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Juniper JN0-351 Exam Syllabus Topics:
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NEW QUESTION # 23
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. The device that is connected to the interface has a static IP address.
- B. MAC limiting is enabled on the interface.
- C. Dynamic ARP inspection is enabled on the interface.
- D. The device that is connected to the interface has performed a DHCPRELEASE.
Answer: A,B
Explanation:
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.
NEW QUESTION # 24
Which two statements about BGP facilitate the prevention of routing loops within an autonomous system? (Choose two.)
- A. Routes learned from IBGP neighbors are not readvertised to other IBGP neighbors.
- B. IBGP sessions must be configured as a physical full mesh.
- C. IBGP sessions must be configured as a logical full mesh.
- D. Routes learned from IBGP neighbors are only advertised to other IBGP neighbors.
Answer: A,C
NEW QUESTION # 25
What are two characteristics of RSTP alternate ports? (Choose two.)
- A. RSTP alternate ports are active ports used to forward frames toward the root bridge.
- B. RSTP alternate ports provide an alternate lower cost path to the root bridge.
- C. RSTP alternate ports provide an alternate higher cost path to the root bridge.
- D. RSTP alternate ports block traffic while receiving superior BPDUs from a neighboring switch.
Answer: C,D
Explanation:
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.
NEW QUESTION # 26
Which two statements about redundant trunk groups on EX Series switches are correct? (Choose two.)
- A. Redundant trunk groups load balance traffic across two designated uplink interfaces.
- B. Redundant trunk groups use spanning tree to provide loop-free redundant uplinks.
- C. If the active link fails, then the secondary link automatically takes over.
- D. Layer 2 control traffic is permitted on the secondary link.
Answer: C,D
Explanation:
Redundant trunk groups are designed to provide link redundancy. If the primary link fails, the secondary link will automatically take over to ensure continued connectivity.
In redundant trunk groups, while regular data traffic is sent over the primary link, Layer 2 control traffic (such as STP, LACP, etc.) is allowed on the secondary link to maintain network stability and protocol operations.
https://www.juniper.net/documentation/us/en/software/junos/multicast-l2/topics/topic- map/redundant-trunk-groups.html
NEW QUESTION # 27
Referring to the exhibit, which two statements are correct? (Choose two.)
- A. The ge-0/0/13 interface will be selected as the forwarding interface.
- B. This device must be selected as the root bridge.
- C. The ge-0/0/10 interface will be part of the RSTP topology but will block incoming BPDUs.
- D. The ge-0/0/10 interface will not participate in the RSTP topology.
Answer: A,D
NEW QUESTION # 28
Refer to the exhibit.
Referring to the output shown in the exhibit, which statement is correct?
- A. The state is normal for a DRother neighbor
- B. An MTU mismatch exists between the OSPF neighbors.
- C. An area ID mismatch exists between the OSPF neighbors
- D. The state is normal for a DR neighbor.
Answer: A
Explanation:
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.
NEW QUESTION # 29
What is the management IP address of the device shown in the exhibit?
- A. 172.23.12.100
- B. 10.210.20.233
- C. 128.0.0.1
- D. 172.23.11.10
Answer: B
Explanation:
The management IP address of the device shown in the exhibit is indicated by the interface
"me0." In the provided output, the "me0" interface is listed with the IP address 10.210.20.233.
NEW QUESTION # 30
Which two mechanisms are part of building and maintaining a Layer 2 bridge table? (Choose two.)
- A. flooding
- B. blocking
- C. listening
- D. learning
Answer: A,D
Explanation:
Transparent bridging uses five mechanisms to create and maintain Ethernet switching tables on the switch:
- Learning
- Forwarding
- Flooding
- Filtering
- Aging
NEW QUESTION # 31
Referring to the output shown in the exhibit, which statement is correct?
- A. The state is normal for a DRother neighbor
- B. An MTU mismatch exists between the OSPF neighbors.
- C. An area ID mismatch exists between the OSPF neighbors
- D. The state is normal for a DR neighbor.
Answer: A
Explanation:
In OSPF, the state of the neighbor relationship is determined by the exchange of OSPF packets between routers. The state "2Way" as shown in the exhibit indicates that bi-directional communication has been established between the two OSPF routers. 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 network. These neighbors are often referred to as "DRothers". Therefore, option B is correct.
