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Question 101
Which OSPF network type uses DR and BDR election on broadcast networks?
A) Point-to-Point
B) Broadcast
C) Non-Broadcast
D) Point-to-Multipoint
Answer: B
Explanation:
OSPF (Open Shortest Path First) designates certain network types to optimize routing efficiency and reduce unnecessary flooding. Broadcast networks, commonly Ethernet segments with multiple routers, rely on Designated Router (DR) and Backup Designated Router (BDR) elections to minimize LSA flooding. This ensures that routers do not send routing updates to every other router directly, which could otherwise create excessive overhead and redundant traffic.
Option B) is correct because in a broadcast network, OSPF routers dynamically elect a DR and a BDR. The DR is responsible for disseminating LSAs to all routers on the segment, while the BDR acts as a standby in case the DR fails. Point-to-Point links, A), connect exactly two routers and do not require DR/BDR elections. Non-Broadcast networks, C), also require DR/BDR but often need manual neighbor configuration due to the lack of automatic broadcast. Point-to-Multipoint networks, D), treat each link individually as point-to-point and generally do not use DR/BDR elections.
The DR election process is based on OSPF router priority and router ID, allowing deterministic selection. Routers with higher priorities have a better chance of becoming DR. The BDR ensures high availability by taking over the DR role seamlessly in case of failure, which is critical for reducing convergence time and maintaining network stability.
Understanding DR and BDR is vital for enterprise network design, as it affects LSA propagation, convergence speed, and routing stability. In large enterprise LANs, efficient DR/BDR selection reduces unnecessary flooding of LSAs, conserving CPU and memory resources on routers. Additionally, properly configured DR and BDR roles prevent network partitions and routing inconsistencies, which could disrupt mission-critical applications such as VoIP, video conferencing, or ERP systems.
For ENARSI candidates, mastering DR/BDR election and broadcast network behavior demonstrates deep knowledge of OSPF design, network optimization, and hierarchical routing concepts. Proper implementation ensures networks are resilient, predictable, and capable of handling high-performance enterprise traffic without unnecessary overhead or instability.
Question 102
Which BGP feature prevents routing loops across autonomous systems?
A) Local Preference
B) AS Path
C) MED
D) Community
Answer: B
Explanation:
BGP (Border Gateway Protocol) relies on several attributes to control route selection and prevent routing loops, especially across multiple autonomous systems (ASes). The AS Path attribute is fundamental for loop prevention. Every time a BGP route traverses an AS, the AS number is prepended to the route’s AS Path. If a router receives a route advertisement containing its own AS number in the path, it automatically rejects the route, thus preventing a loop across AS boundaries.
Option B) is correct because AS Path is specifically designed for inter-AS loop prevention. Local Preference, A), only affects internal path preference and does not control loops. MED, C), signals external path preference but does not prevent loops. Community, D), is a tagging mechanism for policy application and is unrelated to loop prevention.
AS Path also plays a role in path selection, as BGP prefers routes with shorter AS Paths, optimizing outbound traffic flow and minimizing traversal through multiple ASes unnecessarily. This is critical in multi-homed enterprise networks to ensure efficient routing and predictable traffic patterns.
Loop prevention with AS Path is essential for enterprise networks connecting to multiple ISPs or participating in large-scale MPLS or WAN architectures. Without it, BGP could mistakenly accept a route that would create a circular path, resulting in instability, routing oscillations, or packet loss. Correct understanding of AS Path behavior ensures that network engineers can implement reliable, redundant, and loop-free inter-AS connectivity.
For ENARSI exam preparation, grasping AS Path usage is critical because it highlights advanced BGP policy enforcement, traffic engineering, and loop mitigation strategies. Engineers must know how to combine AS Path filtering, prepending, and other attributes to maintain enterprise network integrity while optimizing performance. Mastery of AS Path ensures predictable, secure, and resilient connectivity, which is the hallmark of enterprise-grade BGP deployments.
Question 103
Which EIGRP feature allows load balancing over unequal-cost paths?
A) Variance
B) Feasible Successor
C) Passive Interface
D) Split Horizon
Answer: A
Explanation:
EIGRP (Enhanced Interior Gateway Routing Protocol) provides a unique mechanism for load balancing over unequal-cost paths, called Variance. By default, EIGRP balances traffic only across equal-cost paths. The variance command multiplies the metric of the best path by a given factor, allowing routers to install backup routes that are within the specified range in the routing table for traffic distribution.
