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

 

Question 141

What operational purpose does the Junos commit check command serve?

1. Applying configuration changes to the active running database instantly
2. Validating syntax correctness without activating the configuration
3. Rebuilding internal flash memory partitions safely
4. Rebooting the routing engine hardware platform

Correct Answer: 2

Explanation

The commit check command in Junos OS allows administrators to verify the syntactic and semantic validity of candidate configuration changes before formally applying them to the running environment. When executed, the device parser checks all defined statements for errors, missing dependencies, or conflicting parameters without modifying the active operational state. This proactive verification prevents accidental syntax errors from disrupting production network services, ensuring high reliability during complex administrative updates.

Question 142

Which feature does Mist Wired Assurance provide to streamline switch deployments across campuses?

1. Dynamic port profiles and automated provisioning
2. Static routing table redistribution metrics
3. Wireless roaming performance tuning algorithms
4. Bluetooth low energy asset beacon calibration

Correct Answer: 1

Explanation

Mist Wired Assurance leverages advanced cloud intelligence to automate switch management and simplify campus network operations. By utilizing dynamic port profiles, administrators can define configuration templates that automatically recognize connected endpoint types—such as IP phones, printers, or access points—and apply appropriate VLANs and security policies instantly. This eliminates tedious manual interface configurations, reduces human error, and accelerates onboarding times across enterprise switching architectures.

Question 143

Which OSPF Link-State Advertisement type represents a router describing its directly connected links?

1. AS-external LSA
2. Summary LSA
3. Router LSA
4. Network LSA

Correct Answer: 3

Explanation

Type 1 Router LSAs are generated by every OSPF router within a specific area to describe the operational states and cost metrics of its directly connected active interfaces. These link-state advertisements remain confined within their local area boundaries and are utilized by the SPF algorithm to calculate shortest-path tree topologies. Understanding LSA types is critical for network engineers analyzing routing protocol databases and optimizing multi-area OSPF enterprise network designs.

Question 144

How does a Juniper Virtual Chassis handle software version synchronization across member switches?

1. Requiring manual TFTP image flashing on every individual switch
2. Automatically synchronizing the active software version to new members
3. Booting into secondary backup ROM partitions exclusively
4. Restricting firmware updates to local USB flash drive connections

Correct Answer: 2

Explanation

Juniper Virtual Chassis technology simplifies software lifecycle management by automatically synchronizing operating system images across all member switches. When a new or replacement member switch joins the stack, the Master routing engine verifies its Junos version and distributes the matching software image automatically. This seamless synchronization ensures version consistency across the entire stacked logical entity, preventing operational incompatibilities and streamlining day-two maintenance operations.

Question 145

Which command restores a saved rescue configuration on a Junos routing device?

1. rollback rescue
2. rollback 0
3. clear rescue
4. load rescue

Correct Answer: 1

Explanation

The rollback rescue command allows an administrator to instantly revert the candidate configuration back to a previously saved, trusted baseline rescue configuration file. This is an essential disaster recovery mechanism if an operator misconfigures network services or locks out remote management access. By invoking the rescue configuration, administrative control is restored immediately without needing complex physical intervention or manual configuration reconstruction.

Question 146

Which BGP path selection attribute is evaluated based on the source protocol type of the route?

1. Origin code attribute
2. AS-Path length metric
3. Local preference value
4. Multi-Exit Discriminator

Correct Answer: 1

Explanation

The Border Gateway Protocol Origin attribute is a well-known mandatory attribute that indicates how a routing prefix was introduced into BGP. It supports three distinct values: IGP, EGP, or Incomplete. During path selection, BGP favors routes originating from an Interior Gateway Protocol over those learned via exterior protocols or redistributed statically. This attribute helps routers determine the most reliable and direct source of routing updates across federated autonomous systems.

Question 147

What specific wireless parameter does the Mist Roaming Service Level Expectation metric evaluate?

1. Client onboarding authentication speed
2. Inter-access point handover performance
3. RF signal noise floor fluctuations
4. Switch power over ethernet wattage draw

Correct Answer: 2

Explanation

The Roaming Service Level Expectation metric within the Mist platform tracks and evaluates how smoothly wireless client devices transition between different access points as users move throughout a facility. It measures critical roaming parameters such as latency, packet loss, and handoff duration. By continuously monitoring roaming metrics against defined thresholds, network administrators can identify coverage gaps, sticky client behaviors, or configuration issues that cause poor mobility experiences.

