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Question 101:
Which Junos OS routing protocol is used to prevent Layer 2 loops in switched networks?
A) Spanning Tree Protocol (STP)
B) OSPF
C) BGP
D) RIP
Answer: A
Explanation:
This question addresses loop prevention in Layer 2 switched environments, which is fundamental to maintaining stable network operations. Network specialists must understand STP to design and troubleshoot switched networks effectively.
Option A is correct because Spanning Tree Protocol (STP) prevents Layer 2 loops in switched networks by creating a loop-free logical topology from physical networks that may contain redundant paths. STP operates by electing a root bridge, calculating shortest paths to the root, and blocking redundant paths that would create loops while maintaining them as backup paths for automatic failover. When switches exchange Bridge Protocol Data Units (BPDUs) containing bridge IDs and path costs, STP determines which ports should forward traffic and which should block. Junos OS supports multiple STP variants including traditional 802.1D STP, Rapid Spanning Tree Protocol (RSTP/802.1w) providing faster convergence, and Multiple Spanning Tree Protocol (MSTP/802.1s) supporting VLAN-aware topologies. Without STP or similar loop prevention, broadcast storms would rapidly consume all network bandwidth and crash switches.
Option B describes OSPF, which is a Layer 3 routing protocol for determining best paths in routed networks. While OSPF prevents routing loops through mechanisms like sequence numbers and area design, it operates at Layer 3 rather than preventing Layer 2 switching loops.
Option C refers to BGP, which is used for inter-domain routing particularly in service provider and large enterprise networks. BGP prevents routing loops through AS path attributes but doesn’t address Layer 2 switching loops.
Option D mentions RIP, which is a distance-vector routing protocol preventing routing loops through hop count limits and split horizon. Like OSPF and BGP, RIP operates at Layer 3 rather than preventing Layer 2 loops.
Network specialists should understand STP operation including root bridge election based on bridge priority and MAC address, port role assignment (root, designated, alternate, backup), port states (blocking, listening, learning, forwarding, disabled), BPDU format and exchange, path cost calculation, topology change handling, RSTP’s rapid convergence improvements through proposal/agreement mechanism, MSTP’s VLAN grouping into instances, protection features like BPDU guard preventing rogue switches, root guard preventing unauthorized root bridges, and loop guard detecting unidirectional link failures that could create loops.
Question 102:
What is the default administrative distance for OSPF routes in Junos OS?
A) 10
B) 15
C) 20
D) 110
Answer: A
Explanation:
This question tests knowledge of route preference values in Junos OS, which determine route selection when multiple protocols provide routes to the same destination. Understanding preference values is essential for controlling routing behavior in multi-protocol environments.
Option A is correct because Junos OS assigns OSPF internal routes a default preference value of 10, making them preferred over most other routing protocols in default configurations. Junos OS uses “preference” terminology equivalent to “administrative distance” in other vendors’ terminology. OSPF external routes receive default preference of 150, distinguishing between routes learned within OSPF domains versus redistributed from other protocols. These preference values ensure that internal topology information is trusted over external routes potentially originating from less reliable sources. Understanding preference is critical when multiple protocols provide routes to the same prefix, as Junos OS selects the route with lowest preference value regardless of metrics like hop count or cost.
Option B represents the default preference for IS-IS Level 1 internal routes in Junos OS, not OSPF. While both are link-state protocols, they have different default preferences.
Option C is not a standard default preference for major routing protocols in Junos OS. This value might be used for custom static routes but doesn’t represent OSPF’s default.
Option D represents administrative distance for OSPF in Cisco IOS and other vendors’ implementations, not Junos OS default. This common confusion point emphasizes understanding vendor-specific differences.
Network specialists should understand Junos OS preference values for all routing protocols including direct routes (0), static routes (5), OSPF internal (10), IS-IS Level 1 internal (15), IS-IS Level 2 internal (18), RIP (100), OSPF external (150), BGP (170), know that lower values are preferred, configure custom preferences using “preference” statement under routing protocol configuration, understand that preference comparison occurs before metric comparison, recognize situations requiring preference modification like preferring static routes over dynamic protocols, use preference for traffic engineering by influencing route selection, understand interaction between preference and route selection in routing tables, and troubleshoot unexpected routing behavior by verifying preference values.
Question 103:
Which command displays the current active configuration on a Junos device?
A) show configuration
B) show running-config
C) display configuration
D) get config
Answer: A
Explanation:
This question addresses basic Junos OS command syntax for viewing configurations. Network specialists must master fundamental commands to manage and troubleshoot Junos devices effectively.
Option A is correct because “show configuration” displays the current active configuration on Junos OS devices, showing all configured elements in hierarchical format. This command can be executed from operational mode and supports numerous options for filtering output including “show configuration protocols” for routing protocol configuration, “show configuration interfaces” for interface settings, “show configuration | display set” for set-command format, and “show configuration | compare” for comparing candidate and active configurations. Understanding configuration viewing is fundamental to verifying settings, troubleshooting issues, documenting configurations, and planning changes. Junos OS maintains separate candidate and active configurations, with “show configuration” displaying the currently running active configuration unless executed in configuration mode where it shows the candidate.
Option B represents Cisco IOS command syntax rather than Junos OS. This common confusion point emphasizes understanding vendor-specific CLI differences between Junos and IOS.
Option C uses incorrect command syntax for Junos OS. While “display” is used as a pipe modifier (like “| display set”), it’s not the primary command for viewing configurations.
