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

 

Question 21. Which Junos OS component is primarily responsible for maintaining the routing tables and running routing protocols?

1. Switching Fabric
2. Interface ASIC
3. Routing Engine
4. Packet Forwarding Engine

Correct Answer: 3. Routing Engine

Explanation:
The Routing Engine (RE) is the control-plane component of a Juniper device. It runs the Junos OS control processes, maintains routing tables, executes routing protocols such as OSPF and BGP, and determines the appropriate forwarding information. The resulting forwarding information is then installed into the Packet Forwarding Engine (PFE), which handles high-speed packet forwarding. Keeping control-plane processing separate from forwarding allows the device to process routing information without requiring every packet to be handled by the RE. This architecture is fundamental to Junos-based platforms and helps provide predictable forwarding performance.

Question 22. Which BGP attribute is normally used to influence the preferred exit point from an autonomous system for outbound traffic?

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

Correct Answer: 1. 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 preferred. Because local preference is propagated through the AS, it can consistently influence the route selected by multiple internal BGP speakers. It is commonly configured through routing policy when an organization wants to prefer one external connection over another. In contrast, MED is generally used to influence how neighboring autonomous systems enter your network, while AS path length is commonly used as another BGP route-selection factor.

Question 23. What does the Junos commit confirmed command provide?

1. It copies the configuration to another device
2. It automatically rolls back the configuration if it is not confirmed within the specified time
3. It immediately reboots the Routing Engine
4. It permanently deletes the previous configuration

Correct Answer: 2. It automatically rolls back the configuration if it is not confirmed within the specified time

Explanation:
The commit confirmed command is particularly useful when making changes remotely. It activates the candidate configuration but starts a confirmation timer. If the administrator does not issue a regular commit before the timer expires, Junos automatically rolls the configuration back to the previous committed state. This mechanism helps prevent accidental loss of management connectivity caused by an incorrect configuration. It is commonly used when changing interfaces, routing policies, management access, or other settings that could potentially disconnect the administrator from the device.

Question 24. Which OSPF packet type is used to discover and maintain OSPF neighbors?

1. Link State Acknowledgment
2. Database Description
3. Link State Update
4. Hello

Correct Answer: 4. Hello

Explanation:
OSPF Hello packets are used to discover neighboring OSPF routers and maintain neighbor relationships. They are periodically transmitted through OSPF-enabled interfaces and contain information such as the router ID, area, timers, and other parameters required for establishing adjacency. If expected Hello packets are no longer received within the configured dead interval, the neighbor relationship can be removed. Other OSPF packet types serve different purposes: Database Description packets summarize link-state databases, Link State Updates carry LSAs, and Link State Acknowledgments confirm receipt of LSAs.

Question 25. What is the primary purpose of a routing policy in Junos OS?

1. To encrypt all routing protocol packets
2. To physically connect interfaces
3. To replace the forwarding engine
4. To control how routing information is accepted, rejected, modified, imported, or exported

Correct Answer: 4. To control how routing information is accepted, rejected, modified, imported, or exported

Explanation:
Junos routing policies provide granular control over routing information. Policies can match characteristics such as route prefixes, protocols, communities, AS paths, or other attributes and then perform actions such as accepting, rejecting, modifying, or setting route attributes. Policies are commonly applied during route import or export and are especially important for protocols such as BGP. For example, an administrator can use a policy to advertise only selected prefixes to a BGP neighbor or to assign a preferred local preference to routes learned from a particular peer.

Question 26. Which command displays a summary of BGP peer sessions and their current states?

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

Correct Answer: 2. show bgp summary

Explanation:
The show bgp summary command provides a concise overview of BGP sessions on a Junos device. It displays information such as configured BGP peers, peer addresses, autonomous system information, session state, and route counts. It is one of the most useful first commands when troubleshooting BGP because it quickly shows whether sessions are established or remain in states such as Active or Idle. More detailed BGP commands can then be used to inspect individual peers, received routes, advertised routes, or BGP attributes when additional troubleshooting information is required.

Question 27. In an MPLS network, what is the primary purpose of an LSP?

1. To provide Ethernet loop prevention
2. To assign IP addresses to interfaces
3. To replace all routing protocols
4. To provide a predefined label-switched path through the MPLS network

Correct Answer: 4. To provide a predefined label-switched path through the MPLS network

Explanation:
An MPLS Label-Switched Path (LSP) provides a path through an MPLS network along which packets can be forwarded using labels. Instead of relying solely on an IP lookup at every hop, MPLS routers use label information to determine the next forwarding action. Depending on the MPLS control mechanism, LSPs can be established using protocols such as LDP, RSVP-TE, or other technologies. LSPs form the foundation for many MPLS services, including Layer 3 VPNs and traffic-engineering applications. The ingress router typically imposes a label, intermediate routers switch labels, and the egress side removes the relevant label.

