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

 

Question 81. Which Junos feature allows multiple physical interfaces to operate as a single logical link?

1. VLAN tagging
2. Link Aggregation Group
3. Port mirroring
4. Virtual Chassis

Correct Answer: 2. Link Aggregation Group

Explanation:
A Link Aggregation Group (LAG) combines multiple physical Ethernet interfaces into one logical interface. This arrangement can provide greater aggregate bandwidth and redundancy because traffic can be distributed across multiple member links. LACP can be used to dynamically establish and monitor the aggregated connection between compatible devices. From the network’s logical perspective, the member interfaces operate as one aggregated interface. LAGs are commonly used between switches, routers, and servers where additional bandwidth or link resilience is required. Administrators should also consider hashing behavior when troubleshooting uneven traffic distribution across individual LAG members.

Question 82. Which BGP attribute is generally preferred when it has a higher value during route selection?

1. Local preference
2. MED
3. AS path length
4. Origin type

Correct Answer: 1. Local preference

Explanation:
Local preference is a BGP attribute for influencing outbound path selection within an autonomous system. When comparing otherwise eligible BGP routes, a higher local-preference value is generally preferred. This makes it useful for directing outbound traffic through a desired external connection. Administrators commonly set local preference through routing policies based on factors such as the BGP neighbor, received prefix, or community. This behavior differs from MED, where a lower value is generally preferred under applicable comparison conditions. Understanding which attributes favor higher or lower values is important when analyzing BGP route-selection behavior.

Question 83. Which OSPF packet is used to exchange summaries of the link-state database between neighbors?

1. Hello
2. Link State Update
3. Database Description
4. Link State Acknowledgment

Correct Answer: 3. Database Description

Explanation:
OSPF Database Description (DBD) packets are used during adjacency formation to exchange summaries of the link-state database between neighboring routers. The DBD packets allow routers to determine which LSAs they already have and which LSAs they need to request. This process occurs during the Exchange state of OSPF adjacency formation. Hello packets establish and maintain neighbor relationships, Link State Update packets carry LSAs, and Link State Acknowledgment packets confirm LSA receipt. Understanding the purpose of each OSPF packet type is useful when troubleshooting neighbors that become stuck during adjacency establishment.

Question 84. What is the primary purpose of a Junos prefix list in routing policy?

1. To define a collection of IP prefixes that can be matched by policy terms
2. To establish MPLS LSPs
3. To assign interface addresses automatically
4. To store BGP neighbor passwords

Correct Answer: 1. To define a collection of IP prefixes that can be matched by policy terms

Explanation:
A Junos prefix list provides a reusable collection of IP prefixes that can be referenced by routing policy terms. Instead of repeatedly writing individual prefixes within multiple policies, an administrator can maintain the relevant prefixes in one named list and use that list as a match condition. Prefix lists are useful for controlling route advertisements, filtering received routes, and applying consistent policy decisions. More specific prefix matching behavior can also be implemented using route-filter statements when required. Proper use of prefix-based policy helps administrators maintain predictable and manageable routing configurations.

Question 85. Which protocol is commonly used to provide loop prevention and a spanning-tree topology in Ethernet switching networks?

1. BGP
2. OSPF
3. STP
4. LDP

Correct Answer: 3. STP

Explanation:
Spanning Tree Protocol (STP) prevents Layer 2 forwarding loops by logically blocking redundant paths in an Ethernet switching topology. Without loop-prevention mechanisms, redundant Ethernet links can create broadcast storms, MAC-table instability, and excessive traffic. STP elects a root bridge and determines which ports should forward or block traffic to create a loop-free logical topology. Related protocols such as RSTP and MSTP provide faster convergence or additional topology capabilities. STP operates at Layer 2 and is therefore different from routing protocols such as OSPF and BGP, which calculate Layer 3 paths.

Question 86. Which BGP attribute is commonly used to indicate the preferred entry point into a network when multiple links connect the same autonomous systems?

1. MED
2. Local preference
3. Community
4. Originator ID

Correct Answer: 1. MED

Explanation:
The Multi-Exit Discriminator (MED) is commonly used to provide a neighboring autonomous system with information about preferred entry points when multiple links connect the same autonomous systems. A lower MED is generally preferred when MED is compared under the applicable BGP route-selection conditions. MED is primarily intended to influence inbound traffic from the neighboring AS toward the advertising network. It differs from local preference, which is used internally to influence outbound traffic. Because MED comparison can depend on configuration and route-selection context, administrators should consider the complete BGP decision process when analyzing its effect.

Question 87. Which Junos command displays information about the routing table for a particular routing instance?

