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Question 181:

Which OSPF mechanism allows routers on a broadcast network to reduce the number of full adjacencies?

1. Route reflector
2. Designated Router
3. Area Border Router
4. Route summarization

Correct Answer: 2

Explanation:

On broadcast multi-access networks, OSPF uses a Designated Router (DR) and Backup Designated Router (BDR) to reduce the number of full adjacency relationships required. Without a DR, every OSPF router on the segment would need to establish a full adjacency with every other router, creating unnecessary protocol overhead as the number of routers increases. The DR acts as a central point for exchanging link-state information on the shared segment, while the BDR provides redundancy if the DR fails. Ethernet networks are a common example of broadcast multi-access networks. Understanding DR and BDR behavior is important when troubleshooting OSPF adjacency formation and database synchronization.

Question 182:

Which OSPF router is elected to provide backup functionality for the Designated Router?

1. ABR
2. ASBR
3. BDR
4. Route reflector

Correct Answer: 3

Explanation:

The Backup Designated Router, or BDR, is elected to provide redundancy for the Designated Router on an OSPF broadcast network. The BDR maintains the necessary OSPF relationships so that it can take over if the current DR fails. This helps prevent a complete disruption of OSPF operations on the multi-access segment. DR and BDR elections are performed according to OSPF rules and router priority, with the router ID also influencing the election when priorities are equal. Point-to-point network types generally do not require DR or BDR elections. Monitoring DR and BDR status is useful when diagnosing unexpected OSPF neighbor behavior on Ethernet networks.

Question 183:

Which OSPF parameter is used to influence the preferred path through an OSPF topology?

1. Community
2. Route target
3. Cost
4. MED

Correct Answer: 3

Explanation:

OSPF uses interface cost as an important metric for selecting preferred paths. When multiple paths to a destination are available, the SPF calculation considers the accumulated cost of each path. A path with a lower total OSPF cost is generally preferred. Administrators can configure interface costs to influence routing decisions when the default values do not provide the desired traffic distribution. Cost should be designed carefully because changing it can affect many destinations throughout the topology. Unlike BGP attributes such as local preference or MED, OSPF cost is an interior gateway protocol metric used to calculate shortest paths within the OSPF domain.

Question 184:

Which OSPF packet is used when a router requests a specific missing LSA from a neighbor?

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

Correct Answer: 1

Explanation:

An OSPF Link State Request packet is used when a router determines that it needs specific link-state information from a neighboring router. During database synchronization, routers exchange Database Description packets containing summaries of their LSDB contents. If one router identifies LSAs that it does not have or that require updating, it sends a Link State Request for those LSAs. The neighbor can then respond with Link State Update packets containing the requested information. This process allows OSPF routers to synchronize their link-state databases efficiently. Understanding these packet types can help identify where an adjacency is failing during database exchange.

Question 185:

Which BGP attribute provides information about the next router to which traffic should be forwarded for a route?

1. Community
2. Next hop
3. MED
4. Local preference

Correct Answer: 2

Explanation:

The BGP next-hop attribute identifies the IP address that should be used as the next hop toward a BGP-advertised destination. The receiving router must have appropriate reachability to that next-hop address before it can use the BGP route for forwarding. Next-hop processing can vary depending on whether the route is learned through eBGP or iBGP and on the configured routing policy. If the next hop is unreachable, the BGP route may not be installed as an active route. Therefore, troubleshooting BGP reachability often requires checking both the BGP session and the underlying route to the advertised next-hop address.

Question 186:

Which BGP attribute can be modified to influence the preferred outbound path from an autonomous system?

1. Local preference
2. Ethernet Segment Identifier
3. VNI
4. OSPF area ID

Correct Answer: 1

Explanation:

Local preference is commonly used to influence outbound path selection within an autonomous system. A higher local preference is generally preferred, allowing administrators to designate a primary exit path and lower-priority backup paths. Routing policies can assign different local preference values based on the source of the route, destination prefix, community, or other characteristics. Because local preference is carried through iBGP, multiple routers within the autonomous system can make consistent decisions. This makes it particularly useful for organizations with multiple upstream connections. Local preference should not be confused with MED, which is generally used to influence path selection from the neighboring autonomous system’s perspective.

Question 187:

What is the main purpose of a BGP next-hop policy or next-hop modification?

1. To influence the IP address used as the forwarding next hop
2. To change the VLAN ID
3. To establish an OSPF area
4. To assign PoE power

Correct Answer: 1

Explanation:

BGP next-hop modification can change the next-hop information associated with a BGP route so that the receiving router has a usable forwarding path. This is particularly important in designs where the original next-hop address is not directly reachable by the receiving router. A common example is an internal BGP deployment where a route reflector or another internal router advertises external routes but the original next hop may not be appropriate for all clients. Administrators can use routing policy or protocol-specific configuration to control next-hop behavior. Correct next-hop resolution is essential because a BGP route with an unreachable next hop cannot normally be used for forwarding.

