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

 

Question 201: Which BGP attribute is used to identify the sequence of autonomous systems a route has traversed?

1. Local Preference
2. MED
3. AS Path
4. Originator ID

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 attribute used during BGP path selection and also helps prevent routing loops. When a BGP router advertises a route to an external peer, its own autonomous system number is normally added to the AS Path. A route containing an already-known local AS can therefore be rejected as a potential loop. AS Path length is also commonly considered when comparing otherwise suitable routes. Local Preference is used primarily for outbound path selection within an AS, while MED provides information about preferred entry points into an AS.

Question 202: What happens when a BGP route is assigned a higher Local Preference value than another otherwise comparable route?

1. The higher Local Preference route is generally preferred for outbound traffic
2. The route is automatically withdrawn
3. The route is preferred only for inbound traffic
4. The route is converted into an OSPF route

Correct Answer: 1. The higher Local Preference route is generally preferred for outbound traffic

Explanation:
Local Preference is a BGP attribute used within an autonomous system to influence which exit path should be selected for outbound traffic. When comparable BGP routes are evaluated, a higher Local Preference value is generally preferred. Because Local Preference is distributed through iBGP, it can influence path selection across multiple routers within the same AS. It is therefore commonly used to identify a preferred exit from the autonomous system. This differs from MED, which is generally used to communicate a preferred entry point into an AS. Local Preference is not intended to directly control how an external AS sends traffic toward the local network.

Question 203: Which BGP community is commonly used to prevent a route from being advertised outside the local autonomous system while still allowing internal propagation?

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

Correct Answer: 2. NO_EXPORT

Explanation:
The well-known BGP community NO_EXPORT indicates that a route should not be advertised outside the local autonomous system or applicable confederation boundary. The route can still be propagated internally according to the network’s policies. This differs from NO_ADVERTISE, which is more restrictive and indicates that the route should not be advertised to any other BGP peer. Communities provide a flexible way to attach policy information to routes. Network administrators can then use routing policies to control route advertisement, acceptance, or other behavior based on those community values. Correctly distinguishing NO_EXPORT from NO_ADVERTISE is important when troubleshooting BGP route propagation.

Question 204: Which BGP attribute is primarily used to communicate a preferred entry point into an autonomous system?

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

Correct Answer: 4. MED

Explanation:
The Multi-Exit Discriminator (MED) is a BGP attribute commonly used to indicate a preferred entry point into an autonomous system when multiple links connect neighboring autonomous systems. A lower MED is generally preferred when comparing otherwise appropriate routes from the same neighboring AS. MED is therefore useful for influencing inbound traffic decisions made by a neighboring autonomous system. It differs from Local Preference, which is primarily used inside an autonomous system to influence outbound traffic. The effectiveness of MED depends on BGP policy and the participating network design, so administrators should not assume that simply setting a MED value guarantees a particular inbound traffic pattern.

Question 205: In Junos OS, which command displays the current candidate configuration differences compared with the active configuration?

1. show | compare
2. show route
3. show interfaces terse
4. commit check

Correct Answer: 1. show | compare

Explanation:
The Junos command show | compare is used from configuration mode to display differences between the candidate configuration and the currently active configuration. This is useful for reviewing pending changes before committing them. Administrators can verify that the intended statements have been added, modified, or deleted and can identify unexpected changes before they affect the device. commit check performs configuration validation but does not provide the same change comparison output. show route displays routing information, while show interfaces terse provides interface status. Reviewing configuration differences is an important step in controlled Junos configuration management.

Question 206: Which protocol is commonly used to provide rapid failure detection for routing protocols such as OSPF and BGP?

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

Correct Answer: 3. BFD

Explanation:
Bidirectional Forwarding Detection (BFD) provides rapid detection of failures between neighboring devices. It can work with routing protocols such as OSPF, IS-IS, and BGP to allow those protocols to react more quickly than they might using their normal protocol timers. BFD establishes a session and exchanges control packets at configured intervals. If the expected packets stop arriving, the failure can be detected quickly. LLDP is used primarily for neighbor discovery, LACP manages link aggregation, and DHCP provides address configuration. BFD is particularly useful in networks where fast convergence is important and normal routing-protocol failure detection would be too slow.

Question 207: In OSPF, which area type normally connects non-backbone areas to the OSPF backbone?

1. Stub area
2. Area 0
3. NSSA
4. Totally stubby area

Correct Answer: 2. Area 0

Explanation:
OSPF Area 0 is the backbone area and provides the central interconnection point for other OSPF areas. In a conventional hierarchical OSPF design, non-backbone areas connect to Area 0 through Area Border Routers. This structure helps limit the amount of link-state information that must be maintained within each area and supports scalable routing. Stub areas and NSSAs modify the types of external routes that can be advertised or received, but they do not replace the role of the backbone. Proper Area 0 connectivity is therefore important when designing and troubleshooting multi-area OSPF networks.

