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Question 181

Which IS-IS device performs DIS election on broadcast networks?

1. Designated Intermediate System
2. Routing Engine
3. Area Border Router
4. Label Switching Router

Correct Answer: 1

Explanation:

In IS-IS, the Designated Intermediate System, commonly called the DIS, is elected on broadcast-capable networks. The DIS creates and maintains a pseudonode representation of the multiaccess network. This reduces the amount of individual adjacency information that every participating router needs to represent. IS-IS uses the pseudonode concept to model the broadcast segment efficiently within its link-state database. The DIS election is based on interface priority and, when necessary, the MAC address as a tiebreaker. Unlike OSPF, IS-IS does not use a separate backup DIS role. Understanding the DIS function is important when troubleshooting IS-IS adjacencies and database synchronization.

Question 182

Which Junos command verifies the current forwarding table entries?

1. show route advertising-protocol
2. show route forwarding-table
3. show system commit
4. show configuration interfaces

Correct Answer: 2

Explanation:

The show route forwarding-table command displays information from the forwarding table used to make packet-forwarding decisions. This differs from examining only the routing table, because routes selected by the routing process are ultimately installed into forwarding structures used by the Packet Forwarding Engine. Administrators can use this command when investigating whether a destination has an active forwarding entry and which next hop is being used. It is especially useful when routing information appears correct but traffic behavior does not match expectations. The command therefore provides operational visibility into the forwarding state rather than simply displaying configured routing information.

Question 183

What mechanism allows BGP to advertise multiple paths simultaneously?

1. Route reflection
2. Prefix aggregation
3. Add-Path
4. Route damping

Correct Answer: 3

Explanation:

BGP Add-Path allows a BGP speaker to advertise multiple paths for the same destination prefix instead of restricting advertisements to a single best path. Normally, BGP selects one best route and advertises that route according to its policies. Add-Path can improve path diversity and reduce problems caused by hiding alternative routes. It can be particularly useful in networks where multiple forwarding paths exist and downstream devices benefit from receiving more than one route. The capability requires support and configuration on participating BGP speakers. It is distinct from route reflection because Add-Path specifically addresses the advertisement of multiple paths for the same prefix.

Question 184

Which Junos feature safely validates configuration before committing changes?

1. commit check
2. rollback 3
3. load factory-default
4. request system snapshot

Correct Answer: 1

Explanation:

The Junos commit check command validates the candidate configuration without activating it as the current operational configuration. This makes it useful for identifying configuration syntax or structural problems before performing an actual commit. Administrators can make several changes in configuration mode and then use commit check as a validation step. A successful check does not itself make the configuration active. The distinction is important because commit check provides validation while commit performs the actual activation. This workflow helps reduce configuration mistakes, especially when changes involve multiple interconnected statements or services.

Question 185

Which protocol discovers IPv6 multicast listeners on local networks?

1. IGMP
2. MLD
3. PIM
4. MSDP

Correct Answer: 2

Explanation:

Multicast Listener Discovery, or MLD, is the IPv6 protocol used by hosts and routers to discover multicast listeners on a local link. MLD performs a role similar to IGMP in IPv4 environments, but it operates as part of IPv6 Neighbor Discovery mechanisms and uses ICMPv6 messages. Routers use MLD information to determine which multicast groups have interested listeners on their directly connected networks. This information can then influence multicast forwarding decisions. MLD is therefore associated specifically with IPv6 multicast membership, while PIM handles multicast routing between routers and MSDP can exchange source information between multicast domains.

Question 186

What Junos component primarily handles packet forwarding operations?

1. Routing Engine
2. Management daemon
3. Packet Forwarding Engine
4. Configuration database

Correct Answer: 3

Explanation:

The Packet Forwarding Engine, or PFE, is responsible for high-speed packet forwarding in Junos devices. It uses forwarding information installed by the control-plane processes to determine how packets should be handled. The Routing Engine performs control-plane functions such as maintaining routing information, running protocols, and managing configuration. Once forwarding decisions are calculated, the relevant information is communicated to the forwarding plane. Separating these responsibilities allows packet forwarding to occur efficiently without requiring every packet to be processed directly by the Routing Engine. Understanding this architecture is useful when diagnosing differences between routing information and actual packet-forwarding behavior.

Question 187

Which Junos command displays learned Ethernet MAC address entries?

1. show ethernet-switching table
2. show interfaces diagnostics optics
3. show firewall log
4. show route receive-protocol

Correct Answer: 1

Explanation:

The show ethernet-switching table command displays Ethernet switching information, including learned MAC addresses and the interfaces or logical switching contexts associated with those addresses. Switches dynamically learn MAC addresses by examining source MAC addresses in incoming Ethernet frames. This information is stored in the forwarding database and helps the switch send subsequent frames toward the appropriate interface rather than flooding them unnecessarily. The command is particularly useful when troubleshooting Layer 2 connectivity, unexpected flooding, or MAC-learning behavior. It provides a view of the switch’s learned Ethernet forwarding information rather than Layer 3 routing entries.