Option A) is correct because Variance allows multiple paths to be used even if their metrics differ, as long as they satisfy the feasibility condition. Feasible Successor, B), ensures loop-free backup paths but does not directly influence load balancing. Passive Interface, C), suppresses EIGRP updates on specific interfaces. Split Horizon, D), prevents advertising a route back through the interface it was learned from.
Using variance improves network efficiency by distributing traffic across multiple links, optimizing bandwidth utilization in WANs or complex enterprise topologies. For example, an enterprise may have a primary high-speed link and a secondary slightly slower link. Without variance, EIGRP would not use the slower path for active traffic. By setting an appropriate variance value, traffic can flow over both links without violating loop-free guarantees, enhancing resiliency and redundancy.
Variance is crucial for ENARSI candidates because it demonstrates understanding of advanced routing techniques, traffic engineering, and failover strategies. Proper use of variance ensures that enterprise networks maintain predictable performance, make efficient use of available resources, and support critical applications with minimal downtime. Misconfiguration could lead to suboptimal routing or overloading of a primary path, highlighting the importance of metric calculation, feasibility conditions, and EIGRP topology table awareness.
Question 104
Which OSPF area type allows limited external routes using Type 7 LSAs?
A) Stub
B) NSSA
C) Totally Stubby
D) Backbone
Answer: B
Explanation:
The Not-So-Stubby Area (NSSA) is an OSPF area type designed to combine the benefits of stub areas with the ability to inject limited external routes. NSSAs generate Type 7 LSAs for external networks, which can later be translated into Type 5 LSAs by the ABR when propagating to other areas. This allows branch or remote areas to redistribute external routes without overloading the area with full Type 5 LSA information.
Option B) is correct because NSSAs are specifically configured for partial external route visibility. Stub areas, A), block all Type 5 LSAs. Totally Stubby Areas, C), block Type 3 inter-area LSAs in addition to Type 5. Backbone, D), does not restrict LSAs.
NSSAs are ideal for remote office scenarios, where only select external routes are necessary for connectivity, reducing routing table size, LSA flooding, and router CPU load. The ABR in an NSSA converts Type 7 LSAs into Type 5 LSAs for propagation across non-NSSA areas, maintaining consistent reachability while optimizing OSPF scaling and performance.
For ENARSI candidates, understanding NSSA areas is critical because it reflects advanced OSPF area design, hierarchical scalability, and external route management. Proper configuration allows enterprise networks to maintain efficient routing tables, ensure high availability, and reduce convergence time, especially in multi-area topologies with redistribution requirements. Mastery of NSSA concepts is essential for designing robust, resilient, and scalable enterprise OSPF networks.
Question 105
Which BGP attribute signals path preference to external neighbors?
A) Weight
B) Local Preference
C) MED
D) AS Path
Answer: C
Explanation:
The Multi-Exit Discriminator (MED) is a BGP attribute used to influence inbound traffic selection from neighboring autonomous systems. MED indicates to an external AS which path is preferred into your network when multiple entry points exist. Unlike Local Preference, which affects internal route selection, MED is propagated only to eBGP neighbors and helps coordinate traffic engineering with upstream providers.
Option C) is correct because MED signals preferred ingress points for external traffic. Weight, A), is local to the router and affects only outbound traffic. Local Preference, B), controls internal preference. AS Path, D), prevents loops and is used for path selection but does not signal neighbor preference directly.
MED is essential in multi-homed enterprise networks, where traffic optimization is critical for redundancy, bandwidth efficiency, and cost-effective routing. For instance, if an enterprise has two ISPs, a lower MED can be assigned to the preferred ISP to ensure most inbound traffic enters through the optimal link, while the secondary link serves as a backup. This enhances predictable traffic flow, reduces congestion, and ensures high availability.
For ENARSI candidates, understanding MED demonstrates proficiency in BGP traffic engineering, inter-AS policy implementation, and sophisticated route control strategies. Proper configuration ensures that enterprise networks efficiently utilize multiple links, maintain redundancy, and influence external traffic patterns in alignment with business objectives. Mismanagement of MED could lead to suboptimal routing, congestion, or uneven traffic distribution, underscoring its importance in large-scale BGP deployments.
Question 106
Which EIGRP feature ensures loop-free backup paths using the feasibility condition?
