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Question 21
Which EIGRP feature allows for loop-free backup paths while maintaining rapid convergence in enterprise networks?
A) Feasible successor
B) Route dampening
C) Stub routing
D) Variance load balancing
Answer: A
Explanation:
In enterprise networks using EIGRP, achieving loop-free backup paths is crucial to maintain reliable connectivity without causing network instability. The feasible successor mechanism is a foundational feature of EIGRP that allows routers to maintain a backup path to a destination that is loop-free. Unlike the primary successor, which is the path chosen for forwarding traffic based on the lowest composite metric, a feasible successor is only considered if it satisfies the feasibility condition: its reported distance (RD) must be less than the feasible distance (FD) of the current successor.
This mechanism ensures that the backup path cannot form a routing loop, even in the presence of topology changes. When the primary path fails, EIGRP can immediately switch to the feasible successor without recalculating the entire topology, providing rapid convergence, which is vital for mission-critical enterprise applications where downtime can lead to significant operational loss.
Option B) route dampening is used in BGP to suppress flapping routes but does not apply to EIGRP.
Option C) stub routing in EIGRP limits query propagation and reduces unnecessary traffic but does not guarantee loop-free backup paths.
Option D) variance load balancing allows unequal-cost load sharing but requires feasible successors to exist for loop-free operation.
Feasible successors are stored in the topology table, along with their metrics and next-hop information. During a failure of the primary successor, EIGRP instantly promotes a feasible successor as the new successor, minimizing packet loss and downtime. This feature is particularly beneficial in multi-branch enterprises, redundant WAN topologies, and high-availability data centers, ensuring reliable failover and predictable routing behavior. By leveraging feasible successors, enterprises achieve efficient use of network resources, avoid network loops, and maintain deterministic path selection across complex topologies. Therefore, A) is the correct choice.
Question 22
How can OSPF route summarization improve scalability and stability in large multi-area enterprise networks?
A) Summarizes routes at ABRs to reduce LSA flooding
B) Converts all routers to backbone area for faster SPF
C) Uses static routes instead of dynamic updates
D) Disables OSPF timers to prevent recalculations
Answer: A
Explanation:
OSPF route summarization is a critical best practice for large-scale, multi-area enterprise networks. When a network grows with hundreds or thousands of prefixes, Link-State Advertisements (LSAs) can flood the network and increase SPF computation overhead. To address this, Area Border Routers (ABRs) can summarize multiple internal prefixes into a single summary route when advertising them into other areas.
Option A) is correct because summarization reduces the number of LSAs propagated across areas, which decreases SPF recalculation frequency and improves network stability. Summarized routes also simplify routing tables, reducing memory and CPU usage on internal routers, which is essential for maintaining optimal network performance.
Option B) converting all routers to backbone area increases SPF workload and is impractical.
Option C) using static routes sacrifices scalability, as manual configuration cannot adapt to dynamic topology changes.
Option D) disabling OSPF timers prevents recalculation but causes routing inconsistencies and may lead to network instability.
Summarization also provides fault isolation: when a link within a summarized block fails, only the ABR needs to propagate the updated LSA, preventing unnecessary recalculation in other areas. This ensures high availability and predictable convergence. Enterprises with multiple branch offices, redundant WAN links, and data center interconnections benefit from reduced LSA flooding, smaller routing tables, and smoother SPF operations. Route summarization is essential for scaling OSPF efficiently while maintaining loop-free, stable routing. Therefore, A) is the correct answer.
Question 23
What is the primary advantage of EIGRP stub configuration for branch routers in large enterprise WANs?
A) Limits query propagation and reduces unnecessary traffic
B) Prevents the use of feasible successors for load balancing
C) Increases convergence time for better stability
D) Forces all traffic through the primary successor
Answer: A
Explanation:
In large enterprise WANs, branch routers often have limited resources and serve as end nodes rather than transit points. Configuring these routers as EIGRP stub routers provides a significant advantage by limiting query propagation during route recalculations. Stub routers do not advertise routes learned from other EIGRP neighbors except for those directly connected, preventing unnecessary queries from flooding the network during topology changes.
Option A) is correct because stub configuration ensures that the branch router does not participate in the full route discovery process, which reduces CPU utilization, memory consumption, and network bandwidth usage. This is particularly beneficial in hub-and-spoke topologies, where hub routers maintain full routing information and branch routers act as leaf nodes.
Option B) is incorrect because stub routers can still have feasible successors for load balancing within their limited scope.