Option D represents command syntax from other vendors’ devices rather than Junos OS standard operational commands.
Network specialists should master Junos OS configuration commands including “show configuration” for viewing active config, “show configuration | compare” for seeing uncommitted changes, “show configuration | display set” for set-command format useful for scripting, “show configuration | display inheritance” for viewing inherited configuration, “show | compare rollback” for comparing with previous configurations, understand configuration modes including operational mode where “show” commands execute and configuration mode entered with “configure” command, use “commit” to activate candidate configuration changes, leverage “commit confirmed” for safe changes with automatic rollback, utilize “rollback” for reverting to previous configurations, and structure configuration viewing efficiently using hierarchy levels and filters.
Question 104:
What is the purpose of a Virtual Chassis in Juniper switching technology?
A) To interconnect multiple physical switches into a single logical switch for simplified management
B) To provide wireless connectivity for mobile devices
C) To encrypt all traffic between switches
D) To separate network traffic into isolated security zones
Answer: A
Explanation:
This question examines Virtual Chassis technology enabling switch stacking for operational simplification. Network specialists must understand Virtual Chassis to design and manage scalable campus switching architectures.
Option A is correct because Virtual Chassis interconnects multiple physical EX Series switches using dedicated Virtual Chassis Port (VCP) connections or standard network ports into a single logical switch with unified management plane, single IP address, one configuration file, and distributed forwarding plane. Virtual Chassis provides operational benefits including simplified management through single device configuration, seamless failover with sub-second convergence, linear scalability adding switches without complex configurations, and distributed processing where member switches share forwarding load. Virtual Chassis members elect a Master Routing Engine providing control plane functions and Backup Routing Engine for redundancy, while all members participate in forwarding. Member switches can be geographically distributed with proper uplink design, supporting campus networks with consistent configuration across locations.
Option B describes wireless access point functionality rather than Virtual Chassis switching technology. While switches may connect to wireless controllers, Virtual Chassis specifically addresses switch interconnection.
Option C incorrectly focuses on encryption. While Virtual Chassis supports MACsec encryption on interconnect links, its primary purpose is logical unification for management simplification rather than security.
Option D describes security zoning typically implemented through VLANs, firewalls, or routing, not Virtual Chassis technology. Virtual Chassis provides operational unification rather than traffic isolation.
Network specialists should understand Virtual Chassis architecture including master/backup/linecard member roles, VCP connections providing high-bandwidth low-latency interconnects, uplink management for redundant connectivity to distribution layers, split and merge detection preventing configuration conflicts when Virtual Chassis separates, member preprovisioning allowing configuration before physical installation, mixed-mode operation supporting different switch models, configuration including virtual-chassis stanza defining member roles and IDs, monitoring using “show virtual-chassis status” commands, troubleshooting Virtual Chassis issues through log analysis, and comparing Virtual Chassis with alternative architectures like stacked switches or distributed configurations.
Question 105:
Which BGP attribute is used to prevent routing loops in BGP?
A) AS Path
B) Local Preference
C) MED
D) Origin
Answer: A
Explanation:
This question addresses BGP loop prevention mechanisms critical for stable inter-domain routing. Network specialists must understand BGP attributes to design and troubleshoot BGP deployments effectively.
Option A is correct because AS Path is the BGP well-known mandatory attribute listing autonomous system numbers the route advertisement has traversed, preventing routing loops by rejecting routes containing the local AS number in their AS Path. When a BGP speaker receives a route advertisement, it checks the AS Path attribute and discards any routes listing its own AS number, preventing acceptance of routes that have already transited through the local AS creating loops. AS Path also influences route selection as shorter paths are generally preferred, supports path manipulation through AS Path prepending for traffic engineering, and provides visibility into routing topology showing which autonomous systems routes traverse. Loop prevention through AS Path is fundamental to BGP’s scalability across the Internet’s distributed autonomous system architecture.
Option B describes Local Preference, which is used within an AS to influence route selection by indicating which exit point to prefer for reaching external destinations. Local Preference affects best path selection but doesn’t prevent loops.
Option C refers to Multi-Exit Discriminator (MED), which suggests to neighboring autonomous systems which entry point to prefer when multiple connections exist. MED influences inbound traffic but doesn’t prevent routing loops.
Option D mentions Origin attribute indicating how routes were introduced into BGP (IGP, EGP, or incomplete). While Origin affects route selection, it doesn’t provide loop prevention.
Network specialists should understand BGP loop prevention including AS Path’s role rejecting routes containing local AS, confederation sub-AS handling where confederation segments appear in AS Path, AS Path manipulation through prepending for traffic engineering, route reflection considerations where reflected routes maintain original AS Path, loop prevention in route server scenarios using transparent AS mode, private AS number handling at autonomous system boundaries, AS Path regular expression filtering for route policies, verification using “show route protocol bgp detail” displaying AS Paths, troubleshooting loops by analyzing AS Path sequences, and understanding that BGP’s loop prevention differs fundamentally from IGP distance-vector protocols using hop count or link-state protocols using sequence numbers.
Question 106:
What is the purpose of the “commit confirmed” command in Junos OS?
A) To automatically roll back configuration changes if not confirmed within a specified time
B) To permanently commit changes without any rollback option
C) To display configuration differences before committing
D) To synchronize configurations across all devices in a cluster
Answer: A
Explanation:
This question examines the safety mechanism for configuration changes that prevent accidental lockout. Network specialists must understand commit confirmed to safely implement changes on production devices.