A) Successor
B) Feasible Successor
C) Variance
D) Passive Interface
Answer: B
Explanation:
EIGRP (Enhanced Interior Gateway Routing Protocol) is known for its advanced routing capabilities and loop-free operation, achieved through the use of the feasibility condition. The feasibility condition states that for a path to be considered a feasible successor, its reported distance must be less than the feasible distance of the current successor path. The successor is the primary route that has the lowest metric and is installed in the routing table, while the feasible successor serves as a backup route. This backup route is immediately available if the primary path fails, which significantly reduces network convergence time.
Option B) is correct because the feasible successor ensures that only loop-free paths are considered as backup, which prevents routing loops—a critical requirement for enterprise network stability. Option A), successor, refers to the primary route and does not directly manage backup paths. Option C), variance, allows unequal-cost load balancing but does not guarantee loop-free backup paths. Option D), passive interface, suppresses EIGRP updates on a specific interface, which is unrelated to feasible successors.
The concept of feasible successors is fundamental to EIGRP’s dual algorithm, which combines distance-vector and link-state principles to offer rapid convergence without loops. By pre-calculating feasible successors, EIGRP routers can immediately switch to backup routes when a primary route becomes unavailable, maintaining high network availability and minimal packet loss.
For enterprise networks, the practical benefits of feasible successors include reduced downtime, predictable failover behavior, and optimized routing efficiency. This is especially critical in networks supporting mission-critical applications such as financial systems, VoIP, or cloud-based services, where even minor outages can impact business operations. ENARSI candidates must understand how EIGRP calculates feasible distances, evaluates reported distances, and determines feasible successors, as this knowledge is essential for designing robust enterprise networks with minimal convergence time and maximum stability.
Proper understanding of feasible successors also allows network engineers to troubleshoot routing issues effectively, optimize backup path utilization, and configure advanced features like variance-based load balancing alongside feasible successor selection. Mastery of this topic ensures resilient and scalable EIGRP deployments across large-scale enterprise environments.
Question 107
Which OSPF LSA type is used to advertise external routes into an area?
A) Type 1
B) Type 2
C) Type 5
D) Type 7
Answer: C
Explanation:
OSPF (Open Shortest Path First) uses several Link-State Advertisement (LSA) types to distribute routing information. Type 5 LSAs are specifically used to advertise external routes, typically learned via redistribution from other routing protocols like BGP, EIGRP, or static routes, into an OSPF network. These LSAs are generated by Autonomous System Boundary Routers (ASBRs) and flooded throughout all OSPF areas, except for stub areas which do not accept Type 5 LSAs.
Option C) is correct because Type 5 LSAs carry external routing information for networks outside the OSPF autonomous system, ensuring that internal routers can reach external destinations. Type 1 LSAs, A), describe the router itself and its interfaces. Type 2 LSAs, B), describe broadcast network topology. Type 7 LSAs, D), are used within Not-So-Stubby Areas (NSSAs) and later translated to Type 5 by the ABR.
Understanding Type 5 LSAs is crucial for multi-protocol network integration, where enterprises often redistribute routes between OSPF and external protocols. Type 5 LSAs allow seamless connectivity while maintaining OSPF’s hierarchical design and loop-free guarantees. ASBRs use these LSAs to inform all internal routers of external destinations, and proper design ensures controlled flooding, minimal routing table bloat, and efficient convergence.
For ENARSI exam preparation, mastering Type 5 LSA behavior demonstrates in-depth knowledge of OSPF area types, redistribution, and inter-protocol routing strategies. Misconfigurations, such as redistributing excessive external routes, can cause network instability, increased LSA flooding, and router CPU overload, impacting enterprise network performance. Effective use of Type 5 LSAs also requires understanding route tagging, filtering, and summarization, ensuring that external routing information is shared efficiently without compromising internal OSPF operation.
Question 108
Which BGP attribute determines the preferred exit path for internal routers?
A) Local Preference
B) MED
C) Weight
D) AS Path
Answer: A
Explanation:
BGP (Border Gateway Protocol) uses various attributes to influence route selection both internally and externally. Local Preference is a well-known attribute that determines which egress path an internal BGP (iBGP) router will prefer when multiple routes to the same external destination exist. The route with the highest local preference value is selected as the preferred path for traffic leaving the autonomous system.
Option A) is correct because Local Preference directly affects internal path selection, enabling enterprises to control outbound traffic efficiently. MED, B), influences inbound traffic preference for neighboring ASes. Weight, C), is local to the router and only affects BGP route selection on a single device. AS Path, D), determines route selection based on path length and loop prevention but does not control internal preferences.
