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Question 341. Which BGP feature allows multiple eligible paths to be installed for forwarding?

1. Route reflection
2. BGP multipath
3. AS path prepending
4. BGP synchronization

Correct Answer: 2. BGP multipath

Explanation:
BGP multipath allows a Junos device to install multiple eligible BGP paths to the same destination rather than selecting only one path for forwarding. The paths must satisfy the configured multipath and path-selection requirements. This capability can improve traffic distribution and make better use of multiple redundant links. BGP multipath is different from route reflection, which reduces the number of required iBGP sessions, and from AS path prepending, which is used to influence path selection. BGP synchronization is an older routing concept and does not provide the same multipath forwarding function.

Question 342. Which BGP configuration is commonly used to make an internal router advertise itself as the next hop?

1. next-hop self
2. local-preference
3. med
4. as-path prepend

Correct Answer: 1. next-hop self

Explanation:
The BGP next-hop self configuration causes the local router to advertise itself as the next-hop address when sending eligible routes to a neighbor. This is especially useful in iBGP designs where the original next-hop address learned from an external peer may not be reachable by other internal routers. By changing the next hop to a reachable internal router, forwarding can proceed correctly through the network. Local Preference and MED are BGP path attributes, while AS path prepending modifies the AS Path. None of those attributes performs the same next-hop modification function.

Question 343. Which BGP attribute generally has a higher preference when its value is lower?

1. Local Preference
2. MED
3. Weight
4. AS Path length

Correct Answer: 2. MED

Explanation:
The Multi-Exit Discriminator, or MED, is generally preferred when its value is lower when comparable BGP paths are evaluated. MED can be used by an autonomous system to influence which entry point a neighboring autonomous system selects when multiple connections exist between them. Local Preference and weight, where applicable, generally favor higher values. AS Path selection generally favors a shorter path rather than directly comparing a numeric value as a preference attribute. MED is therefore commonly used to signal a preferred inbound path to a neighboring autonomous system.

Question 344. Which BGP community is normally used to prevent advertisement outside the local autonomous system?

1. NO_ADVERTISE
2. INTERNET
3. NOPEER
4. NO_EXPORT

Correct Answer: 4. NO_EXPORT

Explanation:
The well-known NO_EXPORT BGP community tells a BGP speaker not to advertise the associated route outside the local autonomous system or applicable confederation. This can be useful when routes should remain within a particular routing domain. NO_ADVERTISE is more restrictive because it prevents the route from being advertised to any other BGP peer. The INTERNET community allows normal advertisement, while NOPEER provides peer-related propagation control. Correct use of these communities gives network operators fine-grained control over how routes are propagated between BGP speakers.

Question 345. What is the primary reason route reflectors use Originator ID and Cluster List information?

1. To assign MPLS labels
2. To provide loop-prevention mechanisms
3. To calculate OSPF costs
4. To establish LACP sessions

Correct Answer: 2. To provide loop-prevention mechanisms

Explanation:
BGP route reflection uses attributes such as Originator ID and Cluster List to help prevent routing loops within route-reflector topologies. The Originator ID identifies the original iBGP speaker that originated the route, while the Cluster List records route-reflector cluster information as routes are reflected. A route reflector can use these values to detect routes that should not be reflected again. These mechanisms are specifically related to route-reflection loop prevention and do not assign MPLS labels, calculate OSPF costs, or establish Ethernet link aggregation sessions.

Question 346. In IS-IS, which packet is responsible for neighbor discovery and adjacency maintenance?

1. CSNP
2. PSNP
3. IIH
4. LSP

Correct Answer: 3. IIH

Explanation:
IS-IS Intermediate System-to-Intermediate System Hello packets, or IIHs, are used to discover neighboring IS-IS routers and establish or maintain adjacencies. They contain information that allows routers to verify neighbor relationships and maintain the appropriate adjacency state. LSPs distribute link-state information after adjacencies are established. CSNPs provide summaries of link-state database contents, while PSNPs are used for requesting or acknowledging specific LSP information. Therefore, IIH is the protocol data unit directly associated with IS-IS neighbor discovery and adjacency maintenance.

Question 347. Which IS-IS PDU carries detailed link-state information used to build the topology database?

1. LSP
2. IIH
3. PSNP
4. CSNP

Correct Answer: 1. LSP

Explanation:
IS-IS Link State PDUs, or LSPs, carry the link-state and reachability information used by routers to construct their link-state databases. This information can include router connectivity, metrics, reachable prefixes, and other details represented through TLVs. IIH packets are used for neighbor discovery and adjacency maintenance. CSNPs summarize database contents, while PSNPs request or acknowledge particular LSPs. By flooding LSPs throughout the appropriate IS-IS level, routers develop a consistent view of network topology and can calculate paths using the shortest-path algorithm.

