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

 

Question 381. Which BGP feature allows a router to install multiple equal-cost BGP paths into the routing table?

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

Correct Answer: 2. BGP multipath

Explanation:
BGP multipath allows a Junos device to install multiple BGP paths for the same destination when the paths meet the configured multipath requirements. Instead of selecting only one best BGP path, the router can use several equal-cost paths for forwarding. This can provide load sharing and improve utilization of redundant links. The paths must satisfy Junos BGP multipath and routing requirements, including appropriate attributes and next-hop reachability. Route reflection is used to distribute BGP routes within an autonomous system, while MED and AS path prepending influence route selection rather than directly enabling multiple paths to be installed.

Question 382. Which BGP attribute is commonly used to prevent an iBGP router from advertising a route learned from one iBGP peer to another iBGP peer?

1. Split horizon
2. MED
3. Local Preference
4. iBGP split-horizon rule

Correct Answer: 4. iBGP split-horizon rule

Explanation:
The iBGP split-horizon rule states that a route learned through iBGP is normally not advertised to another iBGP peer. This rule exists to prevent routing loops within an autonomous system. Because a full mesh of iBGP sessions would otherwise be required, large networks commonly use route reflectors or BGP confederations to overcome this scaling limitation. Local Preference is a BGP path-selection attribute, while MED is primarily used to influence inbound path selection from neighboring autonomous systems. Neither attribute implements the iBGP split-horizon behavior.

Question 383. In Junos, what is the primary purpose of the next-hop self BGP policy/action?

1. Replace the BGP next hop with the local router’s address
2. Remove the AS path from the route
3. Set the route’s MED to zero
4. Convert an eBGP session into an iBGP session

Correct Answer: 1. Replace the BGP next hop with the local router’s address

Explanation:
Setting the BGP next hop to self causes the local router to advertise itself as the next hop for selected BGP routes. This is commonly useful when an iBGP router needs to advertise routes learned from an external BGP neighbor but the internal router cannot directly reach the original external next-hop address. Making the advertising router the next hop simplifies internal forwarding and ensures that the route points toward a reachable device. This action does not remove AS-path information, modify the MED automatically, or change the type of BGP session.

Question 384. Which BGP community prevents a route from being advertised outside the local autonomous system?

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

Correct Answer: 2. NO_EXPORT

Explanation:
The NO_EXPORT well-known BGP community tells a receiving BGP speaker not to advertise the route to eBGP peers outside the local autonomous system or confederation boundary. This allows a route to be distributed internally while restricting its propagation beyond the intended administrative domain. NO_ADVERTISE is more restrictive because a route carrying that community should not be advertised to any BGP peer. LOCAL_PREF is a path-selection attribute rather than a community with this propagation behavior, and INTERNET represents the standard community indicating that the route has no such community-based restriction.

Question 385. What is the primary purpose of a BGP route reflector?

1. Replace OSPF area boundaries
2. Provide MPLS labels for BGP routes
3. Reduce the requirement for a full mesh of iBGP sessions
4. Encrypt BGP updates

Correct Answer: 3. Reduce the requirement for a full mesh of iBGP sessions

Explanation:
A BGP route reflector improves iBGP scalability by allowing selected routers to act as route reflectors for client routers. Instead of requiring every iBGP router to maintain a session with every other iBGP router, clients can establish sessions with route reflectors. The route reflector then redistributes eligible routes between its clients and other BGP peers according to the route-reflection rules. Route reflection does not provide encryption, does not replace OSPF area design, and does not itself create MPLS labels. It is primarily a control-plane scalability mechanism for iBGP.

Question 386. Which IS-IS PDU is used to establish and maintain IS-IS neighbor adjacencies?

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

Correct Answer: 1. IIH

Explanation:
IS-IS Intermediate System-to-Intermediate System Hello, or IIH, PDUs are used to establish and maintain adjacencies between IS-IS neighbors. Routers periodically exchange hello information to verify that neighboring systems are reachable and that the adjacency remains operational. Link State PDUs, or LSPs, carry link-state information used to build the IS-IS database. CSNPs summarize the contents of a link-state database, while PSNPs are used to acknowledge or request specific LSP information. Therefore, IIH is the PDU directly associated with neighbor discovery and adjacency maintenance.

Question 387. In IS-IS, what is the primary role of a Level 2 router?

1. Forward only within a single LAN segment
2. Exchange routing information between different IS-IS areas
3. Replace the IP routing table
4. Establish BGP peering sessions

Correct Answer: 4. Exchange routing information between different IS-IS areas

Explanation:
IS-IS Level 2 routers provide routing between different IS-IS areas. Level 1 routing is primarily concerned with destinations within an individual area, while Level 2 routing provides the inter-area backbone function. A router can operate as Level 1, Level 2, or Level 1-2 depending on its configuration and role in the topology. IS-IS does not replace the IP routing table, and Level 2 functionality is unrelated to establishing BGP sessions. Understanding the distinction between Level 1 and Level 2 is important when troubleshooting IS-IS reachability and path selection.