Local Preference is essential for traffic engineering, particularly in multi-homed enterprise networks. By adjusting local preference values, network engineers can steer traffic over preferred exit points to optimize bandwidth usage, reduce latency, and maintain predictable performance. For example, if an enterprise has two ISP links, setting a higher local preference for one link ensures that most traffic exits through that path while keeping the secondary link as a backup.
For ENARSI candidates, mastering Local Preference is critical because it demonstrates expertise in BGP traffic engineering, internal route manipulation, and network resilience. Proper configuration ensures that outbound traffic follows organizational policies and SLAs, minimizes the risk of congestion, and maintains high availability across redundant paths. Additionally, combining Local Preference with other attributes like AS Path, MED, and communities allows precise control over complex inter-domain routing scenarios, which is a common requirement in large-scale enterprise deployments.
Question 109
Which OSPF area type blocks all Type 5 external LSAs but allows inter-area routes?
A) Stub
B) Totally Stubby
C) NSSA
D) Backbone
Answer: A
Explanation:
OSPF areas are designed to reduce routing overhead, improve convergence, and optimize resource usage. A stub area is one such area type that blocks all Type 5 LSAs from external sources but continues to accept Type 3 LSAs for inter-area routes. This design significantly reduces LSA flooding, router CPU load, and the size of routing tables within the stub area.
Option A) is correct because stub areas prevent external route advertisements while maintaining connectivity to internal OSPF destinations. Totally Stubby Areas, B), block both Type 3 and Type 5 LSAs, allowing only a default route for all destinations. NSSA, C), allows limited external routes using Type 7 LSAs. Backbone areas, D), serve as transit and accept all LSAs without restrictions.
Stub areas are especially useful in branch office networks with limited routing resources, where external routing information is not needed, but connectivity to internal enterprise networks must be preserved. By reducing routing overhead, stub areas ensure faster convergence, lower memory usage, and predictable performance.
For ENARSI candidates, understanding stub areas is important because it illustrates advanced OSPF area design, hierarchical scaling, and traffic optimization. Correct implementation requires configuring default routes on the ABR to ensure stub area routers can reach external destinations, avoiding misrouting or traffic blackholing. Effective stub area deployment demonstrates proficiency in OSPF optimization, LSA management, and enterprise-grade network planning, which are critical for designing resilient, scalable, and maintainable enterprise routing architectures.
Question 110
Which BGP mechanism reduces routing updates and allows group policy application?
A) Route Reflector
B) Confederation
C) Peer Group
D) Community
Answer: C
Explanation:
BGP Peer Groups are a mechanism used to reduce configuration complexity, improve efficiency, and enable consistent policy application among multiple BGP neighbors. Instead of configuring each neighbor individually, routers within a peer group inherit the same routing policies, timers, and attributes, which simplifies network management in large-scale enterprise networks.
Option C) is correct because Peer Groups allow centralized policy enforcement and minimize CPU overhead, reducing the frequency of routing updates and improving stability. Route Reflectors, A), reduce iBGP full mesh requirements but do not group policies. Confederations, B) break large ASes into smaller sub-ASes for scalability. Communities, D) tag routes for policy purposes but do not inherently reduce update overhead.
Peer Groups are critical in multi-homed or multi-router environments where consistent policy application is necessary. For example, an enterprise with dozens of iBGP neighbors can define a single peer group, apply export/import filters once, and ensure all peers follow the same routing rules. This reduces misconfiguration risk, simplifies network operations, and ensures predictable routing behavior.
For ENARSI candidates, understanding Peer Groups demonstrates expertise in advanced BGP management, enterprise-scale route control, and efficient policy enforcement. Properly implemented peer groups enhance network scalability, reduce CPU utilization, and streamline operational workflows, which are essential for modern enterprise networks that handle high traffic volumes and complex routing requirements. Mastery of peer groups allows candidates to design robust, maintainable, and efficient BGP topologies, ensuring optimal performance and policy compliance across the network.
Question 111
Which EIGRP metric component reflects interface reliability for route selection?
A) Bandwidth
B) Delay
C) Reliability
D) Load
Answer: C
Explanation:
EIGRP calculates routes using a composite metric that combines multiple components: bandwidth, delay, reliability, load, and MTU (optional). Among these, the reliability metric specifically reflects the stability and error rate of an interface. Reliability is measured on a scale from 1 to 255, with 255 representing a perfectly reliable interface. This metric dynamically updates based on interface performance, helping EIGRP choose the most dependable path.
