View Full Juniper JN0-253 Exam Dumps and Practice Test Dumps.

 

Question 361

Which Junos operational command restores the configuration directly to the state immediately preceding the last active commit?

1. rollback 1
2. rollback 0
3. load factory-default
4. request system zeroize

Correct Answer: 1

Explanation

Junos OS maintains a robust historical rollback archive consisting of up to fifty indexed configuration snapshots (ranging from rollback 0 up to rollback 49). Rollback 0 represents the currently active running configuration. When an administrator needs to undo the most recent set of changes immediately following an unverified commit, executing rollback 1 loads the exact configuration state that existed right before that last commit. After reviewing the loaded differences, a subsequent commit applies the restored baseline back to the live production environment.

Question 362

What is the specific architectural role of an OSPF Virtual Link?

1. To encrypt inter-area control plane traffic using AES-256 IPsec keys
2. To connect a non-backbone area to the OSPF backbone area when they do not share a direct physical connection to an ABR
3. To translate OSPF link-state advertisements into BGP path attributes automatically
4. To provide a redundant high-speed backup path across local-area loopback interfaces

Correct Answer: 2

Explanation

OSPF protocol architecture strictly mandates that all non-backbone areas (Area 0.0.0.0) must maintain physical or logical connectivity back to the designated backbone area (Area 0). When physical network designs or topological constraints prevent a non-backbone area from establishing a direct interface connection to an Area Border Router connected to the backbone, an OSPF Virtual Link is engineered. The virtual link acts as a tunneling mechanism across a transit area, logically extending the backbone and ensuring loop-free routing continuity across complex multi-area enterprise networks.

Question 363

Which BGP path attribute is classified as a well-known discretionary attribute that may or may not be supported by all BGP implementations?

1. AS-Path
2. Next-Hop
3. Local Preference
4. Origin

Correct Answer: 3

Explanation

Border Gateway Protocol attributes are categorized into well-known mandatory, well-known discretionary, optional transitive, and optional non-transitive types. Local Preference is a well-known discretionary attribute, meaning it must be recognized by all standard-compliant BGP routers, but it is not strictly required to be included in every route advertisement. Local Preference is utilized exclusively within an internal autonomous system to influence outbound routing exit paths across multiple exit points.

Question 364

What specific operational benefit does Juniper Mist Wired Assurance provide through continuous gRPC streaming telemetry?

1. Replacing manual SNMP polling scripts with real-time data streaming and instant anomaly detection
2. Converting all switch configuration text files into binary backup archives
3. Encrypting physical console cable management ports automatically
4. Routing all wireless guest traffic through external cloud firewalls

Correct Answer: 1

Explanation

Juniper Mist Wired Assurance transforms campus network operations by abandoning legacy, inefficient SNMP polling mechanisms in favor of real-time gRPC streaming telemetry. EX series switches continuously stream operational statistics—including interface error counters, PoE power draw, environmental temperatures, and neighbor states—directly into the Mist cloud analytics engine. This enables artificial intelligence algorithms to detect anomalies instantly, correlate events across wired and wireless infrastructures, and provide proactive insights before network users experience performance degradation.

Question 365

What is the functional difference between a Junos firewall filter term configured with a count action and a log action?

1. Count records packet statistics matching rules, while log copies the packet header to the system log daemon
2. Count drops the packet immediately, while log routes it to a secondary backup gateway
3. Count encrypts packet payloads, while log converts them into plaintext syslog records
4. Count limits bandwidth rates, while log drops excessive traffic flows

Correct Answer: 1

Explanation

Junos firewall filter modifiers provide granular administrative visibility over traffic traversing routing and switching interfaces. A count action increments a named counter variable whenever a packet matches the specified filter criteria, allowing engineers to track traffic volumes and inspect usage statistics via operational commands. Conversely, a log action not only matches the packet but also captures a copy of the packet header and sends it to the system logging daemon (syslog), facilitating detailed security auditing and traffic analysis.

