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Question 81

Which protocol calculates shortest paths from topology information?

1. OSPF
2. BGP
3. LACP
4. SNMP

Correct Answer: 1

Explanation:

OSPF calculates shortest paths by using its link-state database to understand the network topology. Each participating router exchanges link-state information, builds a synchronized database, and then runs the Shortest Path First algorithm to determine appropriate paths toward destinations. This approach allows OSPF to make routing decisions based on the complete topology information available within its area. BGP uses path attributes for interdomain route selection, LACP manages aggregated Ethernet links, and SNMP provides network-management capabilities. Therefore, OSPF is the correct answer because it uses topology information and SPF calculations to determine shortest available paths.

Question 82

Which BGP attribute prefers routes learned from internal peers?

1. MED
2. Local Preference
3. Origin
4. Community

Correct Answer: 2

Explanation:

Local Preference is a BGP attribute used within an autonomous system to influence which exit path should be preferred for outbound traffic. A higher Local Preference value is generally preferred over a lower value. This attribute is distributed through iBGP and allows administrators to establish consistent outbound routing policies across the autonomous system. MED serves a different purpose by providing information about preferred entry points, while Origin describes route origin and Community provides classification tags. Therefore, Local Preference is the correct answer because it is commonly used to influence internal BGP path selection toward external destinations.

Question 83

Which Junos mode executes operational monitoring commands?

1. Configuration mode
2. Shell mode
3. Operational mode
4. Edit mode

Correct Answer: 3

Explanation:

Junos operational mode is used to execute commands that monitor and troubleshoot the device. Commands such as show, monitor, and various operational troubleshooting commands are normally entered from this mode. Configuration mode is used for creating, modifying, and committing configuration statements, while shell mode provides access to the underlying operating-system environment when appropriate. Edit mode is not a separate standard Junos CLI mode in the same sense. Therefore, operational mode is the correct answer because it provides the primary command environment for viewing system status, routing information, interfaces, protocols, and other operational details.

Question 84

Which protocol prevents Ethernet switching loops?

1. BGP
2. STP
3. LDP
4. NTP

Correct Answer: 2

Explanation:

Spanning Tree Protocol, or STP, prevents Layer 2 Ethernet switching loops by logically blocking redundant paths while maintaining them as potential alternatives. Without loop-prevention mechanisms, redundant Ethernet connections can allow broadcast frames and unknown unicast traffic to circulate continuously. STP builds a loop-free logical topology and can unblock alternative links when topology changes occur. BGP handles interdomain routing, LDP distributes MPLS labels, and NTP synchronizes system clocks. Therefore, STP is the correct answer because its primary purpose is preventing Layer 2 forwarding loops in Ethernet switching environments while retaining network redundancy.

Question 85

Which BGP attribute describes how a route entered BGP?

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

Correct Answer: 1

Explanation:

The BGP Origin attribute indicates how a particular route was introduced into BGP. Common origin values include IGP, EGP, and Incomplete. During BGP path selection, a route with a preferred origin type can be selected over another route when relevant preceding criteria do not determine the result. Community is primarily used for route classification and policy, Next Hop identifies the forwarding address, and MED provides information about preferred entry points between neighboring autonomous systems. Therefore, Origin is the correct answer because it describes the method by which the route was introduced into the BGP system.

Question 86

Which technology separates customer routing instances?

1. STP
2. VRF
3. LACP
4. BFD

Correct Answer: 2

Explanation:

Virtual Routing and Forwarding, or VRF, creates separate routing and forwarding contexts on the same physical network device. In service-provider environments, VRFs are commonly used to keep different customers’ routes logically separated even when those customers use overlapping address spaces. Each VRF can maintain its own routing information and forwarding decisions. STP addresses Layer 2 loop prevention, LACP manages aggregated Ethernet interfaces, and BFD provides rapid failure detection. Therefore, VRF is the correct answer because it provides logical separation between independent routing environments on a shared router or switching platform.

Question 87

Which protocol uses multicast addresses for routing updates?

1. OSPF
2. BGP
3. LACP
4. NTP

Correct Answer: 1

Explanation:

OSPF uses multicast communication on many network types to efficiently exchange protocol information with neighboring routers. For example, OSPFv2 uses specific multicast addresses for communication between participating routers, reducing the need to send identical protocol packets individually to every neighbor. BGP establishes point-to-point sessions using TCP, LACP exchanges control frames directly between link-aggregation peers, and NTP synchronizes time using its own client-server communication process. Therefore, OSPF is the correct answer because multicast communication is an important part of its neighbor and routing-information exchange on appropriate network types.