Question 148

What failure scenario does Spanning Tree Loop Guard specifically protect against in switching topologies?

1. Unidirectional link failures on point-to-point connections
2. Rogue DHCP server packet distribution attacks
3. Unauthorized bridge protocol data unit injection
4. Excessive broadcast traffic storm amplification

Correct Answer: 1

Explanation

Spanning Tree Loop Guard is designed to protect network topologies against bridging loops caused by unidirectional link failures. In scenarios where a fiber or copper link transmits data in one direction but stops receiving it, a blocked alternate or root port might incorrectly transition into a forwarding state, creating a dangerous loop. Loop Guard monitors these links; if BPDUs stop arriving on a non-designated port, it forces the port into a loop-inconsistent blocking state.

Question 149

What purpose do logical unit numbers serve when configuring interfaces in Junos OS?

1. Identifying physical chassis expansion slot numbers
2. Subdividing physical interfaces into logical VLAN channels
3. Assigning autonomous system numbers to BGP peers
4. Indexing hardware firewall filter counter statistics

Correct Answer: 2

Explanation

In Junos OS, physical interfaces are partitioned into logical sub-interfaces using unit numbers, enabling a single physical port to support multiple VLAN encapsulations, subnets, and routing protocols simultaneously. For example, interface ge-0/0/0.10 represents logical unit 10 on physical Gigabit Ethernet port zero. This hierarchical naming convention provides exceptional configuration flexibility, allowing network engineers to terminate diverse VLAN trunk connections and routing protocols on unified physical hardware interfaces efficiently.

Question 150

How do untrusted ports handle DHCP server offer messages when DHCP Snooping is enabled?

1. Dropping rogue server offer packets instantly
2. Encrypting payload data for secure transit
3. Forwarding packets to OSPF neighbors
4. Authenticating 802.1X supplicant credentials

Correct Answer: 1

Explanation

When DHCP Snooping is deployed, switch ports are designated as either trusted or untrusted. Untrusted ports face client endpoints and are strictly prohibited from originating server-side DHCP responses. If an unauthorized rogue device connected to an untrusted port attempts to send DHCP offer or acknowledgment packets, the switch intercepts and drops those frames immediately. This security mechanism protects enterprise clients from IP spoofing and rogue gateway attacks.

Question 151

Which configuration mode command temporarily disables a statement without deleting it in Junos OS?

1. delete
2. disable
3. deactivate
4. suspend

Correct Answer: 3

Explanation

The deactivate command in Junos configuration mode allows an administrator to temporarily disable specific configuration blocks—such as protocols, firewall filters, or interface settings—without permanently removing them from the file. Deactivated statements remain visible in the configuration file marked with an inactive tag and are ignored by the operating system during commits. This is highly useful for troubleshooting network issues by selectively turning off features and testing changes quickly.

Question 152

How does the Marvis Virtual Network Assistant perform automated root cause analysis?

1. By parsing static syslog text files manually
2. Through advanced artificial intelligence and telemetry correlation
3. By executing periodic SNMP polling queries
4. Via manual command-line packet capture scripts

Correct Answer: 2

Explanation

Marvis utilizes sophisticated artificial intelligence and machine learning algorithms to continuously analyze massive streams of cloud telemetry data across wireless, wired, and WAN domains. Instead of requiring engineers to manually sift through logs, Marvis automatically correlates client events, environmental metrics, and device states to isolate exact failure points. This automated root cause analysis drastically reduces mean time to resolution and delivers actionable remediation advice to enterprise IT support teams.

Question 153

What is a defining operational characteristic of an OSPF Not-So-Stubby Area?