Question 366

According to standard Spanning Tree operations, which transition state occurs immediately after a switch port leaves the Listening state?

1. Blocking state
2. Disabled state
3. Learning state
4. Forwarding state

Correct Answer: 3

Explanation

Spanning Tree Protocol utilizes a structured state machine to prevent temporary bridging loops when topology changes occur. When a port becomes active, it progresses through sequential states: Blocking, Listening, Learning, and Forwarding. During the Listening state, the port processes bridge protocol data units but does not populate its MAC address table. Once the forward delay timer expires, the port transitions into the Learning state, where it begins populating its address table with source MAC addresses heard on the segment without yet forwarding normal user data traffic.

Question 367

What is the operational characteristic of a Junos layer2-vpn routing instance type?

1. Providing standalone Layer 3 routing tables without protocol daemons
2. Establishing point-to-point or point-to-multipoint Layer 2 pseudowire bridging across an MPLS core
3. Translating private IP addresses into public internet spaces dynamically
4. Encrypting all inter-subnet packet flows with hardware-based IPsec keys

Correct Answer: 2

Explanation

A layer2-vpn routing instance in Junos OS is utilized in service provider and advanced enterprise architectures to deliver virtual private wire service (VPWS) or layer 2 virtual private network connectivity. It encapsulates Layer 2 Ethernet frames and transports them across an MPLS backbone network over established pseudowires. This architecture allows geographically separated enterprise sites to communicate via transparent Layer 2 bridging over a shared core network infrastructure without requiring complex direct physical circuit connections.

Question 368

What performance vector does the Mist Roaming Service Level Expectation framework analyze across wireless environments?

1. Access point radio temperature fluctuations and power draw
2. Client roaming handover success rates, latency, and fast roaming protocol performance
3. Physical copper cabling length limitations in wiring closets
4. Static IP address allocation durations during initial DHCP onboarding

Correct Answer: 2

Explanation

The Roaming Service Level Expectation metric within the Juniper Mist platform monitors and evaluates how seamlessly wireless clients move between access points throughout an enterprise campus. It tracks key metrics including roaming success rates, handover latency, and the performance of fast roaming protocols like 802.11r. By continuously analyzing roaming telemetry, Mist identifies sticky clients, coverage gaps, or authentication delays during handovers, allowing IT teams to optimize radio settings and maintain uninterrupted connectivity.

Question 369

What is the default transmission interval for Link Aggregation Control Protocol (LACP) packets when operating in slow transmission mode?

1. Every 1 second
2. Every 10 seconds
3. Every 30 seconds
4. Every 60 seconds

Correct Answer: 3

Explanation

Link Aggregation Control Protocol defines transmission intervals to regulate how frequently member ports exchange LACP Data Units. By default, LACP operates in slow transmission mode, where member interfaces transmit control heartbeats every 30 seconds. If configured for fast transmission (short timeout) mode, the transmission frequency increases to once every second with a 3-second failure detection timeout. Slow mode minimizes unnecessary control plane overhead on stable links while ensuring reliable bundle health monitoring.

Question 370

Which Junos configuration command restores the active configuration directly back to the previously saved rescue baseline file?

1. rollback rescue
2. load rescue configuration
3. request system rescue restore
4. commit rescue-file

Correct Answer: 2

Explanation

When an administrative configuration error, syntax corruption, or network lockout occurs, network engineers can quickly restore stability by reverting to the designated rescue baseline. Executing the load rescue configuration command instructs the Junos CLI to load the permanent rescue file into the candidate configuration buffer. Following this command with a standard commit statement instantly overwrites the active running configuration with the verified, clean rescue baseline, restoring full management access and operational health.

Question 371

During BGP path selection, which comparison step is evaluated immediately after checking the AS-Path length?