Option C) is correct because the reliability component ensures routes with high interface stability are preferred, which is critical in enterprise networks where packet loss, jitter, or errors can disrupt mission-critical applications. Option A), bandwidth, affects metric by prioritizing higher throughput links. Option B), delay, reflects propagation and queuing delays across a path. Option D), load, considers the current utilization of an interface, impacting traffic engineering but not stability directly.
Understanding the reliability metric is vital for ENARSI candidates because it demonstrates advanced knowledge of EIGRP path selection and how interface health influences route computation. In enterprise deployments, engineers can manipulate EIGRP metrics using K-values to prioritize reliability over bandwidth or delay, depending on the network’s operational priorities.
Using reliability as a key factor can prevent traffic from traversing unstable or error-prone links, which is crucial for applications like VoIP, real-time video, and database replication, where packet loss or retransmissions can significantly degrade performance. Reliability also interacts with feasible successors and overall EIGRP convergence, ensuring that backup routes are also stable before being installed in the routing table.
A strong grasp of this metric allows candidates to tune enterprise networks, applying route manipulation, policy-based routing, and advanced metrics to guarantee high availability and minimal downtime. This knowledge is directly tested on ENARSI, making it a core component of routing expertise. Proper use of reliability metrics, combined with bandwidth and delay, allows for intelligent traffic engineering and ensures network paths are both efficient and robust under varying load conditions, demonstrating the enterprise-grade routing proficiency that Cisco expects from ENARSI-certified professionals.
Question 112
Which OSPF LSA type describes routers within a broadcast network?
A) Type 1
B) Type 2
C) Type 3
D) Type 4
Answer: B
Explanation:
In OSPF, Link-State Advertisements (LSAs) convey information about network topology. Type 2 LSAs, known as network LSAs, are generated by the Designated Router (DR) on broadcast networks, such as Ethernet. These LSAs list all routers connected to the broadcast segment, allowing other routers in the area to understand the network topology and adjacency relationships.
Option B) is correct because Type 2 LSAs summarize the state of all routers on a broadcast segment and are crucial for building the OSPF link-state database. Type 1 LSAs, A), describe individual routers and their interfaces. Type 3 LSAs, C), advertise inter-area routes between OSPF areas. Type 4 LSAs, D), provide reachability information to ASBRs for external routes.
For ENARSI candidates, understanding Type 2 LSAs is fundamental because they facilitate rapid convergence, accurate SPF calculations, and optimal path selection within an OSPF area. On a broadcast network, without Type 2 LSAs, routers could not reliably identify all neighbors, potentially leading to incomplete routing tables or suboptimal paths. Type 2 LSAs also play a role in OSPF design considerations, such as reducing LSA flooding by properly selecting DRs and BDRs to minimize control-plane traffic while maintaining full visibility of the network topology.
This knowledge allows enterprise engineers to design scalable OSPF areas, optimize LSA generation, and implement robust fault-tolerant network topologies. Misconfiguring broadcast networks or failing to understand Type 2 LSAs can result in adjacency failures, delayed convergence, and network instability, all critical considerations in large-scale enterprise deployments. Mastery of OSPF LSAs ensures ENARSI candidates can predict and troubleshoot routing behavior, implement efficient hierarchical network designs, and maintain high availability for mission-critical enterprise services.
Question 113
Which BGP attribute influences route selection across multiple autonomous systems?
A) Local Preference
B) AS Path
C) MED
D) Weight
Answer: B
Explanation:
BGP route selection is determined by multiple attributes, and the AS Path is one of the most critical for controlling routing decisions between autonomous systems (ASes). The AS Path lists all AS numbers that a route has traversed. BGP prefers paths with the shortest AS Path, reducing the number of external hops and avoiding routing loops.
Option B) is correct because the AS Path primarily influences external BGP (eBGP) route selection, determining which route an AS chooses to reach a specific destination. Option A), Local Preference, controls internal exit points but is not considered across AS boundaries. Option C), MED (Multi-Exit Discriminator), suggests preferred entry points to neighboring ASes but is not mandatory for all AS path comparisons. Option D), Weight, is local to a router and does not propagate to other routers.
