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

 

Question 361. Which BGP attribute is commonly used to influence the preferred exit point from an autonomous system?

1. MED
2. AS Path
3. Local Preference
4. Origin

Correct Answer: 3. Local Preference

Explanation:
BGP Local Preference is used within an autonomous system to influence which exit point should be preferred for outbound traffic. A higher Local Preference value is generally preferred, allowing network administrators to establish a preferred external path. Because Local Preference is propagated through iBGP, routers within the same autonomous system can make consistent outbound routing decisions. MED serves a different purpose by influencing how a neighboring AS may select an entry point, while AS Path records autonomous systems traversed by a route. Origin identifies how a route entered BGP. Local Preference is therefore a key tool for controlling outbound path selection.

Question 362. Which BGP attribute is used to prevent a route from being accepted if the local AS number appears in the path?

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

Correct Answer: 1. AS Path

Explanation:
The AS Path attribute contains the sequence of autonomous systems through which a BGP route advertisement has passed. When a BGP router receives a route whose AS Path contains its own autonomous system number, the router can recognize the advertisement as a potential routing loop and reject it. This makes AS Path a fundamental loop-prevention mechanism in inter-domain BGP. Local Preference controls outbound path preference, MED can influence inbound path selection by a neighboring AS, and Next Hop identifies the forwarding next hop. AS Path therefore has both path-selection and loop-prevention significance.

Question 363. Which BGP community prevents a route from being advertised to any other BGP peer?

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

Correct Answer: 4. NO_ADVERTISE

Explanation:
The well-known NO_ADVERTISE community instructs a BGP speaker not to advertise the associated route to any other BGP peer. This is more restrictive than NO_EXPORT, which generally prevents advertisement outside the local autonomous system or applicable confederation. The INTERNET community permits normal advertisement behavior, while NOPEER can restrict advertisement to peer relationships. BGP communities provide a flexible way to control route propagation through policy without changing the underlying topology. Correctly distinguishing these communities is important when troubleshooting unexpected BGP route advertisements.

Question 364. What is the main purpose of BGP route reflection?

1. To replace the IGP
2. To reduce the need for a full iBGP mesh
3. To encrypt BGP sessions
4. To distribute MPLS labels

Correct Answer: 2. To reduce the need for a full iBGP mesh

Explanation:
BGP route reflection provides a scalable alternative to requiring every iBGP router to maintain a direct session with every other iBGP router. A route reflector receives routes from its clients and reflects eligible routes to other clients and peers according to BGP rules. This reduces the number of iBGP sessions needed in a large autonomous system. Route reflection does not replace the underlying IGP, encrypt BGP traffic, or distribute MPLS labels. Additional mechanisms such as Originator ID and Cluster List help prevent routing loops within route-reflector topologies.

Question 365. Which IS-IS level primarily provides routing within a single IS-IS area?

1. Level 2
2. Level 1
3. Level 1-2 only
4. Level 3

Correct Answer: 4. Level 1

Explanation:
IS-IS Level 1 routing is primarily responsible for routing within an individual IS-IS area. Level 2 provides the backbone function that connects different areas. A router configured as Level 1-2 can participate in both intra-area and inter-area routing. IS-IS does not define Level 3 as another routing hierarchy equivalent to Levels 1 and 2. Understanding the distinction is important when troubleshooting why a route is available inside an area but requires Level 2 connectivity to reach another area.

Question 366. What is the role of the IS-IS Designated Intermediate System on a broadcast network?

1. It represents the LAN through a pseudonode in the link-state database
2. It assigns IP addresses to IS-IS routers
3. It distributes BGP communities
4. It acts as the only Layer 3 gateway

Correct Answer: 1. It represents the LAN through a pseudonode in the link-state database

Explanation:
The IS-IS Designated Intermediate System, or DIS, provides an efficient representation of a broadcast LAN in the IS-IS link-state database. The DIS generates a pseudonode LSP representing the shared LAN connectivity between participating routers. This reduces the complexity that would result from representing every possible relationship individually. The DIS does not assign IP addresses, distribute BGP communities, or serve as the only Layer 3 gateway. Its primary role is related to efficient link-state representation and database synchronization on multiaccess networks.

Question 367. Which IS-IS PDU is used to summarize the contents of a router’s link-state database?