Option A is correct because “commit confirmed” activates configuration changes temporarily, requiring explicit confirmation within a specified time period (default 10 minutes) or automatically rolling back to the previous configuration, preventing permanent lockout from misconfigured access controls, routing changes, or interface settings. This safety mechanism is particularly valuable when making remote changes that could disrupt connectivity, implementing complex configurations with potential errors, or modifying critical security settings. The syntax “commit confirmed <minutes>” specifies the confirmation timeout, after which Junos OS automatically reverts unless “commit” command confirms the changes. During the confirmation period, the new configuration is active allowing testing, but the system maintains a scheduled rollback job that executes if confirmation doesn’t occur.
Option B contradicts commit confirmed’s purpose. Standard “commit” command permanently activates changes, while “commit confirmed” specifically provides automatic rollback protection.
Option C describes “show | compare” command functionality displaying configuration differences. While useful before committing, this isn’t the purpose of commit confirmed.
Option **D) describes configuration synchronization in chassis clusters or Virtual Chassis, not commit confirmed functionality. Synchronization occurs through different mechanisms like commit synchronize.
Network specialists should understand commit confirmed usage including specifying timeout periods appropriate for testing complexity, executing “commit” command within timeout to confirm changes and prevent rollback, understanding that rollback occurs automatically if confirmation is missed, using commit confirmed for remote changes preventing lockout, combining with “commit comment” documenting change purposes, recognizing commit confirmed doesn’t prevent all misconfigurations only provides rollback safety, troubleshooting by monitoring system logs during commit confirmed period, best practices including always using commit confirmed for remote changes, testing changes quickly within confirmation window, and maintaining alternative access methods like console connections when implementing potentially disruptive changes.
Question 107:
Which routing protocol uses Dijkstra’s algorithm to calculate the shortest path?
A) OSPF
B) RIP
C) BGP
D) Static routing
Answer: A
Explanation:
This question addresses the algorithm underlying OSPF’s route calculation. Understanding routing protocol algorithms helps network specialists troubleshoot convergence issues and optimize network performance.
Option A is correct because OSPF uses Dijkstra’s shortest path first (SPF) algorithm to calculate the shortest path tree from the router’s perspective to all destinations in the link-state database. After routers exchange link-state advertisements building complete network topology databases, each router independently runs Dijkstra’s algorithm placing itself as the root and calculating least-cost paths to all other routers and networks. The algorithm iteratively selects the closest unprocessed node, updates distances to neighbors, and continues until all destinations have calculated paths. This calculation produces the routing table entries OSPF installs. Dijkstra’s algorithm guarantees finding the shortest path but requires significant processing, which is why OSPF supports hierarchical area design reducing SPF calculation scope and partial SPF calculations when topology changes are localized.
Option **B) describes RIP, which uses Bellman-Ford distance-vector algorithm rather than Dijkstra’s. RIP routers exchange distance vectors and update routing tables based on neighbor advertisements without calculating complete topology.
Option C refers to BGP, which uses best path selection algorithm considering multiple attributes in specific order (weight, local preference, locally originated, AS path length, origin, MED, etc.) rather than Dijkstra’s shortest path calculation.
Option D mentions static routing, which doesn’t use any algorithm as routes are manually configured by administrators rather than calculated dynamically.
Network specialists should understand OSPF operation including link-state advertisement exchange building topology database, SPF calculation triggered by topology changes or periodic refresh, partial SPF when changes are localized to specific branches, next-hop calculation determining forwarding interfaces, cost metric calculation based on interface bandwidth by default, hierarchical design reducing SPF calculation scope through areas, ABR route summarization limiting LSA flooding, stub area types reducing database size, monitoring SPF execution using “show ospf statistics” commands, troubleshooting excessive SPF calculations indicating instability, and optimizing OSPF through appropriate area design, summarization, and timer tuning balancing convergence speed against processing overhead.
Question 108:
What is the default VLAN ID on Juniper switches?
A) VLAN 1
B) VLAN 0
C) VLAN 100
D) VLAN 4095
Answer: A
Explanation:
This question tests basic VLAN knowledge essential for switch configuration. Network specialists must understand default VLAN behavior to properly segment and secure switched networks.
Option A is correct because VLAN 1 is the default VLAN on Juniper EX Series switches, automatically created and initially containing all switch ports unless explicitly configured otherwise. VLAN 1 serves as the default for untagged traffic and management functions in default configurations. However, security best practices recommend against using VLAN 1 for production traffic due to its special status and widespread knowledge, instead configuring custom VLANs for traffic segmentation and reserving VLAN 1 for management with strict access controls. Juniper switches support 4094 usable VLANs (IDs 1-4094) with VLAN 0 reserved and VLAN 4095 used internally. Default VLAN membership means ports accept untagged traffic and assign it to the default VLAN unless trunk ports are configured accepting tagged frames.
Option B mentions VLAN 0, which is reserved in 802.1Q standard and not used for regular traffic. VLAN ID 0 appears in priority-tagged frames indicating no VLAN assignment with only priority information.
Option C suggests VLAN 100, which has no special significance and isn’t the default VLAN. Organizations commonly use VLAN 100 and similar IDs for production networks but this isn’t a default value.
Option D refers to VLAN 4095, which is reserved for implementation use and not available for customer configuration on Juniper switches.
