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

 

Question 321

Which Junos firewall filter action is used to enforce bandwidth limits and drop or remark traffic that exceeds a defined transmission rate?

1. accept
2. discard
3. policer
4. reject

Correct Answer: 3

Explanation

In Junos OS, applying a policer within a firewall filter term allows network administrators to control traffic rates by measuring packet flows against specific token bucket parameters. If traffic stays within the committed information rate, packets pass normally. When traffic exceeds the specified threshold, the policer can either drop the excess packets or remark their DSCP/CoS priority bits, enabling effective bandwidth management and ingress traffic policing across enterprise routing and switching interfaces without disrupting normal network operations.

Question 322

What performance parameter does the Mist Throughput Service Level Expectation metric evaluate across enterprise wireless environments?

1. Actual client connection speeds relative to capabilities and environmental interference
2. Physical power supply voltage stability inside wiring closet chassis
3. Total routing table memory utilization on core routing engine modules
4. Ambient room temperature fluctuations near ceiling access point mounts

Correct Answer: 1

Explanation

The Throughput Service Level Expectation metric within the Juniper Mist platform measures and evaluates real-world client data rates across wireless networks. Instead of looking only at theoretical link speeds, the Throughput SLE correlates actual client connection speeds with physical capabilities, signal strength, channel width, and environmental RF interference. If client throughput drops below acceptable thresholds due to congestion, poor signal quality, or legacy client overhead, Mist isolates the anomaly, allowing engineers to optimize channel assignments and radio configurations to maintain high performance.

Question 323

Which BGP path attribute is classified as a well-known mandatory attribute that logs every autonomous system traversed by a route advertisement?

1. Local Preference
2. AS-Path
3. Multi-Exit Discriminator
4. Community

Correct Answer: 2

Explanation

The AS-Path attribute is a well-known mandatory BGP path attribute that must be recognized and supported by all standard-compliant BGP implementations. As a route advertisement is propagated across different autonomous systems, each transit AS prepends its own autonomous system number to the sequence. This chronological listing serves two critical functions: it provides loop detection—preventing a route from looping back into an originating AS—and acts as a primary metric during path selection, where shorter AS paths are preferred over longer ones.

Question 324

What is the defining architectural characteristic of an OSPF Totally Stubby Area?

1. Complete elimination of all internal routing protocol daemons
2. Permission to inject external Type 5 routes via Type 7 LSAs
3. Mandatory requirement for static virtual link tunnels across all switches
4. Blocking of summary Type 3 and Type 4 LSAs in addition to external Type 5 LSAs

Correct Answer: 4

Explanation

An OSPF Totally Stubby Area is a Cisco and vendor-extended refinement of a standard stub area designed to minimize link-state database memory consumption on remote branch routers. In addition to blocking external Type 5 LSAs, an area border router servicing a totally stubby area actively blocks Type 3 summary LSAs and Type 4 ASBR summary LSAs from entering the area. The only routing information allowed into the area is a single default route injected by the ABR, forcing all traffic destined outside the area to flow through that designated gateway.

Question 325

Which Junos operational command displays the active active routing table entries and learned destination prefixes?

1. show route
2. show interfaces terse
3. show bgp summary
4. show system alarms

Correct Answer: 1

Explanation

The show route command is one of the most frequently utilized operational tools in Junos OS. It queries the routing engine’s routing table database to display active prefixes, destination networks, next-hop gateway IP addresses, route preferences, and the protocols that installed each route. Network engineers rely on this command to verify network reachability, debug routing protocol propagation issues, examine active forwarding paths, and ensure that static or dynamic routes are correctly installed before data plane packet forwarding occurs.

Question 326

What primary operational benefit does MACsec provide when implemented across enterprise switch links?

1. Automated translation of private IP addresses into public internet spaces
2. Point-to-point Layer 2 data encryption, integrity, and origin authenticity
3. Dynamic wireless channel tuning to eliminate co-channel interference
4. Centralized routing policy enforcement for multi-vendor BGP sessions

Correct Answer: 2

Explanation

MACsec, standardized under IEEE 802.1AE, provides robust point-to-point security directly at Layer 2 of the OSI model. By securing Ethernet links between switches or client endpoints, MACsec protects enterprise networks against wiretapping, MAC address spoofing, and passive eavesdropping attacks. It encrypts traffic transparently across physical cabling without altering higher-layer network protocols or routing configurations, making it an essential security standard for protecting vulnerable campus backbones and inter-switch uplinks.

Question 327

Which Junos configuration command saves the current candidate configuration as the designated rescue baseline?

