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

 

Question 321. Which BGP attribute is used to indicate the sequence of autonomous systems a route has traversed?

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

Correct Answer: 3. AS Path

Explanation:
The BGP AS Path attribute records the sequence of autonomous systems through which a route advertisement has passed. It is a fundamental component of BGP path selection and also provides an important loop-prevention mechanism. When a BGP speaker receives a route containing its own AS number in the AS Path, it can reject that route as a potential loop. AS Path length can also influence route selection, with shorter paths generally preferred when the relevant earlier attributes are equal. Local Preference, MED, and Next Hop have different functions within BGP path selection and forwarding.

Question 322. Which BGP attribute is normally preferred when its value is higher?

1. Local Preference
2. MED
3. AS Path length
4. IGP metric

Correct Answer: 1. Local Preference

Explanation:
BGP Local Preference is an important attribute used to influence outbound routing decisions within an autonomous system. A higher Local Preference value is generally preferred over a lower value. Network operators can use it to control which external exit point should carry traffic leaving the AS. MED behaves differently because a lower value is generally preferred. AS Path selection generally favors a shorter path, while IGP metrics can be considered later in the BGP decision process depending on the implementation and conditions. Local Preference therefore provides an effective mechanism for establishing preferred outbound paths across an internal BGP environment.

Question 323. What is the purpose of the BGP next-hop attribute?

1. To identify the BGP autonomous system
2. To determine the route’s MED
3. To select the route reflector cluster
4. To identify the IP address that should be used as the next forwarding hop

Correct Answer: 4. To identify the IP address that should be used as the next forwarding hop

Explanation:
The BGP Next Hop attribute identifies the IP address that a router should use as the next hop when forwarding traffic toward a BGP-learned destination. The reachability of this next-hop address is essential because the router must be able to resolve it through its routing table before forwarding traffic. In some designs, next-hop self is configured to make the local router the next hop when advertising routes to internal peers. The Next Hop attribute is therefore directly related to forwarding resolution and is distinct from attributes such as Local Preference, MED, and AS Path.

Question 324. Which BGP community is designed to prevent a route from being advertised to any other BGP peer?

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

Correct Answer: 2. NO_ADVERTISE

Explanation:
The well-known BGP NO_ADVERTISE community tells a receiving BGP speaker not to advertise the associated route to any other BGP peer. This provides a strong route-propagation restriction and can be useful when a route should remain local to the receiving BGP speaker. NO_EXPORT has a different scope and prevents advertisement outside the local autonomous system or applicable confederation. The INTERNET community permits normal advertisement, while NOPEER provides peer-specific propagation restrictions. BGP communities are powerful policy tools because they allow route behavior to be controlled without changing the underlying addressing or topology.

Question 325. What is the main benefit of BGP route reflection in a large iBGP network?

1. It replaces the IGP
2. It eliminates MPLS labels
3. It removes the need for a full iBGP mesh
4. It automatically encrypts BGP traffic

Correct Answer: 3. It removes the need for a full iBGP mesh

Explanation:
BGP route reflection allows an autonomous system to scale its iBGP deployment without requiring every router to establish a direct session with every other iBGP router. Route reflectors receive routes from clients and reflect eligible routes to other clients and peers according to BGP rules. This significantly reduces the number of required iBGP sessions in larger networks. Route reflection does not replace the IGP, remove MPLS labels, or automatically provide encryption. Additional mechanisms such as cluster IDs and originator IDs help prevent routing loops within route-reflector designs.

Question 326. Which IS-IS packet is used to establish and maintain neighbor adjacencies?

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

Correct Answer: 1. IIH

Explanation:
IS-IS uses Intermediate System-to-Intermediate System Hello packets, known as IIHs, to establish and maintain neighbor adjacencies. IIH packets allow routers to discover directly connected IS-IS neighbors and exchange information required for adjacency formation. Once adjacencies exist, routers exchange LSPs to distribute link-state information and use CSNPs and PSNPs as part of database synchronization. IIHs are therefore fundamental to the neighbor-discovery process. They are not used to carry the complete link-state database or to perform MPLS label distribution.

Question 327. Which IS-IS PDU provides a summary of the link-state database contents?

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

Correct Answer: 2. CSNP

Explanation:
A Complete Sequence Number PDU, or CSNP, provides a summary of the link-state information known by an IS-IS router. On broadcast networks, the DIS commonly sends CSNPs so participating routers can compare their databases and identify missing or outdated LSPs. A PSNP can then be used to request or acknowledge specific LSP information. IIHs establish and maintain adjacencies, while LSPs carry the actual link-state information. CSNPs therefore play an important role in maintaining synchronization between IS-IS databases and ensuring that routers have a consistent understanding of the topology.