Question 188:

Which Junos feature allows a configuration change to be automatically rolled back if it is not confirmed within the specified time?

1. Commit confirmed
2. Commit synchronize
3. Rescue configuration
4. Configuration group

Correct Answer: 1

Explanation:

The commit confirmed feature allows an administrator to make a configuration change that automatically rolls back if the change is not confirmed within the specified time. This is particularly useful when making remote changes that could potentially disrupt management connectivity. If the administrator loses access after the configuration is committed, the device can revert to the previous committed configuration when the confirmation timer expires. If the administrator verifies that the change is working correctly, a normal commit can be performed to confirm it. This provides an important safety mechanism for remote configuration changes and reduces the risk of permanently locking administrators out of a device.

Question 189:

Which Junos command can be used to validate configuration syntax without activating the configuration?

1. commit check
2. show route
3. show interfaces terse
4. show arp

Correct Answer: 1

Explanation:

The commit check command validates the candidate configuration without actually committing the changes as the active configuration. It is useful for identifying syntax or configuration consistency problems before making changes active. Administrators can use it as a safety step after modifying several configuration statements. If the validation succeeds, the configuration can then be committed using the appropriate commit command. This workflow is especially useful when making complex changes because it separates configuration validation from activation. Operational commands such as show route and show arp provide runtime network information but do not perform candidate configuration validation.

Question 190:

Which Junos command displays the current committed configuration in a hierarchical format?

1. show configuration
2. show route
3. show interfaces extensive
4. show bgp summary

Correct Answer: 1

Explanation:

The show configuration command displays the current configuration in Junos configuration mode. It is commonly used to review configured protocols, interfaces, policies, security settings, and other system parameters. Reviewing the configuration is important before troubleshooting because it allows an administrator to understand how the device is intended to operate. Junos uses a hierarchical configuration structure, making it possible to navigate from major configuration sections into more specific statements. Operational commands such as show route display runtime state rather than the configuration itself. Administrators can also use filtering options to focus on a specific configuration section or statement.

Question 191:

Which feature allows Junos administrators to save a known-good configuration that can be used for recovery?

1. Rescue configuration
2. BGP community
3. OSPF LSDB
4. VXLAN VNI

Correct Answer: 1

Explanation:

A rescue configuration provides a saved configuration that can be used as a recovery point if the active configuration becomes unusable or causes serious problems. Administrators can create a rescue configuration after verifying that the current device configuration is known to be functional. If a later configuration change causes an issue, the rescue configuration can provide a reliable baseline for recovery. This is especially useful on remotely managed devices where configuration mistakes may affect connectivity. The rescue configuration should be updated whenever a stable and tested configuration is established. It is a configuration-recovery mechanism rather than a routing or switching protocol.

Question 192:

Which Junos command is useful for checking the amount of time a device has been running since its last reboot?

1. show system uptime
2. show route
3. show bgp summary
4. show arp

Correct Answer: 1

Explanation:

The show system uptime command provides information about how long the Junos device has been running since its most recent reboot. This information can be useful during troubleshooting because unexpected reboots, system restarts, or recent maintenance may explain changes in network behavior. The command can also provide additional system-time information depending on the Junos version and platform. Administrators can compare uptime with system logs to determine whether a reported network problem coincides with a reboot or system event. Routing commands such as show route do not provide this system-level information, while BGP and ARP commands focus on specific networking functions.

Question 193:

Which protocol is commonly used to synchronize the time of network devices?

1. NTP
2. BGP
3. EVPN
4. VXLAN

Correct Answer: 1

Explanation:

Network Time Protocol, or NTP, is commonly used to synchronize the clocks of network devices with an authoritative time source. Accurate time is important for network operations because timestamps are used in system logs, troubleshooting, security analysis, and monitoring. When multiple devices have synchronized clocks, administrators can correlate events across different systems more easily. Junos devices can be configured with appropriate NTP servers or peers depending on the network design. NTP does not participate in route exchange or VXLAN encapsulation. A properly configured time source can significantly improve the usefulness of logs when investigating routing changes, authentication events, or system failures.

Question 194:

Which protocol is commonly used to send system log messages from network devices to a centralized logging server?

1. SNMP
2. Syslog
3. OSPF
4. LLDP

Correct Answer: 2

Explanation:

Syslog is commonly used to send system and event messages from network devices to centralized logging systems. Centralized logging allows administrators to collect information from many devices in one location, making it easier to monitor events and investigate problems. Junos devices can generate messages for events such as interface changes, authentication events, routing changes, and system conditions. A centralized syslog server can retain these messages for later analysis and correlation. SNMP is primarily used for monitoring and management information, while OSPF and LLDP perform networking functions. Effective logging is an important component of network operations and troubleshooting.