Question 88

Which BGP timer controls periodic keepalive transmission?

1. Hold timer
2. Keepalive timer
3. Connect timer
4. Retry timer

Correct Answer: 2

Explanation:

The BGP Keepalive timer determines how frequently a BGP speaker sends KEEPALIVE messages to maintain an established session. These messages help confirm that the BGP connection remains active when no other qualifying BGP messages are being exchanged. The Hold timer has a different role: it determines how long a router can wait for an acceptable BGP message before considering the peer unreachable. Connect-related behavior concerns establishing the underlying TCP session. Therefore, the Keepalive timer is the correct answer because it controls the periodic transmission of BGP KEEPALIVE messages used to maintain session liveness.

Question 89

Which MPLS operation removes the top label?

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

Correct Answer: 3

Explanation:

The MPLS pop operation removes the top label from an MPLS label stack. This operation is commonly associated with routers that are finishing a label-switched path or performing penultimate-hop popping when an implicit-null label is used. Push adds a label to a packet, while swap replaces one label with another as the packet moves through the MPLS network. Stack describes the collection of labels rather than a specific removal operation. Therefore, pop is the correct answer because it specifically represents removing the top MPLS label before the packet continues toward its destination.

Question 90

Which protocol discovers neighboring network devices automatically?

1. LLDP
2. ARP
3. DHCP
4. RIP

Correct Answer: 1

Explanation:

Link Layer Discovery Protocol, or LLDP, allows network devices to advertise identification and capability information to directly connected neighbors. Administrators can use the collected information to understand physical topology, identify connected devices, and troubleshoot connectivity. LLDP operates at the data-link layer and is particularly useful when determining which device and interface are connected across an Ethernet segment. ARP resolves IPv4 addresses to MAC addresses, DHCP provides configuration information, and RIP exchanges routing information. Therefore, LLDP is the correct answer because its primary function is discovering and identifying directly connected network devices.

Question 91

Which BGP attribute can influence inbound traffic selection?

1. Local Preference
2. MED
3. Keepalive
4. Router ID

Correct Answer: 2

Explanation:

The BGP Multi-Exit Discriminator, or MED, can provide neighboring autonomous systems with information about which entry point is preferred when multiple links connect the same autonomous systems. It is therefore commonly associated with influencing inbound traffic decisions from a neighboring autonomous system. Local Preference is primarily used within an autonomous system to influence outbound path selection. Keepalive relates to session maintenance, while Router ID identifies a BGP speaker. Therefore, MED is the correct answer because it can communicate a preference regarding which connection should be selected for traffic entering an autonomous system.

Question 92

Which Junos command displays active BGP neighbor sessions?

1. show bgp neighbor
2. show route
3. show interfaces
4. show system users

Correct Answer: 1

Explanation:

The Junos show bgp neighbor command provides detailed information about BGP peer relationships. It can display information such as neighbor addresses, session state, negotiated parameters, counters, timers, and other protocol details. This makes the command useful when troubleshooting individual BGP peer sessions or examining the operational state of a particular neighbor. show route focuses on routing-table information, show interfaces displays interface information, and show system users identifies logged-in users. Therefore, show bgp neighbor is the correct answer when detailed information about an individual BGP neighbor session is required.

Question 93

Which routing table stores multicast forwarding information?

1. inet.0
2. inet6.0
3. mpls.0
4. inet.2

Correct Answer: 4

Explanation:

In Junos, the inet.2 routing table is associated with multicast-related routing information and is used in environments where multicast routing protocols and reverse-path information are involved. The inet.0 table is the primary IPv4 unicast routing table, while inet6.0 is associated with IPv6 unicast routing. The mpls.0 table contains MPLS-related forwarding information. Understanding the purpose of individual Junos routing tables is important when troubleshooting specialized forwarding behavior. Therefore, inet.2 is the correct answer for multicast forwarding-related routing information in the Junos routing architecture.

Question 94

Which protocol detects unidirectional forwarding failures rapidly?