Question 208: Which Junos command is commonly used to inspect OSPF neighbor adjacencies?

1. show bgp summary
2. show ldp neighbor
3. show ospf neighbor
4. show route advertising-protocol bgp

Correct Answer: 3. show ospf neighbor

Explanation:
The Junos command show ospf neighbor displays information about OSPF neighbors and their adjacency states. It is useful when determining whether expected OSPF adjacencies have formed and whether neighbors have reached the appropriate state. The output can help identify issues involving interface participation, authentication, area configuration, timers, or network connectivity. show bgp summary is used for BGP sessions, while show ldp neighbor displays LDP neighbor information. When troubleshooting OSPF, checking the neighbor state is an important first step before examining the detailed OSPF database or routing table.

Question 209: What is the main purpose of a route distinguisher in an MPLS Layer 3 VPN?

1. To encrypt VPN traffic
2. To determine which VRFs import a route
3. To make overlapping customer prefixes unique
4. To select the MPLS transport label

Correct Answer: 3. To make overlapping customer prefixes unique

Explanation:
A Route Distinguisher (RD) is used in MPLS Layer 3 VPNs to make otherwise identical customer prefixes unique within the provider’s VPN routing environment. Multiple customers may independently use the same private address space, such as 192.168.1.0/24. By associating each prefix with a distinct RD, the resulting VPN-IPv4 routes can be differentiated. The RD does not determine which VRFs receive the route; that function is handled by Route Targets. Similarly, an RD does not provide encryption and is not itself the MPLS transport label. Understanding the separate roles of RD and RT is fundamental to MPLS VPN troubleshooting.

Question 210: Which Junos command displays the forwarding table used by the Packet Forwarding Engine?

1. show route
2. show interfaces terse
3. show bgp summary
4. show route forwarding-table

Correct Answer: 4. show route forwarding-table

Explanation:
The Junos command show route forwarding-table displays information about the forwarding table used for packet forwarding. The routing table contains routes learned and selected by the control plane, while the forwarding table contains the information used by the forwarding plane to make packet-forwarding decisions. Comparing routing and forwarding information can therefore be useful when troubleshooting situations where a route appears correct in the routing table but traffic does not follow the expected path. The Packet Forwarding Engine uses the forwarding information to process packets at high speed. This command is especially useful for deeper forwarding-plane troubleshooting.

Question 211: Which IS-IS level is responsible for routing within an individual IS-IS area?

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

Correct Answer: 1. Level 1

Explanation:
IS-IS Level 1 routing is primarily responsible for routing within an individual IS-IS area. Level 1 routers maintain information about destinations inside their own area and use Level 2 connectivity for reaching destinations outside the local area. Level 2 routing forms the inter-area backbone. Routers operating as Level 1-2 can participate in both levels and provide connectivity between the local area and the broader IS-IS domain. This hierarchical design allows IS-IS to scale by limiting the detailed topology information that individual Level 1 routers need to maintain about other areas.

Question 212: Which protocol is used to discover directly connected network devices and advertise information such as system identity and interface details?

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

Correct Answer: 2. LLDP

Explanation:
Link Layer Discovery Protocol (LLDP) allows directly connected network devices to exchange information about themselves. This can include system identity, port information, capabilities, and other management-related details. LLDP is useful for network discovery and troubleshooting because administrators can identify which device is connected to a particular interface without relying solely on physical documentation. RSTP is used to prevent Layer 2 loops, BFD provides rapid failure detection, and VRRP provides first-hop gateway redundancy. LLDP operates at the data-link layer and is particularly useful in environments containing equipment from multiple vendors.

Question 213: In LACP, what is the purpose of bundling multiple physical links into one logical interface?

1. To increase aggregate bandwidth and provide link redundancy
2. To create an OSPF area
3. To replace IP routing
4. To assign MPLS labels

Correct Answer: 1. To increase aggregate bandwidth and provide link redundancy

Explanation:
Link Aggregation Control Protocol (LACP) allows multiple physical Ethernet links to operate together as a logical aggregated interface. This can provide increased aggregate bandwidth while also offering redundancy if one of the member links fails. Traffic can be distributed across available member links according to the device’s hashing and load-balancing behavior. LACP does not replace IP routing or create OSPF areas. It also does not assign MPLS labels. Aggregated interfaces are commonly used between switches, routers, servers, and other network devices where both capacity and resiliency are important.

Question 214: Which Junos configuration statement is used to define actions that should be taken when a routing policy term matches?