Network specialists should understand VLAN configuration in Junos OS including creating VLANs with “set vlans <name> vlan-id <id>” commands, assigning ports to VLANs using interface configuration, configuring trunk ports accepting tagged frames with “port-mode trunk”, setting native VLAN for untagged traffic on trunk ports, implementing inter-VLAN routing through routed VLAN interfaces (RVIs) or Layer 3 interfaces, security considerations including changing default VLAN, disabling unused VLANs, implementing VLAN access control, VLAN troubleshooting using “show vlans” and “show ethernet-switching table” commands, understanding VLAN tagging with 802.1Q adding 4-byte tag, and designing VLAN architectures balancing segmentation benefits against complexity and broadcast domain size.
Question 109:
Which protocol is used for dynamic MAC address learning in Ethernet switches?
A) Source MAC address from incoming frames
B) ARP
C) ICMP
D) DHCP
Answer: A
Explanation:
This question addresses fundamental switch operation learning MAC addresses for forwarding decisions. Understanding MAC learning is essential for troubleshooting switching issues and understanding network behavior.
Option A is correct because Ethernet switches dynamically learn MAC addresses by examining the source MAC address of incoming frames and associating those addresses with the ports on which frames arrive, building forwarding tables (MAC address tables) that map MAC addresses to specific switch ports. When a switch receives a frame, it records the source MAC address, the ingress port, and typically the VLAN ID in its MAC address table, creating forwarding state for that address. Subsequently, when frames destined for that MAC address arrive, the switch forwards them out the learned port rather than flooding to all ports. This dynamic learning eliminates manual configuration, automatically adapts to topology changes as devices move between ports, and ages out entries after inactivity periods removing stale information. MAC learning is fundamental to transparent bridging where switches operate without requiring end host configuration.
Option B describes ARP (Address Resolution Protocol), which maps Layer 3 IP addresses to Layer 2 MAC addresses enabling communication in IP networks. While ARP involves MAC addresses, switches don’t use ARP for learning – they passively observe frame source addresses.
Option C refers to ICMP (Internet Control Message Protocol), which is used for error reporting and network diagnostics at Layer 3. ICMP doesn’t participate in MAC address learning which occurs at Layer 2.
Option D mentions DHCP (Dynamic Host Configuration Protocol), which assigns IP addresses to hosts. DHCP operates at Layer 3 and above, while MAC learning is a Layer 2 function independent of IP addressing.
Network specialists should understand MAC address table operation including learning source addresses from incoming frames, aging mechanism removing inactive entries after timeout (default typically 300 seconds in Junos), static MAC entries configured manually for security or specific forwarding requirements, MAC address table size limits depending on switch model, flooding behavior when destination MAC is unknown, troubleshooting using “show ethernet-switching table” displaying learned addresses, “clear ethernet-switching table” removing learned entries, MAC address table inconsistencies from duplicate MAC addresses, security threats like MAC flooding attacks overwhelming table capacity, and MAC address table management in Virtual Chassis where tables are distributed across member switches.
Question 110:
What is the purpose of a Route Reflector in BGP?
A) To reduce the number of iBGP peering sessions required in large networks
B) To filter routes between autonomous systems
C) To convert BGP routes to OSPF routes
D) To provide backup routes in case of primary route failure
Answer: A
Explanation:
This question examines BGP scaling techniques essential for large networks. Network specialists must understand route reflection to design scalable iBGP architectures.
Option A is correct because Route Reflectors reduce iBGP peering requirements by allowing iBGP routers to reflect routes learned from one iBGP peer to other iBGP peers, eliminating the need for full mesh iBGP peering where every router peers with every other router. In standard iBGP, full mesh peering is required because routers don’t advertise routes learned from one iBGP peer to another iBGP peer (preventing loops), necessitating n(n-1)/2 peering sessions for n routers. Route Reflectors relax this restriction allowing designated routers (route reflectors) to redistribute iBGP-learned routes to other iBGP clients, reducing peering to hub-and-spoke topologies. Route Reflectors mark routes with originator ID and cluster list attributes preventing loops when reflected routes circulate. This scaling technique dramatically reduces configuration complexity and CPU/memory overhead in large networks.
Option B describes route filtering typically implemented through BGP policies rather than route reflection’s scaling purpose. While route reflectors can apply policies, their primary purpose is reducing peering requirements.
Option **C) incorrectly suggests protocol conversion. Route Reflectors maintain BGP routing within autonomous systems rather than converting between protocols, which requires redistribution.
Option D describes backup routing which BGP provides through multiple paths and best path selection rather than route reflection’s specific purpose of reducing peering requirements.
Network specialists should understand route reflector configuration including designating route reflectors with “cluster” and configuring clients with “neighbor <address> cluster <id>”, cluster ID preventing loops when routes reflect through multiple RRs, originator ID identifying original route source, route reflector hierarchies where RRs can be clients of other RRs creating hierarchy, route selection considerations where RRs must consistently select best paths, redundancy through multiple route reflectors in a cluster, comparing route reflection with confederation alternative for iBGP scaling, troubleshooting route reflection issues including missing routes due to misconfigured client relationships, and designing RR topologies considering traffic flow patterns and resiliency requirements.
Question 111:
Which command is used to save the current configuration permanently on a Junos device?
A) commit
B) save configuration
C) write memory
D) copy running-config startup-config
Answer: A
Explanation:
This question tests fundamental configuration management knowledge in Junos OS. Network specialists must understand the commit model to safely manage device configurations.
