View Full Juniper JN0-637 Exam Dumps and Practice Test Dumps

 

Question 61. Which Junos component is responsible for running routing protocols and maintaining the routing information base?

1. Packet Forwarding Engine
2. Routing Engine
3. Firewall filter
4. Interface ASIC

Correct Answer: 2. Routing Engine

Explanation:
The Routing Engine (RE) performs the primary control-plane functions of a Junos device. It runs routing protocols such as BGP, OSPF, and IS-IS, maintains routing information, and calculates the routes that should be used for forwarding. The RE communicates the resulting forwarding information to the Packet Forwarding Engine, which performs high-speed packet forwarding. This separation allows the control plane and forwarding plane to operate independently. Understanding the responsibilities of the RE is important when troubleshooting routing protocols, route selection, configuration processing, and other control-plane functions on Juniper platforms.

Question 62. Which BGP mechanism is commonly used to prevent routing loops between autonomous systems?

1. AS path
2. Local preference
3. MED
4. Community

Correct Answer: 1. AS path

Explanation:
The BGP AS path attribute helps prevent routing loops between autonomous systems. When a route is advertised through eBGP, the advertising autonomous system typically adds its AS number to the AS path. If a BGP router receives a route containing its own AS number in the path, it can reject the route because accepting it could create a routing loop. The AS path also contributes to BGP route selection, where a shorter path can generally be preferred when other relevant factors are equal. This makes AS path both a loop-prevention mechanism and an important routing attribute.

Question 63. What is the purpose of the next-hop attribute in a routing table entry?

1. It identifies the next router or forwarding destination toward the route
2. It defines the route’s administrative owner
3. It specifies the route’s BGP community
4. It determines the physical chassis slot

Correct Answer: 1. It identifies the next router or forwarding destination toward the route

Explanation:
The next-hop information associated with a route identifies where packets should be sent to reach the destination prefix. Depending on the route and protocol, the next hop may be a directly connected address, a neighboring router, or another forwarding destination. Routing protocols can advertise next-hop information, and routing policies can sometimes modify it. In BGP, next-hop processing is particularly important because an otherwise valid route may not be usable if its next-hop cannot be resolved. Examining next-hop information is therefore a common step when troubleshooting route installation and forwarding problems.

Question 64. Which Junos command is useful for displaying the configuration differences between the candidate and committed configurations?

1. show route
2. show | compare
3. show chassis hardware
4. show ospf neighbor

Correct Answer: 2. show | compare

Explanation:
The show | compare command is commonly used in Junos configuration mode to display differences between the candidate configuration and the currently committed configuration. It allows administrators to review additions, deletions, and modifications before committing changes. This is especially useful when working with complex configurations or when multiple changes have been made during a configuration session. Reviewing differences before a commit helps verify that only the intended statements are being changed. It also provides a convenient way to detect accidental modifications before they become active on the device.

Question 65. Which OSPF LSA type is commonly used by routers within an area to describe their directly connected links?

1. Type 5
2. Type 3
3. Type 1
4. Type 7

Correct Answer: 3. Type 1

Explanation:
OSPF Type 1 LSAs, known as Router LSAs, are generated by every OSPF router and describe the router’s links and interfaces within an area. They provide information about the router’s directly connected OSPF topology and are fundamental to constructing the area’s link-state database. Type 2 Network LSAs are generated by the Designated Router on applicable multi-access networks, while Type 3 LSAs describe inter-area routes. Type 5 LSAs are used for external routes. Understanding LSA types helps administrators interpret the OSPF database and troubleshoot route propagation and topology information.

Question 66. What is the main purpose of an iBGP route reflector?

1. To replace the OSPF backbone
2. To reduce the need for a full mesh of iBGP sessions
3. To assign MPLS labels
4. To provide Ethernet loop prevention

Correct Answer: 2. To reduce the need for a full mesh of iBGP sessions

Explanation:
An iBGP route reflector reduces the requirement for every iBGP speaker in an autonomous system to establish a direct session with every other iBGP speaker. In a traditional iBGP design, a full mesh may be required as the network grows, creating significant session-management overhead. A route reflector can receive routes from its clients and reflect eligible routes to other clients or non-client peers according to BGP rules. This provides a scalable alternative for large networks. Route reflectors are commonly deployed in service-provider and enterprise BGP architectures where many internal BGP speakers are present.

Question 67. Which Junos feature allows an administrator to temporarily revert to a previous configuration automatically if a new configuration causes connectivity problems?

1. commit confirmed
2. show | compare
3. commit check
4. request system snapshot

Correct Answer: 1. commit confirmed

Explanation:
The commit confirmed feature provides a safety mechanism for configuration changes that might affect management connectivity. The administrator commits the candidate configuration with a confirmation timer. If the administrator does not confirm the configuration by issuing another commit before the timer expires, Junos automatically rolls back to the previous committed configuration. This is particularly valuable when making remote changes to interfaces, routing, firewall filters, or management access. It reduces the risk of being permanently locked out because of an incorrect configuration. The feature should be used carefully, with the confirmation deadline selected appropriately for the maintenance task.

