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Question 321:

Which OSPF feature allows multiple equal-cost paths to be installed for forwarding?

1. Route aggregation
2. ECMP
3. Route redistribution
4. Stub area

Correct Answer: 2

Explanation:

Equal-Cost Multipath (ECMP) allows a router to install multiple routes to the same destination when those routes have equal routing cost. In an OSPF environment, ECMP can improve traffic distribution and provide redundancy because traffic can use more than one available path. Instead of selecting only one path, the routing system can maintain multiple next hops. The forwarding behavior depends on the platform and configuration, but the purpose of ECMP is to distribute traffic across equivalent paths. This can be particularly useful in enterprise networks with redundant links between routers. ECMP is different from unequal-cost load balancing, where paths have different metrics.

Question 322:

In OSPF, what does the interface cost primarily influence?

1. The router ID selection
2. The DR election priority
3. The preference of one path over another
4. The OSPF authentication method

Correct Answer: 3

Explanation:

OSPF interface cost is a metric used when calculating the shortest path through the network. When multiple possible paths exist, OSPF uses accumulated interface costs to determine which path is preferred. A lower total cost generally represents a more desirable path. The cost can be automatically derived from interface characteristics or explicitly configured by the administrator. Changing the cost can therefore influence routing decisions without changing the physical topology. Interface cost does not determine the router ID, authentication mechanism, or directly control DR election priority. Understanding OSPF cost is important when troubleshooting unexpected paths or intentionally engineering traffic through particular links.

Question 323:

Which OSPF mechanism is responsible for distributing LSAs throughout an area?

1. LSA flooding
2. NAT translation
3. BGP peering
4. DHCP relay

Correct Answer: 1

Explanation:

OSPF uses LSA flooding to distribute link-state information throughout an OSPF area. When an OSPF router originates or receives relevant link-state information, the LSA is propagated to appropriate neighboring routers. This allows routers in the area to build a consistent Link-State Database (LSDB). Each router then runs the SPF algorithm against the information in its LSDB to calculate routes. Flooding must be controlled carefully so that updates reach the necessary routers without creating excessive unnecessary traffic. OSPF uses sequence numbers, aging, and acknowledgments to help maintain reliable LSA distribution. Proper LSA flooding is therefore fundamental to maintaining a synchronized OSPF topology database.

Question 324:

What is a major benefit of dividing an OSPF network into multiple areas?

1. It eliminates the need for SPF calculations
2. It reduces the scope of certain link-state information
3. It removes the need for ABRs
4. It converts OSPF into a distance-vector protocol

Correct Answer: 2

Explanation:

Multiple OSPF areas help improve scalability by limiting the scope of certain link-state information and reducing the amount of topology information that every router must process. Area 0 serves as the backbone, while other areas connect through Area Border Routers (ABRs). This design can reduce the size of LSDBs and limit the impact of topology changes to the affected area. OSPF does not stop using SPF calculations when multiple areas are configured, and ABRs remain an important part of inter-area connectivity. Proper area design is especially useful in large enterprise networks where maintaining one massive OSPF area could increase processing and operational complexity.

Question 325:

Which Junos command is useful for viewing OSPF statistics?

1. show ospf statistics
2. show bgp statistics
3. show ethernet-switching statistics
4. show chassis ospf

Correct Answer: 1

Explanation:

The Junos command show ospf statistics can be used to examine OSPF-related statistics and operational information. Such information can help administrators troubleshoot OSPF behavior by providing visibility into protocol activity. Monitoring statistics is useful when investigating issues such as unexpected neighbor behavior, packet processing, or changes in OSPF operation. Other commands are used for different protocols or subsystems. For example, BGP commands are appropriate for BGP sessions and routes, while Ethernet-switching commands focus on Layer 2 switching information. Operational commands such as these are an important part of Junos troubleshooting because they allow administrators to verify how a routing protocol is functioning without changing the configuration.

Question 326:

What is the primary purpose of configuring an OSPF interface as passive?

1. To stop the interface from forwarding IP traffic
2. To prevent OSPF neighbor formation on that interface while still advertising its network
3. To disable the interface completely
4. To remove the connected route from the routing table

Correct Answer: 2

Explanation:

A passive OSPF interface does not form OSPF adjacencies with neighbors on that interface, while the connected network can still be advertised into OSPF. This is useful on interfaces where no OSPF neighbor should exist, such as user-facing or management networks. Configuring such interfaces as passive reduces unnecessary OSPF protocol traffic and prevents unexpected neighbor relationships. It does not shut down the physical interface or remove its connected network from the routing table. Passive-interface behavior is therefore useful for improving security and controlling where OSPF adjacencies are permitted. Administrators should carefully choose passive interfaces to avoid accidentally preventing required routing adjacencies.

Question 327:

In Junos, what is a common purpose of a BGP routing policy?