Option A is correct because “commit” is the Junos OS command that validates the candidate configuration for syntax and referential integrity errors, then activates it as the running configuration and saves it permanently to storage. Junos OS uses a candidate configuration model where changes are made to a candidate copy without immediately affecting device operation, allowing multiple changes to be made and validated together before activation. The commit process checks for errors, and only if validation succeeds does it activate changes and save them persistently. This differs fundamentally from immediate-mode configuration in other vendors’ devices. Junos also supports commit options including “commit check” validating without activating, “commit confirmed” with automatic rollback, and “commit synchronize” in chassis clusters.
Option B represents incorrect Junos command syntax. While conceptually describing the goal, “save configuration” isn’t a valid Junos command for making configurations permanent.
Option C represents Cisco IOS command syntax rather than Junos OS. This common confusion point emphasizes understanding vendor-specific CLI differences.
Option D also represents Cisco IOS command syntax for copying running configuration to startup configuration, not applicable to Junos OS which uses the commit model.
Network specialists should understand Junos configuration model including candidate configuration where changes are made, active configuration currently running on device, commit process validating and activating changes, automatic configuration backup where Junos maintains multiple previous configurations, rollback capability reverting to previous configurations using “rollback <number>”, commit operations including standard commit, commit confirmed for safety, commit check for validation without activation, commit comment documenting changes, configuration archival automatically saving configurations to external servers, rescue configuration as known-good configuration for emergency recovery, and differences from other vendors’ immediate-mode configuration requiring explicit save operations.
Question 112:
What is the function of the VRRP (Virtual Router Redundancy Protocol)?
A) To provide gateway redundancy allowing multiple routers to share a virtual IP address
B) To load balance traffic across multiple links
C) To prevent Layer 2 loops in switched networks
D) To provide dynamic routing updates between routers
Answer: A
Explanation:
This question addresses first-hop redundancy protocols essential for high availability. Network specialists must understand VRRP to design resilient network architectures preventing single points of failure.
Option A is correct because VRRP provides gateway redundancy by allowing multiple routers to participate in a virtual router group sharing a virtual IP address that serves as the default gateway for hosts, with one router acting as master forwarding traffic while others serve as backups ready to assume forwarding if the master fails. VRRP routers exchange advertisements communicating health and priority, with highest priority router becoming master. If the master fails (stops sending advertisements), the backup with next-highest priority transitions to master and begins responding to ARP requests for the virtual IP address, typically converging within seconds. VRRP supports multiple virtual routers on the same physical interfaces enabling load distribution by configuring different hosts with different virtual gateway addresses. This redundancy prevents network outages from single router failures without requiring hosts to support dynamic gateway discovery protocols.
Option B describes load balancing which can be implemented through various mechanisms but isn’t VRRP’s primary purpose. While VRRP enables basic load distribution through multiple virtual routers, its focus is redundancy rather than traffic distribution.
Option C describes Spanning Tree Protocol’s function preventing Layer 2 loops. VRRP operates at Layer 3 providing gateway redundancy rather than Layer 2 loop prevention.
Option D describes dynamic routing protocols like OSPF or BGP exchanging routing information. VRRP provides first-hop redundancy rather than routing protocol functionality.
Network specialists should understand VRRP operation including virtual router groups sharing virtual IP and MAC addresses, master/backup roles with master forwarding traffic, priority values determining master election with highest priority winning, advertisement exchange for health monitoring, preemption allowing higher-priority router to reclaim master role, authentication preventing unauthorized routers from participating, VRRP tracking monitoring uplink interfaces and adjusting priority when failures occur, configuration in Junos including virtual-address, priority, and tracking settings, monitoring using “show vrrp” commands, troubleshooting VRRP issues including split-brain scenarios with multiple masters, and comparing VRRP with alternatives like HSRP (Cisco-proprietary) and GLBP providing load balancing with redundancy.
Question 113:
Which OSPF area type does not allow external routes but allows summary routes?
A) Stub Area
B) Backbone Area
C) Totally Stubby Area
D) NSSA (Not-So-Stubby Area)
Answer: A
Explanation:
This question examines OSPF area types used for hierarchical design and route optimization. Understanding area types helps network specialists design scalable OSPF networks with controlled routing information propagation.
Option A is correct because Stub Areas prevent external routes (Type 5 LSAs) from being flooded into the area while still allowing summary routes (Type 3 LSAs) from other areas, reducing routing table size and LSA processing overhead in the stub area. Area Border Routers (ABRs) connecting stub areas to other areas block Type 5 external LSAs and instead inject a default route for reaching external destinations. This design is appropriate for areas containing primarily end users without external connectivity requirements, reducing memory and CPU consumption on routers in the stub area. Stub area configuration requires all routers in the area to be configured as stub including the ABR, and stub areas cannot contain ASBRs (Autonomous System Boundary Routers) originating external routes.
Option B describes Backbone Area (Area 0), which is a special area serving as the transit area through which all inter-area traffic passes. Backbone areas allow all LSA types including external routes and don’t have the restrictions of stub areas.
Option C refers to Totally Stubby Areas (Cisco terminology), which are even more restrictive than stub areas, blocking both external routes (Type 5) and summary routes (Type 3) from other areas, only allowing a default route for reaching destinations outside the area.
Option D mentions NSSA which allows external routes to be originated within the area using Type 7 LSAs (converted to Type 5 by ABR for other areas) while blocking Type 5 LSAs from entering the area, designed for areas needing to inject external routes despite being mostly stub-like.
