasons for this problem? (Choose two.)
- A. The Level 2 routers have mismatched areas.
- B. The lo0 interface is not included as an IS-IS interface.
- C. IP subnets are not a /30 address.
- D. MTU is not at least 1492 bytes.
正解：B、D
解説：
Explanation
Option A suggests that the MTU is not at least 1492 bytes. This is correct because IS-IS requires a minimum MTU of 1492 bytes to establish adjacencies1. If the MTU is less than this, IS-IS adjacencies will not be established1.
Option D suggests that the lo0 interface is not included as an IS-IS interface. This is also correct because the loopback interface (lo0) is typically used as the router ID in IS-IS1. If the loopback interface is not included in IS-IS, it could prevent IS-IS adjacencies from being established1.
Therefore, options A and D are correct.
質問 # 49
You deployed a new EX Series switch with DHCP snooping enabled and you do not see any entries in the snooping databases for an interface. Which two Juniper configurations for that interface caused this issue?
(Choose two.)
- A. Dynamic ARP inspection is enabled on the interface.
- B. MAC limiting is enabled on the interface.
- C. The interface is configured as a trunk port.
- D. The interface is configured as a disabled port.
正解：C、D
解説：
A is correct because the interface is configured as a disabled port. A disabled port does not forward any traffic, including DHCP packets. Therefore, DHCP snooping cannot learn any MAC addresses or lease information from a disabled port1.
C is correct because the interface is configured as a trunk port. By default, all trunk ports on the switch are trusted for DHCP snooping2. This means that DHCP snooping does not inspect or filter any DHCP packets received on a trunk port. Therefore, DHCP snooping does not add any entries to the snooping database for a trunk port2.
質問 # 50
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