Question 348. What is the primary purpose of an IS-IS Partial Sequence Number PDU?

1. To establish a TCP connection
2. To request or acknowledge specific LSP information
3. To elect a DIS
4. To assign an IP address

Correct Answer: 2. To request or acknowledge specific LSP information

Explanation:
Partial Sequence Number PDUs, or PSNPs, are used during IS-IS database synchronization to request missing or outdated LSP information and to acknowledge receipt of specific LSPs. This allows routers to correct differences in their link-state databases without exchanging all topology information unnecessarily. CSNPs provide a broader summary of database contents, while PSNPs focus on individual LSP information. PSNPs do not establish TCP connections, elect a DIS, or assign IP addresses. Their role is specifically related to maintaining consistency between IS-IS link-state databases.

Question 349. Which MPLS operation replaces an incoming label with an outgoing label at a transit router?

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

Correct Answer: 3. Swap

Explanation:
An MPLS transit Label Switching Router commonly performs a label swap. It examines the incoming label, consults its label forwarding information, removes the incoming label, and replaces it with the appropriate outgoing label before transmitting the packet toward the next hop. Push adds a label, while pop removes a label. Encryption is not one of the fundamental MPLS label operations. Label swapping allows packets to move through the MPLS core efficiently using label-based forwarding rather than requiring a complete IP routing lookup at every transit hop.

Question 350. What does Penultimate Hop Popping accomplish in an MPLS LSP?

1. It removes the outer MPLS label at the penultimate hop
2. It adds a second MPLS label
3. It changes the BGP AS Path
4. It establishes an LDP neighbor

Correct Answer: 1. It removes the outer MPLS label at the penultimate hop

Explanation:
Penultimate Hop Popping, or PHP, allows the router immediately before the MPLS egress router to remove the outer MPLS label. This reduces the label-processing work required at the egress router because the final label removal has already occurred. PHP is an MPLS forwarding behavior and does not change BGP attributes or establish LDP neighbor relationships. Depending on the LSP and service being provided, different label behaviors can be used, but the defining feature of PHP is that the penultimate router performs the label removal.

Question 351. What is the primary purpose of a VRF in an MPLS Layer 3 VPN environment?

1. To elect an OSPF DR
2. To maintain an independent routing and forwarding table
3. To distribute LDP labels
4. To select the BGP MED

Correct Answer: 2. To maintain an independent routing and forwarding table

Explanation:
A Virtual Routing and Forwarding instance, or VRF, provides a separate routing and forwarding context for a customer or VPN. This allows multiple customers to use overlapping address spaces while keeping their routes isolated from one another. VRFs are fundamental to MPLS Layer 3 VPN architectures and are associated with mechanisms such as Route Distinguishers and Route Targets. A VRF does not elect an OSPF DR, distribute MPLS labels, or directly select BGP MED. Those functions belong to other routing or forwarding mechanisms.

Question 352. What is the difference between a Route Distinguisher and a Route Target?

1. An RD controls import, while an RT creates prefix uniqueness
2. Both perform exactly the same function
3. An RD provides VPN route uniqueness, while an RT controls route import/export
4. An RT replaces the MPLS label

Correct Answer: 3. An RD provides VPN route uniqueness, while an RT controls route import/export

Explanation:
Route Distinguishers and Route Targets have different functions in MPLS Layer 3 VPNs. An RD makes overlapping customer prefixes unique within the provider’s VPN routing space, allowing identical prefixes from different customers to coexist. A Route Target is an extended BGP community used to control which VPN routes are imported into or exported from VRFs. Keeping these roles separate is important when troubleshooting VPN route distribution. Neither RD nor RT replaces the MPLS label, and their functions should not be treated as interchangeable.

Question 353. Which Junos command displays routes received from a specific BGP peer?

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

Correct Answer: 1. show route receive-protocol bgp <peer>

Explanation:
The show route receive-protocol bgp <peer> command displays routes received from a specified BGP neighbor. It is useful for troubleshooting inbound route advertisements and verifying which prefixes are being learned from a particular peer. The advertising-protocol command provides the opposite perspective by showing routes being advertised to a peer. Interface and hardware commands provide unrelated operational information. Checking received routes is especially useful when determining whether a neighbor is sending a prefix, whether policy is affecting the route, and whether the route is present in the local routing information.

