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Question 261

Which Junos technology enables nonstop routing during control-plane failures?

1. GRES
2. Port mirroring
3. IGMP snooping
4. Configuration groups

Correct Answer: 1

Explanation:

Graceful Routing Engine Switchover, or GRES, is a Junos high-availability feature designed to reduce disruption when a Routing Engine switchover occurs. It allows the forwarding plane to continue operating while control-plane responsibility moves between Routing Engines. This can help preserve packet forwarding during certain Routing Engine failures or planned switchover events. GRES should be distinguished from other high-availability technologies because its primary purpose is maintaining forwarding continuity during Routing Engine switchover. Features such as port mirroring, IGMP snooping, and configuration groups address traffic monitoring, multicast forwarding efficiency, and configuration reuse rather than Routing Engine redundancy.

Question 262

Which Junos feature preserves protocol sessions during Routing Engine switchover?

1. NSR
2. SLAAC
3. ECMP
4. MACsec

Correct Answer: 1

Explanation:

Nonstop Active Routing, or NSR, is designed to preserve routing protocol state during a Routing Engine switchover. By maintaining protocol state across the Routing Engines, NSR can reduce the need for routing sessions to restart after certain control-plane events. This helps minimize routing disruption and can support higher network availability. GRES focuses primarily on forwarding continuity during Routing Engine switchover, while NSR addresses preservation of routing protocol state. SLAAC provides IPv6 address autoconfiguration, ECMP distributes traffic across equal-cost paths, and MACsec protects Ethernet frames. NSR is therefore the mechanism specifically associated with maintaining routing protocol sessions.

Question 263

Which Junos upgrade technology minimizes service interruption during software upgrades?

1. ISSU
2. IGMP
3. LACP
4. DHCP

Correct Answer: 1

Explanation:

In-Service Software Upgrade, or ISSU, is designed to upgrade supported Junos software with minimal service interruption. The technology aims to maintain network operation while software components are upgraded in a controlled sequence. Exact capabilities and supported platforms depend on the Junos release and hardware architecture. ISSU is particularly relevant in environments where prolonged downtime is undesirable and maintenance must occur while services remain available. IGMP manages IPv4 multicast membership, LACP handles link aggregation, and DHCP provides host configuration. ISSU therefore addresses software-maintenance availability rather than ordinary traffic forwarding or endpoint configuration.

Question 264

Which Junos hardware component contains multiple interface cards?

1. FPC
2. Routing Engine
3. Power supply
4. Fan tray

Correct Answer: 1

Explanation:

A Flexible PIC Concentrator, or FPC, is a modular hardware component used in supported Junos chassis to house Packet Interface Controllers or PICs. The FPC provides the physical structure through which supported interface hardware connects to the routing platform. Depending on the platform, FPCs can support different combinations of interface modules and port types. The Routing Engine performs control-plane functions, while power supplies and fan trays provide system-support functions. Understanding FPC and PIC relationships is important when working with modular Junos platforms because interface hardware is often organized hierarchically within chassis slots.

Question 265

Which component provides physical network ports within an FPC?

1. PIC
2. Routing Engine
3. Switch fabric
4. Control board

Correct Answer: 1

Explanation:

A Packet Interface Controller, or PIC, provides network interface connectivity within supported modular Junos hardware. PICs are associated with FPCs and provide specific physical interfaces or port types depending on the platform. This modular architecture allows hardware to support different interface technologies and densities. The Routing Engine handles control-plane functions, while the switch fabric provides internal packet-transfer capabilities between forwarding components. A control board can perform other platform-specific hardware functions. Understanding the relationship between FPCs and PICs helps administrators identify where physical interfaces reside within a modular chassis and diagnose hardware-related interface problems.

Question 266

Which Junos feature creates completely separate administrative environments?

1. Logical systems
2. Interface descriptions
3. Forwarding classes
4. Static routes

Correct Answer: 1

Explanation:

Junos logical systems allow a single physical device to provide multiple logically independent administrative environments. Each logical system can have its own configuration, interfaces, routing information, and administrative context according to platform capabilities. This can be useful when multiple organizations, departments, or operational domains need separation while sharing the same physical hardware. Logical systems are different from routing instances because they provide broader administrative and configuration separation. Interface descriptions simply document interfaces, forwarding classes support traffic treatment, and static routes define specific forwarding paths. Logical systems therefore provide a higher level of logical device separation.

Question 267

Which CoS component determines how packets enter forwarding queues?