Question 28. Which BGP attribute represents the sequence of autonomous systems through which a route has passed?

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

Correct Answer: 1. AS path

Explanation:
The BGP AS path attribute records the sequence of autonomous systems through which a BGP route has passed. Each autonomous system typically adds its AS number when advertising a route to an external BGP neighbor. The AS path serves several purposes, including helping prevent routing loops and participating in BGP route selection. In many basic BGP decisions, a shorter AS path is preferred when other relevant factors are equal. Administrators can also manipulate AS path information through routing policies when implementing specific routing strategies or influencing traffic flows.

Question 29. Which Junos command is commonly used to view detailed information about a specific interface?

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

Correct Answer: 3. show interfaces

Explanation:
The show interfaces command displays operational information about interfaces on a Junos device. Depending on the command options, it can provide details such as interface status, physical and logical properties, packet statistics, errors, MTU, protocol state, and other operational information. This makes it useful for troubleshooting connectivity and interface-related problems. Administrators can also specify an individual interface to focus on a particular port. The show interfaces terse command provides a shorter summary, while the standard show interfaces command provides considerably more detailed information.

Question 30. What is the primary purpose of a route distinguisher in a BGP/MPLS Layer 3 VPN?

1. To determine the physical interface used for forwarding
2. To replace the route distinguisher
3. To encrypt VPN traffic
4. To make otherwise identical VPN routes globally unique

Correct Answer: 4. To make otherwise identical VPN routes globally unique

Explanation:
A route distinguisher (RD) is used in BGP/MPLS Layer 3 VPNs to make VPN routes unique within the BGP VPN routing system. Different customer VPNs may use the same IPv4 prefix, such as 10.1.1.0/24. The RD is combined with the IPv4 prefix to create a VPN-IPv4 route that can be distinguished from the same prefix belonging to another VPN. The RD itself does not determine whether a route is imported into a particular VRF. Route targets are used for that purpose. This distinction between RDs and route targets is important when troubleshooting MPLS VPNs.

Question 31. Which Junos feature allows an administrator to return the configuration to an earlier committed version?

1. refresh
2. rollback
3. clear
4. restart

Correct Answer: 2. rollback

Explanation:
The Junos rollback mechanism allows administrators to load a previous committed configuration into the candidate configuration. Junos maintains multiple previous configuration versions, making rollback useful when a recent configuration change causes an unexpected problem. After loading the desired previous configuration, the administrator can review it and commit it if appropriate. This is different from immediately rebooting the device or restarting a process. The rollback capability is an important part of Junos configuration management because it provides a controlled way to recover from configuration mistakes while preserving operational continuity.

Question 32. What is the main function of a route target in a Layer 3 VPN?

1. To replace the route distinguisher
2. To control VPN route import and export between VRFs
3. To determine MPLS label size
4. To uniquely identify a physical interface

Correct Answer: 2. To control VPN route import and export between VRFs

Explanation:
Route targets (RTs) are extended BGP communities used to control the import and export of VPN routes between VRFs. An export route target can be attached to routes leaving a VRF, while an import route target determines which VPN routes a VRF accepts. This mechanism allows service providers to define which customer sites can exchange routing information. Unlike the route distinguisher, which provides uniqueness to VPN routes, route targets express membership and route-sharing relationships. Correctly configuring RT import and export policies is therefore essential for controlling connectivity between sites in an MPLS Layer 3 VPN.

Question 33. Which protocol is commonly used as an Interior Gateway Protocol for exchanging routing information within an autonomous system?

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

Correct Answer: 2. OSPF

Explanation:
OSPF is an Interior Gateway Protocol (IGP) designed to exchange routing information within an 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 network design through areas, with Area 0 serving as the backbone area in a standard multi-area deployment. Other IGPs include IS-IS and RIP, while BGP is commonly used as an Exterior Gateway Protocol. Application protocols such as HTTP, FTP, and SMTP are not routing protocols and do not perform network route calculation.

Question 34. What does the show route forwarding-table command primarily help an administrator inspect?

1. The forwarding table used to determine packet forwarding actions
2. Candidate configuration differences
3. OSPF database contents
4. BGP neighbor authentication

Correct Answer: 1. The forwarding table used to determine packet forwarding actions

Explanation:
The forwarding table contains information used by the forwarding plane to determine how packets should be forwarded. The show route forwarding-table command helps administrators inspect this operational forwarding information. This is distinct from the routing table, which contains routes learned or calculated by routing protocols and other sources. A route may exist in the routing table but not necessarily be installed in the forwarding table if it is not selected or cannot be programmed. Comparing routing and forwarding information can therefore be useful when troubleshooting unexpected packet-forwarding behavior.