Option C) increasing convergence time is undesirable; stub configuration actually improves convergence predictability by containing query scope.
Option D) forcing traffic through a primary successor does not leverage the benefits of loop-free backups.
Stub routers also improve network stability by isolating network failures to smaller segments and preventing ripple effects. This design ensures deterministic routing behavior, optimal bandwidth usage, and predictable failover. Enterprises with hundreds of branch offices, redundant WAN links, and DMVPN overlays rely on stub routers to reduce unnecessary overhead while maintaining connectivity to core services and other branches. Implementing EIGRP stubs is an essential practice for scalable, resilient, and efficient WAN design. Therefore, A) is the correct answer.
Question 24
Why is BGP next-hop tracking critical in multi-homed enterprise networks to ensure proper path selection and loop prevention?
A) Verifies reachability of next-hop before installing route in the table
B) Automatically adjusts MED values for optimal load balancing
C) Disables all redundant paths to simplify routing
D) Converts BGP routes into OSPF internal prefixes
Answer: A
Explanation:
In multi-homed enterprise networks, where a router is connected to multiple external ISPs or autonomous systems, BGP path selection must ensure that advertised routes are reachable and do not create routing loops. Next-hop tracking is a fundamental BGP feature that guarantees every BGP route points to a valid, reachable IP address. Before installing a BGP route into the routing table, the router verifies the next-hop via recursive lookup, ensuring it can forward packets to that destination.
Option A) is correct because this verification process prevents blackholes and routing loops, which are common in multi-homed designs if next-hop reachability is ignored. Next-hop tracking works in combination with BGP route reflectors, policy-based routing, and iBGP/eBGP peerings, maintaining loop-free operation while allowing scalable deployments.
Option B) adjusting MED values influences path preference but does not inherently prevent loops.
Option C) disabling redundant paths reduces network resilience and is counterproductive in high-availability designs.
Option D) converting BGP into OSPF prefixes is a redistribution task and does not guarantee loop prevention within BGP itself.
Next-hop tracking also supports deterministic routing behavior, ensuring predictable failover when an ISP link fails. Enterprises benefit from reduced downtime, improved network resilience, and enhanced operational efficiency, especially in WANs connecting multiple data centers or hybrid cloud deployments. By validating next-hop reachability, BGP maintains loop-free, optimal path selection, which is critical for multi-homed networks handling hundreds of prefixes and diverse traffic patterns. Therefore, A) is the correct answer.
Question 25
Which DMVPN design practice ensures scalable, resilient, and loop-free connectivity between multiple branches?
A) Hub-and-spoke topology with NHRP, route summarization, and routing protocol optimization
B) Full-mesh tunnels between all branches for redundancy
C) Static routing between all spokes
D) BGP-only deployment for all DMVPN connections
Answer: A
Explanation:
Dynamic Multipoint VPN (DMVPN) is widely used in enterprise networks to provide secure, on-demand connectivity between multiple branches without requiring full-mesh VPN tunnels. The most scalable and resilient design leverages a hub-and-spoke topology, where the hub serves as the central point for initial tunnel establishment, and spokes dynamically form direct tunnels with other spokes as needed.
Option A) is correct because combining NHRP (Next Hop Resolution Protocol), route summarization, and routing protocol optimization ensures efficient, loop-free routing. NHRP dynamically resolves spoke IP addresses for direct tunnel creation, reducing the management overhead associated with static full-mesh configurations. Route summarization at hubs minimizes routing table size, reduces LSA or EIGRP updates, and improves convergence times. Routing protocol tuning (e.g., variance for EIGRP or SPF timers for OSPF) ensures fast recovery from link failures without network instability.
Option B) full-mesh tunnels are not scalable and increase bandwidth consumption exponentially.
Option C) static routing requires manual configuration, which is impractical in large networks and reduces flexibility.
Option D) BGP-only deployment adds operational complexity and is unnecessary when EIGRP or OSPF can efficiently manage DMVPN routing.
By implementing these best practices, enterprises achieve loop-free, deterministic routing, improved bandwidth utilization, and high resiliency across multiple branches. DMVPN with optimized routing protocols and summarization ensures predictable convergence, minimal downtime, and scalable deployment for WAN networks spanning hundreds of remote offices. Therefore, A) is the correct choice.
Question 26
Which OSPF feature prevents unnecessary SPF recalculations and reduces routing table churn in enterprise networks?
