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

 

Question 121: Which BGP attribute is used to identify the next-hop router that should be used to reach a destination?

1. Origin
2. Community
3. Next hop
4. MED

Correct Answer: 3. Next hop

Explanation:
The BGP next-hop attribute identifies the IP address of the router that should be used as the next hop to reach a particular BGP destination. BGP uses this information when installing routes and determining how traffic should be forwarded toward the advertised prefix. The next-hop value can be modified through routing policy when network requirements call for a different forwarding path. It is distinct from attributes such as local preference, MED, and origin, which influence path selection in different ways. Proper next-hop reachability is essential for a BGP route to be usable, because a route with an unreachable next hop may not be installed as an active route.

Question 122: Which IS-IS packet type is used to establish and maintain an adjacency between neighboring routers?

1. IIH
2. LSP
3. SNP
4. LSU

Correct Answer: 1. IIH

Explanation:
IS-IS uses Intermediate System-to-Intermediate System Hello (IIH) packets to establish and maintain adjacencies between neighboring IS-IS routers. These packets allow routers to discover each other and exchange information necessary to form an adjacency. Once adjacencies are established, routers can exchange link-state information using Link State PDUs and synchronize databases using Sequence Number PDUs. IIH packets therefore serve a role similar to hello mechanisms found in other link-state routing protocols. When troubleshooting IS-IS neighbor relationships, checking interface configuration, authentication, addressing, and hello-related parameters can help determine why an expected adjacency is not forming.

Question 123: What is the primary purpose of a route distinguisher in an MPLS Layer 3 VPN?

1. To select the preferred outbound route
2. To make overlapping customer prefixes unique
3. To determine the MPLS transport label
4. To define an OSPF area

Correct Answer: 2. To make overlapping customer prefixes unique

Explanation:
A route distinguisher (RD) is used in MPLS Layer 3 VPNs to make customer routes unique within the provider’s VPN routing tables. Different customers can use the same IPv4 prefix, such as 10.1.1.0/24, without causing ambiguity because the RD creates a unique VPNv4 or VPNv6 route representation. The RD itself does not determine which VPNs are allowed to exchange routes; that function is associated with route targets. Similarly, the RD does not directly select the preferred path or define an OSPF area. Understanding the difference between route distinguishers and route targets is fundamental to MPLS VPN configuration and troubleshooting.

Question 124: Which BGP path attribute is generally preferred when comparing routes based on AS path length?

1. The route with the longer AS path
2. The route with the higher MED
3. The route with the shorter AS path
4. The route with the lower local preference

Correct Answer: 3. The route with the shorter AS path

Explanation:
AS path length is an important factor in BGP route selection. When the relevant higher-priority attributes do not determine a preferred route, BGP generally prefers the route with the shorter AS path. The AS path records the autonomous systems through which the route has passed. A shorter path is normally considered more desirable because it indicates fewer AS-level hops. However, AS path length is only one part of the complete BGP decision process. Attributes such as local preference, origin, MED, and other tie-breaking criteria can be evaluated before or after it depending on the implementation and configuration.

Question 125: Which Junos command can be used to examine the active configuration of the device?

1. show configuration
2. show route
3. show bgp summary
4. show interfaces terse

Correct Answer: 1. show configuration

Explanation:
The Junos show configuration command displays the active configuration in configuration mode. It allows administrators to review configured hierarchy levels, including interfaces, routing protocols, policy options, firewall filters, system settings, and other configuration statements. Reviewing the configuration is useful when troubleshooting because it allows the administrator to compare intended settings with what is actually configured. Commands such as show route and show interfaces terse display operational information rather than the complete active configuration. The show configuration command can also be used at specific hierarchy levels to examine only the relevant portion of the configuration.

Question 126: What is the primary purpose of Bidirectional Forwarding Detection (BFD)?

1. To distribute MPLS labels
2. To provide rapid detection of forwarding-path failures
3. To replace BGP
4. To assign IPv6 addresses

Correct Answer: 2. To provide rapid detection of forwarding-path failures

Explanation:
Bidirectional Forwarding Detection (BFD) provides rapid detection of failures in forwarding paths between network devices. It is designed to detect connectivity problems much faster than many routing protocols can detect them through their normal timers. BFD can be associated with protocols such as BGP, OSPF, and IS-IS so that a detected failure can trigger faster routing convergence. BFD does not replace routing protocols, distribute MPLS labels, or assign IP addresses. Its primary role is failure detection. Fast and reliable failure detection can be particularly valuable in networks where minimizing traffic disruption during link or path failures is important.

Question 127: In an MPLS network, what does the label operation “pop” mean?

