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

 

Question 101: Which BGP attribute is commonly used to influence outbound traffic from an autonomous system?

1. MED
2. Local preference
3. Origin
4. AS path

Correct Answer: 2. Local preference

Explanation:
Local preference is a BGP path attribute used within an autonomous system to influence which exit path is selected for outbound traffic. A higher local preference is generally preferred over a lower value. Because local preference is propagated throughout an AS, it provides a consistent method for routers to select an exit point toward an external destination. Unlike MED, which is primarily used to suggest an entry point into an AS, local preference is intended to influence outbound path selection. It is therefore commonly configured through routing policies when an administrator wants to control which external path the network uses.

Question 102: Which IS-IS level is responsible for routing between different IS-IS areas?

1. Level 1
2. Level 0
3. Level 1-2 only within a LAN
4. Level 2

Correct Answer: 4. Level 2

Explanation:
In IS-IS, Level 2 routing is responsible for inter-area routing. Level 1 routers maintain routing information within their local area, while Level 2 routers form the backbone that connects different areas. A router can operate as Level 1, Level 2, or Level 1-2 depending on the network design. Level 1-2 routers can participate in both local-area and backbone routing. Understanding the distinction is important when troubleshooting IS-IS because a route that must travel between areas depends on Level 2 connectivity. Level 2 therefore performs a role broadly comparable to the backbone function in hierarchical routing designs.

Question 103: In an MPLS network, what does a label-switched router typically do when forwarding a labeled packet through the core?

1. Swaps the incoming MPLS label for another label
2. Assigns an IP address to the packet
3. Performs an IP longest-prefix lookup only
4. Removes the VLAN tag and creates an OSPF adjacency

Correct Answer: 1. Swaps the incoming MPLS label for another label

Explanation:
An MPLS Label-Switched Router (LSR) commonly forwards packets by performing a label swap. The router examines the incoming MPLS label, consults its label forwarding information, and replaces that label with the appropriate outgoing label before forwarding the packet. This allows packets to follow a predetermined label-switched path through the MPLS core without requiring every core router to perform a traditional IP routing lookup for the payload destination. Label operations can also include pushing or popping labels at network edges, depending on the MPLS service and forwarding stage. Label swapping is therefore a fundamental MPLS forwarding operation.

Question 104: Which BGP attribute is primarily associated with the path’s origin type?

1. Community
2. Local preference
3. Origin
4. Next hop

Correct Answer: 3. Origin

Explanation:
The BGP Origin attribute identifies how a route entered BGP. Its commonly encountered values indicate whether the route was originated through an IGP mechanism, through an EGP mechanism, or through redistribution or other means. Origin is considered during BGP path selection after several higher-priority attributes, including local preference and AS path length. The generally preferred order among origin types is IGP over EGP over incomplete. Although origin does not normally provide the primary mechanism for traffic engineering, it contributes to the overall BGP decision process when competing paths remain otherwise comparable.

Question 105: What is the primary purpose of a route target in a Layer 3 VPN?

1. To identify an OSPF area
2. To replace the MPLS transport label
3. To identify the physical interface carrying a VPN route
4. To control which VPN routes are imported or exported between VRF instances

Correct Answer: 4. To control which VPN routes are imported or exported between VRF instances

Explanation:
A route target is an extended BGP community used in MPLS Layer 3 VPNs to control the import and export of VPN routes. When a VPN route is advertised, route-target information can indicate which VRFs are eligible to import that route. Import and export policies determine how routes are exchanged between customer VPN instances. Route targets therefore provide the mechanism for controlling VPN route membership and connectivity. They are different from route distinguishers, which primarily make otherwise overlapping customer prefixes unique within the provider’s VPNv4 or VPNv6 routing infrastructure.

Question 106: Which Junos command is useful for viewing the configuration differences between the candidate configuration and the active configuration?

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

Correct Answer: 3. show | compare

Explanation:
The Junos show | compare command displays differences between the candidate configuration and the currently active configuration. It is particularly useful before committing changes because it allows an administrator to review exactly what has been modified. This can help identify unintended configuration changes and reduce the possibility of committing an incorrect configuration. The command is commonly used from configuration mode after making changes. Reviewing the comparison before a commit is an important operational practice, especially when working on production devices where an unexpected configuration change could affect routing, interfaces, security policies, or other services.

Question 107: Which technology provides a method for discovering directly connected neighboring devices at Layer 2?

1. LLDP
2. OSPF
3. LDP
4. BGP

Correct Answer: 1. LLDP

Explanation:
LLDP, or Link Layer Discovery Protocol, allows network devices to advertise identification and capability information to directly connected neighbors at Layer 2. On Junos devices, LLDP can help administrators identify which device is connected to a particular interface, along with information such as the remote system name and port. This makes LLDP useful for network discovery and troubleshooting physical connectivity. Unlike BGP and OSPF, which are routing protocols, LLDP does not establish IP routing relationships. LDP is associated with MPLS label distribution. LLDP is therefore commonly used to map physical and logical device relationships in an Ethernet network.