1. commit rescue baseline
2. request system rescue save
3. set system rescue-file
4. save configuration rescue

Correct Answer: 2

Explanation

The request system rescue save command allows network administrators to store a known, verified, and fully functional configuration as the official rescue baseline file on a Junos device. Unlike rolling rollback indexes that get overwritten during routine commits, the rescue file remains preserved as a permanent safe haven. If a subsequent configuration change causes catastrophic syntax errors, locks out management access, or breaks network connectivity, administrators can instantly revert the device back to this pristine state using a simple recovery command.

Question 328

What specific topological protection does Spanning Tree Root Guard enforce when enabled on designated switch ports?

1. Disabling ports immediately upon receiving unexpected bridge protocol data units
2. Encrypting all spanning tree control frames with cryptographic pre-shared keys
3. Preventing broadcast storm amplification on multi-access trunk uplinks
4. Blocking ports that receive superior bridge protocol data units from unauthorized devices

Correct Answer: 4

Explanation

Spanning Tree Root Guard is designed to protect the logical placement of the root bridge within an enterprise switched network. When Root Guard is enabled on designated ports, the switch continuously monitors incoming bridge protocol data units. If an external or misconfigured device attempts to inject a superior BPDU in an effort to usurp the root bridge role, Root Guard immediately transitions the affected port into a root-inconsistent blocking state. This safeguards the core network topology from unauthorized modifications and prevents suboptimal traffic forwarding paths.

Question 329

What is the primary function of the DHCP Snooping database (binding table) on enterprise access switches?

1. Storing verified IP-to-MAC address bindings used by security features like Dynamic ARP Inspection
2. Caching web server pages locally to accelerate guest browsing speeds
3. Translating Layer 2 MAC addresses into public IPv6 subnet allocations automatically
4. Maintaining real-time power supply voltage and temperature telemetry logs

Correct Answer: 1

Explanation

The DHCP Snooping binding database is a critical security repository maintained by enterprise switches running DHCP Snooping. As clients complete the DORA DHCP process on untrusted ports, the switch inspects the exchange and records verified parameter pairings—including client MAC address, assigned IP address, lease time, VLAN ID, and trusted port interface. Companion layer two security features, such as Dynamic ARP Inspection and IP Source Guard, query this binding database to validate untrusted packet streams and drop malicious spoofed frames instantly.

Question 330

Which AI-driven component of the Juniper Mist platform allows network engineers to query telemetry data using natural, conversational English?

1. Marvis Virtual Network Assistant Conversational Interface
2. Automated Firmware Staging Engine
3. Dynamic Packet Capture Manager
4. Wired Assurance Port Profiler

Correct Answer: 1

Explanation

The Mist Virtual Network Assistant features a powerful natural language conversational interface powered by Marvis AI. Instead of navigating complex multi-layered dashboards or manually parsing through raw telemetry logs, administrators can type or speak queries in plain English (such as “Why did user device X fail authentication today?”). Marvis instantly interprets the underlying telemetry data, correlates client events across wireless and wired domains, and delivers precise diagnostic breakdowns along with actionable remediation steps to resolve issues rapidly.

Question 331

In Junos routing policies, which clause defines the actions executed when an incoming or outgoing route matches the specified criteria?

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

Correct Answer: 3

Explanation

Junos routing policies are organized into named term blocks, where each term functions as a logical rule container housing matching criteria and execution instructions. The from clause establishes the match conditions that a route must satisfy, while the companion then clause defines the explicit execution actions—such as accepting, rejecting, or modifying route attributes like local preference and community tags. If a route matches the from criteria, the system immediately executes the instructions defined within the then clause.

Question 332

What operational requirement must be met for an LACP link aggregation bundle to form successfully between two neighboring switches?

1. Both switches must be configured with identical MAC addresses
2. At least one peer switch must be configured in active LACP mode
3. Both switches must operate on legacy 10 Mbps half-duplex settings
4. Both switches must share the exact same OSPF area identifier

Correct Answer: 2

Explanation

Link Aggregation Control Protocol defines specific operational modes for member interfaces to govern how protocol control packets are exchanged. An interface configured in active mode actively initiates LACP negotiation by transmitting protocol frames, whereas a passive mode interface responds to incoming LACP frames but does not initiate them on its own. For an LACP bundle to form successfully across peer devices, at least one participating peer must be configured in active mode; if both sides are set to passive, protocol packets are never initiated and the bundle fails to form.

Question 333

Which Junos configuration hierarchy branch is utilized to manage physical and logical network interface parameters?