Question 68. Which protocol is commonly used as a link-state IGP in large service-provider networks?

1. FTP
2. DHCP
3. IS-IS
4. SMTP

Correct Answer: 3. IS-IS

Explanation:
IS-IS is a link-state Interior Gateway Protocol widely used in large service-provider networks. Like OSPF, it builds a link-state database and uses shortest-path calculations to determine routes. IS-IS operates directly over the data-link layer rather than using IP as its transport protocol, which is one of its notable characteristics. It supports hierarchical routing through levels and can carry information for both IPv4 and IPv6. Junos provides extensive support for IS-IS, making knowledge of its adjacencies, levels, link-state database, metrics, and route installation relevant for advanced routing environments.

Question 69. What does a BGP import policy control on a Junos device?

1. Which routes are accepted from a BGP neighbor and how they may be modified
2. Which physical interface is used for Ethernet switching
3. Which OSPF area becomes the backbone
4. Which MPLS labels are generated by the PFE

Correct Answer: 1. Which routes are accepted from a BGP neighbor and how they may be modified

Explanation:
A BGP import policy controls how routes received from a BGP neighbor are processed. The policy can match characteristics such as prefixes, communities, AS paths, protocol information, and other route attributes. Depending on the policy actions, routes can be accepted, rejected, or modified by changing selected attributes. Import policies are therefore important for controlling the routes that enter the local routing system and for influencing subsequent route selection. They complement export policies, which determine what routes are advertised to BGP neighbors. Together, they provide granular control over BGP route exchange.

Question 70. Which MPLS operation removes the top label from a packet before forwarding it toward the destination?

1. Push
2. Swap
3. Encapsulate
4. Pop

Correct Answer: 4. Pop

Explanation:
In MPLS forwarding, a pop operation removes the top label from an MPLS packet. Label operations generally include push, swap, and pop. Push adds a label, swap replaces the existing top label with another label, and pop removes the top label. Penultimate Hop Popping (PHP) is a common MPLS behavior in which the router immediately before the egress router removes the top label. Understanding these operations helps explain how packets move through an MPLS Label-Switched Path and how label stacks are processed at different points in the network.

Question 71. Which Junos command can be used to display detailed information about a BGP neighbor?

1. show bgp neighbor
2. show route summary
3. show ospf database
4. show interfaces terse

Correct Answer: 1. show bgp neighbor

Explanation:
The show bgp neighbor command provides detailed information about BGP peer sessions. Depending on the command and options used, the output can include the peer address, autonomous system, session state, timers, negotiated capabilities, route counts, message statistics, and other operational information. This makes the command useful when investigating why a BGP session is not established or why routes are not being exchanged as expected. The summary command provides a shorter overview, while the neighbor command gives considerably more detail for individual BGP sessions and their operational behavior.

Question 72. Which Junos configuration hierarchy is used to define OSPF settings?

1. protocols ospf
2. system ospf
3. routing-options ospf
4. interfaces ospf

Correct Answer: 1. protocols ospf

Explanation:
OSPF configuration in Junos is defined under the protocols ospf hierarchy. Within this hierarchy, administrators can configure areas, interfaces, authentication, metrics, timers, and other OSPF-related parameters. Interface-specific OSPF participation is also configured through the appropriate OSPF hierarchy and associated interface statements. The routing-options hierarchy contains other routing-related configuration such as static routes and autonomous system settings, but OSPF itself is configured under protocols ospf. Knowing the correct Junos configuration hierarchy is important for both configuration tasks and certification questions involving Junos syntax.

Question 73. What is the primary function of an OSPF designated router on a broadcast segment?

1. To replace every other OSPF router
2. To distribute BGP routes between autonomous systems
3. To reduce the number of OSPF adjacencies and represent the multi-access network
4. To assign IPv6 addresses to hosts

Correct Answer: 3. To reduce the number of OSPF adjacencies and represent the multi-access network

Explanation:
The OSPF Designated Router (DR) is elected on applicable multi-access networks to reduce the number of full OSPF adjacencies. Without a DR, every router on a shared broadcast segment would need to establish a full adjacency with every other router, increasing overhead as the number of routers grows. Routers instead form full adjacencies with the DR and Backup Designated Router. The DR also generates a Network LSA describing the multi-access segment. The BDR provides backup functionality and can take over the DR role if the active DR becomes unavailable.

Question 74. Which BGP attribute is normally propagated throughout an autonomous system and is used to select the preferred outbound path?