Question 188

Which technology authenticates users before granting network access?

1. 802.1X
2. LLDP
3. LACP
4. STP

Correct Answer: 1

Explanation:

IEEE 802.1X provides port-based network access control by requiring authentication before allowing a connected endpoint to obtain normal network access. It commonly involves a supplicant on the endpoint, an authenticator on the network device, and an authentication server such as a RADIUS system. The authenticator controls access to the network-facing port while authentication takes place. This mechanism is useful in enterprise environments where administrators need to restrict access to authorized users or devices. Unlike LLDP, LACP, and STP, which serve discovery, link aggregation, and loop-prevention functions respectively, 802.1X focuses specifically on controlling access through authentication.

Question 189

Which routing feature forwards traffic across equal-cost paths?

1. MED
2. ECMP
3. Route damping
4. AS Path prepending

Correct Answer: 2

Explanation:

Equal-Cost Multipath, or ECMP, allows traffic to be forwarded using multiple paths that have equivalent routing costs. Instead of selecting only one path when several paths have equal preference and metric characteristics, a device can install multiple forwarding paths. Traffic can then be distributed among those paths according to the platform’s forwarding behavior. ECMP can improve link utilization and provide additional path availability without requiring unequal routes to be treated as equivalent. It is different from BGP policy attributes such as MED or AS Path manipulation, which influence route selection rather than directly describing the forwarding behavior of equal-cost paths.

Question 190

Which Junos file preserves a known-good configuration for recovery?

1. Rescue configuration
2. Active log archive
3. Interface snapshot
4. Routing database

Correct Answer: 1

Explanation:

A Junos rescue configuration provides a known-good configuration that can be used for recovery when the active configuration becomes unusable or problematic. Administrators can create a rescue configuration after confirming that the current device configuration is operational. If later changes introduce serious configuration problems, the saved rescue configuration provides a stable reference point for restoration. This is different from the normal candidate or active configuration because it is intentionally maintained as a recovery baseline. Keeping a valid rescue configuration is particularly useful on remotely managed devices where recovering from a configuration mistake may otherwise require more involved administrative intervention.

Question 191

Which protocol carries IPv6 router configuration advertisements to hosts?

1. DHCPv6
2. Router Advertisement
3. ICMP Redirect
4. Neighbor Solicitation

Correct Answer: 2

Explanation:

IPv6 Router Advertisement messages provide hosts with important information about the local IPv6 network. These messages are sent by routers as part of IPv6 Neighbor Discovery and can communicate information such as prefixes, prefix lifetimes, and whether hosts should use automatic address configuration mechanisms. Router Advertisements can also provide a default-router indication to IPv6 hosts. DHCPv6 can provide additional configuration information, but Router Advertisement is the mechanism used by routers to announce essential local IPv6 parameters. Neighbor Solicitation serves a different purpose, such as address resolution and reachability operations within the Neighbor Discovery framework.

Question 192

What does a Junos firewall filter policer primarily control?

1. Interface naming
2. Traffic rate
3. Routing protocol identity
4. VLAN numbering

Correct Answer: 2

Explanation:

A policer controls the rate or volume of traffic that matches specified conditions in a firewall filter or related traffic-processing configuration. Policing can be used to limit traffic to a configured rate and manage bursts according to defined parameters. This provides a mechanism for controlling resource consumption and enforcing traffic-rate policies. When traffic exceeds the configured limits, the device can apply the configured treatment, such as discarding or otherwise handling excess packets. A policer therefore focuses on traffic-rate enforcement rather than interface naming, routing protocol identification, or VLAN numbering.

Question 193

Which BGP capability permits operation using four-octet AS numbers?

1. Route Target
2. Four-Octet AS Number Capability
3. Community Attribute
4. Multiprotocol Extension

Correct Answer: 2

Explanation:

The BGP Four-Octet Autonomous System Number capability allows BGP speakers to exchange and operate with autonomous system numbers larger than the traditional two-octet range. This capability was introduced to accommodate the continued growth in the number of autonomous systems on the Internet. During BGP session establishment, capable peers advertise support for four-octet AS numbers. This allows modern AS values to be represented without depending solely on the older 16-bit AS-number space. The capability is separate from route targets, communities, and multiprotocol extensions, which serve different purposes within BGP and related routing architectures.

Question 194

Which Junos command compares candidate and active configurations?