Question 108: In Junos, which component is primarily responsible for maintaining routing information and running routing protocols?

1. Firewall filter
2. Interface module
3. Routing Engine
4. Packet Forwarding Engine

Correct Answer: 3. Routing Engine

Explanation:
The Routing Engine (RE) is responsible for control-plane operations on a Junos device. It runs routing protocols such as BGP, OSPF, and IS-IS and maintains routing information. The RE also handles system management and participates in configuration and control functions. The Packet Forwarding Engine (PFE), by contrast, is responsible for forwarding packets according to the information programmed into its forwarding tables. Understanding the distinction between the RE and PFE is important for troubleshooting. A routing-protocol problem generally involves the control plane and RE, while packet-forwarding problems may involve the PFE or forwarding infrastructure.

Question 109: What does an MPLS Label Edge Router typically do when a packet enters an MPLS domain?

1. Removes all routing information
2. Adds an MPLS label to an IP packet
3. Creates an OSPF area
4. Converts BGP into IS-IS

Correct Answer: 2. Adds an MPLS label to an IP packet

Explanation:
A Label Edge Router (LER) operates at the boundary of an MPLS domain and can impose an MPLS label on an incoming packet. This process is commonly called label pushing. Once labeled, the packet can be forwarded through the MPLS core using label-switching operations. At the opposite edge of the MPLS domain, an LER can remove or otherwise process the label before forwarding the packet toward its destination. The LER therefore provides an important interface between conventional IP forwarding and MPLS forwarding. Core LSRs generally perform label operations such as swapping labels as packets traverse the MPLS network.

Question 110: Which BGP attribute is commonly used to provide information about the preferred entry point into an autonomous system?

1. Origin
2. MED
3. Cluster ID
4. Local preference

Correct Answer: 2. MED

Explanation:
The Multi-Exit Discriminator (MED) is a BGP attribute that can be used to influence which entry point another autonomous system selects when multiple links exist between the same autonomous systems. In common BGP decision processes, a lower MED is preferred when the relevant comparison is being made. MED is therefore often used to suggest an inbound path into an autonomous system. Local preference serves a different purpose: it influences outbound path selection within an autonomous system. MED should also not be confused with the BGP origin attribute or route-reflector cluster ID, both of which have different roles in BGP operation.

Question 111: Which Junos feature allows a configuration change to automatically roll back if it is not confirmed within a specified period?

1. Commit confirmed
2. Rescue configuration
3. Configuration archival
4. Commit synchronize

Correct Answer: 1. Commit confirmed

Explanation:
The Junos commit confirmed feature allows an administrator to commit a configuration temporarily while providing a confirmation period. If the administrator does not issue a regular commit before the confirmation timer expires, Junos automatically rolls the configuration back to the previous committed state. This feature is especially useful when making remote changes that could accidentally disrupt management connectivity. If a configuration change causes the administrator to lose access, the lack of confirmation allows the device to revert automatically. This provides a safety mechanism for potentially disruptive changes to interfaces, routing, security policies, or other critical configuration elements.

Question 112: Which IPv6 mechanism allows hosts to discover routers and resolve neighboring IPv6 link-layer addresses?

1. ICMP Redirect only
2. ARP
3. Neighbor Discovery Protocol
4. DHCPv4

Correct Answer: 3. Neighbor Discovery Protocol

Explanation:
IPv6 uses Neighbor Discovery Protocol (NDP), which is based on ICMPv6, for functions that include discovering neighboring devices, resolving link-layer addresses, discovering routers, and learning network prefixes. Unlike IPv4, IPv6 does not use ARP for address resolution. NDP uses messages such as Neighbor Solicitation, Neighbor Advertisement, Router Solicitation, and Router Advertisement. These mechanisms provide both host-to-host neighbor discovery and router discovery capabilities. Understanding NDP is important when troubleshooting IPv6 connectivity because failures involving neighbor resolution or router advertisements can prevent successful communication even when the IPv6 addresses themselves appear correctly configured.

Question 113: What is the purpose of a route reflector in an iBGP network?

1. To eliminate the need for MPLS labels
2. To reduce the requirement for a full mesh of iBGP sessions
3. To replace OSPF area borders
4. To assign VLAN IDs automatically

Correct Answer: 2. To reduce the requirement for a full mesh of iBGP sessions

Explanation:
A BGP route reflector allows selected iBGP routes to be reflected between clients, reducing the need for every iBGP router to establish a session with every other iBGP router. Without route reflection, traditional iBGP requires a full mesh because routes learned from one iBGP neighbor are not normally advertised to another iBGP neighbor. A route reflector changes this behavior by reflecting routes between configured clients. This improves scalability in larger autonomous systems. Route reflection is a BGP control-plane function and is independent of MPLS label distribution, VLAN assignment, or OSPF area hierarchy.

