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

 

Question 261: Which BGP attribute is normally propagated within an autonomous system through iBGP and influences outbound path selection?

1. MED
2. Local Preference
3. Origin
4. Next Hop

Correct Answer: 2. Local Preference

Explanation:
Local Preference is a BGP attribute used within an autonomous system to influence the preferred exit path for outbound traffic. A higher Local Preference value is generally preferred when comparing otherwise eligible BGP routes. Because the attribute is carried through iBGP, it can influence path selection across multiple routers within the same AS. This makes Local Preference useful for implementing policies such as preferring one upstream provider over another. MED serves a different purpose by providing information about preferred entry points into an AS. The Origin attribute describes how a route entered BGP, while Next Hop identifies the forwarding next hop.

Question 262: Which BGP capability can allow a router to retain multiple eligible paths instead of installing only one best path?

1. Route aggregation
2. Route reflection
3. BGP multipath
4. Confederation

Correct Answer: 3. BGP multipath

Explanation:
BGP multipath allows multiple eligible paths to the same destination to be installed in the forwarding or routing infrastructure when the configured requirements for multipath are satisfied. This can provide load sharing and additional resiliency. Standard BGP path selection normally results in one best path, even if several routes are available. Route reflection is designed to improve iBGP scalability, while aggregation reduces the number of advertised prefixes. Confederations divide an AS into internal sub-AS structures. Multipath therefore addresses a different requirement: using multiple qualifying paths for the same destination rather than selecting only one.

Question 263: Which BGP attribute identifies the IP address that should be used as the next hop toward a destination?

1. Next Hop
2. AS Path
3. Local Preference
4. Community

Correct Answer: 1. Next Hop

Explanation:
The BGP Next Hop attribute identifies the IP address that a router should use as the next forwarding point for reaching the advertised destination. Correct next-hop reachability is essential because a BGP route may be present and selected while still being unusable if its next hop cannot be resolved through the routing table. In some designs, next-hop self is used to change the next-hop address when routes are advertised internally. AS Path records the autonomous systems traversed, Local Preference influences outbound path selection, and communities carry policy-related information.

Question 264: Which BGP community generally prevents a route from being advertised outside the local autonomous system?

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

Correct Answer: 3. NO_EXPORT

Explanation:
The well-known BGP community NO_EXPORT indicates that a route should not be advertised outside the applicable local autonomous system or confederation boundary. Internal propagation can still occur according to the network’s BGP policies. NO_ADVERTISE is more restrictive because it indicates that the route should not be advertised to any other BGP peer. BGP communities provide a flexible way to attach policy information to routes and then apply routing policies based on those values. Understanding the distinction between NO_EXPORT and NO_ADVERTISE is important when troubleshooting unexpected BGP route propagation.

Question 265: What is the primary reason for using BGP route reflection in a large iBGP network?

1. To eliminate all routing policies
2. To reduce the number of required iBGP sessions
3. To encrypt BGP messages
4. To replace the IGP

Correct Answer: 2. To reduce the number of required iBGP sessions

Explanation:
Traditional iBGP requires a full mesh of sessions between routers, which can become difficult to manage as the network grows. Route reflection addresses this scalability problem by allowing selected routers to act as route reflectors and distribute routes to configured clients. This reduces the number of direct iBGP sessions that need to be established. Route reflection does not replace the IGP, eliminate routing policies, or provide encryption. It is a BGP control-plane scalability mechanism. Proper route-reflector design, including redundancy and appropriate cluster configuration, is important to prevent routing loops and avoid creating unnecessary control-plane dependencies.

Question 266: Which IS-IS PDU is primarily used to establish and maintain neighbor adjacencies?

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

Correct Answer: 4. IIH

Explanation:
IS-IS uses Intermediate System-to-Intermediate System Hello (IIH) PDUs to establish and maintain neighbor adjacencies. These messages allow routers to discover each other and exchange information required to maintain the relationship. Link-State PDUs carry topology and reachability information, while Complete and Partial Sequence Number PDUs are involved in database synchronization and maintenance. When troubleshooting an IS-IS adjacency problem, examining the participating interfaces, addressing, authentication, and IIH exchange can be useful. Understanding the different IS-IS PDU types helps distinguish neighbor-discovery issues from link-state database synchronization problems.

Question 267: Which IS-IS PDU provides a summary of the link-state database contents?