NEW QUESTION # 32
When trying to commit the configuration shown in the exhibit, you receive an error.
What is the problem?
- A. You have omitted the interface-mode accesscommand.
- B. You have not configured an IP address to the interface.
- C. You have not set the interface family correctly.
- D. You have omitted the interface-mode trunkcommand.
Answer: D
NEW QUESTION # 33
Which two statements are correct about tunnels? (Choose two.)
- A. Tunnels add additional overhead to packet size.
- B. Tunnel endpoints must have a valid route to the remote tunnel endpoint.
- C. BFD cannot be used to monitor tunnels.
- D. IP-IP tunnels are stateful.
Answer: A,B
Explanation:
Explanation
A tunnel is a connection between two computer networks, in which data is sent from one network to another through an encrypted link. Tunnels are commonly used to secure data communications between two networks or to connect two networks that use different protocols.
Option B is correct, because tunnel endpoints must have a valid route to the remote tunnel endpoint. A tunnel endpoint is the device that initiates or terminates a tunnel connection. For a tunnel to be established, both endpoints must be able to reach each other over the underlying network. This means that they must have a valid route to the IP address of the remote endpoint1.
Option D is correct, because tunnels add additional overhead to packet size. Tunnels work by encapsulating packets: wrapping packets inside of other packets. This means that the original packet becomes the payload of the surrounding packet, and the surrounding packet has its own header and trailer. The header and trailer of the surrounding packet add extra bytes to the packet size, which is called overhead. Overhead can reduce the efficiency and performance of a network, as it consumes more bandwidth and processing power2.
Option A is incorrect, because BFD can be used to monitor tunnels. BFD is a protocol that can be used to quickly detect failures in the forwarding path between two adjacent routers or switches. BFD can be integrated with various routing protocols and link aggregation protocols to provide faster convergence and fault recovery.
BFD can also be used to monitor the connectivity of tunnels, such as GRE, IPsec, or MPLS.
Option C is incorrect, because IP-IP tunnels are stateless. 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 are stateless, which means that they do not keep track of the state or status of the tunnel connection. Stateless tunnels do not require any signaling or negotiation between the endpoints, but they also do not provide any error detection or recovery mechanisms.
References:
1: What is Tunneling? | Tunneling in Networking 2: What Is Tunnel In Networking, Its Types, And Its Benefits? : [Configuring Bidirectional Forwarding Detection] : [IP-IP Tunneling]
NEW QUESTION # 34
You want to ensure traffic is routed through a GRE tunnel. In this scenario, which two statements will satisfy this requirement? (Choose two.)
- A. Keepalives must be used on stateless tunneling protocols.
- B. All intermediary devices must have a route to the tunnel endpoints.
- C. Tunnel endpoints must have a route that directs traffic into the tunnel.
- D. BFD must be used on the stateless tunneling protocols.
Answer: B,C
Explanation:
Option A is correct. For traffic to be sent through a GRE tunnel, there must be a route that directs the traffic into the tunnel. This is typically accomplished through the use of a static route or a dynamic routing protocol.
Option B is correct. All intermediary devices must have a route to the tunnel endpoints. In real- world scenarios, the tunnel endpoints for a tunnel going over the Internet must have globally reachable internet addresses. Otherwise, intermediate routers in the Internet cannot forward the tunneled packets.
NEW QUESTION # 35
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. The interface is configured as a disabled port.
- B. Dynamic ARP inspection is enabled on the interface.
- C. The interface is configured as a trunk port.
- D. MAC limiting is enabled on the interface.
Answer: A,C
Explanation:
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.
NEW QUESTION # 36
After receiving a BGP route, which two conditions are verified by the receiving router to ensure that the received route is valid? (Choose two)
- A. The loops do not exist.
- B. The AS-path length is greater than 0.
- C. The next hop is reachable.
- D. The local preference is greater than 0.
Answer: A,C
Explanation:
B is correct because the loops do not exist is one of the conditions that are verified by the receiving router to ensure that the received BGP route is valid. A loop in BGP means that a route has been advertised by the same AS more than once, which can cause routing instability and inefficiency1. To prevent loops, BGP uses the AS-path attribute, which lists the AS numbers that a route has traversed from the origin to the destination2. The receiving router checks the AS-path attribute of the received route and discards it if it finds its own AS number in the list2. This way, BGP avoids accepting routes that contain loops.