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

Correct Answer: 2. PSNP

Explanation:
A CSNP, rather than a PSNP, provides a summary of the contents of an IS-IS link-state database. CSNPs allow routers, particularly on broadcast networks, to compare their known LSP information and identify missing or outdated entries. PSNPs have a more focused purpose: they can request or acknowledge specific LSPs. IIHs establish and maintain neighbor adjacencies, while LSPs carry the actual link-state information. Therefore, when examining IS-IS database synchronization, it is important to distinguish the broad summary function of CSNPs from the specific LSP request or acknowledgment function of PSNPs.

Question 368. Which MPLS operation removes the top label from a packet?

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

Correct Answer: 3. Pop

Explanation:
The MPLS pop operation removes the top label from an MPLS packet. Label removal can occur at an egress router or at the penultimate hop when Penultimate Hop Popping is used. A swap operation replaces an incoming label with an outgoing label, while push adds a new label to the packet. Classification is not one of the basic MPLS label operations. Understanding these operations helps engineers interpret MPLS forwarding behavior and troubleshoot whether labels are being imposed, exchanged, or removed at the expected points along a label-switched path.

Question 369. Which component typically performs label swapping inside the MPLS provider core?

1. Label Switching Router
2. Route Reflector
3. DHCP Server
4. VRF

Correct Answer: 1. Label Switching Router

Explanation:
A Label Switching Router, or LSR, performs label-based forwarding within an MPLS network. When a labeled packet reaches a transit LSR, the router examines the incoming label, determines the appropriate forwarding action, and commonly swaps it for the next label in the LSP. Edge routers have additional responsibilities when traffic enters or exits the MPLS domain. A Route Reflector handles BGP scalability, a DHCP server provides address configuration, and a VRF provides routing isolation. The LSR is therefore the primary device responsible for label switching in the MPLS core.

Question 370. What is the purpose of LDP in an MPLS network?

1. To elect an OSPF DR
2. To distribute label bindings between LDP peers
3. To assign VPN Route Targets
4. To provide Ethernet loop prevention

Correct Answer: 4. To distribute label bindings between LDP peers

Explanation:
Label Distribution Protocol, or LDP, distributes MPLS label bindings between participating routers. These bindings associate labels with forwarding equivalence classes and allow routers to establish label-switched forwarding paths through the network. LDP is a control-plane protocol specifically associated with MPLS label distribution. It does not elect OSPF designated routers, assign VPN Route Targets, or provide Ethernet loop prevention. When troubleshooting an LDP-based MPLS network, engineers can examine neighbor sessions and label information to determine whether the control plane has successfully established the required label bindings.

Question 371. What does an MPLS ingress edge router normally do to an IP packet entering an MPLS LSP?

1. Removes the IP header
2. Adds an MPLS label
3. Removes the MPLS label
4. Changes the OSPF area

Correct Answer: 2. Adds an MPLS label

Explanation:
An MPLS ingress Label Edge Router normally classifies an incoming IP packet into a forwarding equivalence class and imposes an MPLS label before forwarding it into the MPLS domain. The label allows subsequent transit routers to forward the packet using label-based operations. Removing labels is associated with pop behavior, while changing OSPF areas is unrelated to MPLS label imposition. The ingress edge router therefore provides the transition from IP-based forwarding into the label-switched portion of the network.

Question 372. In an MPLS Layer 3 VPN, what does a Route Target primarily control?

1. Physical interface speed
2. OSPF router ID selection
3. VPN route import and export
4. MPLS label swapping

Correct Answer: 3. VPN route import and export

Explanation:
Route Targets are BGP extended communities used to control the import and export of VPN routes between provider-edge routers and VRFs. An export Route Target can be attached to routes leaving a VRF, while import configuration determines which VPN routes are accepted into a VRF. This mechanism allows providers to define which customer sites should communicate with one another. Route Targets do not determine physical interface speed, OSPF router IDs, or MPLS label-swapping operations. Route Target policy is therefore a key component of MPLS Layer 3 VPN route distribution.

Question 373. Which Junos command displays a concise summary of routing-table statistics?

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

Correct Answer: 4. show route summary

Explanation:
The show route summary command provides a summary of routing-table information, including useful statistics about route counts and routing-table contents. It is helpful when quickly assessing the scale and state of the routing information on a Junos device. show interfaces terse focuses on interface status, show chassis hardware displays hardware inventory, and show bgp summary provides BGP session and route-related information. A routing summary is particularly useful during troubleshooting when an engineer needs to determine whether routes exist and whether the routing table has an unexpected number of entries.