Network specialists should understand OSPF area types including normal areas allowing all LSA types, stub areas blocking Type 5 LSAs but allowing Type 3 summaries, totally stubby areas blocking both Type 5 and Type 3 LSAs, NSSA allowing Type 7 external LSAs within the area, NSSA totally stubby combining NSSA and totally stubby characteristics, configuration requirements where all routers in an area must agree on area type, design considerations including placing ASBRs in normal areas, using stub areas for branch locations, LSA type functions including Type 1 router LSAs, Type 2 network LSAs, Type 3 summary LSAs, Type 4 ASBR summary LSAs, Type 5 external LSAs, and Type 7 NSSA external LSAs.
Question 114:
What is the purpose of LAG (Link Aggregation Group) in Juniper networks?
A) To combine multiple physical links into a single logical link for increased bandwidth and redundancy
B) To separate traffic into different VLANs
C) To provide wireless connectivity
D) To encrypt traffic between switches
Answer: A
Explanation:
This question addresses link aggregation technology improving bandwidth and resilience. Network specialists must understand LAG to design high-performance, redundant network connections.
Option A is correct because Link Aggregation Group (also known as Link Aggregation or LAG, based on IEEE 802.3ad/802.1AX standards) combines multiple physical Ethernet links between two devices into a single logical link, providing increased bandwidth through load distribution across member links and redundancy through automatic failover if member links fail. LAG operates by distributing traffic across member links using hash algorithms based on packet headers (source/destination MAC, IP addresses, or ports) ensuring packets from the same flow follow the same path maintaining packet order. Link Aggregation Control Protocol (LACP) dynamically negotiates and monitors LAG membership, detecting link failures and removing failed links from the bundle. Junos OS supports LAG through aggregated Ethernet (ae) interfaces containing multiple member physical interfaces, with configurable minimum-links thresholds ensuring LAG remains active only with sufficient operational members.
Option B describes VLAN functionality providing traffic segmentation at Layer 2. While LAG interfaces can carry VLAN-tagged traffic as trunk ports, LAG’s purpose is link aggregation rather than VLAN segmentation.
Option **C) refers to wireless connectivity provided by access points rather than LAG technology which aggregates wired Ethernet connections between switches, routers, or servers.
Option D describes encryption functionality which can be implemented through MACSec or IPSec rather than LAG. While LAG can carry encrypted traffic, its purpose is bandwidth aggregation and redundancy rather than security.
Network specialists should understand LAG configuration in Junos including creating aggregated Ethernet interfaces, assigning physical interfaces as members using “ether-options 802.3ad” configuration, configuring LACP for dynamic negotiation, selecting load-balancing algorithms affecting traffic distribution, setting minimum-links thresholds preventing insufficient bandwidth scenarios, monitoring LAG status using “show lacp interfaces” and “show interfaces <ae-x>”, troubleshooting LAG issues including member link failures, LACP negotiation problems, or configuration mismatches between LAG endpoints, understanding LAG limitations including requirement for same-speed links, connected-to-same-remote-device requirement, and comparing with alternative multi-link approaches like ECMP at Layer 3.
Question 115:
Which Junos OS feature allows you to filter and manipulate routing information?
A) Routing Policies
B) Access Control Lists (ACLs)
C) NAT (Network Address Translation)
D) DHCP
Answer: A
Explanation:
This question examines routing policies essential for controlling route advertisement and selection. Network specialists must master routing policies to implement traffic engineering and inter-domain routing requirements.
Option A is correct because Routing Policies in Junos OS provide powerful mechanisms for filtering and manipulating routing information including accepting or rejecting routes based on criteria, modifying route attributes like preference, metrics, communities, or AS paths, and controlling which routes are advertised to routing protocol neighbors or installed in the routing table. Routing policies consist of terms containing match conditions (from statements) and actions (then statements), evaluated in order until a match occurs. Policies apply at various points including import (filtering routes received from neighbors before table installation), export (filtering routes advertised to neighbors), and within routing tables. Policy framework supports complex logic using prefix-lists, AS-path regular expressions, community matching, and route-filters enabling sophisticated traffic engineering, route aggregation, and multi-homed network designs.
Option B describes firewall filters (ACLs in other vendors’ terminology) controlling packet forwarding rather than routing information manipulation. While firewall filters affect traffic flow, they operate on forwarded packets rather than routing protocol advertisements and route selection.
Option C refers to NAT which translates IP addresses for connectivity between private and public networks. NAT modifies packet addresses during forwarding rather than manipulating routing information or route selection.
Option D mentions DHCP which dynamically assigns IP addresses to hosts. DHCP operates as a service providing address allocation rather than filtering or manipulating routing information.
Network specialists should understand routing policy structure including policy statements containing terms, match conditions using “from” clauses specifying prefixes, protocols, AS paths, communities, or metrics, actions using “then” clauses accepting, rejecting, or modifying routes, default policy behavior when no explicit match occurs, policy application points including import and export under protocols, policy chaining where multiple policies can be sequentially applied, common policy uses including filtering routes based on prefix length, prepending AS paths for traffic engineering, setting communities for route tagging, adjusting local preference for path selection, implementing route summarization, troubleshooting policies using “show route receive-protocol” and “show route advertising-protocol”, testing policies with “test policy” command, and best practices including documenting policy purposes, structuring policies logically, and regularly reviewing policies for correctness and efficiency.