1. Classifier
2. Scheduler
3. Rewrite rule
4. Policier

Correct Answer: 1

Explanation:

A Class of Service classifier determines how incoming packets are assigned to forwarding classes based on characteristics such as packet markings or other supported criteria. Once traffic has been classified, subsequent CoS mechanisms can determine queue placement, scheduling behavior, and packet marking. A scheduler controls how queued traffic is transmitted, while a rewrite rule can modify packet markings before transmission. A policer controls traffic rates rather than primarily determining the forwarding classification. The classifier therefore serves as an important first step in a CoS design by identifying how traffic should be treated within the device.

Question 268

Which CoS mechanism controls transmission order among traffic queues?

1. Scheduler
2. Classifier
3. Rewrite rule
4. Filter term

Correct Answer: 1

Explanation:

A CoS scheduler determines how traffic is transmitted from queues toward an interface. It can control factors such as scheduling priority, bandwidth allocation, and queue-service behavior depending on the platform and configuration. This allows administrators to give different traffic classes appropriate forwarding treatment when congestion occurs. A classifier determines the forwarding class assigned to traffic, while a rewrite rule modifies packet markings. A firewall filter term performs packet matching and actions rather than queue scheduling. Schedulers are therefore central to controlling how queued traffic receives transmission opportunities on a congested interface.

Question 269

Which CoS feature modifies packet markings before transmission?

1. Rewrite rule
2. Scheduler
3. Classifier
4. Routing policy

Correct Answer: 1

Explanation:

A CoS rewrite rule modifies supported packet markings before traffic leaves an interface. This allows a device to change fields used by downstream devices for traffic classification or differentiated treatment. For example, an administrator can configure a rewrite behavior so that packets receive markings appropriate for the next network segment. A classifier performs incoming traffic classification, while a scheduler controls queue transmission. Routing policies operate on routing information rather than packet markings. Rewrite rules therefore provide an important mechanism for maintaining consistent QoS treatment across network boundaries where packet markings may need to be adjusted.

Question 270

Which MPLS diagnostic tool tests Label Switched Path connectivity?

1. LSP ping
2. IGMP query
3. ARP probe
4. DHCP discover

Correct Answer: 1

Explanation:

MPLS LSP ping is a diagnostic mechanism used to test connectivity across a Label Switched Path. It can help verify whether an MPLS path is functioning correctly and identify forwarding problems within the label-switched network. The mechanism provides information that can be useful when troubleshooting MPLS transport issues where ordinary IP connectivity tests may not fully validate label-based forwarding. IGMP queries concern multicast membership, ARP probes resolve IPv4 neighbors, and DHCP Discover messages initiate host configuration. LSP ping is therefore specifically associated with validating MPLS Label Switched Path operation.

Question 271

Which MPLS diagnostic method traces a Label Switched Path?

1. LSP traceroute
2. Ethernet OAM
3. IPv6 DAD
4. BGP monitoring

Correct Answer: 1

Explanation:

MPLS LSP traceroute provides a method for tracing the path taken through an MPLS Label Switched Path. It can help identify where forwarding problems occur by examining the sequence of MPLS-capable devices involved in the path. This is particularly useful when an MPLS service appears unreachable even though ordinary IP connectivity may seem functional. Ethernet OAM focuses on Ethernet service monitoring, IPv6 DAD checks address uniqueness, and BGP monitoring examines routing-protocol information. LSP traceroute therefore provides specialized visibility into MPLS forwarding paths and can complement other MPLS troubleshooting tools.

Question 272

Which MPLS label instructs a router to retain explicit IPv4 context?

1. Explicit Null
2. Implicit Null
3. Aggregate Label
4. Reserved Label

Correct Answer: 1

Explanation:

An Explicit Null label can be used when the penultimate router should send a labeled packet toward the egress router while retaining an explicit label value. For IPv4, label value 0 represents the IPv4 Explicit Null label. Retaining this label can preserve information needed for certain traffic-engineering or QoS-related behaviors at the egress. Implicit Null, by contrast, indicates that the label should be removed before the packet reaches the egress. Aggregate and Reserved Label are not equivalent to the Explicit Null function described here. Understanding explicit versus implicit label handling is important in MPLS forwarding analysis.

Question 273

Which BGP security feature authenticates neighboring session messages?

1. TCP authentication
2. IGMP authentication
3. DHCP authentication
4. ARP authentication

Correct Answer: 1

Explanation:

BGP sessions can use TCP authentication mechanisms to help protect the routing session from unauthorized peers or forged TCP segments. A commonly supported method is TCP MD5 authentication, where both BGP neighbors use a shared secret to authenticate TCP segments associated with the session. Authentication adds protection against certain forms of session spoofing or unauthorized interaction. IGMP, DHCP, and ARP have different security mechanisms and purposes. BGP session authentication should be configured consistently on both peers; otherwise, the session may fail to establish or maintain communication.

Question 274

Which BGP mechanism limits external spoofed session attempts?