A) LSA throttling
B) Route summarization
C) Stub area configuration
D) Graceful restart
Answer: B
Explanation:
In large-scale enterprise networks, OSPF routers handle numerous prefixes, and frequent topology changes can trigger SPF recalculations, consuming CPU resources and potentially causing instability. Route summarization is a key technique used to optimize OSPF performance by reducing the number of individual prefixes advertised between areas. By consolidating multiple contiguous routes into a single summarized address, the Area Border Router (ABR) minimizes the flooding of LSAs across areas.
Option B) is correct because summarization not only decreases SPF recalculation frequency but also simplifies routing tables, reduces memory usage, and enhances network stability. Summarization effectively isolates failures within an area, preventing minor disruptions from impacting the entire OSPF domain.
Option A) LSA throttling helps limit LSA generation during flapping events but does not inherently reduce routing table churn.
Option C) stub areas limit query propagation and reduce certain types of traffic but are not a general solution for all OSPF performance issues.
Option D) graceful restart allows routers to maintain routing information temporarily during restarts but does not reduce the computational complexity of SPF.
Route summarization is particularly crucial in enterprises with hierarchical network designs, multi-area topologies, and numerous branch offices. It ensures predictable convergence times, minimizes routing overhead, and prevents excessive recalculations during network changes. By advertising fewer, aggregated routes, enterprises achieve loop-free, scalable, and stable OSPF deployments, enhancing WAN efficiency and application performance. Summarization also improves troubleshooting efficiency by reducing the number of routes administrators must analyze when diagnosing connectivity issues.
Question 27
What EIGRP technique enables unequal-cost load balancing for efficient bandwidth utilization across multiple paths?
A) Variance
B) Feasible distance
C) Stub routing
D) Route filtering
Answer: A
Explanation:
In enterprise networks, leveraging multiple paths for traffic forwarding increases redundancy and optimizes bandwidth utilization. EIGRP’s variance feature allows routers to perform unequal-cost load balancing, where traffic is distributed over multiple routes whose metrics fall within a specified variance multiplier. By default, EIGRP forwards traffic only along the primary successor path, but enabling variance expands this behavior to include feasible successors with metrics less than the product of the variance value and the minimum feasible distance.
Option A) is correct because variance allows efficient usage of available links while maintaining loop-free forwarding, provided that feasible successors satisfy the feasibility condition. This is particularly beneficial in WAN environments with multiple links of varying bandwidth and cost, ensuring no available capacity is wasted.
Option B) feasible distance is a metric used to select the primary successor and does not directly enable unequal-cost load balancing.
Option C) stub routing restricts query propagation to improve scalability but does not affect load balancing.
Option D) route filtering prevents certain routes from being advertised but does not contribute to balanced traffic distribution.
Implementing variance in EIGRP requires careful planning: selecting an appropriate multiplier ensures only efficient paths are utilized and avoids introducing loops. Enterprises benefit from increased resiliency, efficient utilization of all available paths, and predictable traffic engineering. This feature is particularly relevant for multi-branch WANs, redundant MPLS circuits, and hybrid cloud deployments, where traffic load can vary dynamically and deterministic routing behavior is necessary. By configuring variance properly, EIGRP provides both high availability and performance optimization, enabling network engineers to maximize throughput while maintaining stability across large, complex networks.
Question 28
Why is OSPF sham-link configuration used in MPLS VPN environments to maintain proper inter-site routing?
A) Prevents traffic blackholing between sites using virtual links
B) Enables faster SPF computation in backbone area
C) Converts all VPN routes into OSPF internal prefixes
D) Disables summarization for remote sites
Answer: A
Explanation:
In MPLS VPN deployments, OSPF is often used as the interior gateway protocol within sites, while MPLS handles inter-site connectivity over a service provider backbone. When an enterprise implements OSPF across multiple sites, the VPN’s internal routes may appear as external or unreachable within the backbone. A sham-link is a logical OSPF link configured between customer edge routers over the MPLS VPN to maintain the appearance of a backbone connection.
Option A) is correct because sham-links prevent traffic blackholing, ensuring that OSPF sees a contiguous backbone path and can advertise inter-site prefixes properly. Without sham-links, OSPF might incorrectly prefer non-optimal routes, causing traffic to loop or be dropped.
Option B) faster SPF computation is unrelated to sham-links; sham-links primarily address routing visibility, not convergence speed.
Option C) converting VPN routes to internal prefixes is a redistribution task and does not inherently solve inter-site visibility issues.
Option D) disabling summarization is unnecessary; sham-links function with or without summarization.