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

Correct Answer: 3. CSNP

Explanation:
A Complete Sequence Number PDU (CSNP) provides a summary of the link-state information known to an IS-IS router. It can be used to help synchronize link-state databases and identify missing or outdated LSPs. Partial Sequence Number PDUs perform a related but more selective function by acknowledging or requesting particular LSP information. IIH PDUs are used for adjacency establishment and maintenance, while LSPs carry the actual topology and reachability information. Understanding CSNP and PSNP behavior can be especially useful when troubleshooting IS-IS database synchronization on broadcast or point-to-point environments.

Question 268: In IS-IS, what is the primary purpose of a Partial Sequence Number PDU (PSNP)?

1. To establish an IPsec tunnel
2. To provide DHCP information
3. To request or acknowledge specific LSP information
4. To elect a BGP route reflector

Correct Answer: 3. To request or acknowledge specific LSP information

Explanation:
Partial Sequence Number PDUs (PSNPs) are used by IS-IS to request or acknowledge specific Link-State PDUs. They therefore support reliable synchronization and maintenance of the IS-IS link-state database. A router can use a PSNP to indicate that particular LSP information is missing or needs attention, depending on the operational context. CSNPs provide a broader summary of database contents, while IIH PDUs are used for neighbor discovery and adjacency maintenance. IPsec, DHCP, and BGP route reflection are separate technologies and are not the purpose of PSNP messages.

Question 269: What does the MPLS label operation “push” mean?

1. A label is added to the packet
2. A label is replaced
3. A label is removed
4. The IP header is encrypted

Correct Answer: 1. A label is added to the packet

Explanation:
In MPLS terminology, a push operation adds an MPLS label to a packet. This is commonly associated with the ingress edge of an MPLS network, where an unlabeled IP packet is classified and assigned to an appropriate forwarding equivalence class. A transit router may then perform a label swap, replacing one label with another. A pop operation removes a label, such as during penultimate hop popping or at an appropriate egress operation. These label operations form the basis of MPLS forwarding. Understanding whether a device is pushing, swapping, or popping labels helps when troubleshooting an MPLS forwarding path.

Question 270: What is the main purpose of MPLS penultimate hop popping?

1. To add an additional VPN label
2. To remove the top label before the packet reaches the egress router
3. To change the BGP AS Path
4. To establish an LDP session

Correct Answer: 2. To remove the top label before the packet reaches the egress router

Explanation:
Penultimate hop popping (PHP) removes the top MPLS label at the router immediately before the egress Label Edge Router. This can reduce the label-processing work required by the egress device. Instead of receiving a packet with the outer transport label still present, the egress router can receive the packet after the penultimate router has performed the pop operation. PHP is therefore an MPLS forwarding optimization. It is not a mechanism for changing BGP attributes or establishing LDP sessions. In VPN environments, additional labels may be involved, so understanding the exact label stack and which label is being removed is important during troubleshooting.

Question 271: In an MPLS Layer 3 VPN, what makes identical IPv4 prefixes from different customers distinguishable?

1. MED
2. Route Target
3. Route Distinguisher
4. Local Preference

Correct Answer: 3. Route Distinguisher

Explanation:
The Route Distinguisher (RD) makes otherwise identical customer IPv4 prefixes unique in the provider’s VPN routing environment. For example, two customers can both use 10.10.10.0/24 while the provider still maintains separate VPN routes because different RDs are associated with those prefixes. The RD is therefore concerned with route uniqueness. Route Targets perform a different function by controlling which VRFs import or export VPN routes. MED and Local Preference are BGP path-selection attributes and do not provide the same VPN-prefix uniqueness function. Keeping RD and RT roles separate is essential when troubleshooting MPLS VPN routing.

Question 272: Which component determines whether an MPLS VPN route should be imported into a particular VRF?

1. Route Target
2. Route Distinguisher
3. LDP label
4. OSPF cost

Correct Answer: 1. Route Target

Explanation:
Route Targets are used to control VPN route import and export between VRFs. When a route is exported from a VRF, an RT can be attached to the route as a BGP extended community. A receiving VRF then compares the route’s RT values against its configured import targets to determine whether the route should be imported. The RD is responsible for making overlapping prefixes unique rather than controlling their distribution. LDP labels support MPLS forwarding, while OSPF cost is used for OSPF path selection. Route Target configuration is therefore a key part of determining VPN connectivity.

Question 273: Which Junos command displays the currently committed configuration from operational mode?

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

Correct Answer: 1. show configuration

Explanation:
The Junos show configuration command displays the active committed configuration when used from operational mode. It provides a hierarchical view of the configuration currently applied to the device. Administrators can use more specific forms of the command to inspect particular configuration sections, such as protocols, interfaces, routing options, or policy options. This is different from configuration mode, where show displays the candidate configuration that is being edited. Understanding the distinction between candidate and active configuration is important when making changes and verifying whether a configuration has actually been committed.