Question 114: Which Junos command can be used to display information about configured BGP neighbors and their session states?

1. show ldp neighbor
2. show route forwarding-table
3. show ospf database
4. show bgp summary

Correct Answer: 4. show bgp summary

Explanation:
The Junos show bgp summary command provides a concise overview of BGP sessions, including configured peers, autonomous system information, message counters, and session state or received-prefix information. It is commonly used as an initial troubleshooting command when verifying BGP operation. If a BGP session is not established, the summary can help identify whether the peer is in an active, idle, connect, or established state. More detailed commands can then be used to investigate a specific peer or route. The other commands listed are associated with OSPF, LDP, and packet forwarding rather than BGP session status.

Question 115: Which spanning-tree protocol is designed to provide faster convergence than traditional STP?

1. RSTP
2. VRRP
3. BGP
4. LDP

Correct Answer: 1. RSTP

Explanation:
Rapid Spanning Tree Protocol (RSTP) is designed to provide faster convergence than traditional Spanning Tree Protocol. It improves the process used to transition ports between forwarding and blocking-related states after topology changes. RSTP retains the fundamental purpose of preventing Layer 2 switching loops while improving convergence behavior. BGP and LDP are routing and label-distribution technologies, respectively, while VRRP provides first-hop gateway redundancy rather than loop prevention. RSTP is therefore relevant when a Layer 2 Ethernet network requires spanning-tree protection while also seeking faster recovery from topology changes.

Question 116: What is the primary function of a BGP community?

1. To replace the BGP next-hop attribute
2. To identify an OSPF area
3. To attach policy-related tags to routes
4. To assign an IP address to an interface

Correct Answer: 3. To attach policy-related tags to routes

Explanation:
BGP communities provide a way to attach tags to routes so that routing policies can identify and process groups of routes consistently. Administrators can use communities to mark routes according to their origin, intended treatment, customer, service, or other policy requirements. A routing policy can then match a community and perform an action such as modifying local preference, changing MED, controlling export, or setting another attribute. Communities therefore provide a flexible mechanism for implementing routing policy at scale. They do not assign interface addresses or identify OSPF areas, and they are not a replacement for the BGP next-hop attribute.

Question 117: Which Junos command displays the routing table for the default routing instance?

1. show route
2. show system users
3. show configuration routing-options
4. show interfaces terse

Correct Answer: 1. show route

Explanation:
The Junos show route command displays routes in the routing table, including information such as destination prefixes, next hops, protocol sources, route preferences, and active or inactive route status. When used without additional routing-instance arguments, it displays information associated with the default routing instance. This command is one of the most frequently used tools for troubleshooting routing behavior. Administrators can add filters or specify particular prefixes to narrow the output. Other commands provide interface, configuration, or hardware information, but show route directly examines the device’s routing information.

Question 118: In a Junos firewall filter, which section defines the conditions that must be matched before an action is applied?

1. protocols
2. from
3. then
4. routing-options

Correct Answer: 2. from

Explanation:
In a Junos firewall filter term, the from section defines the match conditions used to identify packets. Conditions can include source or destination addresses, protocols, ports, interface information, packet fields, and other supported criteria. If a packet satisfies the specified conditions, the action defined in the then section is applied. The then section can perform actions such as accepting, discarding, counting, logging, or applying other processing. Understanding the distinction between from and then is essential when building or troubleshooting firewall filters because the former identifies traffic while the latter determines what happens to matching traffic.

Question 119: Which high-availability technology allows a pair of Junos devices to provide a redundant default gateway for hosts?

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

Correct Answer: 2. VRRP

Explanation:
Virtual Router Redundancy Protocol (VRRP) allows multiple routers to participate in a redundant virtual gateway arrangement. Hosts can use a virtual IP address as their default gateway while multiple physical routers provide redundancy behind that address. One router operates as the active master for forwarding, while another can assume the role if the active device becomes unavailable. VRRP improves gateway availability without requiring hosts to change their configured default gateway. LACP is used for link aggregation, LLDP provides neighbor discovery, and BFD provides rapid detection of forwarding-path failures. These technologies therefore serve different purposes from first-hop gateway redundancy.

Question 120: Which Junos command is useful for checking the status of configured interfaces in a concise format?

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

Correct Answer: 3. show interfaces terse

Explanation:
The Junos show interfaces terse command provides a concise summary of interfaces and their operational and administrative states. It can quickly show whether interfaces are administratively enabled, operationally up or down, and whether logical units have been configured. This makes it useful during initial troubleshooting of connectivity and interface-state problems. For deeper troubleshooting, administrators can use more detailed interface commands that provide statistics, errors, configuration details, and hardware information. show route examines routing information, show bgp summary focuses on BGP sessions, and show system users provides information about logged-in users rather than interface status.