1. show chassis hardware
2. show route instance <instance-name>
3. show interfaces terse
4. show system users

Correct Answer: 2. show route instance <instance-name>

Explanation:
The show route instance <instance-name> command can be used to inspect routing information associated with a specified routing instance. Routing instances maintain separate routing contexts, so identifying the correct instance is important when troubleshooting routes in environments containing multiple virtual routers or VPNs. The command helps administrators examine routes associated with the selected instance rather than focusing only on the main routing table. Additional route options can be used to investigate specific prefixes, protocols, or route details. This capability is especially useful in multi-tenant and service-provider environments.

Question 88. What is the primary purpose of a route preference in Junos OS?

1. To determine which route source is preferred when multiple sources provide the same destination
2. To identify an MPLS label
3. To assign an OSPF router ID
4. To define an Ethernet VLAN

Correct Answer: 1. To determine which route source is preferred when multiple sources provide the same destination

Explanation:
Junos route preference is used to determine which routing information source is preferred when multiple protocols or route sources provide reachability to the same destination. A lower preference value is generally more preferred. This allows Junos to select among routes learned from sources such as direct routes, static routes, OSPF, and BGP according to their relative preference. Route preference should not be confused with BGP local preference. BGP local preference is an attribute used within BGP to influence outbound path selection, whereas route preference is part of the broader Junos route-selection process.

Question 89. Which OSPF area is normally used as the central backbone for inter-area routing?

1. Area 1
2. Area 10
3. Area 0
4. Area 100

Correct Answer: 3. Area 0

Explanation:
OSPF Area 0, also called the backbone area, provides the central inter-area routing structure in a standard multi-area OSPF design. Other OSPF areas normally connect to Area 0 through Area Border Routers. Inter-area routing information is exchanged through the backbone, helping maintain a hierarchical OSPF architecture. Although special mechanisms such as virtual links can address certain topology situations, a well-designed OSPF network generally maintains connectivity between non-backbone areas and Area 0. Understanding the role of Area 0 is essential when designing multi-area OSPF and troubleshooting inter-area reachability.

Question 90. Which Junos command can be used to inspect the details of a specific routing policy?

1. show configuration policy-options
2. show interfaces terse
3. show chassis alarms
4. show route forwarding-table

Correct Answer: 1. show configuration policy-options

Explanation:
The show configuration policy-options command displays configuration under the Junos policy-options hierarchy. This hierarchy commonly contains routing policies, prefix lists, community definitions, AS-path definitions, and related policy objects. Reviewing this configuration is useful when troubleshooting route import, export, filtering, and attribute modification. Administrators can inspect the individual policy terms to determine which routes are being matched and what actions are applied. Operational verification should also be performed because a correctly written policy may still behave differently if it is not applied to the intended protocol or routing process.

Question 91. Which Junos command is commonly used to display BGP routes received from a particular peer?

1. show ospf neighbor
2. show route receive-protocol bgp <peer>
3. show interfaces terse
4. show chassis hardware

Correct Answer: 2. show route receive-protocol bgp <peer>

Explanation:
The show route receive-protocol bgp <peer> command can be used to examine routes received from a specified BGP peer before considering the effects of local route selection and export behavior. It is particularly useful when troubleshooting whether a neighbor is actually advertising an expected prefix. If a route is missing, administrators can investigate the BGP session, import policy, next-hop resolution, and other route-processing factors. This command differs from commands that show the active routing table because it focuses on information received from the specified protocol neighbor.

Question 92. Which Junos feature allows multiple logical Layer 3 interfaces to be configured on a single physical Ethernet interface?

1. Routing Engine redundancy
2. Logical units
3. Route reflection
4. MPLS PHP

Correct Answer: 2. Logical units

Explanation:
Junos uses logical units to create multiple logical interfaces under a single physical interface. Each logical unit can have its own protocol configuration, IP addressing, VLAN tagging, or other supported characteristics. This allows one physical interface to participate in multiple logical networks without requiring a separate physical port for each connection. Logical units are commonly represented with notation such as ge-0/0/0.0, where the physical interface is followed by a logical unit number. Proper encapsulation and VLAN configuration may be required depending on the platform and intended use.

Question 93. What is the primary purpose of an autonomous system number in BGP?

1. To identify an autonomous system participating in BGP
2. To identify an Ethernet interface
3. To assign an IPv6 prefix
4. To specify an MPLS label

Correct Answer: 1. To identify an autonomous system participating in BGP

Explanation:
An autonomous system number (ASN) identifies an autonomous system in BGP routing. AS numbers are used in BGP sessions and are included in the AS path of externally advertised routes. This identification supports inter-domain routing and provides information that can be used for loop prevention and route-selection decisions. BGP distinguishes between internal and external sessions based partly on whether the peers belong to the same or different autonomous systems. AS numbers are therefore fundamental to BGP operation and are distinct from router IDs, interface identifiers, IP prefixes, and MPLS labels.