Question 116:
What is the default behavior when a route matches multiple terms in a Junos routing policy?
A) The first matching term’s action is taken and policy evaluation stops
B) All matching terms’ actions are applied cumulatively
C) The last matching term’s action is taken
D) No action is taken and the route is rejected
Answer: A
Explanation:
This question tests understanding of routing policy evaluation logic critical for predictable policy behavior. Network specialists must understand evaluation order to design policies that produce intended results.
Option A is correct because Junos OS routing policies evaluate terms in sequential order, and when a route matches a term’s conditions, the specified action (accept, reject, or modification) is taken and policy evaluation terminates unless the action includes “next term” modifier continuing to subsequent terms. This first-match behavior means term ordering is critical, with more specific match conditions typically placed before general conditions to ensure proper evaluation. If a route doesn’t match any terms, default policy action applies which varies by context (typically accept for import, reject for export). Understanding this evaluation model is essential for policy design, as incorrectly ordered terms can produce unexpected results where specific exceptions are never evaluated because broader matches occur first.
Option B incorrectly suggests cumulative application. While multiple actions can be applied using “next term” to continue evaluation, default behavior is termination after first match rather than automatic cumulative application.
Option **C) incorrectly suggests evaluation continues to last match. Junos policy evaluation stops at first match unless explicitly configured otherwise using “next term” statement.
Option D incorrectly implies rejection by default. When routes match terms, specified actions are taken. If no match occurs, default policy applies which depends on context but isn’t necessarily rejection.
Network specialists should understand policy evaluation including sequential term processing, termination on first match by default, “next term” statement continuing evaluation for cumulative modifications, “next policy” statement moving to next chained policy, default policy behavior varying by application point, term ordering importance with specific before general conditions, testing policy behavior using “test policy” command, debugging using “traceoptions” for policy evaluation visibility, common mistakes including incorrect term ordering, missing default actions, and overly broad match conditions preventing specific exceptions, and policy optimization techniques including consolidating terms, using prefix-lists efficiently, and avoiding unnecessary complexity that complicates troubleshooting.
Question 117:
Which protocol does Junos use for loop detection in Ethernet switching?
A) Spanning Tree Protocol (STP/RSTP/MSTP)
B) RIP
C) EIGRP
D) IS-IS
Answer: A
Explanation:
This question reinforces spanning tree protocol knowledge fundamental to switched network stability. Network specialists must understand spanning tree variants to prevent and troubleshoot Layer 2 loops.
Option A is correct because Junos OS EX Series switches implement IEEE 802.1D Spanning Tree Protocol (STP), 802.1w Rapid Spanning Tree Protocol (RSTP), and 802.1s Multiple Spanning Tree Protocol (MSTP) for Layer 2 loop detection and prevention in Ethernet switched networks. These protocols create loop-free logical topologies by blocking redundant paths while maintaining them for failover. RSTP provides faster convergence than traditional STP through proposal/agreement mechanism and alternate port roles. MSTP extends RSTP supporting multiple spanning tree instances mapped to VLAN groups, enabling load balancing and reducing convergence overhead. Junos switches default to RSTP (known as STP protocol-version rstp in configuration), providing backward compatibility with traditional STP while offering improved convergence. Protection features like BPDU protection, root protection, and loop protection enhance stability in production deployments.
Option **B) describes RIP, a Layer 3 distance-vector routing protocol using hop count to prevent routing loops. RIP operates at the network layer rather than detecting Layer 2 switching loops.
Option C mentions EIGRP, a Cisco-proprietary Layer 3 routing protocol. EIGRP isn’t supported in Junos OS and addresses routing loops rather than Layer 2 switching loops.
Option D refers to IS-IS, a Layer 3 link-state routing protocol that prevents routing loops through database synchronization and SPF calculation rather than addressing Layer 2 switching loops.
Network specialists should understand spanning tree implementation in Junos including configuring RSTP (default) or MSTP protocols, root bridge configuration using bridge-priority values, port roles (root, designated, alternate, backup) assigned based on topology, port states (discarding, learning, forwarding) in RSTP, topology change handling and rapid convergence mechanisms, MSTP instance configuration mapping VLANs to instances, protection features including BPDU protection preventing loops from unauthorized switches, root protection preventing unauthorized root bridges, loop protection detecting unidirectional failures, monitoring using “show spanning-tree interface”, “show spanning-tree bridge”, troubleshooting convergence issues and loops, optimizing through proper root bridge placement and load balancing, and understanding spanning tree interaction with features like link aggregation where LAG members are treated as single logical link.
Question 118:
What is the purpose of the “family inet” configuration under interfaces in Junos?
A) To configure IPv4 addressing and parameters on the interface
B) To configure IPv6 addressing on the interface
C) To configure Layer 2 switching parameters
D) To configure MPLS label switching
Answer: A
Explanation:
This question addresses Junos interface configuration hierarchy distinguishing protocol families. Understanding address families is essential for properly configuring interfaces supporting different network layer protocols.
Option A is correct because “family inet” under interface configuration specifies IPv4 protocol family, enabling IPv4 addressing and parameters on the interface including IPv4 addresses using “address” statements, unnumbered interfaces referencing other interfaces for addressing, MTU settings specific to IPv4, filters applied to IPv4 traffic, and sampling configurations for IPv4 packets. Junos OS organizes interface configuration hierarchically with physical parameters at top level, then protocol families (inet for IPv4, inet6 for IPv6, ethernet-switching for Layer 2, mpls for label switching) containing protocol-specific settings. This structure allows single physical interface to support multiple protocol families simultaneously, each with independent addressing and policies. The family inet configuration is fundamental to routing and Layer 3 forwarding, as interfaces require inet family configuration with addresses to forward IPv4 traffic.