Question 35. What is the purpose of a firewall filter in Junos OS?

1. To create MPLS labels
2. To establish BGP sessions
3. To classify and control packets based on defined match conditions and actions
4. To calculate OSPF shortest paths

Correct Answer: 3. To classify and control packets based on defined match conditions and actions

Explanation:
A Junos firewall filter provides stateless packet filtering and control based on defined match conditions and actions. Match criteria can include source and destination addresses, protocols, ports, interface information, packet characteristics, and other supported fields. Actions can include accepting, discarding, rejecting, counting, logging, policing, or assigning forwarding-related characteristics depending on the platform and configuration. Firewall filters can be applied at appropriate interfaces or logical processing points. They are commonly used for traffic control and protection, including restricting unwanted traffic or protecting the device’s control plane.

Question 36. Which BGP attribute is generally intended to provide a neighboring autonomous system with information about the preferred entry point into your network?

1. Weight
2. MED
3. Local preference
4. Router ID

Correct Answer: 2. MED

Explanation:
The Multi-Exit Discriminator (MED) is a BGP attribute commonly used to influence which entry point a neighboring autonomous system should prefer when multiple connections exist between the same autonomous systems. A lower MED is generally preferred when comparing otherwise eligible routes from the same neighboring AS. MED is primarily an external BGP attribute used to provide guidance to a neighboring AS about how traffic should enter the advertising network. This differs from local preference, which is used within an autonomous system to influence outbound path selection and is normally preferred at a higher value.

Question 37. Which command is useful for viewing the active configuration hierarchy in Junos OS?

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

Correct Answer: 3. show configuration

Explanation:
The show configuration command displays the configuration currently loaded in the configuration database at the relevant configuration level. It is commonly used to review configured interfaces, protocols, policies, routing options, system settings, and other Junos configuration statements. When used from operational mode, it displays the committed configuration. Within configuration mode, administrators can use related commands to inspect the candidate configuration before committing changes. This separation between candidate and active configuration is a key feature of Junos and allows administrators to review changes before applying them to the running system.

Question 38. In an Ethernet network using LACP, what is the primary purpose of a Link Aggregation Group?

1. To encrypt Layer 2 traffic
2. To combine multiple physical links into one logical link
3. To replace IP routing
4. To assign BGP communities

Correct Answer: 2. To combine multiple physical links into one logical link

Explanation:
A Link Aggregation Group (LAG) combines multiple physical Ethernet interfaces into a single logical interface. LACP, the Link Aggregation Control Protocol, can dynamically negotiate and monitor member links so that compatible devices can form an aggregated connection. LAGs can provide increased aggregate bandwidth and redundancy because traffic can use multiple physical links. From a logical perspective, the collection is treated as one aggregated interface. LAG behavior, hashing, member-link status, and LACP state are important considerations when troubleshooting traffic distribution or connectivity across aggregated Ethernet links.

Question 39. Which OSPF area type is designed to reduce the amount of external routing information carried into the area?

1. Virtual link
2. Backbone area
3. Stub area
4. Transit area

Correct Answer: 3. Stub area

Explanation:
An OSPF stub area reduces the amount of external routing information that must be carried within the area. External routes are not normally advertised into a stub area as external LSAs; instead, a default route can be used to provide reachability toward destinations outside the area. This can reduce the size of the link-state database and routing information that routers within the area must process. OSPF defines several specialized area types with different restrictions and behaviors, so the exact handling of external and summary information depends on the selected area configuration.

Question 40. What is the primary role of the Packet Forwarding Engine in a Junos device?

1. Maintaining the master routing database
2. Performing high-speed packet forwarding using programmed forwarding information
3. Running BGP and OSPF processes
4. Managing the candidate configuration

Correct Answer: 2. Performing high-speed packet forwarding using programmed forwarding information

Explanation:
The Packet Forwarding Engine (PFE) is responsible for high-speed packet forwarding on Juniper devices. It uses forwarding information programmed by the control plane to determine how packets should be processed and sent toward their destinations. The Routing Engine performs control-plane functions such as running routing protocols and calculating routes, while the PFE handles the actual forwarding of transit traffic. This separation allows forwarding to occur efficiently without requiring the Routing Engine to process every packet individually. Understanding the distinction between the RE and PFE is essential for Junos architecture and troubleshooting.