1. Lowest Multi-Exit Discriminator value
2. Lowest Origin code type (IGP over EGP over Incomplete)
3. Highest local preference weight
4. Oldest router ID identifier

Correct Answer: 2

Explanation

Border Gateway Protocol follows a rigorous, sequential decision process to select the optimal path to any destination prefix. Once the router compares Local Preference and AS-Path length, it proceeds to evaluate the Origin code attribute. The origin code indicates how the routing information was originally learned: IGP (‘i’), EGP (‘e’), or Incomplete (‘?’). Lower numerical precedence is given to IGP paths over EGP, and EGP over Incomplete, ensuring predictable path selection across multi-provider autonomous system environments.

Question 372

What is the primary function of an OSPF Type 3 Summary LSA?

1. Advertising external network prefixes redistributed from outside the OSPF domain
2. Describing router neighbor adjacencies on multi-access broadcast segments
3. Advertising network reachability prefixes from one OSPF area into another area
4. Locating the exact physical position of an Autonomous System Boundary Router

Correct Answer: 3

Explanation

Type 3 Summary LSAs are generated and flooded by Area Border Routers when propagating prefix reachability information from one OSPF area into another. Because OSPF areas maintain isolated link-state databases, internal routers in Area 1 do not know the internal topology of Area 2. To bridge this gap, the ABR summarizes prefixes learned in one area and floods Type 3 LSAs into adjacent areas, enabling inter-area routing without forcing every router to store a massive, unified link-state database.

Question 373

How does an enterprise switch distinguish between trusted and untrusted ports when running DHCP Snooping?

1. Based on whether the port is connected to a known authorized DHCP server or upstream core switch
2. Based on whether the connected client device is running Windows or Linux operating systems
3. Based on the physical color of the RJ45 Ethernet patch cable plugged into the port
4. Based on whether the interface speed is running at 10 Mbps or 1000 Mbps

Correct Answer: 1

Explanation

DHCP Snooping relies on administrators explicitly designating switch ports as either trusted or untrusted to maintain security integrity. Trusted ports are connected to authorized DHCP servers, core switches, or upstream network gateways that are permitted to supply DORA offer and acknowledgment messages. Untrusted ports typically connect to user access workstations or guest devices where rogue DHCP servers might be maliciously attached. The switch drops DHCP server reply packets originating from untrusted access ports to prevent IP spoofing and man-in-the-middle attacks.

Question 374

Which OSI layer is secured by MACsec (IEEE 802.1AE) to provide transparent point-to-point data encryption and integrity?

1. Layer 1 Physical layer
2. Layer 2 Data Link layer
3. Layer 3 Network layer
4. Layer 4 Transport layer

Correct Answer: 2

Explanation

MACsec, standardized under IEEE 802.1AE, provides robust point-to-point data encryption, data integrity, and origin authenticity directly at Layer 2 (Data Link layer) of the OSI model. By securing Ethernet links between switches or client endpoints, MACsec protects enterprise networks against wiretapping, MAC tampering, and passive eavesdropping attacks. It encrypts traffic transparently across physical cabling without altering higher-layer network protocols or routing configurations.

Question 375

How does Marvis Actions assist enterprise IT support teams in resolving network incidents?

1. By automatically generating random support tickets every calendar hour
2. By analyzing scope, impact, and frequency of anomalies to isolate root causes and recommend remediation
3. By rebooting physical switch power supplies whenever CPU usage spikes
4. By converting all network traffic into encrypted packet capture dumps

Correct Answer: 2

Explanation

Marvis Actions uses advanced artificial intelligence and machine learning telemetry correlation to transform reactive troubleshooting into proactive remediation. Instead of treating all alerts equally, Marvis evaluates the scope, impact, and frequency of network anomalies, intelligently prioritizing critical root causes so IT teams can resolve high-impact issues first. This automated triage capability drastically reduces mean-time-to-resolution and eliminates alert fatigue for enterprise network administrators.

Question 376

What is the default routing policy export behavior in Junos OS when no explicit export policy is applied to a routing protocol?