Option B describes “family inet6” used for IPv6 configuration rather than “family inet” which specifically addresses IPv4. Junos separates IPv4 and IPv6 configuration into distinct families.
Option C refers to “family ethernet-switching” used for Layer 2 switching configuration on EX Series switches including VLAN membership and port modes rather than IPv4 addressing.
Option D mentions “family mpls” used for MPLS label switching configuration rather than IPv4 addressing that family inet provides.
Network specialists should understand Junos address family configuration including “family inet” for IPv4 with address statements, subnet masks in CIDR notation, secondary addresses for multiple subnets, preferred source address configuration, “family inet6” for IPv6 with address statements and neighbor discovery, “family ethernet-switching” for Layer 2 with VLAN configuration and port modes, “family mpls” for label switching, multiple families on single interface enabling protocol coexistence, troubleshooting interface addressing issues using “show interfaces” with various options, verifying address family configuration, understanding that family configuration is required for protocol operation, and recognizing that missing or incorrect family configuration is common source of connectivity issues.
Question 119:
Which command would you use to view the routing table on a Junos device?
A) show route
B) show ip route
C) display route
D) get route
Answer: A
Explanation:
This question tests basic operational command knowledge for viewing routing information. Network specialists must master routing table examination for troubleshooting and verification.
Option A is correct because “show route” is the primary Junos OS operational mode command for displaying routing table contents, showing destination prefixes, next hops, preferences, metrics, and route sources (protocols). The command supports numerous options including “show route protocol <protocol>” filtering by routing protocol, “show route <prefix>” displaying specific destinations, “show route detail” providing comprehensive route information including communities and AS paths for BGP routes, “show route extensive” showing even more detailed information including route age and preferences, and “show route summary” displaying routing table statistics. Understanding routing table structure with primary routes (active routes forwarded) versus secondary routes (backup routes not installed in forwarding table) is essential for interpreting output and troubleshooting routing issues.
Option B represents Cisco IOS command syntax rather than Junos OS. This common confusion emphasizes understanding vendor-specific CLI differences between platforms.
Option C uses incorrect Junos command syntax. While “display” is used as pipe modifier for formatting output (like “| display xml”), it’s not the primary command for viewing routes.
Option D represents command syntax from other vendors rather than Junos OS operational commands using “show” verb for displaying operational state.
Network specialists should master routing table commands including “show route” for basic table viewing, “show route protocol ospf” or similar for protocol-specific routes, “show route <destination>” for specific prefix lookup, “show route detail” for comprehensive route information, “show route extensive” for maximum verbosity, “show route hidden” for routes hidden by routing policy, “show route summary” for statistical overview, “show route forwarding-table” for FIB contents used for actual forwarding, understanding routing table structure including destination prefix, next hop, preference, metric, protocol indicator, age, and flags, interpreting active versus inactive routes where active routes install in forwarding table, troubleshooting routing issues by verifying expected routes exist, and comparing routing table with forwarding table to identify installation issues.
Question 120:
What is the function of a firewall filter in Junos OS?
A) To match and take actions on packets based on defined criteria
B) To dynamically learn MAC addresses
C) To provide DHCP services to clients
D) To perform network address translation
Answer: A
Explanation:
This question examines firewall filters which are Junos’s packet filtering mechanism. Network specialists must understand firewall filters to implement security policies, QoS, and traffic management.
Option A is correct because firewall filters in Junos OS (equivalent to ACLs in other vendors’ terminology) match packets against defined criteria and take specified actions, providing packet filtering, security policies, quality of service, traffic sampling, and forwarding control. Filters consist of terms containing match conditions (from statements) specifying packet characteristics like source/destination addresses, protocols, ports, ICMP types, TCP flags, or DSCP values, and actions (then statements) including accept, discard, reject, count, log, policer, or forwarding-class. Filters apply at various points including interface input/output, loopback for control plane protection, and forwarding table for post-routing filtering. Filter framework supports stateless packet filtering with flexible matching and actions, complementing stateful inspection available on SRX Series security devices.
Option B describes MAC address learning performed automatically by switch forwarding engines rather than firewall filters. While filters can match MAC addresses, they don’t perform learning which is switch data plane function.
Option C refers to DHCP services providing address allocation rather than firewall filter functionality. DHCP operates as network service while filters control packet forwarding.
Option D describes NAT functionality translating addresses rather than filtering packets. While both NAT and filters affect packet processing, they serve different purposes with NAT modifying addresses versus filters controlling forwarding decisions.
Network specialists should understand firewall filter configuration including defining filters with terms, match conditions using “from” statements, actions using “then” statements, filter application using “firewall” configuration at interface or routing level, common uses including edge filtering for security, traffic classification for QoS, sampling for monitoring, rate limiting with policers, control plane protection on loopback interface, filter optimization techniques including term ordering with specific before general, using prefix-lists and applications (port definitions), combining related matches, monitoring filter statistics using “show firewall” commands, troubleshooting by verifying filter application points and match conditions, and understanding performance implications where complex filters can impact forwarding performance requiring careful design in high-throughput environments.