Question 328. Which IS-IS level provides the backbone function between different IS-IS areas?

1. Level 1 only
2. Level 0
3. Level 3
4. Level 2

Correct Answer: 4. Level 2

Explanation:
IS-IS Level 2 provides the backbone function that connects different IS-IS areas. Level 1 routing is focused on destinations within an individual area, while Level 2 routers maintain connectivity between areas. A router can be configured as Level 1-2 and participate in both functions. The Level 2 topology therefore provides the inter-area routing structure of an IS-IS network. IS-IS does not use Level 0 or Level 3 as equivalent routing levels. Understanding these roles is important when troubleshooting why a destination is reachable within an area but not correctly reachable across area boundaries.

Question 329. What is the primary purpose of MPLS Label Distribution Protocol (LDP)?

1. To distribute label bindings for forwarding equivalence classes
2. To establish BGP communities
3. To elect an OSPF DR
4. To provide DHCP address allocation

Correct Answer: 1. To distribute label bindings for forwarding equivalence classes

Explanation:
LDP is used to distribute MPLS label bindings between routers. It allows routers to associate labels with forwarding equivalence classes and communicate those bindings to neighboring LDP speakers. This information contributes to the creation of label-switched paths through the MPLS network. LDP is distinct from BGP, OSPF, and DHCP, which serve different control-plane or network-service functions. When troubleshooting an MPLS network using LDP, engineers commonly examine LDP sessions, label bindings, and the corresponding forwarding state to determine whether labels are being learned and installed correctly.

Question 330. Which operation adds an MPLS label to a packet entering an MPLS domain?

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

Correct Answer: 4. Push

Explanation:
A push operation adds an MPLS label to a packet. This commonly occurs at an MPLS ingress edge router when IP traffic is classified into a forwarding equivalence class and introduced into an MPLS LSP. A transit Label Switching Router typically performs a swap, replacing the incoming label with an outgoing label. A pop operation removes a label, while rewrite is not the standard name for the fundamental MPLS label operation of adding a label. Understanding push, swap, and pop is essential when analyzing how packets move through an MPLS label-switched path.

Question 331. What is the main purpose of a Route Distinguisher in an MPLS Layer 3 VPN?

1. To select the BGP MED
2. To make overlapping VPN prefixes unique
3. To elect a VRRP master
4. To establish an LDP session

Correct Answer: 2. To make overlapping VPN prefixes unique

Explanation:
A Route Distinguisher, or RD, is used to make otherwise identical customer prefixes unique within the provider’s VPN routing space. This is especially important when different customers use overlapping private address ranges. The RD is combined with the IPv4 or IPv6 prefix to create a unique VPN route representation, such as a VPNv4 or VPNv6 route. Route Targets perform a different function by controlling VPN route import and export. RDs do not determine BGP MED, elect VRRP masters, or establish LDP sessions. Keeping RD and RT functions distinct is essential when troubleshooting MPLS Layer 3 VPNs.

Question 332. What is the purpose of a Route Target in an MPLS Layer 3 VPN?

1. To calculate the IGP shortest path
2. To control which VPN routes are imported into or exported from a VRF
3. To uniquely identify a physical interface
4. To replace the MPLS label

Correct Answer: 3. To control which VPN routes are imported into or exported from a VRF

Explanation:
Route Targets are BGP extended communities used to control VPN route distribution. An export Route Target can be attached to routes leaving a VRF, while import configuration determines which routes are accepted into another VRF based on matching Route Targets. This allows providers to create different customer connectivity models, such as full mesh, hub-and-spoke, or restricted communication between selected sites. Route Targets do not calculate IGP paths, identify physical interfaces, or replace MPLS labels. Their primary role is controlling VPN route membership and distribution across provider-edge devices.

Question 333. Which Junos command displays the operational status of all interfaces in a concise format?

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

Correct Answer: 1. show interfaces terse

Explanation:
The show interfaces terse command provides a concise overview of interface status and addressing information. It is commonly used during troubleshooting to quickly determine whether interfaces are administratively and operationally up or down. The command can also provide useful information about logical units and protocol states without producing the extensive output associated with the detailed interface command. show route summary focuses on routing-table information, show chassis hardware displays hardware inventory, and show bgp summary provides BGP session information. The terse interface command is therefore particularly useful as an initial interface-status check.

Question 334. Which Junos command displays the hardware inventory of a device?