1. Add a new MPLS label
2. Replace one label with another
3. Remove an MPLS label
4. Convert the label into an IP address

Correct Answer: 3. Remove an MPLS label

Explanation:
In MPLS forwarding, a pop operation removes an MPLS label from a packet. Label removal is commonly performed near the end of an MPLS forwarding path, allowing the packet to continue toward its destination without the particular MPLS label. This operation differs from pushing, which adds a label, and swapping, which replaces an incoming label with another outgoing label. Label operations are programmed according to the forwarding information associated with the MPLS service or path. Understanding push, swap, and pop operations is important when troubleshooting MPLS forwarding and verifying how labeled traffic moves through the network.

Question 128: Which Junos command can be used to display information about OSPF neighbors?

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

Correct Answer: 1. show ospf neighbor

Explanation:
The Junos show ospf neighbor command displays information about OSPF neighbor relationships. The output can help administrators determine whether expected adjacencies have formed and identify their current states. It can also provide information about the neighbor’s router ID, interface, address, and adjacency status. This command is especially useful when troubleshooting OSPF problems caused by mismatched areas, authentication, network types, timers, addressing, or interface configuration. The other commands serve different purposes: BGP summary examines BGP sessions, LDP neighbor examines MPLS label-distribution relationships, and the forwarding-table command focuses on packet forwarding information.

Question 129: Which Junos feature allows an administrator to return the configuration to a previously committed version?

1. commit synchronize
2. rollback
3. show | compare
4. load merge

Correct Answer: 2. rollback

Explanation:
The Junos rollback command allows an administrator to load a previously committed configuration version into the candidate configuration. This can be useful when a recent configuration change needs to be reversed or when an administrator wants to restore an earlier configuration state. After loading the desired rollback version, the administrator can review the resulting configuration and commit it if appropriate. Rollback is different from commit confirmed, which automatically returns to the previous committed state if a confirmation is not received. Using rollback carefully can provide a controlled method for recovering from configuration changes that produce unexpected results.

Question 130: Which BGP mechanism allows routes to be tagged so that routing policies can match and process them?

1. BGP community
2. AS path
3. Router ID
4. TCP port

Correct Answer: 1. BGP community

Explanation:
BGP communities provide tags that can be attached to routes and later matched by routing policies. This allows administrators to group routes according to characteristics such as customer, geographic location, service type, or desired routing treatment. Policies can then use those communities to modify attributes, control route advertisement, or apply other actions. Communities are especially useful in larger networks because they reduce the need to create complex policies based solely on individual prefixes. The AS path, router ID, and TCP port have different purposes in BGP operation and do not provide the same flexible route-tagging mechanism as communities.

Question 131: Which OSPF area type is designed to reduce the amount of external routing information carried inside the area?

1. Backbone area
2. Stub area
3. Transit area
4. Ethernet area

Correct Answer: 2. Stub area

Explanation:
An OSPF stub area is designed to reduce the amount of external routing information that must be maintained inside the area. Instead of receiving individual external routes, routers within a stub area can use a default route toward an Area Border Router (ABR) for destinations outside the area. This can reduce the size and complexity of the link-state database and routing table. Stub areas are therefore useful in network designs where detailed external route information is not required by every router. The backbone area has a different role, while terms such as Ethernet area and transit area do not describe standard OSPF area types.

Question 132: Which Junos command is commonly used to display the routing table summary?

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

Correct Answer: 1. show route summary

Explanation:
The Junos show route summary command provides a summarized view of routing-table information. It can show information such as the number of routes and their distribution by protocol or route type. This makes it useful for quickly assessing the overall state of the routing table without reviewing every individual route. If an administrator needs details about a specific prefix, commands such as show route <prefix> can provide more targeted information. show interfaces terse focuses on interfaces, while chassis and system-user commands provide hardware and user information. Routing summaries are useful during troubleshooting and capacity reviews.

Question 133: In an Ethernet network using LACP, what is the primary purpose of the protocol?

1. To exchange OSPF LSAs
2. To distribute BGP routes
3. To dynamically form and maintain link aggregation
4. To assign IP addresses

Correct Answer: 3. To dynamically form and maintain link aggregation

Explanation:
Link Aggregation Control Protocol (LACP) is used to negotiate and maintain a logical aggregated link composed of multiple physical Ethernet interfaces. Link aggregation can provide increased bandwidth and redundancy by allowing several physical links to operate as a single logical connection. LACP exchanges control information between participating devices and helps determine which links can become active members of the aggregated bundle. It is not a routing protocol and does not exchange OSPF or BGP routes. LACP also does not assign IP addresses. Proper configuration on both sides of the aggregated connection is important for successful operation.

Question 134: Which BGP attribute is normally preferred when its value is higher?