Understanding the AS Path attribute is essential for ENARSI candidates because it allows precise inter-AS traffic engineering, controlling which external routes are selected and influencing both inbound and outbound traffic flows. By manipulating AS Paths using techniques like AS prepending, network engineers can make a path appear longer, discouraging its use by external peers. This is crucial in multi-homed enterprises, where controlling traffic for cost efficiency, performance optimization, or redundancy purposes is necessary.
Additionally, AS Path knowledge supports loop prevention in BGP, as routers reject routes that contain their own AS number. This ensures stable and reliable inter-AS routing, which is a cornerstone of enterprise-grade WAN design. Proper use of AS Path, combined with other BGP attributes like MED and Local Preference, allows engineers to create predictable, policy-driven routing topologies, essential for complex enterprise and service provider networks. ENARSI candidates must understand the interplay of BGP attributes to implement robust, scalable, and maintainable routing policies across diverse network environments.
Question 114
Which OSPF area type supports limited external routes using Type 7 LSAs?
A) Stub
B) Totally Stubby
C) NSSA
D) Backbone
Answer: C
Explanation:
An OSPF Not-So-Stubby Area (NSSA) is designed to allow limited redistribution of external routes without fully exposing the area to all Type 5 LSAs. NSSAs generate Type 7 LSAs to carry external route information within the area. These LSAs are later converted to Type 5 by the ABR, allowing external reachability while still reducing LSA flooding within the area.
Option C) is correct because NSSAs combine the benefits of stub areas—reduced routing overhead—with selective external route support. Option A), Stub, blocks all Type 5 LSAs. Totally Stubby Areas, B), block both inter-area and external LSAs except for a default route. Backbone areas, D), are the core OSPF transit areas and accept all LSA types.
Understanding NSSAs is crucial for ENARSI candidates because it enables flexible network designs where branch offices or limited-resource networks require external connectivity without overloading routers with unnecessary LSAs. NSSAs maintain OSPF hierarchical structure, reduce memory usage, and improve convergence, all while allowing strategic external route distribution.
In enterprise networks, NSSAs are particularly useful when redistributing routes from other protocols like EIGRP or BGP into OSPF, especially in multi-site WANs. The conversion of Type 7 to Type 5 LSAs ensures that external routes propagate correctly without disrupting stub area principles. Correct NSSA deployment requires understanding ABR functionality, LSA translation, and default route injection, which are essential skills for ENARSI-certified professionals tasked with designing resilient, scalable enterprise routing infrastructures.
Question 115
Which EIGRP command shows the feasible distance and successor for all routes?
A) show ip route
B) show ip eigrp topology
C) show ip protocols
D) show running-config
Answer: B
Explanation:
In EIGRP, the command show ip eigrp topology displays detailed information about all known routes, including successors, feasible successors, reported distances, and feasible distances. This command is critical for troubleshooting, verifying route selection, and understanding how EIGRP computes its routing table.
Option B) is correct because it provides both primary and backup path metrics, along with their status, enabling engineers to analyze convergence behavior and failover readiness. Option A), show ip route, displays only routes installed in the routing table without feasible successor details. Option C), show ip protocols, shows EIGRP process information but not metric details. Option D), show running-config, only displays the current configuration without runtime metric insights.
Mastering this command is essential for ENARSI candidates because it allows them to validate EIGRP metric calculations, troubleshoot routing anomalies, and optimize network convergence. By examining the feasible distance, network engineers can confirm that backup paths meet the feasibility condition and are loop-free. The output also shows how EIGRP evaluates multiple paths, which is critical for configuring unequal-cost load balancing using the variance command.
In enterprise networks, show ip eigrp topology helps identify potential routing issues, such as high-delay or low-reliability paths, before they impact production traffic. It allows engineers to preemptively adjust metrics, influence successor selection, and implement traffic engineering strategies that improve overall network stability and performance. ENARSI candidates must be proficient with this command to demonstrate full operational knowledge of advanced EIGRP mechanisms, ensuring robust and predictable routing behavior across complex enterprise topologies.
Question 116
Which OSPF router type summarizes external routes into a backbone area?
A) ABR
B) ASBR
C) Internal Router
D) Backbone Router
Answer: B
Explanation:
In OSPF, the Autonomous System Boundary Router (ASBR) is responsible for redistributing external routes from other protocols such as EIGRP, BGP, or static routes into the OSPF domain. These routes are then advertised into OSPF using Type 5 LSAs, which are propagated throughout all non-stubby areas, including the backbone (Area 0). ASBRs play a crucial role in interconnecting OSPF networks with other routing domains, providing a bridge for external route injection, and enabling enterprise networks to maintain a consistent routing topology.