Question 388. Which IS-IS PDU provides a summary of the link-state database?

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

Correct Answer: 3. PSNP

Explanation:
A Partial Sequence Number PDU, or PSNP, is used for specific acknowledgments and requests involving IS-IS link-state information. CSNPs provide a summary of the LSPs contained in an IS-IS database, particularly during database synchronization. LSPs themselves carry the actual link-state information, while IIHs establish and maintain adjacencies. When troubleshooting IS-IS database synchronization, understanding the different PDU roles is important. The distinction between CSNP and PSNP is especially significant: CSNP provides a database summary, whereas PSNP can acknowledge or request specific LSPs.

Question 389. What does an MPLS ingress router typically do when forwarding an unlabeled IP packet into an MPLS LSP?

1. Pop the existing MPLS label
2. Swap the packet’s IP address
3. Push an MPLS label onto the packet
4. Remove the IP header

Correct Answer: 3. Push an MPLS label onto the packet

Explanation:
At the ingress of an MPLS network, the router classifies the incoming packet into an appropriate forwarding equivalence class and typically imposes, or pushes, an MPLS label before forwarding it through the label-switched path. The label then guides subsequent MPLS forwarding decisions. A transit router may swap the incoming label for another label, while an egress router removes the label before forwarding the resulting IP packet toward its destination. MPLS does not require the ingress router to remove the IP header or change the packet’s IP addressing simply because a label is being imposed.

Question 390. What is the function of Penultimate Hop Popping (PHP) in MPLS?

1. The penultimate router removes the MPLS label before the egress router
2. The ingress router adds two labels
3. The egress router creates a new LSP
4. The penultimate router changes the destination IP address

Correct Answer: 1. The penultimate router removes the MPLS label before the egress router

Explanation:
Penultimate Hop Popping allows the router immediately before the MPLS egress router to remove the outer MPLS label. This reduces the amount of label-processing work required by the egress router and can improve forwarding efficiency. With PHP, the egress router receives the packet without the label that it would otherwise need to remove itself. PHP does not involve changing the destination IP address or creating a new LSP. The exact label behavior depends on the MPLS service and label distribution configuration, but PHP is commonly associated with removing the label at the penultimate hop.

Question 391. In an MPLS Layer 3 VPN, what is the primary purpose of a Route Distinguisher (RD)?

1. Select the preferred BGP path
2. Make otherwise overlapping VPN prefixes unique
3. Encrypt VPN traffic
4. Identify the physical PE interface

Correct Answer: 2. Make otherwise overlapping VPN prefixes unique

Explanation:
A Route Distinguisher makes VPN routes globally unique within the provider’s VPN routing infrastructure. It is particularly important when different customers use identical IPv4 prefixes, such as 10.0.0.0/8. The RD is combined with the customer IPv4 prefix to create a VPN-IPv4 route that can be uniquely represented in the provider network. The RD does not determine whether a route is imported into a particular VRF; that function is primarily associated with Route Targets. It also does not encrypt traffic or identify a physical interface.

Question 392. What is the primary function of a Route Target in an MPLS Layer 3 VPN?

1. Determine the MPLS label stack depth
2. Create a unique VPN-IPv4 prefix
3. Control which VPN routes are imported into or exported from VRFs
4. Establish an IGP adjacency

Correct Answer: 3. Control which VPN routes are imported into or exported from VRFs

Explanation:
Route Targets are extended BGP communities used to control the distribution of VPN routes between VRFs. An export Route Target is attached to routes leaving a VRF, while import Route Targets determine which VPN routes are accepted into a VRF. This mechanism allows a provider to implement different VPN topologies, including hub-and-spoke and shared-service designs. The Route Distinguisher, rather than the Route Target, provides uniqueness for overlapping customer prefixes. Route Targets do not establish IGP adjacencies or directly determine the number of MPLS labels used.

Question 393. Which Junos command is most useful for viewing the routes received from a specific BGP neighbor?

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

Correct Answer: 4. show route receive-protocol bgp <peer>

Explanation:
The show route receive-protocol bgp <peer> command displays routes received from the specified BGP neighbor. It is useful for troubleshooting whether expected routes are actually being learned from a particular peer and for examining policy-related behavior. This is different from checking the forwarding table, which shows routes selected for forwarding, or interface information, which provides operational details about interfaces. When investigating BGP problems, comparing received routes with accepted routes and the active routing table can help identify filtering, policy, or path-selection issues.

Question 394. Which Junos command displays the configuration differences between the candidate configuration and the active configuration?