Question 94. Which command can be used to display the forwarding table entries associated with a specific destination?

1. show configuration
2. show route receive-protocol
3. show route forwarding-table destination <prefix>
4. show ospf database

Correct Answer: 3. show route forwarding-table destination <prefix>

Explanation:
The forwarding table contains the information used by the forwarding plane to make packet-forwarding decisions. A destination-specific forwarding-table command allows an administrator to inspect the forwarding information associated with a particular prefix. This can help determine the next hop, interface, and other forwarding details actually programmed for traffic. Examining the forwarding table can be valuable when the routing table appears correct but packets are not being forwarded as expected. It also helps distinguish control-plane route information from the forwarding information installed for actual packet processing.

Question 95. Which BGP session type is normally used between two routers in different autonomous systems?

1. iBGP
2. OSPF
3. eBGP
4. IS-IS

Correct Answer: 3. eBGP

Explanation:
External BGP, or eBGP, is used to exchange routing information between BGP speakers belonging to different autonomous systems. eBGP is fundamental to inter-domain routing and is commonly used between service providers, enterprises, and external network organizations. In contrast, iBGP is used between BGP speakers within the same autonomous system. eBGP sessions typically have different default behaviors from iBGP sessions, including how next-hop processing and AS path information are handled. Understanding whether a BGP relationship is internal or external is essential when analyzing route propagation and BGP policy behavior.

Question 96. What is the primary function of the then section of a Junos routing policy term?

1. It defines the conditions that must be matched
2. It specifies the actions performed when the term matches
3. It establishes the BGP neighbor
4. It defines the physical interface

Correct Answer: 2. It specifies the actions performed when the term matches

Explanation:
The then section of a Junos routing policy term defines what action should be taken when a route satisfies the conditions in the from section. Actions can include accepting or rejecting the route, modifying attributes, adding communities, changing local preference, setting MED, or performing other supported policy operations. This separation allows a routing policy to first identify relevant routes and then determine how those routes should be handled. If a term does not contain a from section, its actions can potentially apply broadly, depending on the overall policy structure and processing order.

Question 97. Which Junos command is commonly used to view system log messages?

1. show log messages
2. show route
3. show bgp summary
4. show interfaces terse

Correct Answer: 1. show log messages

Explanation:
The show log messages command displays entries from the system messages log, assuming the relevant log file is configured and available. System logs can contain information about interface changes, protocol events, system processes, authentication events, errors, and other operational conditions. Reviewing logs is an important part of troubleshooting because they can provide chronological context that may not be visible from a single operational command. Administrators can use additional filtering or other log files when investigating specific events. Log configuration and available files depend on the device configuration and Junos platform.

Question 98. Which MPLS device role typically adds the initial label to an IP packet entering an MPLS domain?

1. Penultimate Hop Router
2. Label Edge Router
3. Label Switching Router
4. Core-only Router

Correct Answer: 2. Label Edge Router

Explanation:
A Label Edge Router (LER) operates at the edge of an MPLS domain and can impose or remove MPLS labels as packets enter or leave the MPLS network. When an IP packet enters an MPLS forwarding domain, the ingress edge router determines the appropriate forwarding treatment and can add the required label. Core Label Switching Routers then forward the packet based on label information rather than performing the same type of edge processing. At the egress edge, labels are removed as the packet leaves the MPLS domain. This edge-versus-core distinction is fundamental to understanding MPLS forwarding.

Question 99. Which Junos protocol is commonly used to provide dynamic link-state routing for IPv6 networks?

1. OSPFv3
2. FTP
3. LACP
4. ARP

Correct Answer: 1. OSPFv3

Explanation:
OSPFv3 is the version of OSPF designed to support IPv6 routing. It provides link-state routing capabilities and uses the same general shortest-path principles associated with OSPF while adapting operation for IPv6. OSPFv3 forms neighbor relationships, exchanges link-state information, and calculates routes using the Shortest Path First algorithm. It is distinct from ARP, which is not used by IPv6, while LACP provides link aggregation and FTP is an application-layer protocol. Junos supports OSPFv3 configuration and operational commands for IPv6 routing environments.

Question 100. Which Junos operational command can help determine whether a specific route is active and which protocol installed it?

1. show route <prefix>
2. show chassis hardware
3. show interfaces terse
4. show system uptime

Correct Answer: 1. show route <prefix>

Explanation:
The show route <prefix> command provides routing information for a specified destination prefix. It can show whether the route is active, its protocol or route source, next-hop information, preference, and other relevant attributes. This makes it a fundamental troubleshooting command when determining why traffic is following a particular path or why a destination is unreachable. If multiple routes exist, the output can help reveal which route has been selected and which alternatives are available. Additional protocol-specific commands can then be used to investigate the underlying routing information in greater detail.