Option B) is correct because the ASBR’s primary function is the redistribution of external network reachability information into the OSPF domain. Option A), the Area Border Router (ABR), is responsible for summarizing inter-area routes and connecting multiple OSPF areas to the backbone. Option C), Internal Routers, only maintain intra-area routes and do not handle external route redistribution. Option D), Backbone Routers, are routers within Area 0 that maintain connectivity but are not inherently responsible for external route summarization unless they also function as ASBRs.
Understanding the role of ASBRs is essential for ENARSI candidates because they must design robust, scalable enterprise networks that efficiently integrate with external routing domains. ASBRs influence LSA flooding behavior, network convergence, and route selection throughout the OSPF topology. Improper configuration of ASBRs can lead to routing loops, suboptimal paths, and excessive LSA generation, which can degrade network performance.
In enterprise networks, ASBRs are often deployed in data centers, WAN aggregation points, or multi-homed sites where OSPF interacts with other protocols such as BGP for Internet connectivity or EIGRP for legacy internal networks. They allow network engineers to implement route filtering, summarization, and policy-based redistribution to control routing behavior and ensure security and scalability. Mastery of ASBR functionality is a cornerstone of ENARSI, reflecting a candidate’s ability to design and maintain enterprise-grade advanced routing infrastructures. Effective ASBR implementation directly impacts network stability, convergence speed, and overall operational efficiency, making it a critical skill for Cisco-certified professionals.
Question 117
Which EIGRP command limits the number of routes shared with neighbors?
A) passive-interface
B) distribute-list
C) offset-list
D) summary-address
Answer: B
Explanation:
The EIGRP distribute-list command is used to filter or limit the propagation of routing updates to specified neighbors, effectively controlling which routes are advertised or accepted. This command is crucial for traffic engineering, security, and route optimization, allowing network engineers to prevent unnecessary or sensitive routes from being sent to specific neighbors, thereby reducing routing table size and improving convergence.
Option B) is correct because distribute-lists can be applied inbound or outbound to control the flow of EIGRP routes using access lists or prefix lists. Option A), passive-interface, stops EIGRP updates from being sent on an interface but does not selectively filter routes. Option C), offset-list, is used to manipulate routing metrics but does not filter routes. Option D), summary-address, aggregates routes but does not selectively restrict neighbor advertisements.
For ENARSI candidates, understanding the distribute-list command is essential because it enables fine-grained control over routing domain visibility. It helps prevent routing loops, enforce administrative policies, and optimize network performance in large-scale enterprise environments where multiple EIGRP neighbors are present. Proper use of distribute-lists ensures that routing information is strategically shared, reducing unnecessary network overhead and preventing inadvertent route propagation.
Distribute-lists also work in combination with route summarization and administrative distance manipulation to provide a comprehensive traffic engineering framework. In enterprise networks, particularly those with multiple sites, controlling EIGRP updates ensures that critical paths receive priority, network stability is maintained, and sensitive segments remain isolated. ENARSI candidates must be proficient in applying distribute-lists, testing their behavior with commands such as show ip eigrp neighbors, show ip route, and show ip protocols, and understanding the interaction between EIGRP metric computation and route propagation. This capability is a core skill for enterprise routing engineers, as it allows the design of secure, efficient, and scalable EIGRP topologies.
Question 118
Which BGP attribute is used to influence outbound traffic from a local AS?
A) MED
B) Local Preference
C) Weight
D) Community
Answer: C
Explanation:
The BGP Weight attribute is a Cisco-proprietary parameter used to influence outbound routing decisions on a local router. Unlike Local Preference, which is propagated throughout the AS, Weight is local to the router and has the highest priority in the BGP path selection process. Routes with higher Weight are preferred when multiple paths exist to the same destination.
Option C) is correct because Weight directly controls which route the local router uses for outbound traffic, making it ideal for implementing precise traffic engineering policies within a single router. Option A), MED, suggests a preferred entry point to neighboring ASes but is not authoritative for outbound selection. Option B), Local Preference, influences path selection within an AS but is not router-specific. Option D), Community, is used for tagging and route filtering but does not directly influence selection unless policies are applied.