1. show route summary
2. show | compare
3. show configuration
4. show system commit

Correct Answer: 2. show | compare

Explanation:
The show | compare command is used while working in configuration mode to display differences between the candidate configuration and the currently active configuration. It is particularly useful before committing changes because it lets an administrator review exactly what has been modified. show configuration displays configuration statements but does not specifically provide the same candidate-versus-active comparison. Reviewing the comparison before committing is a common operational practice that helps identify unintended changes and reduces configuration mistakes.

Question 395. What is the purpose of Junos commit confirmed?

1. Immediately delete the candidate configuration
2. Permanently disable configuration rollback
3. Automatically reboot the device after committing
4. Automatically roll back the commit if it is not confirmed within the specified interval

Correct Answer: 4. Automatically roll back the commit if it is not confirmed within the specified interval

Explanation:
The commit confirmed feature provides protection when making potentially disruptive configuration changes, especially on remote devices. The configuration is committed temporarily, and the administrator must confirm the commit within the specified interval. If confirmation does not occur, Junos automatically rolls the configuration back to the previous committed state. This helps prevent an administrator from becoming permanently locked out because of an incorrect interface, routing, firewall, or management configuration. It does not reboot the device or disable the normal rollback mechanisms.

Question 396. Which Junos high-availability feature allows the control plane to restart routing processes with minimal disruption while preserving forwarding state?

1. Graceful Routing Engine Switchover (GRES)
2. VLAN tagging
3. LACP
4. LLDP

Correct Answer: 1. Graceful Routing Engine Switchover (GRES)

Explanation:
Graceful Routing Engine Switchover, or GRES, allows a Junos device with redundant Routing Engines to transition control-plane responsibility between Routing Engines while minimizing forwarding disruption. The forwarding plane can continue operating while the backup Routing Engine assumes control. GRES is a high-availability mechanism and is different from protocols such as LACP and LLDP, which address link aggregation and neighbor discovery respectively. Graceful restart and nonstop routing are related high-availability concepts but have distinct operational purposes and configuration requirements.

Question 397. Which protocol is used by Junos devices to discover directly connected neighboring devices and advertise system information?

1. BFD
2. LLDP
3. LDP
4. RSTP

Correct Answer: 2. LLDP

Explanation:
Link Layer Discovery Protocol, or LLDP, allows network devices to advertise and learn information about directly connected neighbors at Layer 2. The information can include system identity, port information, capabilities, and other operational details. LLDP is particularly useful for network discovery and troubleshooting physical connectivity. BFD is designed for fast failure detection, LDP distributes MPLS labels, and RSTP prevents Layer 2 bridging loops. LLDP does not establish IP routing adjacencies; its primary purpose is neighbor discovery and exchange of device information.

Question 398. What is the primary purpose of LACP on a Junos switch?

1. Establish OSPF adjacencies
2. Distribute MPLS labels
3. Dynamically negotiate and maintain link aggregation
4. Provide IPv6 neighbor discovery

Correct Answer: 3. Dynamically negotiate and maintain link aggregation

Explanation:
The Link Aggregation Control Protocol, or LACP, is used to dynamically establish and maintain aggregated Ethernet links. By combining multiple physical links into a logical aggregated interface, a network can gain redundancy and increased aggregate bandwidth. LACP exchanges control information between devices to determine whether links can participate in the same aggregation group. It is not an IP routing protocol and does not distribute MPLS labels. IPv6 neighbor discovery is handled by NDP, while OSPF uses its own separate adjacency mechanism.

Question 399. Which Junos feature can protect the Routing Engine by filtering unwanted traffic destined for the control plane?

1. CoS rewrite rules
2. Control plane firewall filters
3. LACP
4. Route reflectors

Correct Answer: 1. CoS rewrite rules

Explanation:
CoS rewrite rules are used to modify packet markings as traffic leaves an interface and are not the primary mechanism for protecting the Routing Engine. Control-plane protection in Junos is commonly implemented using firewall filters applied to the appropriate control-plane interface or mechanism, allowing administrators to restrict which packets can reach the Routing Engine. Such filters can help limit unnecessary or unwanted management and protocol traffic. LACP and route reflection serve completely different functions. When implementing control-plane protection, care must be taken not to block legitimate routing, management, or infrastructure traffic.

Question 400. Which Junos command is commonly used to verify the operational status and details of interfaces?

1. show route advertising-protocol bgp <peer>
2. show configuration policy-options
3. show bgp neighbor
4. show interfaces

Correct Answer: 3. show bgp neighbor

Explanation:
The show bgp neighbor command provides information about BGP peer sessions, including session state, peer details, counters, and protocol information. It is therefore useful when troubleshooting BGP connectivity and operation. The show interfaces command is instead used to inspect interface operational and statistical information. show configuration policy-options displays routing-policy configuration, while show route advertising-protocol bgp <peer> focuses on routes being advertised to a specific BGP neighbor. Choosing the correct operational command is important when narrowing down whether a problem is related to interfaces, routing policy, or BGP peering.