1. set interfaces
2. set protocols
3. set system
4. set firewall

Correct Answer: 1

Explanation

In Junos OS, all hardware and software network interface configurations are managed under the interfaces hierarchy. Administrators use this branch to configure physical port properties—such as link speeds, duplex modes, and descriptions—as well as logical sub-interfaces (unit), VLAN encapsulations, family inet address assignments, and traffic policing rules. The hierarchical structure ensures that interface parameters are organized logically, making configuration audits and script-based automation straightforward and reliable across enterprise routing and switching platforms.

Question 334

How is the OSPF Router ID determined on a Junos routing platform when no explicit static Router ID is configured by the administrator?

1. By selecting the highest IP address configured on any active loopback interface
2. By choosing the lowest MAC address on the physical management port
3. By assigning the default IP address of the primary default gateway
4. By querying the nearest external DHCP server during boot initialization

Correct Answer: 1

Explanation

The OSPF Router ID is a 32-bit dotted-decimal identifier required to uniquely identify every router participating in an OSPF domain. When configuring OSPF on Junos devices, administrators can explicitly define a static Router ID. If this optional statement is omitted, Junos follows a deterministic fallback election process: it automatically selects the highest IP address configured across any active loopback interfaces (lo0). If no loopback interfaces have IP addresses assigned, the system selects the highest IP address configured on any active physical interface.

Question 335

What specific BGP session state confirms that two peer routers have completed capability negotiations and are actively exchanging routing tables?

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

Correct Answer: 3

Explanation

The BGP Established state signifies that two peer routers have successfully completed their TCP handshakes, exchanged and verified Open messages, negotiated optional capabilities, and processed matching Keepalive confirmations. In this final operational state, the routing session is fully active, and the routers continuously exchange routing table updates, prefix announcements, and keepalive heartbeats. Monitoring peering states to ensure they remain in the Established condition is critical for verifying wide area network connectivity and dynamic path stability.

Question 336

What protocol tunneling methods are supported by Mist Edge to extend enterprise campus networks to remote branch office deployments?

1. SNMP and Syslog
2. IPsec and GRE
3. OSPF and BGP
4. HTTP and HTTPS

Correct Answer: 2

Explanation

Mist Edge is a specialized appliance engineered to extend enterprise campus networks and provide distributed tunnel aggregation capabilities for remote access point deployments. It terminates secure IPsec or GRE tunnels originating from remote branch access point deployments right back to the central data center or campus edge. This allows network administrators to maintain centralized tunneling policies, dynamic VLAN mapping, and secure traffic steering while still leveraging decentralized wireless architectures across various branch offices seamlessly.

Question 337

Which Junos operational command is used to display active system alarms and hardware warning conditions?

1. show system alarms
2. show route summary
3. show bgp neighbor
4. show interface terse

Correct Answer: 1

Explanation

The show system alarms command is a vital operational tool used by network engineers to inspect active system-level warnings and critical hardware alerts on Junos devices. When executed, it categorizes alarms into major and minor classifications, displaying issues such as power supply failures, cooling fan speed drops, high CPU utilization spikes, or temperature threshold warnings. Regularly checking system alarms allows operations teams to identify and remediate infrastructure faults proactively before they impact production network performance.

Question 338

How does Weighted Round Robin (WRR) scheduling manage output queue servicing during periods of interface congestion?

1. By dropping all packets in low-priority queues instantly
2. By servicing multiple output queues in a cyclic manner proportional to their assigned weights
3. By converting packet headers into binary protocol buffer streams
4. By transmitting only real-time voice priority frames while freezing others

Correct Answer: 2

Explanation

Weighted Round Robin is a popular queue scheduling algorithm utilized in enterprise switches and routers to manage traffic during congestion. Instead of servicing queues strictly in order or favoring a single queue, WRR services multiple output queues in a cyclic round-robin fashion, allocating transmission bandwidth opportunities proportional to each queue’s configured weight. This ensures that high-priority queues receive sufficient network capacity while preventing lower-priority traffic classes from experiencing total starvation during high utilization periods.

Question 339

Within a Juniper Virtual Chassis configuration, what role is assigned to the member switch possessing the second-highest routing engine priority value?

1. Primary standalone root gateway
2. Passive unmanaged bridge mode
3. Backup routing engine role
4. Standalone core firewall appliance

Correct Answer: 3

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, while the switch with the second-highest priority automatically assumes the Backup role. All remaining member switches function as line card routing units, participating in the distributed forwarding plane while maintaining synchronization with the shared control plane to ensure high availability.

Question 340

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.