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

Correct Answer: 2. Local preference

Explanation:
Local preference is a BGP attribute for influencing outbound route selection within an autonomous system, and a higher value is generally preferred. Administrators can use routing policies to assign different local-preference values to routes learned from different external peers. This allows the network to select a preferred exit path for outbound traffic. Local preference is propagated through the AS, making it suitable for consistent internal decision-making. It should not be confused with MED, where a lower value is generally preferred during the relevant comparison. AS path is evaluated based on path length, while origin has its own ordered values.

Question 135: Which protocol is commonly used to exchange routing information between routers belonging to the same autonomous system?

1. OSPF
2. eBGP
3. FTP
4. HTTP

Correct Answer: 1. OSPF

Explanation:
OSPF is an Interior Gateway Protocol (IGP) commonly used to exchange routing information between routers within the same autonomous system. It is a link-state routing protocol that builds a link-state database and uses the Shortest Path First algorithm to calculate routes. OSPF supports hierarchical designs using areas, with Area 0 serving as the backbone. Other protocols can also be used as IGPs, including IS-IS, but OSPF is a widely deployed example. eBGP is primarily used to exchange routing information between autonomous systems, while FTP and HTTP are application-layer protocols unrelated to routing.

Question 136: What is the purpose of a forwarding class in Junos CoS?

1. To identify an OSPF neighbor
2. To determine how packets are grouped for forwarding treatment
3. To assign a BGP autonomous system number
4. To create an MPLS route distinguisher

Correct Answer: 2. To determine how packets are grouped for forwarding treatment

Explanation:
In Junos Class of Service (CoS), forwarding classes categorize packets so that different traffic types can receive different forwarding treatment. A forwarding class can be associated with a queue and scheduling behavior, allowing network administrators to provide differentiated treatment to traffic such as voice, video, control traffic, or ordinary data. Classification mechanisms determine which forwarding class a packet belongs to, while schedulers and related CoS features influence how traffic is transmitted. Forwarding classes are therefore part of traffic-management and quality-of-service design rather than routing-protocol operation, MPLS VPN identification, or autonomous-system numbering.

Question 137: Which Junos command can be used to inspect the configured routing policies?

1. show configuration policy-options
2. show interfaces terse
3. show chassis hardware
4. show system uptime

Correct Answer: 1. show configuration policy-options

Explanation:
The show configuration policy-options command displays the configured policy-options hierarchy, including routing policies, prefix lists, community definitions, and related policy objects. This is useful when troubleshooting route import, export, filtering, or attribute manipulation. Routing policies determine how routes are accepted, modified, or advertised, so examining the configured policy statements can help identify unexpected routing behavior. The interface, chassis, and system commands provide different types of operational information. Reviewing policy configuration together with route and protocol outputs can help administrators determine whether a routing policy is responsible for a particular route-selection or advertisement result.

Question 138: Which IPv6 routing protocol is specifically designed as an extension of OSPF for IPv6 networks?

1. RIP
2. OSPFv3
3. LACP
4. VRRP

Correct Answer: 2. OSPFv3

Explanation:
OSPFv3 is the version of OSPF designed to support IPv6 routing. It retains the fundamental link-state architecture of OSPF while adapting protocol operation to IPv6. OSPFv3 routers establish adjacencies, exchange link-state information, and calculate shortest paths within an area. IPv6 addressing and neighbor discovery are handled differently from IPv4, but OSPFv3 provides the routing functionality needed to exchange IPv6 reachability information. RIP, LACP, and VRRP have different purposes. OSPFv3 is therefore the appropriate protocol when a Junos network requires dynamic link-state routing for IPv6 destinations.

Question 139: What does a route policy’s export function generally control?

1. Which routes are advertised from a routing table or protocol to another routing domain or peer
2. Which physical interface receives power
3. Which OSPF router becomes the DR
4. Which MPLS label is physically stored in memory

Correct Answer: 1. Which routes are advertised from a routing table or protocol to another routing domain or peer

Explanation:
An export routing policy controls which routes are exported or advertised from a routing table or routing protocol toward another routing domain, protocol, or peer. Export policies can filter routes and modify attributes before advertisement. For example, a BGP export policy can determine which locally learned or locally generated routes are sent to a particular BGP neighbor. This provides administrators with control over route advertisement and helps prevent unintended prefixes from being propagated. Export policies are distinct from import policies, which control how routes received from another source are accepted or modified before being installed or used.

Question 140: Which Junos command can be used to verify the hardware components detected by the device?

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

Correct Answer: 4. show chassis hardware

Explanation:
The Junos show chassis hardware command displays information about hardware components detected by the device. Depending on the platform, the output can include chassis information, Routing Engines, line cards, modules, and other installed hardware components. This command is useful when verifying the physical configuration of a Junos device or troubleshooting hardware-related issues. It differs from show interfaces terse, which focuses on interface status, and show route, which displays routing information. Hardware verification can be especially useful after installing or replacing components to confirm that the device recognizes the expected hardware.