Question 374. Which Junos command displays the configured routing policies under policy-options?

1. show route
2. show configuration policy-options
3. show interfaces
4. show chassis hardware

Correct Answer: 2. show configuration policy-options

Explanation:
The show configuration policy-options command displays configuration statements under the Junos policy-options hierarchy. This hierarchy commonly contains routing policies, prefix lists, communities, AS path definitions, and other policy-related objects. Reviewing this configuration is useful when troubleshooting route filtering, import and export policies, and BGP attribute manipulation. The other commands focus on operational routing, interface information, or hardware inventory. Using the correct hierarchy-specific command helps distinguish what has been configured from what is currently occurring in the operational routing state.

Question 375. What is the main purpose of BFD on a Junos device?

1. To provide rapid detection of forwarding-path failures
2. To assign IP addresses
3. To distribute BGP communities
4. To create VLANs

Correct Answer: 1. To provide rapid detection of forwarding-path failures

Explanation:
Bidirectional Forwarding Detection, or BFD, provides rapid detection of forwarding-path failures between network devices. It can operate alongside routing protocols so that a routing session can react more quickly to a failure than relying solely on normal protocol timers. BFD is particularly useful on critical links where fast failure detection is important. It does not assign IP addresses, distribute BGP communities, or create VLANs. The routing protocol and BFD work together so that BFD can signal a detected failure and allow the associated protocol to take appropriate action.

Question 376. Which Layer 2 protocol helps prevent switching loops while providing faster convergence than traditional STP?

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

Correct Answer: 3. RSTP

Explanation:
Rapid Spanning Tree Protocol, or RSTP, provides Layer 2 loop prevention while offering faster convergence than traditional Spanning Tree Protocol. RSTP rapidly transitions appropriate ports through its state model and can react more quickly to topology changes. LACP is used for link aggregation, LLDP discovers directly connected devices, and BFD provides rapid failure detection at the forwarding/control-plane interaction level. RSTP is therefore the protocol specifically designed to prevent Ethernet switching loops while improving convergence behavior compared with classic STP.

Question 377. Which protocol dynamically negotiates Ethernet link aggregation between compatible devices?

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

Correct Answer: 2. LACP

Explanation:
The Link Aggregation Control Protocol, or LACP, dynamically negotiates and maintains an aggregated Ethernet bundle between compatible devices. Multiple physical interfaces can operate as a single logical link, providing increased aggregate capacity and redundancy. LACP helps determine which links can participate in the aggregation and reacts when individual members become unavailable. LLDP provides neighbor discovery, RSTP prevents Layer 2 loops, and OSPF is a Layer 3 routing protocol. LACP is therefore the appropriate protocol when the goal is to dynamically form and maintain an Ethernet link aggregation group.

Question 378. Which Junos mechanism provides automatic rollback when a remote configuration change is not confirmed?

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

Correct Answer: 4. commit confirmed

Explanation:
Junos commit confirmed allows an administrator to commit a configuration temporarily while requiring confirmation within a specified interval. If the change is not confirmed before the timer expires, the device automatically rolls back to the previous committed configuration. This is particularly useful when making changes remotely because an incorrect configuration could otherwise cause loss of management access. commit check validates a configuration without activating it, while show | compare displays differences and show configuration displays configuration data. The timed rollback behavior is specifically provided by commit confirmed.

Question 379. Which Junos command can be used to verify the chassis hardware components installed in a device?

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

Correct Answer: 3. show chassis hardware

Explanation:
The show chassis hardware command provides information about the hardware components installed in a Junos device. Depending on the platform, the output can include the chassis, Routing Engines, line cards, interface modules, and other hardware components. This command is useful for inventory verification and hardware troubleshooting. show route summary provides routing statistics, show bgp summary provides BGP session information, and show interfaces terse provides concise interface status. Hardware inventory should therefore be checked with the chassis hardware command.

Question 380. Which Junos command provides a concise view of physical and logical interface states?

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

Correct Answer: 1. show interfaces terse

Explanation:
The show interfaces terse command provides a concise operational view of physical interfaces and their logical units. It is commonly used to quickly determine whether interfaces are administratively and operationally up or down and to review associated addressing information. The command is especially useful as an initial troubleshooting step before using more detailed interface commands. show route and show route summary focus on routing information, while show chassis hardware provides hardware inventory. For a quick interface-status overview, show interfaces terse is the appropriate Junos command.