1. TTL security
2. Route aggregation
3. Community tagging
4. Local preference

Correct Answer: 1

Explanation:

BGP TTL security can help protect external BGP sessions by requiring incoming packets to have an expected TTL-related value. The mechanism is particularly useful because external BGP peers are often directly connected or located within a limited number of hops. By validating the expected TTL behavior, the device can reject packets that appear to originate from an unexpected distance. Route aggregation reduces routing-table size, communities carry policy information, and Local Preference influences internal BGP path selection. TTL security therefore provides a protection mechanism specifically aimed at reducing certain unauthorized or spoofed BGP session attempts.

Question 275

Which routing option creates a route without requiring dynamic protocols?

1. Static route
2. Aggregated route
3. Generated route
4. Learned route

Correct Answer: 1

Explanation:

A static route is manually configured by an administrator and does not depend on a dynamic routing protocol to discover the destination path. Static routes are useful for simple networks, specific destinations, default paths, or backup connectivity designs. Their next-hop information is explicitly defined in configuration. Aggregated and generated routes can also be locally created, but they have different purposes and behaviors within the routing system. Learned routes are obtained through routing protocols or other dynamic mechanisms. Static routing is therefore the straightforward method when an administrator needs to define a route manually without relying on dynamic route exchange.

Question 276

Which route type summarizes multiple more-specific routing prefixes?

1. Aggregate route
2. Host route
3. Martian route
4. Discard route

Correct Answer: 1

Explanation:

An aggregate route represents a summarized prefix that can encompass multiple more-specific routes. Route aggregation helps reduce routing-table size and can simplify the information advertised to other routing domains. For example, several contiguous networks may be represented by a broader summary prefix when the network design allows such summarization. A host route represents a specific individual address, while a martian route refers to an address considered invalid or inappropriate for normal routing. A discard route intentionally sends matching traffic toward a discard action. Aggregate routes specifically address summarizing multiple destination prefixes.

Question 277

Which Junos feature provides automatic packet loss protection through redundancy?

1. Bidirectional Forwarding Detection
2. Link aggregation
3. Graceful Routing Engine Switchover
4. Equal-Cost Multipath

Correct Answer: 4

Explanation:

Equal-Cost Multipath, or ECMP, provides multiple equivalent forwarding paths toward a destination. If one path becomes unavailable, traffic can continue using another available path, provided the remaining forwarding information is valid. This creates path-level redundancy and can also improve utilization by distributing traffic among equivalent paths. BFD detects failures quickly but does not itself provide multiple forwarding paths. GRES protects forwarding during Routing Engine switchover, while link aggregation provides redundancy across bundled physical links. ECMP is therefore particularly useful when multiple routed paths have equivalent characteristics and the network requires resilient forwarding.

Question 278

Which Junos protocol feature distributes routes between routing instances?

1. Route leaking
2. Interface mirroring
3. Packet sampling
4. Queue scheduling

Correct Answer: 1

Explanation:

Route leaking allows selected routing information to be exchanged between otherwise separate routing instances. This can be useful when logically isolated routing environments need controlled connectivity to specific destinations. Rather than merging the complete routing tables, administrators can selectively make routes available according to the required design and policy. Interface mirroring copies traffic for monitoring, packet sampling collects traffic statistics, and queue scheduling controls transmission behavior. Route leaking therefore addresses controlled sharing of routing information between routing domains while preserving the broader separation provided by routing instances.

Question 279

Which monitoring technology exports sampled traffic statistics externally?

1. sFlow
2. NETCONF
3. YANG
4. NTP

Correct Answer: 1

Explanation:

sFlow is a traffic-monitoring technology that can sample packets and interface counters and export flow-related information to an external collector. Because it uses sampling rather than necessarily examining every packet in detail, sFlow can provide visibility while limiting monitoring overhead. It is useful for traffic analysis, capacity planning, and identifying major traffic patterns across network infrastructure. NETCONF provides structured management access, YANG defines data models, and NTP synchronizes clocks. sFlow is therefore specifically associated with exporting sampled traffic statistics to monitoring systems for analysis.

Question 280

Which Junos mechanism commits configuration changes across redundant Routing Engines?

1. commit synchronize
2. commit check
3. commit confirmed
4. commit at

Correct Answer: 1

Explanation:

The Junos commit synchronize command is used on supported dual-Routing-Engine systems to synchronize a committed configuration between the Routing Engines. This helps maintain consistent configuration state across redundant control-plane components. Configuration synchronization is particularly important in high-availability environments because the standby Routing Engine should have an appropriate configuration available if a switchover occurs. commit check validates configuration without activating it, commit confirmed provides timed rollback protection, and commit at schedules a future commit. commit synchronize therefore addresses configuration consistency across redundant Routing Engines rather than validation, scheduling, or temporary confirmation.