Question 274: Which Junos command compares the candidate configuration with the currently active configuration?

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

Correct Answer: 1. show | compare

Explanation:
In Junos configuration mode, show | compare displays the differences between the candidate configuration and the active committed configuration. This allows an administrator to review pending changes before activating them. The output can show additions, deletions, and modifications, making it useful for verifying that the intended configuration has been entered correctly. commit check validates the configuration but does not serve the same purpose as a change comparison. Reviewing the differences before committing is a useful operational safeguard, particularly when changes involve routing, security policies, or remote management access.

Question 275: Which Junos feature can automatically restore the previous configuration if a remote administrator fails to confirm a change?

1. commit confirmed
2. show | compare
3. commit synchronize
4. load override

Correct Answer: 1. commit confirmed

Explanation:
The commit confirmed feature is designed to protect administrators from losing access after making potentially disruptive configuration changes. When used, the candidate configuration becomes active and a confirmation timer starts. If the administrator does not perform a regular commit before the timer expires, Junos automatically rolls back to the previous committed configuration. This is particularly valuable for remote changes involving management interfaces, routing, firewall filters, or other settings that could interrupt connectivity. show | compare only displays configuration differences, while commit synchronize serves a different purpose on supported redundant systems.

Question 276: Which Junos command displays concise interface status and addressing information?

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

Correct Answer: 1. show interfaces terse

Explanation:
The show interfaces terse command provides a concise summary of interface status and, where applicable, addressing information. It is commonly used as a first troubleshooting step to quickly determine whether interfaces are administratively enabled and operationally up. When more detailed information is required, show interfaces can provide counters, physical information, traffic statistics, and additional operational details. The other commands focus on routing-table statistics, BGP sessions, or chassis alarms. The terse interface view is therefore useful when quickly checking the overall state of a Junos device’s interfaces.

Question 277: Which Junos command displays detailed information about the device’s installed hardware components?

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

Correct Answer: 2. show chassis hardware

Explanation:
The show chassis hardware command displays the hardware inventory of a Junos device. Depending on the platform, this can include information about the chassis, Routing Engines, line cards, modules, and other installed components. It is useful for confirming hardware presence and identifying platform components during troubleshooting or maintenance. The command does not provide routing-table information or interface operational status. Hardware inventory can be particularly important when diagnosing a problem that may be associated with a specific physical component or when verifying that a replacement module has been recognized correctly.

Question 278: Which Junos command checks whether a candidate configuration can be committed without actually activating it?

1. rollback
2. commit confirmed
3. commit check
4. show configuration

Correct Answer: 3. commit check

Explanation:
The Junos commit check command validates the candidate configuration without activating it. It is useful before a normal commit because it can identify syntax or configuration consistency problems. Administrators can use it as a validation step after making changes to interfaces, routing protocols, policies, or other configuration areas. commit confirmed actually activates the configuration while providing an automatic rollback safety mechanism. rollback loads an earlier configuration, while show configuration displays configuration information. Separating validation from activation allows administrators to detect many configuration problems before they affect the running device.

Question 279: Which CoS component determines how traffic in a forwarding class is serviced when congestion occurs?

1. Scheduler
2. Classifier
3. Route Target
4. BGP policy

Correct Answer: 1. Scheduler

Explanation:
A CoS scheduler determines how traffic queues are serviced and how available transmission resources are allocated among forwarding classes. Scheduler configuration can influence bandwidth allocation, priority, and other queue-service characteristics. A classifier performs a different function by determining the forwarding class and loss priority based on packet characteristics. Routing policies and Route Targets are associated with routing rather than packet scheduling. Proper scheduler configuration allows network administrators to differentiate traffic treatment during congestion and provide appropriate forwarding behavior for applications with different performance requirements.

Question 280: Which CoS mechanism can classify packets based on markings such as DSCP or IEEE 802.1p?

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

Correct Answer: 2. Classifier

Explanation:
A CoS classifier examines packet characteristics and assigns traffic to an appropriate forwarding class and loss priority. Depending on the configuration, classification can use markings such as DSCP or IEEE 802.1p values. After classification, schedulers determine how traffic receives transmission resources, while rewrite rules can modify markings before packets leave an interface. LACP performs link aggregation and is unrelated to CoS classification. Classification is therefore an important first step in applying differentiated forwarding treatment, allowing subsequent CoS components to handle traffic according to the desired service requirements.