1. from
2. match
3. then
4. protocol

Correct Answer: 3. then

Explanation:
In a Junos routing policy term, the from section specifies the conditions used to match routes, while the then section defines the actions to take when those conditions are satisfied. Actions can include accepting or rejecting a route, modifying attributes, adding communities, changing Local Preference, or performing other supported policy operations. Understanding this distinction is important when troubleshooting route import and export policies. A policy can contain multiple terms, and the order and behavior of those terms can affect the final result. The then statement therefore represents the action portion of a routing policy term.

Question 215: What is the primary function of VRRP in an IP network?

1. To provide redundant default-gateway functionality
2. To exchange BGP routes
3. To establish MPLS LSPs
4. To prevent Layer 2 loops

Correct Answer: 1. To provide redundant default-gateway functionality

Explanation:
Virtual Router Redundancy Protocol (VRRP) provides first-hop gateway redundancy by allowing multiple routers to participate in a virtual router group. Hosts can use the virtual IP address as their default gateway rather than depending on a single physical router. One router operates as the active or master device while another can assume responsibility if the active device becomes unavailable. This improves gateway availability without requiring hosts to change their configured default gateway. VRRP is unrelated to BGP route exchange, MPLS LSP signaling, or Layer 2 loop prevention. It is specifically designed to provide resilient first-hop routing.

Question 216: Which Junos command can be used to verify the configuration before committing it?

1. rollback 1
2. commit check
3. show route
4. request system reboot

Correct Answer: 2. commit check

Explanation:
The Junos commit check command validates the candidate configuration without actually activating the changes. It can identify configuration syntax errors, missing required statements, or other validation problems before a normal commit is performed. This provides an additional safety step when making configuration changes. rollback is used to load a previous configuration, while show route displays routing information and does not validate the candidate configuration. Performing a configuration check before committing can help reduce the risk of activating an invalid configuration, especially when changes affect critical routing, interface, or security settings.

Question 217: Which OSPF packet type is used to request specific link-state information from a neighboring router?

1. Database Description
2. Link-State Update
3. Link-State Acknowledgment
4. Link-State Request

Correct Answer: 4. Link-State Request

Explanation:
The OSPF Link-State Request (LSR) packet is used when a router needs specific link-state information from a neighbor. During database synchronization, routers exchange information about the link-state database and can request missing or more recent LSAs using LSR packets. Link-State Update packets carry LSAs, while Link-State Acknowledgment packets confirm receipt of LSAs. Database Description packets provide summaries of the contents of a router’s link-state database during adjacency establishment. Understanding these packet types can help diagnose OSPF adjacency and database synchronization problems.

Question 218: Which Junos command is useful for examining the configuration of routing policies?

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

Correct Answer: 1. show configuration policy-options

Explanation:
The Junos command show configuration policy-options displays the configured routing policies and related policy objects under the policy-options hierarchy. This is useful when troubleshooting route import and export behavior, BGP policy, community definitions, prefix lists, and related routing-policy components. Examining the policy configuration can help determine whether the intended match conditions and actions are actually present. Other commands provide different information: show chassis hardware focuses on hardware inventory, show interfaces terse provides interface status, and show route forwarding-table displays forwarding information. Policy inspection is an important part of routing troubleshooting.

Question 219: In an EVPN-VXLAN environment, what is VXLAN primarily used to provide?

1. A Layer 2 overlay carried across an IP underlay
2. BGP authentication
3. Physical link aggregation
4. OSPF neighbor discovery

Correct Answer: 1. A Layer 2 overlay carried across an IP underlay

Explanation:
VXLAN provides an overlay mechanism that can extend Layer 2 network segments across a Layer 3 IP underlay. It encapsulates Ethernet frames inside UDP/IP packets, allowing geographically distributed endpoints or virtual networks to communicate across an IP-based transport network. In EVPN-VXLAN designs, EVPN commonly provides the control-plane mechanisms for learning and advertising endpoint and MAC/IP reachability information. VXLAN itself is therefore primarily associated with the data-plane encapsulation of the overlay. It does not perform physical link aggregation, BGP authentication, or OSPF neighbor discovery.

Question 220: Which Junos operational command provides a concise summary of interface administrative and operational states?

1. show route summary
2. show bgp summary
3. show interfaces terse
4. show ospf neighbor

Correct Answer: 3. show interfaces terse

Explanation:
The Junos command show interfaces terse provides a concise summary of interfaces and their administrative and operational states. It is commonly used as a quick troubleshooting command to determine whether interfaces are configured, enabled, and operational. The output can also provide basic addressing information depending on the interface and platform. More detailed interface information can be obtained with commands such as show interfaces when deeper troubleshooting is required. The other commands focus on routing-table summaries, BGP sessions, or OSPF neighbors. Starting with a concise interface overview is often useful when diagnosing connectivity problems.