1. show configuration | display inheritance
2. show | compare
3. show system rollback
4. show chassis environment

Correct Answer: 2

Explanation:

The Junos show | compare command displays differences between the candidate configuration and the currently active configuration. This is useful after making configuration changes because administrators can review exactly what will change before committing. The output helps identify added, modified, or removed configuration statements. It can therefore act as a verification step in a controlled configuration workflow. Unlike commands that display system status, rollback information, or inherited configuration details, show | compare focuses specifically on configuration differences. Reviewing these changes before committing can reduce the risk of unintentionally activating an incorrect or incomplete configuration.

Question 195

Which multicast protocol manages IPv4 host group membership?

1. IGMP
2. MLD
3. PIM
4. MSDP

Correct Answer: 1

Explanation:

Internet Group Management Protocol, or IGMP, manages IPv4 multicast group membership between hosts and their directly connected multicast routers. Hosts use IGMP messages to indicate interest in receiving traffic for particular multicast groups. Routers use this membership information when determining whether multicast traffic should be forwarded onto a local network segment. IGMP is different from PIM, which establishes multicast routing between routers, and MSDP, which can exchange information about multicast sources between routing domains. MLD performs a comparable membership-management function for IPv6 multicast. Understanding these protocol roles helps distinguish host membership from inter-router multicast routing.

Question 196

Which Junos process maintains routing protocol control-plane information?

1. rpd
2. mgd
3. chassisd
4. snmpd

Correct Answer: 1

Explanation:

The Junos Routing Protocol Daemon, commonly identified as rpd, manages routing protocol operations and maintains routing-related control-plane information. It participates in protocols such as BGP, OSPF, IS-IS, and other supported routing mechanisms. The daemon processes protocol information, calculates routing decisions, and contributes routes to the routing table. Other Junos processes perform different functions. For example, mgd handles management and configuration interactions, while other daemons are responsible for chassis or management-related operations. Knowing the role of rpd is valuable when troubleshooting routing behavior or examining Junos process-level operational information.

Question 197

Which mechanism protects switches from unauthorized BPDU participation?

1. Root guard
2. BPDU protection
3. Loop protection
4. MAC limiting

Correct Answer: 2

Explanation:

BPDU protection is designed to protect access-facing switch ports from receiving unexpected Bridge Protocol Data Units. It is commonly applied to interfaces where administrators expect end devices rather than other spanning-tree participants. If a protected interface receives a BPDU, the configured protection mechanism can take action to prevent the unexpected device from influencing the Layer 2 topology. Root protection serves a different purpose by preventing an interface from becoming an unintended path toward a root bridge. Loop protection addresses certain spanning-tree failure conditions, while MAC limiting controls learned MAC addresses. These mechanisms therefore address different Layer 2 risks.

Question 198

Which Junos architecture component runs routing protocol processes?

1. Packet Forwarding Engine
2. Routing Engine
3. Flexible PIC Concentrator
4. Switch fabric

Correct Answer: 2

Explanation:

The Routing Engine is the Junos component responsible for control-plane operations, including running routing protocol processes and maintaining routing information. It communicates with neighboring routers using protocols such as BGP, OSPF, and IS-IS, processes routing updates, and determines the appropriate routing information. The resulting forwarding information is then made available to the forwarding plane. The Packet Forwarding Engine handles high-speed packet forwarding, while components such as PICs and switching fabrics serve hardware-specific forwarding and connectivity roles. Understanding the separation between the Routing Engine and Packet Forwarding Engine is fundamental to understanding Junos architecture and troubleshooting.

Question 199

Which Junos feature automatically executes actions after defined system events?

1. Event policy
2. Static route
3. Prefix list
4. Authentication profile

Correct Answer: 1

Explanation:

Junos event policies allow administrators to define automated actions that occur when specified system events are detected. An event can trigger actions such as executing operational commands, generating messages, or initiating other configured responses. This capability can reduce the need for constant manual monitoring and can help automate responses to predictable operational conditions. Event policies are distinct from routing policies, prefix lists, and authentication profiles because their primary purpose is event-driven automation. They can be particularly useful in operational environments where administrators want the device to react automatically to defined conditions.

Question 200

Which Junos technology provides structured data modeling for automation?

1. SNMP MIBs
2. YANG
3. Syslog templates
4. CLI aliases

Correct Answer: 2

Explanation:

YANG is a data-modeling language used to define structured configuration and operational data for network management and automation. It provides a standardized way to describe data elements, their relationships, constraints, and hierarchical organization. Technologies such as NETCONF can use YANG-based models to exchange structured information with network devices. This approach allows automation systems to work with well-defined data rather than relying exclusively on manually formatted CLI commands. SNMP MIBs serve a different management-data model, while syslog templates and CLI aliases address logging or command convenience. YANG is therefore an important foundation for modern model-driven network automation.