Sham-links are particularly important in multi-branch enterprises with overlapping or discontiguous OSPF areas. By creating a virtual point-to-point connection, they allow OSPF to maintain logical backbone continuity, which is essential for inter-area routing. Additionally, sham-links enable route preference control and proper metric propagation, ensuring that traffic follows predictable paths across the MPLS VPN. This design supports redundancy, scalability, and loop-free operation, critical for enterprises relying on hybrid WAN architectures, disaster recovery plans, and high-availability applications. Properly configured sham-links reduce troubleshooting complexity, maintain predictable routing behavior, and prevent misrouting that could affect critical business applications.
Question 29
What is the main purpose of BGP route reflectors in large enterprise networks with multiple iBGP peers?
A) Reduces full mesh requirement and simplifies iBGP scalability
B) Automatically adjusts local preference values
C) Converts all eBGP routes into OSPF prefixes
D) Limits route advertisements to stub routers only
Answer: A
Explanation:
In large enterprise networks using BGP, each iBGP peer typically must maintain a full-mesh peering to exchange routing information. This approach quickly becomes unmanageable as the number of routers increases because the required peering sessions grow exponentially. BGP route reflectors (RRs) address this scalability issue by allowing iBGP routers to receive routes from a central RR, which then reflects those routes to other iBGP peers, eliminating the need for a full mesh.
Option A) is correct because route reflectors reduce configuration complexity and enhance operational scalability. Enterprises with dozens or hundreds of iBGP peers rely on RRs to manage routing efficiently without overloading routers with numerous BGP sessions.
Option B) adjusting local preference is a policy function and not the primary role of RRs.
Option C) converting eBGP to OSPF prefixes is unrelated to iBGP scalability; redistribution tasks are separate from route reflection.
Option D) limiting advertisements to stub routers only is unrelated; route reflectors reflect routes to all clients within their cluster.
Route reflectors provide several additional benefits: they simplify topology management, reduce CPU and memory overhead, and allow for centralized routing policy enforcement. In multi-branch WANs, data centers, or cloud-connected enterprises, RRs enable predictable routing, reduce the likelihood of loops, and ensure that BGP updates propagate efficiently. Proper RR deployment also allows hierarchical designs, where multiple RRs form clusters, enhancing redundancy while maintaining loop-free iBGP operation. Enterprises benefit from scalable, maintainable, and resilient routing, ensuring optimal traffic flow, high availability, and simplified network management.
Question 30
Which EIGRP feature improves convergence time by maintaining a backup path without recalculating the entire topology?
A) Feasible successor
B) Stub routing
C) Variance load balancing
D) Route summarization
Answer: A
Explanation:
EIGRP is designed for rapid convergence in enterprise networks, which is critical for maintaining high availability and minimizing packet loss during topology changes. The feasible successor is a mechanism that allows EIGRP to maintain a pre-computed, loop-free backup path in the topology table. When the primary successor fails, EIGRP can immediately promote a feasible successor to the active route, avoiding the need for a complete topology recalculation.
Option A) is correct because feasible successors satisfy the feasibility condition, ensuring loop-free backup paths. This mechanism allows EIGRP to converge in milliseconds for many network topologies, making it ideal for enterprise WANs, redundant data center interconnections, and multi-branch environments.
Option B) stub routing reduces query propagation and improves scalability but does not directly maintain backup paths.
Option C) variance load balancing enables unequal-cost paths for traffic distribution but does not guarantee immediate convergence upon failure.
Option D) route summarization reduces LSA updates and table size in OSPF but is not an EIGRP-specific convergence optimization.
By using feasible successors, enterprises achieve deterministic routing, high reliability, and efficient use of multiple paths. This feature is essential in redundant WAN designs, high-performance data centers, and critical enterprise applications requiring near-zero downtime. Feasible successors minimize network instability and allow engineers to design topologies that leverage backup paths without compromising performance. Consequently, the mechanism plays a central role in network resiliency planning, load optimization, and rapid failover strategies across complex, multi-layered enterprise infrastructures.
Question 31
Which BGP attribute determines the preferred outbound path for traffic leaving an autonomous system?
A) Local preference
B) AS path
C) MED
D) Next-hop
Answer: A
Explanation:
In large-scale enterprise networks, BGP is commonly used to manage inter-domain routing across multiple autonomous systems. One of the critical challenges in BGP is controlling the outbound path selection, ensuring traffic leaves the network through the most optimal link according to organizational policies, bandwidth availability, or cost considerations. The local preference attribute is a numeric value configured on routers to influence BGP path selection within the same autonomous system. Higher local preference values indicate more preferred routes.