1. Complete blocking of all external routing information
2. Permitting external routes via Type 7 LSAs translated to Type 5
3. Requiring full mesh adjacencies across all routers
4. Disabling interior routing protocol calculations entirely

Correct Answer: 2

Explanation

An OSPF Not-So-Stubby Area is an extension of stub area design that allows external routes to be injected into the area from an external autonomous system border router residing within it. NSSA achieves this by utilizing specialized Type 7 LSAs to carry external routes across the stub area. The NSSA Area Border Router then translates these Type 7 LSAs into standard Type 5 AS-external LSAs before flooding them into the rest of the OSPF routing domain.

Question 154

What primary role does the Backup routing engine fulfill in a Juniper Virtual Chassis?

1. Forwarding all data traffic while the Master sleeps
2. Taking over control plane functions if the Master fails
3. Managing external power supply unit redundancy only
4. Storing archival backup configuration files on USB

Correct Answer: 2

Explanation

In a Juniper Virtual Chassis stack, the Backup routing engine maintains synchronization with the Master routing engine’s control plane databases and routing tables. If the primary Master switch encounters a hardware failure, power outage, or reboot event, the Backup switch detects the loss of communication and transitions seamlessly into the Master role. This hitless failover capability ensures high availability and continuous control plane uptime across enterprise network environments.

Question 155

Which operational command displays configured firewall filters and match counters on a Junos device?

1. show firewall
2. show route table
3. show interface filters
4. show system firewall

Correct Answer: 1

Explanation

The show firewall command is the primary operational tool used to inspect firewall filter configurations, applied interfaces, and hardware match counter statistics on Junos platforms. When executed, it outputs packet and byte counts for every term defined within active firewall filters. Monitoring these counters allows network engineers to verify whether security policies are matching intended traffic streams, troubleshoot traffic blocking issues, and analyze denial-of-service mitigation effectiveness.

Question 156

What operational state indicates that a BGP peering session has successfully exchanged routing tables?

1. Active state
2. Established state
3. OpenSent state
4. Idle state

Correct Answer: 2

Explanation

The BGP Established state signifies that two peer routers have successfully completed their TCP handshakes, exchanged and verified Open messages, and established full operational adjacencies. In this state, the routers actively exchange routing table updates, prefix announcements, and keepalive messages. Monitoring peering states to ensure they remain in the Established condition is critical for verifying wide area network connectivity and dynamic path stability.

Question 157

What is the primary benefit of deploying site templates within the Mist cloud platform?

1. Configuring individual switches one port at a time
2. Ensuring global configuration consistency across multiple locations
3. Performing manual radio frequency channel surveys
4. Submitting hardware RMA replacement requests

Correct Answer: 2

Explanation

Site templates in the Juniper Mist platform empower network administrators to define standardized configuration policies—including VLANs, firewall rules, Wi-Fi SSIDs, and switch profiles—at a global level and push them seamlessly across hundreds of remote branch locations. This eliminates repetitive manual configurations, ensures strict compliance and policy consistency across the entire enterprise footprint, and simplifies day-two operational management as new sites are provisioned onto the network.

Question 158

Which OSI layer does MACsec encryption operate on to secure Ethernet links?

1. Layer 2
2. Layer 3
3. Layer 4
4. Layer 7

Correct Answer: 1

Explanation

MACsec, standardized under IEEE 802.1AE, provides point-to-point data encryption, data integrity, and data origin authenticity at Layer 2 of the OSI model. By securing Ethernet links between switches or client endpoints, MACsec protects against man-in-the-middle wiretapping, MAC tampering, and passive eavesdropping attacks. It encrypts traffic transparently across physical cabling without altering higher-layer routing protocols, making it an essential security standard for sensitive campus backbones and data center interconnects.

Question 159

Which statement component defines the matching criteria within a Junos routing policy?

1. from
2. then
3. action
4. match

Correct Answer: 1

Explanation

In Junos routing policy architecture, every policy term consists of match conditions and action clauses. The from statement defines the specific criteria—such as prefix lists, protocol types, or community tags—that incoming routes must satisfy. If a route matches the from criteria, the policy executes the corresponding actions defined within the then statement, such as accepting, rejecting, or modifying route attributes like local preference and metric values.

Question 160

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

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

Correct Answer: 1

Explanation

Dynamic ARP Inspection is a robust layer two security feature that leverages valid 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 IP-to-MAC bindings, discarding anomalous or conflicting frames immediately.