1. NTP
2. BFD
3. SNMP
4. LLDP

Correct Answer: 2

Explanation:

Bidirectional Forwarding Detection, or BFD, can detect forwarding-path failures quickly, including situations where communication is not functioning correctly in one direction. This capability allows dependent routing protocols and forwarding mechanisms to react faster than they might using conventional protocol timers alone. BFD exchanges control information at configured intervals and determines whether the forwarding path remains operational according to the negotiated session parameters. NTP provides time synchronization, SNMP supports network monitoring, and LLDP identifies directly connected devices. Therefore, BFD is the correct answer because rapid forwarding failure detection is its primary purpose.

Question 95

Which BGP identifier must remain unique within routing domains?

1. Community
2. Router ID
3. MED
4. Origin

Correct Answer: 2

Explanation:

The BGP Router ID is a four-byte identifier used to uniquely identify a BGP speaker within the relevant routing environment. It plays an important role in BGP operations, including identifying the local router and participating in path-selection and session-related processes. A stable and appropriate Router ID helps maintain predictable protocol behavior and simplifies troubleshooting. Community is used for policy classification, MED provides path-entry information, and Origin describes how routes entered BGP. Therefore, Router ID is the correct answer because it serves as the identifying value for a BGP speaker and should be uniquely assigned where required.

Question 96

Which protocol provides centralized network-management information?

1. SNMP
2. OSPF
3. LACP
4. PIM

Correct Answer: 1

Explanation:

Simple Network Management Protocol, or SNMP, provides a standardized framework for monitoring and managing network devices. Management systems can use SNMP to retrieve operational information from devices and, where supported and configured, modify certain parameters. Network administrators commonly use SNMP-based monitoring to observe interface statistics, system information, alarms, and other operational data from centralized management platforms. OSPF handles internal routing, LACP manages link aggregation, and PIM supports multicast routing. Therefore, SNMP is the correct answer because it is specifically designed to facilitate centralized network monitoring and management.

Question 97

Which MPLS operation replaces one label with another?

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

Correct Answer: 3

Explanation:

MPLS swap is the operation in which an incoming label is replaced with another label before the packet is forwarded to the next hop. This is a fundamental label-switching behavior performed by transit MPLS routers. The router examines the incoming label, consults its forwarding information, replaces the label according to the forwarding entry, and sends the packet toward the next MPLS hop. Push adds an additional label, while pop removes a label. Therefore, swap is the correct answer because it specifically describes replacing an existing MPLS label with a new label during forwarding.

Question 98

Which OSPF mechanism elects a designated router?

1. SPF calculation
2. DR election
3. Route aggregation
4. Label distribution

Correct Answer: 2

Explanation:

OSPF uses a Designated Router election on broadcast and certain multiaccess network types. The DR helps reduce the number of full adjacency relationships and simplifies link-state database synchronization among multiple routers sharing the same segment. A Backup Designated Router is also elected to provide redundancy if the DR becomes unavailable. SPF calculation determines shortest paths after topology information is available, route aggregation summarizes prefixes, and label distribution belongs to MPLS mechanisms. Therefore, DR election is the correct answer because OSPF specifically uses this process to select the router responsible for coordinating certain multiaccess network operations.

Question 99

Which BGP attribute identifies autonomous systems traversed?

1. Origin
2. AS Path
3. Next Hop
4. Community

Correct Answer: 2

Explanation:

The BGP AS Path attribute records the sequence of autonomous systems through which a route advertisement has traveled. This information is important for interdomain routing because it helps routers evaluate available paths and provides a mechanism for detecting routing loops. When a BGP router receives an advertisement containing its own autonomous system number in the AS Path, it can recognize that the route has already passed through its autonomous system. Origin describes route introduction, Next Hop identifies forwarding information, and Community provides policy classification. Therefore, AS Path is the correct answer because it records traversed autonomous systems.

Question 100

Which Junos command displays hardware inventory details?

1. show chassis hardware
2. show route forwarding-table
3. show bgp summary
4. show system processes

Correct Answer: 1

Explanation:

The Junos show chassis hardware command displays hardware inventory information for the device. It can provide details about installed chassis components, including hardware modules and other physical components recognized by the system. This information is useful when verifying installed hardware, checking component identification, or troubleshooting physical equipment. The routing forwarding-table command focuses on forwarding entries, BGP summary displays BGP session information, and system processes provides information about running processes. Therefore, show chassis hardware is the correct answer because it is specifically intended for examining the device’s physical hardware inventory.