C is correct because the next hop is reachable is one of the conditions that are verified by the receiving router to ensure that the received BGP route is valid. The next hop is the IP address of the next router that is used to forward packets to the destination network3. The receiving router checks the next hop attribute of the received route and verifies that it has a valid route to reach it3. If the next hop is not reachable, the received route is not usable and is rejected by the receiving router3. This way, BGP ensures that only feasible routes are accepted.
NEW QUESTION # 37
What is the maximum allowable MTU size for a default GRE tunnel without IPv4 traffic fragmentation?
- A. 1476 bytes
- B. 1500 bytes
- C. 1480 bytes
- D. 1496 bytes
Answer: A
Explanation:
Explanation
The maximum allowable MTU size for a default GRE tunnel without IPv4 traffic fragmentation is 1476 bytes1. This is because GRE packets are formed by the addition of the original packets and the required GRE headers1. These headers are 24-bytes in length and since these headers are added to the original frame, depending on the original size of the packet we may run into IP MTU problems1. The most common IP MTU is 1500-bytes in length (Ethernet)1. When the tunnel is created, it deducts the 24-bytes it needs to encapsulate the passenger protocols and that is the IP MTU it will use1. For example, if we are forming a tunnel over FastEthernet (IP MTU 1500)the IOS calculates the IP MTU on the tunnel as: 1500-bytes from Ethernet -
24-bytes for the GRE encapsulation = 1476-Bytes1.
NEW QUESTION # 38
R1 was started at 4:00 PM. R2 and R3 were started at 6:00 PM. R4 was started at 10:00 PM. All routers are in Area 0 and there are no point-to-point links.
Referring to the exhibit, which router is the designated router?
- A. R2
- B. R3
- C. R4
- D. R1
Answer: D
NEW QUESTION # 39
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 routers are exchanging IPv4 routes.
- B. Peer 10.32.1.2 is configured for AS 63645.
- C. The BGP session is not established.
- D. The R1 is configured for AS 65400.
Answer: C,D
Explanation:
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.
NEW QUESTION # 40
Exhibit
You are troubleshooting an issue where traffic to 192.168.10.0/24 is being sent to R1 instead of your desired path through R2.
Referring to the exhibit, what is the reason for the problem?
- A. R1's route is the best path due to the shorter AS path.
- B. R2's route is not the best path due to a lower origin code.
- C. R1's route is the best path due to a higher local preference
- D. R2's route is not the best path due to loop prevention.
Answer: C
Explanation:
The exhibit shows the output of the command show ip bgp, which displays information about the BGP routes in the routing table1. The output shows two routes for the destination 192.168.10.0/24, one from R1 and one from R2.
The route from R1 has a local preference of 200, while the route from R2 has a local preference of
100. Local preference is a BGP attribute that indicates the degree of preference for a route within an autonomous system (AS)2. A higher local preference means a more preferred route2.
BGP uses a best path selection algorithm to choose the best route for each destination among multiple paths. The algorithm compares different attributes of the routes in a specific order of precedence3. The first attribute that is compared is weight, which is a Cisco-specific attribute that is local to the router3. If the weight is equal or not set, the next attribute that is compared is local preference3.
In this case, both routes have the same weight of 0, which means that they are learned from external BGP (eBGP) peers3. Therefore, the next attribute that is compared is local preference. Since R1's route has a higher local preference than R2's route, it is chosen as the best path and installed in the routing table3. The other attributes, such as origin code and AS path, are not considered in this case.
NEW QUESTION # 41
A host is connected to your EX Series switch using an interface with persistent MAC learning enabled. When you connect the host to another interface on the same switch, all traffic generated by the host is dropped. Which action should you perform to solve the problem?
- A. Enter the clear dhcp snooping databasecommand.
- B. Configure the interface as a trunk port.
- C. Enter the clear ethernet switching table persistent learningcommand.
- D. Disable dynamic ARP inspection.
Answer: C
NEW QUESTION # 42
Which two statements about DHCP snooping are correct? (Choose two.)
- A. DHCP snooping inspects all DHCP packets on untrusted ports.
- B. By default, the Junos OS treats access ports as trusted and trunk ports as untrusted.
- C. The DHCP database maps IP addresses, MAC addresses, and the associated VLAN.
- D. DHCP snooping uses ARP to add statically defined IP addresses to its database.
Answer: A,C
NEW QUESTION # 43
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