Option A) is correct because local preference is explicitly designed to affect outbound routing decisions. By manipulating local preference, network engineers can direct traffic over preferred links while maintaining redundancy and controlling load across multiple WAN connections. Enterprises with dual Internet providers or redundant MPLS circuits often rely on local preference to distribute traffic efficiently and maintain predictable performance.
Option B) AS path primarily influences inbound traffic by making routes with shorter AS paths more attractive to other autonomous systems, but it does not control internal outbound path preference.
Option C) MED (Multi-Exit Discriminator) is used to indicate a preferred entry point into an autonomous system from an external neighbor, affecting inbound routing decisions rather than outbound.
Option D) next-hop information tells routers where to forward packets but does not influence preference among multiple available paths.
Configuring local preference properly requires a deep understanding of the network’s topology, business requirements, and redundancy needs. For example, traffic destined for a critical cloud service may be preferred over a high-bandwidth backup link with a lower local preference. Combining local preference with route maps and prefix-lists allows granular traffic engineering across complex enterprise topologies. This approach ensures predictable behavior during link failures or maintenance events, reduces congestion, and enhances overall reliability. Enterprises benefit from controlled outbound traffic patterns, compliance with Service Level Agreements (SLAs), and optimized performance for latency-sensitive applications. By leveraging local preference, BGP administrators can implement strategic routing decisions that enhance network stability, efficiency, and resilience across global enterprise environments.
Question 32
What is the primary purpose of OSPF NSSA (Not-So-Stubby Area) in enterprise designs?
A) Allows external route import while limiting backbone flooding
B) Speeds up SPF computation within backbone areas
C) Converts external routes to internal OSPF metrics
D) Enables inter-VRF routing in MPLS networks
Answer: A
Explanation:
In enterprise networks with complex hierarchies, OSPF area types help manage scalability and performance. A Not-So-Stubby Area (NSSA) is a special area type that combines the advantages of stub areas with the ability to import limited external routes. Traditional stub areas block external routes (type 5 LSAs) to reduce flooding and simplify SPF calculations. However, some networks require limited external route injection, for example, routes redistributed from EIGRP or static routes from branch offices. NSSA allows these external routes to enter the OSPF domain as type 7 LSAs, which are converted to type 5 LSAs at the ABR if needed.
Option A) is correct because NSSA enables the controlled import of external routes while maintaining the reduced flooding characteristics of stub areas. This design optimizes routing efficiency in enterprise backbones and branch networks, preventing unnecessary SPF recalculations while still accommodating essential external connectivity.
Option B) speeding SPF computation is a benefit of stub areas in general but is not the primary purpose of NSSA.
Option C) converting external routes to internal metrics is misleading; NSSA preserves external route distinction and allows controlled conversion by the ABR.
Option D) enabling inter-VRF routing is unrelated to NSSA; VRFs are typically handled through MPLS VPN or route-target policies.
NSSA areas are especially valuable in multi-site enterprises where certain branch offices need to redistribute local routes into the backbone without causing excessive SPF recalculations or instability in the core network. By isolating type 7 LSAs within the NSSA and controlling their propagation to the backbone, engineers can ensure predictable convergence, minimize unnecessary routing overhead, and maintain a scalable OSPF hierarchy. Proper NSSA implementation ensures branch networks can participate in dynamic routing while maintaining the integrity of the enterprise backbone, allowing loop-free, resilient, and high-performance OSPF operations. Additionally, NSSA provides flexibility in handling gradual network expansion, temporary external connections, and migration strategies without compromising core network stability
Question 33
Which EIGRP feature allows selective advertisement of routes to reduce unnecessary updates to neighbor routers?
A) Route filtering
B) Feasible successor
C) Stub routing
D) Variance
Answer: C
Explanation:
EIGRP supports several mechanisms for optimizing routing updates and maintaining network efficiency. One key feature is stub routing, which allows routers to declare themselves as leaf nodes within the EIGRP topology. When a router is configured as a stub, it limits the types of routes advertised to neighbors, thereby reducing unnecessary query propagation and network chatter. Stub routers do not advertise transit routes and typically only advertise connected, summary, or redistributed routes, depending on the configuration.
Option C) is correct because stub routing effectively controls routing information exchange and prevents excessive updates from propagating throughout the network. This feature is particularly useful in enterprise WAN designs where branch offices connect to a central hub router but do not need to forward transit traffic. By reducing unnecessary routing updates, stub routing improves convergence speed, conserves bandwidth, and minimizes CPU usage on routers.