1. All transit routes learned via interior or exterior routing protocols are rejected by default
2. All routes are exported automatically to all connected neighbors without restriction
3. Only static routes are permitted while dynamic routes are blocked
4. All routes are assigned a default preference value of 255

Correct Answer: 1

Explanation

Junos OS enforces strict default routing policy rules to balance operational usability with control-plane security. While default import behavior accepts all valid routing updates learned from active protocol neighbors, default export behavior completely rejects all transit routes learned via interior or exterior protocols unless an explicit export policy permits them. This asymmetric default design ensures that routers automatically learn external topology information while preventing accidental route leakage back out to external networks.

Question 377

Within a Juniper Virtual Chassis stack, what operational role is automatically assigned to the member switch possessing the highest routing engine priority value?

1. Passive unmanaged bridge role
2. Master routing engine role
3. Backup routing engine role
4. Standalone core firewall appliance

Correct Answer: 2

Explanation

Within a Juniper Virtual Chassis architecture, member switches are assigned specific operational roles to manage the combined logical entity efficiently. The switch configured with the highest routing engine priority value assumes the Master role, taking charge of control plane operations, routing protocol execution, and management interfaces. The switch with the second-highest priority assumes the Backup role, while remaining member switches function as line card routing units, ensuring high availability and automated failover resiliency.

Question 378

What validation mechanism does Dynamic ARP Inspection use to discard malicious ARP spoofing frames?

1. Encrypting ARP payload headers with pre-shared cryptographic keys
2. Checking incoming packets against valid DHCP snooping binding database entries
3. Filtering OSPF hello adjacency timers dynamically across local links
4. Enforcing strict MAC address count limits per physical switch port

Correct Answer: 2

Explanation

Dynamic ARP Inspection is a robust layer two security feature that leverages valid IP-to-MAC bindings stored within the DHCP snooping database to intercept, inspect, and drop malicious ARP packets. In typical enterprise networks, attackers attempt man-in-the-middle attacks by poisoning ARP caches with forged address bindings, tricking devices into sending traffic to unauthorized MAC addresses. DAI validates every untrusted ARP packet against verified database entries, discarding anomalous or conflicting frames immediately.

Question 379

What is the primary architectural purpose of deploying Mist Edge in a distributed enterprise network?

1. Storing local offline web cache files for faster guest browsing
2. Terminating secure IPsec or GRE tunnels from remote branch access points back to central data centers
3. Executing real-time OSPF route calculations for branch routers
4. Powering remote PoE switches over long-distance copper cabling runs

Correct Answer: 2

Explanation

Mist Edge is a dedicated hardware and software appliance engineered to extend enterprise campus networks and provide scalable tunneling aggregation for remote branch access point deployments. In architectures where remote access points require centralized data handling, Mist Edge terminates secure IPsec or GRE tunnels originating from branch locations right back to the central data center or campus edge. This allows network administrators to enforce centralized firewall rules, dynamic VLAN mapping, and consistent security policies across distributed branch offices.

Question 380

How are logical interface units formatted and configured under the physical interface hierarchy in Junos OS?

1. Using slash-separated notation (e.g., ge-0/0/0/1)
2. Using dot-separated notation (e.g., ge-0/0/0.0)
3. Using colon-separated notation (e.g., ge-0/0/0:1)
4. Using hyphen-separated notation (e.g., ge-0/0/0-unit1)

Correct Answer: 2

Explanation

Junos OS utilizes a highly structured, modular interface naming convention where physical interfaces are identified by media type, FPC slot, PIC slot, and port number (e.g., ge-0/0/0). To configure logical sub-interfaces, VLAN encapsulations, or layer three IP addresses, administrators append a dot followed by the logical unit number (e.g., ge-0/0/0.0). This dot notation clearly separates physical port hardware identification from logical software-defined sub-interfaces, simplifying firewall filtering and routing instance assignments.