1. To control how routes are imported or exported
2. To assign physical interface speed
3. To create Ethernet cables
4. To replace the routing table with an ARP table

Correct Answer: 1

Explanation:

Junos routing policies provide control over how routes are accepted, modified, or advertised. In BGP, policies can be applied during route import or export processing. An administrator can use policy terms to match routes based on characteristics such as prefixes, communities, or other route attributes and then perform actions such as accepting, rejecting, or modifying attributes. This makes routing policy an important tool for traffic engineering and controlling route propagation between peers. Routing policies do not configure physical interface characteristics or replace routing tables with ARP tables. A clear understanding of policy direction and term evaluation is essential when troubleshooting why a BGP route is or is not being advertised.

Question 328:

What is the result when a Junos routing policy term explicitly rejects a matching route?

1. The route is automatically converted to static
2. The route is rejected according to the policy
3. The route is assigned a higher MED
4. The route is placed in the ARP table

Correct Answer: 2

Explanation:

A routing policy can explicitly reject routes that match a policy term. The reject action prevents the route from being accepted or advertised in the context where that policy is applied. For example, an export policy can prevent selected routes from being advertised to a BGP neighbor. An import policy can prevent selected received routes from being accepted into the routing information used by the local system. The exact result depends on where the policy is applied and how the policy is structured. Explicit accept and reject actions provide administrators with precise control over route propagation and selection, making routing policy a central component of Junos network design.

Question 329:

Which Junos configuration mode is used to make configuration changes?

1. Operational mode
2. Shell mode
3. Configuration mode
4. Monitor mode

Correct Answer: 3

Explanation:

Junos uses configuration mode for making changes to the device configuration. Administrators enter configuration mode from operational mode and can then navigate the hierarchical configuration structure. Commands such as set, delete, and edit are commonly used to modify configuration statements. Changes made in configuration mode are not normally active in the running configuration until they are committed. Operational mode is primarily used for monitoring, troubleshooting, and executing operational commands. This separation between configuration and operational functions is an important characteristic of Junos and helps administrators review and validate configuration changes before applying them to the active system.

Question 330:

What does the Junos commit check command primarily do?

1. Reboots the router
2. Validates the candidate configuration without activating it
3. Deletes the candidate configuration
4. Displays the ARP table

Correct Answer: 2

Explanation:

The Junos commit check command validates the candidate configuration without actually activating the changes. It can detect configuration syntax or consistency problems before an administrator performs a normal commit. This is useful when making significant configuration changes because it provides an opportunity to identify errors before they affect the running system. A successful commit check does not mean that the configuration has been activated; a normal commit is still required. Administrators often use this validation step as part of a careful change-management process. It is especially helpful when configuring routing protocols, interfaces, security policies, or other interdependent Junos features.

Question 331:

What is the main purpose of commit confirmed in Junos?

1. To automatically save a rescue configuration
2. To apply changes with an automatic rollback if they are not confirmed
3. To disable configuration validation
4. To restart all routing protocols

Correct Answer: 2

Explanation:

commit confirmed is designed to protect administrators from losing management access after making a configuration change. It activates the candidate configuration but starts a confirmation timer. If the administrator does not issue a regular commit before the timer expires, Junos automatically rolls back to the previous configuration. This is particularly useful when making remote changes to interfaces, routing, firewall filters, or management access. If the change works correctly, the administrator performs a normal commit to confirm it permanently. This safety mechanism helps reduce the risk of becoming locked out of a remotely managed device because of an incorrect configuration change.

Question 332:

After using commit confirmed, what should an administrator normally do if the change is working correctly?

1. Reboot the router
2. Issue another normal commit
3. Delete the entire configuration
4. Disable the management interface

Correct Answer: 2

Explanation:

After a commit confirmed operation, the administrator should perform a normal commit once the configuration has been verified and is working as expected. The normal commit confirms the change so that the automatic rollback timer will no longer revert the configuration. This workflow is especially useful for remote administration because it provides a recovery mechanism if the new configuration causes connectivity problems. If the administrator does nothing and the confirmation timer expires, Junos can roll back the confirmed configuration. Therefore, testing connectivity and functionality immediately after a confirmed commit is important before permanently confirming the changes.

Question 333:

Which Junos command can display the differences between the candidate configuration and the active configuration while in configuration mode?

1. show | compare
2. show interfaces terse
3. show route forwarding-table
4. show arp

Correct Answer: 1

Explanation:

The Junos show | compare command is commonly used in configuration mode to display differences between the candidate configuration and the currently active configuration. It helps administrators review pending changes before committing them. This is particularly useful when making multiple configuration modifications because it allows the administrator to confirm exactly what will be added, changed, or removed. Reviewing configuration differences can prevent accidental changes from being committed. Commands such as show interfaces terse, show route forwarding-table, and show arp provide operational information instead and do not serve the same purpose. Using show | compare is therefore an important step in controlled Junos configuration management.

Question 334:

Which Junos command displays the current configuration hierarchy from operational mode?

1. show route
2. show configuration
3. show ospf neighbor
4. show system uptime

Correct Answer: 2

Explanation:

The show configuration command displays the current Junos configuration hierarchy. It is commonly used from operational mode to review configured interfaces, routing protocols, policies, system services, and other configuration statements. This command is useful when troubleshooting because administrators can compare the configured settings with expected network behavior. It can also help verify whether a particular feature has been configured. Commands such as show route focus on routing information, while show ospf neighbor displays OSPF adjacency information and show system uptime provides system runtime information. Reviewing the configuration is therefore an essential part of diagnosing configuration-related problems on Junos devices.