Option A) route filtering is used to control which routes are advertised or received but does not inherently optimize query propagation like stub routing.
Option B) feasible successors maintain backup paths for rapid failover but do not control route advertisement to neighbors.
Option D) variance enables unequal-cost load balancing but does not limit the routes advertised to peers.
Stub routing is critical for maintaining scalable, predictable, and efficient EIGRP topologies in enterprise networks with numerous remote branches. By reducing query propagation, it prevents unnecessary stress on core routers, minimizes convergence delays during failures, and allows branch routers to focus on local traffic. This is especially relevant in WAN designs with limited bandwidth or high latency links, where excessive routing chatter can degrade application performance. Implementing stub routing ensures that routing policies align with topology hierarchy, redundancy requirements, and operational efficiency, supporting enterprise goals for reliable, cost-effective, and maintainable network designs.
Question 34
Why is OSPF route summarization at ABRs important in multi-area enterprise networks?
A) Reduces LSA flooding and SPF computation overhead
B) Converts external routes into internal OSPF metrics
C) Increases OSPF convergence speed in stub areas only
D) Prevents MPLS VPN route leakage
Answer: A
Explanation:
OSPF is a link-state routing protocol widely deployed in enterprise networks due to its fast convergence and hierarchical scalability. In multi-area OSPF designs, Area Border Routers (ABRs) interconnect areas and propagate summarized routes between them. Route summarization consolidates multiple contiguous subnets into a single advertisement, significantly reducing the number of LSAs flooded into other areas. This optimization decreases SPF recalculation frequency and conserves router CPU and memory resources.
Option A) is correct because summarization reduces LSA flooding, lowers SPF computation overhead, and stabilizes routing in large networks. Enterprises with multiple branch offices, redundant cores, and hierarchical designs benefit from summarization, ensuring predictable convergence and manageable routing tables. Summarization also helps contain instability: if a subnet in one area flaps, the ABR can advertise the summarized prefix without triggering full SPF recalculation across the entire OSPF domain.
Option B) converting external routes into internal metrics is related to redistribution, not summarization.
Option C) improving convergence in stub areas is a general OSPF optimization but not the core purpose of ABR summarization.
Option D) preventing MPLS VPN route leakage is unrelated; MPLS uses VRF and route-target policies for isolation.
Proper summarization requires careful design: selecting contiguous prefixes and choosing summarization points that minimize the impact of route flaps. Enterprise networks with multi-level hierarchies, such as campus, distribution, and branch networks, benefit from ABR summarization because it reduces routing complexity, convergence time, and operational troubleshooting efforts. Additionally, summarization supports policy-based routing and efficient network expansion by allowing administrators to plan IP space hierarchically while avoiding large-scale routing disruptions. Overall, ABR summarization is a foundational technique for scalable, resilient, and high-performance OSPF deployments in complex enterprise networks.
Question 35
Which BGP feature allows different routing policies for inbound and outbound traffic on the same link?
A) Route maps
B) Local preference
C) AS path prepending
D) MED
Answer: A
Explanation:
BGP is the de facto protocol for inter-domain routing in enterprises and service provider environments. Controlling routing policies on a per-link basis is critical for traffic engineering, redundancy, and compliance with SLAs. Route maps are a flexible BGP feature that allows administrators to manipulate routing decisions for both inbound and outbound traffic. Route maps work with attributes such as local preference, MED, community tags, and AS path to define granular routing behavior. They can filter prefixes, assign metrics, or influence route propagation based on complex conditions.
Option A) is correct because route maps allow independent routing policies for inbound and outbound traffic. For instance, traffic leaving a data center to the Internet might be directed over a high-capacity link using local preference manipulation, while inbound traffic from an ISP can be influenced using MED or community-based policies. This flexibility is essential in multi-homed enterprise networks where load balancing, redundancy, and cost management are critical considerations.
Option B) local preference influences outbound path selection but does not provide full per-prefix, per-direction policy control.
Option C) AS path prepending is a simple method to influence inbound traffic but lacks granular control for complex routing requirements.
Option D) MED indicates preferred entry points for neighbors but is limited in scope and requires cooperation from upstream ASes.