1. MED
2. Local preference
3. AS path
4. Next-hop address

Correct Answer: 2. Local preference

Explanation:
Local preference is a BGP attribute used within an autonomous system to influence outbound route selection. A higher local-preference value is normally preferred over a lower value. Because it is distributed to internal BGP speakers, it can provide consistent path-selection behavior across an autonomous system. Network administrators commonly use routing policies to assign different local-preference values to routes learned from different external connections. This allows an organization to prefer one provider or exit point for outbound traffic while retaining alternative paths for redundancy. Local preference differs from MED, which is primarily intended to provide guidance about inbound traffic.

Question 75. Which Junos command displays concise operational status information for physical and logical interfaces?

1. show interfaces terse
2. show route
3. show chassis hardware
4. show configuration

Correct Answer: 1. show interfaces terse

Explanation:
The show interfaces terse command provides a concise summary of interface status. It typically displays interface names, administrative state, link state, and logical interface information without the large amount of detail produced by the full show interfaces command. This makes it particularly useful as an initial troubleshooting command when checking whether interfaces are physically and logically operational. Administrators can then use more detailed interface commands to investigate errors, counters, MTU settings, protocol status, or other characteristics when a problem is identified.

Question 76. What is the purpose of a route reflector cluster ID in an iBGP design?

1. To assign an MPLS label to every route
2. To identify a group of route reflectors and help prevent reflection loops
3. To determine the OSPF area ID
4. To select the physical interface for forwarding

Correct Answer: 2. To identify a group of route reflectors and help prevent reflection loops

Explanation:
A route reflector cluster ID identifies a route reflector cluster and helps prevent routing loops involving reflected iBGP routes. When multiple route reflectors operate as part of a cluster, the cluster ID can be included in the cluster-list attribute associated with reflected routes. A route reflector can use this information to recognize routes that have already passed through its cluster and avoid inappropriate reflection. This mechanism supports scalable iBGP architectures while maintaining loop-prevention behavior. Cluster IDs are separate from router IDs and OSPF area identifiers, which serve different purposes in network operation.

Question 77. Which Junos command is useful for examining active routing protocols and their associated route counts?

1. show chassis hardware
2. show route summary
3. show interfaces terse
4. show configuration system

Correct Answer: 2. show route summary

Explanation:
The show route summary command provides a summary of routing information in the routing table, including route counts and information about different route types. It can help administrators quickly understand the size and composition of the routing table without displaying every individual prefix. This can be useful when troubleshooting unexpected changes in routing information, such as a sudden increase or decrease in learned routes. More specific commands can then be used to inspect particular protocols, destinations, or routes. The command focuses on routing information rather than physical hardware or interface status.

Question 78. Which technology is used to exchange IPv4 and IPv6 VPN routes through BGP in an MPLS VPN environment?

1. MP-BGP
2. STP
3. LACP
4. LLDP

Correct Answer: 1. MP-BGP

Explanation:
Multiprotocol BGP (MP-BGP) extends BGP so that it can carry routing information for multiple address families. In MPLS VPN environments, MP-BGP is commonly used to exchange VPN-IPv4 and VPN-IPv6 routes between provider edge routers. The routes can include route distinguishers and extended communities such as route targets, allowing providers to maintain customer-specific routing separation and control route import and export. MP-BGP therefore plays an important role in service-provider VPN architectures. Protocols such as LACP, LLDP, and STP serve Layer 2 functions and do not perform this VPN route exchange role.

Question 79. What is the primary purpose of a Junos firewall filter applied to the loopback interface for control-plane protection?

1. To increase the speed of MPLS label switching
2. To control traffic destined for the device itself
3. To create additional routing instances
4. To establish BGP route reflection

Correct Answer: 2. To control traffic destined for the device itself

Explanation:
A firewall filter applied at an appropriate control-plane interface or processing point can help protect the device by controlling traffic destined for the router itself. Such filtering can restrict unwanted or unexpected packets while permitting legitimate management, routing-protocol, and operational traffic. This type of protection is commonly associated with protecting the Routing Engine from unnecessary traffic. The exact application point and supported filter behavior depend on the Juniper platform and configuration. Control-plane protection should be designed carefully so that legitimate routing and management traffic is not unintentionally blocked.

Question 80. Which command is commonly used to verify the status of an MPLS LDP session on a Junos device?

1. show ldp neighbor
2. show ospf neighbor
3. show bgp summary
4. show interfaces terse

Correct Answer: 1. show ldp neighbor

Explanation:
The show ldp neighbor command displays information about LDP neighbors and their sessions. It can help administrators verify whether LDP has successfully established relationships with neighboring MPLS routers. When troubleshooting MPLS forwarding, checking LDP neighbor status is useful because label distribution depends on functioning LDP sessions when LDP is the selected label-distribution mechanism. Administrators can combine this command with MPLS route and label information, interface status, and IGP neighbor information to determine where an MPLS path may be failing. A healthy IGP alone does not guarantee that LDP sessions are operational.