Question 195:

Which protocol is commonly used by network management systems to monitor device statistics and status?

1. SNMP
2. VXLAN
3. BGP
4. RSTP

Correct Answer: 1

Explanation:

Simple Network Management Protocol, or SNMP, is widely used to monitor network devices and collect operational information. A network management system can use SNMP to retrieve information such as interface statistics, device health indicators, and other management data exposed through supported MIBs. SNMP can therefore help administrators monitor network performance and identify potential problems before they become service-impacting incidents. It is not a routing protocol and does not establish VXLAN tunnels or BGP sessions. Proper SNMP configuration should include appropriate security controls, particularly when management information is being accessed across production networks.

Question 196:

Which Layer 2 protocol helps prevent Ethernet switching loops by placing redundant paths into a controlled forwarding state?

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

Correct Answer: 1

Explanation:

Spanning Tree Protocol, or STP, helps prevent Layer 2 switching loops in Ethernet networks containing redundant physical paths. STP calculates a loop-free logical topology and can place selected redundant interfaces into a blocking or non-forwarding state. If an active forwarding path fails, the spanning-tree process can allow an appropriate redundant path to become available. Without loop prevention, Ethernet broadcasts and unknown unicast traffic could circulate repeatedly and consume network resources. STP is therefore a fundamental Layer 2 protection mechanism. Routing protocols such as OSPF and BGP operate at Layer 3 and do not directly provide Ethernet loop prevention.

Question 197:

What is the primary advantage of Rapid Spanning Tree Protocol compared with traditional STP?

1. Faster convergence after topology changes
2. Larger BGP tables
3. Stronger RADIUS authentication
4. VXLAN encapsulation

Correct Answer: 1

Explanation:

Rapid Spanning Tree Protocol, or RSTP, is designed to achieve faster convergence after changes in the Layer 2 topology compared with traditional STP. Faster convergence allows the network to restore forwarding through appropriate redundant paths more quickly when a link or device fails. RSTP uses improved port roles and transition mechanisms to reduce the time required to establish a new loop-free topology. It still serves the fundamental purpose of preventing Layer 2 loops. RSTP does not increase BGP scalability, perform user authentication, or provide VXLAN encapsulation. Understanding RSTP behavior is important when troubleshooting redundant Ethernet switching environments.

Question 198:

Which protocol can bundle multiple physical Ethernet links into a single logical link for increased bandwidth and redundancy?

1. LACP
2. LLDP
3. RADIUS
4. NTP

Correct Answer: 1

Explanation:

Link Aggregation Control Protocol, or LACP, is used to dynamically negotiate and maintain link aggregation between compatible network devices. Multiple physical Ethernet interfaces can be combined into a logical aggregated interface, providing increased available bandwidth and redundancy. If one member link fails, traffic can continue using the remaining active members, subject to the configured design and available capacity. LACP helps ensure that both sides agree on the links participating in the aggregation. It is important to configure compatible settings on both devices. LLDP is used for neighbor discovery, RADIUS for authentication, and NTP for time synchronization, so they do not perform link aggregation.

Question 199:

Which technology allows multiple Ethernet links to operate as members of one logical interface in Junos?

1. Aggregated Ethernet
2. Loopback interface
3. IRB interface
4. Management interface

Correct Answer: 1

Explanation:

Aggregated Ethernet, commonly represented by an interface such as ae0, allows multiple physical Ethernet interfaces to operate as members of one logical interface. Link aggregation can provide increased bandwidth, redundancy, and simplified logical configuration. LACP may be used to dynamically negotiate the member relationship with a compatible device. Higher-level configuration can then be applied to the aggregated interface rather than individually configuring the same logical behavior on every physical member. This design is frequently used between switches, routers, and servers where both capacity and resiliency are important. Proper member-link configuration and compatible aggregation settings are necessary for reliable operation.

Question 200:

Which Junos command is most appropriate for viewing detailed operational information and statistics for a network interface?

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

Correct Answer: 1

Explanation:

The show interfaces extensive command provides detailed operational information about a network interface. It can include interface state, physical and logical properties, traffic statistics, error counters, packet information, and other operational details depending on the interface and platform. This makes it particularly useful when troubleshooting physical connectivity, packet loss, interface errors, or unexpected traffic behavior. Administrators often begin with show interfaces terse for a quick overview and then use show interfaces extensive when more detailed information is required. The other commands focus on routing protocols or routing information rather than comprehensive interface statistics and operational state.