Using route maps effectively requires deep understanding of BGP attributes, network topology, and traffic patterns. Enterprises often deploy route maps in conjunction with prefix lists, community tagging, and BGP policy tools to create highly predictable and controllable routing behavior. This capability supports high availability, optimized bandwidth utilization, compliance with regulatory requirements, and strategic traffic engineering. Proper implementation ensures predictable path selection, simplifies troubleshooting, and provides a robust mechanism for maintaining service performance across diverse WAN links. Overall, route maps are a cornerstone of enterprise BGP strategy, enabling precise, scalable, and resilient routing policies.
Question 36
Which EIGRP metric component can be adjusted to influence path selection without changing bandwidth?
A) Delay
B) Load
C) Reliability
D) K-values
Answer: D
Explanation:
EIGRP uses a composite metric to determine the best path to a destination. The composite metric includes bandwidth, delay, load, reliability, and MTU (MTU is not used in the metric calculation but considered for reachability). Normally, EIGRP calculates a route metric based on default K-values, where K1 (bandwidth) and K3 (delay) are used by default, and K2, K4, K5 can be adjusted. Adjusting K-values allows administrators to fine-tune route selection without physically changing the link bandwidth or modifying delay.
Option D) is correct because modifying K-values changes the weight of metric components, influencing path selection while leaving physical properties untouched. For example, in a network with multiple parallel links, engineers might adjust K-values to prefer a longer path with lower delay over a shorter but higher-delay link, optimizing latency-sensitive applications such as VoIP or video conferencing.
Option A) delay is a metric component, but adjusting it directly on an interface can affect other dependent processes.
Option B) load is dynamic and reflects current utilization, but influencing path selection by artificially adjusting load is not recommended.
Option C) reliability is also dynamic and reflects error rates; it cannot be used alone to predictably influence path selection.
Properly tuning K-values allows enterprises to perform advanced traffic engineering using EIGRP without introducing complex redistribution or policy-based routing. This capability is crucial in large-scale WAN designs, multi-homed environments, and hybrid networks where deterministic routing behavior is needed. By strategically configuring K-values, administrators can prioritize certain paths over others, maintain redundancy, and optimize network performance while keeping convergence times stable. Moreover, K-value tuning can prevent suboptimal routing loops, ensure efficient resource utilization, and maintain predictable failover behavior across critical links. The combination of composite metrics and K-value adjustment gives EIGRP a unique advantage in enterprise networks, enabling both fine-grained control and operational flexibility.
Question 37
What is the function of OSPF virtual links in multi-area topologies?
A) Connect non-backbone areas to the backbone through another area
B) Summarize external routes into a stub area
C) Isolate unstable links from SPF calculation
D) Provide load balancing between ABRs
Answer: A
Explanation:
OSPF requires that all areas connect to the backbone area (Area 0) to maintain consistent routing information. In some enterprise topologies, physical constraints or legacy network designs prevent direct connectivity to Area 0. OSPF virtual links provide a logical tunnel through an intermediate area to connect a non-backbone area to the backbone. This ensures LSAs can propagate correctly, allowing routers in isolated areas to participate fully in OSPF routing.
Option A) is correct because virtual links are specifically designed to connect remote areas indirectly to Area 0 through an ABR in another area. Virtual links maintain the backbone’s integrity, allowing multi-area OSPF networks to converge properly.
Option B) summarizing external routes is a different OSPF feature, typically performed at ABRs or ASBRs.
Option C) isolating unstable links does not describe virtual links; it may be achieved using SPF timers or stub areas.
Option D) load balancing between ABRs is not the primary purpose of virtual links; equal-cost multipath (ECMP) handles load distribution.
Using virtual links is particularly useful during network migrations, expansions, or mergers, when certain areas cannot physically connect to Area 0. However, they require careful configuration: the transit area must be normal (not a stub), and authentication settings must match. Virtual links can impact network stability if the transit area experiences flapping because the virtual link depends on the underlying area’s connectivity. Therefore, network engineers typically plan redundancy and monitor virtual link stability proactively. Enterprises using virtual links benefit from flexibility in hierarchical design, preservation of OSPF area integrity, and uninterrupted LSA propagation, ensuring multi-area OSPF networks remain convergent, resilient, and scalable.
Question 38
Which BGP feature is used to influence inbound traffic from multiple ISPs?
A) AS path prepending
B) Local preference
C) Route maps
D) Weight
Answer: A
Explanation:
Enterprises that maintain multi-homed Internet connections often need to control inbound traffic from different ISPs to optimize bandwidth usage, reduce latency, and balance costs. Unlike outbound traffic, which can be influenced using local preference or route maps, inbound traffic is controlled using attributes visible to external ASes. One of the primary mechanisms is AS path prepending, which artificially lengthens the AS path advertised to upstream providers. BGP prefers shorter AS paths, so a longer AS path makes a route less attractive to external peers.