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

Correct Answer: 2. show chassis hardware

Explanation:
The show chassis hardware command displays hardware inventory information for a Junos device. Depending on the platform, the output can include chassis components, Routing Engines, line cards, interface modules, and other installed hardware. This command is useful when verifying hardware installation or identifying components during troubleshooting and maintenance. show route displays routing information, show interfaces terse provides concise interface status, and show configuration displays configuration data. Hardware inventory should therefore be checked with the chassis hardware command rather than routing or configuration commands.

Question 335. Which Junos high-availability feature allows a Routing Engine switchover while preserving forwarding operations?

1. GRES
2. LACP
3. LLDP
4. RSTP

Correct Answer: 1. GRES

Explanation:
Graceful Routing Engine Switchover, or GRES, is a Junos high-availability feature designed to allow forwarding to continue while control-plane responsibility transitions between Routing Engines. GRES helps reduce service disruption during an RE switchover, although additional mechanisms such as Nonstop Active Routing can preserve routing protocol state more extensively. LACP handles link aggregation, LLDP provides neighbor discovery, and RSTP provides Layer 2 loop prevention and rapid convergence. GRES is therefore specifically associated with Routing Engine redundancy and graceful control-plane transitions.

Question 336. What is the primary purpose of Nonstop Active Routing (NSR) in Junos?

1. To assign IP addresses
2. To maintain routing protocol state across a Routing Engine switchover
3. To aggregate Ethernet links
4. To distribute DHCP leases

Correct Answer: 3. To maintain routing protocol state across a Routing Engine switchover

Explanation:
Nonstop Active Routing, or NSR, is designed to maintain routing protocol state during a Routing Engine switchover. By synchronizing relevant control-plane information between Routing Engines, NSR can reduce the need for routing protocols to restart or re-establish their state after a switchover. This complements other high-availability mechanisms such as GRES. NSR is not an IP address assignment system, link aggregation protocol, or DHCP service. It is particularly valuable in environments where maintaining stable routing protocol operation during control-plane transitions is important.

Question 337. Which CoS component controls how packets in a forwarding class are transmitted from a queue?

1. Classifier
2. Scheduler
3. Rewrite rule
4. Route Target

Correct Answer: 2. Scheduler

Explanation:
A CoS scheduler determines how traffic in queues is transmitted by controlling factors such as transmission rate, priority, and available bandwidth according to the configured scheduling behavior. Traffic is typically classified first, placed into forwarding classes and queues, and then scheduled for transmission. A classifier determines how packets are assigned to forwarding classes, while a rewrite rule can modify packet markings before transmission. Route Targets belong to MPLS VPN routing policy and are unrelated to CoS scheduling. Understanding the roles of classifiers, queues, schedulers, and rewrite rules is essential when designing and troubleshooting quality-of-service behavior.

Question 338. Which protocol is commonly used by Junos devices for structured network configuration and management automation?

1. RSTP
2. NETCONF
3. VRRP
4. LACP

Correct Answer: 4. NETCONF

Explanation:
NETCONF is a protocol designed for structured network configuration and management. It allows management systems and automation tools to interact with network devices using structured data rather than relying only on interactive command-line sessions. Junos supports NETCONF-based management as part of its automation capabilities. RSTP is a Layer 2 spanning-tree protocol, VRRP provides first-hop gateway redundancy, and LACP manages link aggregation. NETCONF can be especially useful in automated environments where configurations need to be consistently generated, validated, retrieved, and modified through programmatic workflows.

Question 339. What is the primary function of a firewall filter applied to the Junos control plane?

1. To distribute MPLS labels
2. To elect an OSPF DR
3. To control traffic destined for the device’s control plane
4. To calculate BGP path length

Correct Answer: 3. To control traffic destined for the device’s control plane

Explanation:
A firewall filter applied to protect the control plane can be used to control traffic destined for the Routing Engine or other control-plane processing resources. Such filters can permit required management and routing protocol traffic while restricting unwanted or potentially harmful packets. This is an important part of protecting the device itself rather than merely filtering transit traffic. Firewall filters do not distribute MPLS labels, perform OSPF elections, or calculate BGP path length. Proper control-plane protection can help reduce unnecessary traffic reaching critical routing and management processes.

Question 340. Which Junos feature allows a configuration change to be automatically rolled back if confirmation is not received within the specified time?

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

Correct Answer: 1. commit confirmed

Explanation:
The commit confirmed feature allows an administrator to activate a configuration temporarily while requiring confirmation within a specified interval. If the administrator does not confirm the change by performing another commit before the timer expires, Junos automatically rolls back to the previous committed configuration. This is particularly useful when making remote changes that could potentially disrupt management access. commit check validates configuration without activating it, while show | compare displays differences between configuration states. show configuration displays configuration information. The automatic rollback behavior is therefore specifically associated with commit confirmed.