Understanding Weight is critical for ENARSI candidates because it enables deterministic traffic management on enterprise edge routers, ensuring predictable outbound paths for Internet traffic or inter-AS connections. In multi-homed enterprise networks, manipulating Weight allows engineers to prioritize certain ISPs or backup links, improving redundancy and load balancing. Weight also interacts with other BGP attributes, such as AS Path, MED, and Local Preference, forming a comprehensive route selection hierarchy that candidates must master.
By using Weight, engineers can implement policy-driven traffic engineering, minimizing network latency, optimizing bandwidth utilization, and ensuring service-level agreements (SLAs) are maintained. ENARSI candidates must demonstrate proficiency in BGP route manipulation techniques, including Weight assignment, route maps, and policy application, to design enterprise networks that are robust, scalable, and capable of handling complex routing scenarios. Mastery of Weight ensures control over outbound traffic behavior, which is essential in multi-homed WAN environments, enterprise edge deployments, and high-availability network designs.
Question 119
Which OSPF command displays detailed SPF calculation information per area?
A) show ip ospf database
B) show ip ospf neighbor
C) show ip ospf interface
D) show ip ospf route
Answer: A
Explanation:
The OSPF command show ip ospf database provides comprehensive details about the link-state database, including all LSAs for a given area. This command is essential for verifying topology information, SPF calculations, and route propagation within an OSPF area. It allows engineers to troubleshoot convergence issues and validate that the SPF algorithm has computed routes correctly.
Option A) is correct because the link-state database contains all Type 1–5 (and Type 7 for NSSAs) LSAs, showing relationships between routers, networks, and external paths. Option B), show ip ospf neighbor, displays adjacency states but not SPF computation. Option C), show ip ospf interface, shows interface OSPF configuration and status but not the topology calculation. Option D), show ip ospf route, shows the routing table derived from OSPF but does not provide the raw LSA data needed for SPF analysis.
ENARSI candidates must understand how to interpret the LSA information, including metrics, router IDs, and network masks. By analyzing the output of show ip ospf database, engineers can verify the correctness of SPF calculations, identify inconsistencies in LSAs, detect flapping routers, and optimize OSPF area design. It also helps in troubleshooting hierarchical OSPF networks, such as backbone areas, NSSAs, or totally stubby areas, ensuring proper LSA propagation and efficient route computation.
In enterprise environments, mastering this command supports rapid troubleshooting, proactive monitoring, and performance tuning. Engineers can validate route summarization, DR/BDR election outcomes, and external route injection, ensuring that OSPF is operating efficiently and predictably. ENARSI candidates must use this command in conjunction with other OSPF diagnostic commands to demonstrate deep operational knowledge, maintain network stability, and implement best-practice OSPF designs that meet enterprise reliability and scalability requirements.
Question 120
Which EIGRP feature allows load balancing over unequal-cost paths?
A) Feasible Distance
B) Variance
C) Successor
D) Delay
Answer: B
Explanation:
EIGRP supports unequal-cost load balancing through the variance command, which allows traffic to be distributed over multiple paths that satisfy the feasibility condition. By default, EIGRP only installs equal-cost paths (successors) in the routing table, but setting a variance value greater than 1 allows feasible successors with higher metrics to be included in load balancing.
Option B) is correct because variance is a multiplicative factor applied to the feasible distance of the best path. Paths with feasible distances less than or equal to the feasible distance multiplied by the variance are included in the routing table for load balancing. Option A), Feasible Distance, represents the metric to a destination via the successor but does not by itself enable load balancing. Option C), Successor, is the primary route used in the routing table. Option D), Delay, is a component of the EIGRP metric but does not control load balancing.
For ENARSI candidates, understanding the variance feature is critical for traffic engineering and network optimization. Unequal-cost load balancing allows enterprises to utilize backup or suboptimal paths, improving bandwidth utilization, resilience, and overall network efficiency. Proper configuration requires a thorough understanding of feasible successors, reported distances, and metric calculations, ensuring loop-free and predictable routing behavior.
By adjusting variance, engineers can balance link utilization, prioritize critical paths, and avoid congestion in complex enterprise topologies. This feature also works in conjunction with other EIGRP tools, such as distribute-lists, offset-lists, and passive interfaces, to implement sophisticated routing policies that meet enterprise SLA requirements. Mastery of variance and unequal-cost load balancing demonstrates an advanced level of EIGRP expertise, which is essential for designing resilient, high-performance networks, a core expectation of ENARSI-certified professionals.