Option A) is correct because AS path prepending directly influences how remote ASes select a preferred path to reach the enterprise network. For example, prepending a route through ISP-A while leaving the path to ISP-B short encourages inbound traffic to enter via ISP-B, achieving traffic engineering goals without affecting internal routing.
Option B) local preference influences outbound routing within an AS but does not affect how other autonomous systems route traffic to you.
Option C) route maps provide granular manipulation of attributes but are only effective when combined with other attributes like AS path prepending or community tags.
Option D) weight is a Cisco-specific attribute that affects only local routers’ path selection and does not influence inbound traffic from external peers.
AS path prepending must be used carefully: over-prepending can lead to suboptimal routing, longer latency, and potential policy violations by ISPs. Additionally, prepending is often combined with BGP communities and route maps for more refined traffic engineering. By strategically applying AS path prepending, enterprises can manage redundancy, performance, and cost efficiency for multi-homed Internet connections, ensuring that critical traffic enters the network through the most appropriate links. This approach is vital in high-availability WAN designs where predictable inbound routing patterns are necessary for operational reliability and SLA compliance.
Question 39
In OSPF, what is the purpose of an ABR summarizing routes between areas?
A) Reduce routing table size and SPF calculation overhead
B) Convert EIGRP routes to OSPF external routes
C) Influence path selection for internal routers
D) Isolate backbone instability from branch networks
Answer: A
Explanation:
Enterprise networks with multi-area OSPF require route summarization to manage complexity and ensure scalability. An Area Border Router (ABR) acts as the gateway between areas and can summarize multiple contiguous subnets into a single advertisement when propagating routes between areas. Summarization reduces the number of LSAs flooded into other areas, directly minimizing SPF computation overhead on all routers.
Option A) is correct because summarization at ABRs reduces the size of routing tables and the processing load, improving network efficiency and stability. Large networks with numerous branches benefit significantly because frequent route flaps or topology changes in one area do not unnecessarily trigger SPF recalculations across the entire network.
Option B) converting EIGRP routes to OSPF external routes involves redistribution, not summarization.
Option C) while summarization may indirectly influence path selection by consolidating routes, its primary purpose is efficiency, not preference.
Option D) isolating backbone instability is a secondary effect of proper summarization, but the main goal is to reduce routing table size and SPF recalculations.
Summarization also aids in network planning and hierarchical addressing, making it easier to maintain and expand the network over time. It ensures predictable convergence behavior and helps maintain optimal resource utilization, especially on routers with limited memory or CPU. Summarized routes prevent flooding of unnecessary routing information, preserve bandwidth, and reduce troubleshooting complexity. ABR summarization is a key practice in designing large-scale, resilient, and high-performance OSPF networks where efficiency and stability are paramount.
Question 40
Which feature in EIGRP provides unequal-cost load balancing for traffic engineering?
A) Variance
B) Feasible successor
C) Stub routing
D) Route filtering
Answer: A
Explanation:
EIGRP supports unequal-cost load balancing, allowing multiple routes to a destination to be used even if their metrics differ. The variance command multiplies the feasible distance of the best route by a configured factor to determine which additional paths qualify for load balancing. Only routes that meet the feasibility condition and fall under the calculated variance are installed in the routing table and used for traffic forwarding.
Option A) is correct because variance enables traffic engineering without manual redistribution or policy-based routing. By adjusting the variance value, engineers can influence how traffic is distributed across links with different metrics, ensuring better bandwidth utilization, redundancy, and resilience.
Option B) feasible successors provide backup paths but are used only for rapid convergence, not for load balancing.
Option C) stub routing limits route advertisement to neighbors to reduce query propagation; it does not influence load balancing.
Option D) route filtering restricts which routes are accepted or advertised but does not enable unequal-cost load balancing.
Implementing variance-based load balancing requires careful planning to prevent routing loops, ensure traffic symmetry, and maintain predictable convergence. Enterprises with multiple WAN links or redundant paths often rely on variance to optimize network performance, reduce congestion, and maximize available bandwidth. Variance is particularly useful when one link is underutilized due to a slightly higher metric than the preferred path; adjusting variance allows intelligent utilization of these backup links without compromising network stability. Combined with EIGRP’s rapid convergence and feasible successor mechanism, variance provides a powerful tool for resilient and efficient enterprise WAN routing strategies, ensuring optimized traffic distribution and high availability.