Question 335:

What is the purpose of a Junos rescue configuration?

1. To provide a known-good configuration that can be restored if needed
2. To store BGP routes permanently
3. To replace the routing table
4. To increase interface bandwidth

Correct Answer: 1

Explanation:

A rescue configuration provides a saved configuration that can be used as a known-good recovery point. Administrators can create a rescue configuration after confirming that the device is operating correctly. If a later configuration change causes serious problems, the rescue configuration can provide a way to restore a stable configuration. This is especially useful for remote devices where configuration mistakes could affect management access or routing. The rescue configuration is not a replacement for the active routing table and does not affect interface bandwidth or BGP route storage. Maintaining an up-to-date rescue configuration is a useful operational practice for improving recovery options during configuration failures.

Question 336:

What is the primary function of a Junos CoS classifier?

1. To assign traffic to forwarding classes based on packet characteristics
2. To establish BGP sessions
3. To create OSPF areas
4. To translate private IP addresses

Correct Answer: 1

Explanation:

A CoS classifier examines selected packet characteristics and maps traffic into forwarding classes and, where applicable, loss-priority levels. Classification can be based on fields such as DSCP or other packet markings depending on the configured classifier. Once traffic has been classified, subsequent CoS mechanisms such as schedulers, shaping, and rewrite rules can treat different traffic classes according to their requirements. This allows administrators to provide differentiated handling for applications such as voice, video, business-critical data, and ordinary traffic. A CoS classifier is unrelated to BGP session establishment, OSPF area creation, or IP address translation. It is a fundamental component of Junos traffic-classification architecture.

Question 337:

Which packet field is commonly used by a DSCP-based CoS classifier?

1. TCP source port
2. IPv4/IPv6 DSCP value
3. Ethernet destination MAC only
4. ARP opcode

Correct Answer: 2

Explanation:

DSCP-based classification uses the Differentiated Services Code Point value carried in the IP header. The DSCP field allows network devices to identify traffic classes and apply different forwarding behavior according to configured CoS policies. For example, voice traffic may be marked differently from ordinary data traffic so that it can receive appropriate treatment during congestion. A classifier can map DSCP values to forwarding classes and loss priorities. TCP ports, MAC addresses, and ARP fields can also be useful matching information in other classification mechanisms, but they are not the DSCP value itself. Understanding packet markings is important when designing and troubleshooting end-to-end quality-of-service behavior.

Question 338:

What is the primary role of a CoS scheduler?

1. To determine how queued traffic is serviced
2. To assign IP addresses
3. To establish an OSPF adjacency
4. To authenticate users through RADIUS

Correct Answer: 1

Explanation:

A CoS scheduler determines how traffic waiting in queues is serviced. Scheduling parameters can influence how bandwidth is allocated among forwarding classes and queues, helping prioritize important traffic during congestion. Different scheduling behaviors can be configured to provide appropriate treatment for applications with different requirements. For example, delay-sensitive traffic may receive preferential servicing compared with lower-priority traffic. A scheduler does not assign IP addresses, establish OSPF adjacencies, or perform user authentication. Those functions belong to other network components and protocols. Understanding the relationship between classifiers, forwarding classes, queues, schedulers, and shaping is essential for designing effective Junos Class of Service policies.

Question 339:

What is the purpose of a CoS rewrite rule?

1. To modify packet markings before transmission
2. To create an OSPF neighbor
3. To calculate an SPF tree
4. To establish a BGP session

Correct Answer: 1

Explanation:

A CoS rewrite rule changes selected packet classification markings before the packet leaves an interface. This can be useful when a network needs to communicate QoS information to another device or network domain. For example, a device may classify traffic internally and then rewrite the DSCP or other applicable marking so that downstream devices understand the desired treatment. Rewrite rules are therefore commonly used as part of an end-to-end QoS strategy. They do not create routing adjacencies or calculate routing paths. Classification determines how traffic is treated locally, while rewriting can communicate or preserve the desired QoS marking across a network boundary.

Question 340:

What is the primary purpose of traffic shaping in Junos CoS?

1. To smooth traffic transmission to a configured rate
2. To increase the physical interface speed
3. To create additional VLAN IDs
4. To replace BGP with OSPF

Correct Answer: 1

Explanation:

Traffic shaping controls the rate at which queued traffic is transmitted, smoothing bursts so that traffic conforms more closely to a configured transmission rate. Instead of immediately sending a large burst whenever traffic arrives, shaping can delay packets and release them at an appropriate rate. This can help manage congestion and coordinate traffic with downstream bandwidth constraints. Shaping differs from policing because shaping generally buffers traffic and controls its transmission rate, while a policer typically enforces a rate by taking action when traffic exceeds the configured threshold. Shaping is therefore an important CoS mechanism for controlling traffic behavior and improving predictable network performance.