Question 354. Which Junos command displays routes being advertised to a specific BGP peer?

1. show route
2. show route advertising-protocol bgp <peer>
3. show bgp summary
4. show ospf neighbor

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

Explanation:
The show route advertising-protocol bgp <peer> command is used to examine routes that the local device is advertising to a specific BGP neighbor. This is particularly useful when investigating export policies, route filtering, or unexpected route advertisements. The receive-protocol command instead focuses on routes learned from the peer. show bgp summary provides session-level information, while show ospf neighbor displays OSPF adjacency information. When troubleshooting BGP, comparing received and advertised routes can help identify whether an issue is related to route learning, selection, policy, or outbound propagation.

Question 355. Which Junos command restores a previously committed configuration into the candidate configuration?

1. rollback
2. commit check
3. show | compare
4. show configuration

Correct Answer: 1. rollback

Explanation:
The Junos rollback command is used to load a previously committed configuration into the candidate configuration. This allows administrators to review or restore an earlier configuration state before committing it. The specific rollback number determines which stored configuration is referenced. commit check validates the candidate configuration, show | compare displays differences between configurations, and show configuration displays configuration information. Rollback is therefore an important recovery and change-management mechanism when an earlier configuration needs to be restored or used as the basis for further changes.

Question 356. Which Junos command is commonly used to validate the candidate configuration without activating it?

1. commit confirmed
2. commit check
3. rollback 0
4. show route

Correct Answer: 2. commit check

Explanation:
The commit check command validates the candidate configuration without making it the active configuration. It can identify syntax or configuration consistency problems before a normal commit is performed. This makes it useful when preparing significant changes or when troubleshooting configuration errors. commit confirmed activates a configuration temporarily while requiring confirmation, whereas rollback 0 refers to the current committed configuration state. show route provides routing information and does not validate configuration. Running a configuration check before committing helps reduce the chance of activating an invalid configuration.

Question 357. Which Junos CoS component determines how traffic is assigned to a forwarding class?

1. Scheduler
2. Rewrite rule
3. Classifier
4. Queue

Correct Answer: 3. Classifier

Explanation:
A CoS classifier examines packet characteristics and determines the forwarding class and, where applicable, loss-priority treatment for the packet. Classification can use fields such as DSCP or IEEE 802.1p markings depending on the configured classifier and interface. After classification, traffic can be placed into queues and processed by schedulers. Rewrite rules can modify packet markings before transmission. The classifier therefore provides the initial mapping that determines the packet’s internal forwarding treatment. It does not control queue transmission rates or rewrite outbound markings by itself.

Question 358. What is the primary function of a CoS rewrite rule?

1. To change packet QoS markings before transmission
2. To establish an iBGP session
3. To calculate the shortest OSPF path
4. To distribute IS-IS LSPs

Correct Answer: 4. To change packet QoS markings before transmission

Explanation:
A CoS rewrite rule changes packet classification markings before the packet is transmitted from an interface. Depending on the configuration, this can include rewriting DSCP, 802.1p, or other relevant QoS markings. Rewriting allows a device to communicate the desired forwarding treatment to downstream devices. It does not establish BGP sessions, calculate OSPF paths, or distribute IS-IS LSPs. Classification and rewriting are related but distinct functions: classification determines how traffic is treated internally, while rewriting can modify the markings carried in the outgoing packet.

Question 359. Which Junos command can be used to view the differences between the candidate and active configurations?

1. show route summary
2. show | compare
3. show chassis hardware
4. commit check

Correct Answer: 2. show | compare

Explanation:
The show | compare command displays differences between the candidate configuration and the active configuration. It is useful for reviewing pending configuration changes before committing them. Administrators can use this output to verify that only intended statements have been added, modified, or removed. commit check validates the configuration but does not provide the same comparison view. show route summary displays routing-table statistics, while show chassis hardware provides hardware inventory. Comparing configurations before committing is a useful operational practice for reducing unintended changes.

Question 360. Which Junos command is most appropriate for checking the physical and logical interface status in a concise view?

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

Correct Answer: 3. show interfaces terse

Explanation:
The show interfaces terse command provides a concise view of interface and logical-unit status. It is commonly used to quickly identify whether interfaces are administratively and operationally up or down and to review associated addressing information. show route focuses on routing information, show bgp summary provides BGP session details, and show chassis hardware displays hardware inventory. The terse interface command is therefore an efficient first step when troubleshooting connectivity or verifying the operational state of physical and logical interfaces on a Junos device.