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Question 161
Which BGP attribute influences path selection for traffic leaving the local router?
A) Weight
B) Local Preference
C) AS-path
D) MED
Answer: A
Explanation:
In BGP, the Weight attribute is a Cisco-specific feature used to influence path selection for outbound traffic from the local router. Weight is a local-only parameter, meaning it is not propagated to other routers in the network. It is assigned either manually or by default: routes learned via the local network usually receive the highest weight, ensuring they are preferred over external or less desirable paths. The Weight attribute is evaluated before other BGP path selection attributes, making it a powerful tool for local traffic engineering.
Option A) is correct because Weight directly determines which path the local router chooses to forward traffic. Option B), Local Preference, affects path selection within an AS but is propagated to all routers in the autonomous system. Option C), AS-path, is used to select paths with the shortest AS-path during inter-AS routing, and Option D), MED, provides hints to external neighbors about preferred entry points into an AS but does not control local outbound path selection.
For ENARSI candidates, understanding Weight is crucial when managing enterprise networks with multiple exit points to the Internet or other autonomous systems. Using Weight strategically allows administrators to control traffic flows, optimize bandwidth, and enforce routing policies without affecting other routers in the network. Commands such as show ip bgp and show bgp summary reveal weight values, making it easier to verify routing behavior and troubleshoot traffic issues.
Improper configuration of Weight can lead to suboptimal routing, traffic congestion, or unexpected failover behaviors, especially in multi-homed enterprise topologies. Understanding its interaction with other BGP attributes ensures that network engineers can predict routing decisions and maintain high reliability. Mastery of Weight is critical for designing enterprise-grade BGP solutions, making it a key topic for the ENARSI 300-410 exam.
By mastering Weight, candidates gain the ability to control local path selection precisely, balance traffic across multiple links, and implement efficient, resilient routing strategies within complex enterprise networks.
Question 162
Which OSPF area type blocks external routes but allows inter-area routes?
A) Stub area
B) Totally stubby area
C) NSSA
D) Backbone area
Answer: A
Explanation:
A stub area in OSPF is a specialized area designed to block external Type 5 LSAs while still allowing inter-area Type 3 LSAs. This design reduces the size of the routing table and SPF calculation overhead on routers within the area, which is particularly beneficial for branch offices or networks with limited resources. Stub areas rely on a default route injected by the ABR to reach external destinations, ensuring minimal configuration while maintaining connectivity.
Option A) is correct because stub areas block external routes but allow inter-area routes. Option B), totally stubby areas, block both external and inter-area routes except for a default route. Option C), NSSA, allows controlled injection of external routes using Type 7 LSAs. Option D), backbone area, does not restrict any LSA type.
ENARSI candidates must understand stub areas to design scalable OSPF networks that reduce control plane load and optimize convergence times. Commands like area X stub enable configuration, while show ip ospf database and show ip route ospf help verify proper route propagation.
Improper implementation of stub areas can lead to routing blackholes, inaccessible networks, or excessive SPF recalculation if external reachability is required but not properly configured. Mastery of stub areas allows network engineers to optimize routing table sizes, reduce CPU usage, and enhance network stability, which is essential for enterprise deployments and the ENARSI exam.
Understanding stub areas also allows engineers to plan hierarchical OSPF topologies, maintain predictable routing patterns, and design resilient networks that can scale across multiple sites without overwhelming branch routers.
Question 163
Which EIGRP feature allows fast convergence using backup routes?
A) Feasible successor
B) Variance command
C) Successor route
D) Topology table
Answer: A
Explanation:
The Feasible Successor in EIGRP is a backup route that meets the feasibility condition (its reported distance is less than the feasible distance of the current successor). Feasible successors allow EIGRP to achieve fast convergence when the primary route fails, because these backup routes are precomputed and loop-free, eliminating the need for recalculating the entire topology.
Option A) is correct because feasible successors enable rapid failover. Option B), Variance command, allows unequal-cost load balancing but does not directly provide backup routes. Option C), Successor route, is the primary active path but does not provide automatic backup unless feasible successors exist. Option D), Topology table, stores all feasible routes but requires the feasibility condition to identify viable backups.
ENARSI candidates must understand feasible successors because they ensure high availability, minimal downtime, and predictable network behavior. Commands like show ip eigrp topology display feasible successors, allowing engineers to verify backup path readiness and troubleshoot routing failures effectively.
Misunderstanding feasible successors can lead to slow convergence, packet loss, and network instability, especially in enterprise WANs with multiple redundant paths. Proper use enhances network reliability, reduces recovery time, and supports mission-critical applications.
Feasible successors also interact with variance and unequal-cost load balancing, allowing EIGRP to optimize traffic distribution while maintaining loop-free convergence. Mastery of this concept ensures candidates can design resilient enterprise networks with rapid failover capabilities, making it a key topic for the ENARSI exam.
Question 164
Which BGP attribute indicates the shortest AS path to a destination?
A) Weight
B) Local Preference
C) AS-path
D) MED
Answer: C
Explanation:
The AS-path attribute in BGP records the sequence of autonomous systems a route has traversed. BGP uses AS-path length as a primary factor to select the shortest inter-AS path to a destination. Routes with shorter AS-paths are preferred because they typically represent the most direct and efficient route, reducing latency and the potential for congestion.
Option C) is correct because AS-path explicitly indicates the number of AS hops to the destination. Option A), Weight, influences local path selection only. Option B), Local Preference, is used for intra-AS path preference. Option D), MED, suggests preferred entry points to external ASes but is secondary to AS-path in path selection.
ENARSI candidates must understand AS-path for designing multi-homed enterprise networks, controlling traffic flow, and preventing routing loops. Commands like show ip bgp provide visibility into AS-path information, enabling engineers to predict path selection and troubleshoot inter-AS routing issues effectively.
Mismanagement of AS-path or ignoring its influence can lead to suboptimal routing, inefficient traffic flow, or routing loops, particularly in large-scale enterprise deployments with multiple BGP peers. AS-path also interacts with other attributes such as Local Preference, Weight, and MED, making it critical for fine-tuning BGP routing policies and implementing enterprise traffic engineering strategies.
Mastering AS-path ensures ENARSI candidates can design reliable, scalable, and efficient BGP networks that provide optimal path selection across multiple autonomous systems, a critical skill for the 300-410 exam.
Question 165
Which OSPF command verifies area configuration and LSA propagation?
A) show ip ospf neighbor
B) show ip ospf database
C) show ip route ospf
D) show running-config
Answer: B
Explanation:
The show ip ospf database command is essential for verifying OSPF area configuration and examining LSA propagation across the network. It provides detailed information about router LSAs, network LSAs, summary LSAs, and external LSAs, enabling engineers to ensure proper route distribution and area connectivity.
Option B) is correct because it directly displays the LSAs and their types. Option A), show ip ospf neighbor, only verifies adjacency states and neighbor relationships. Option C), show ip route ospf, displays the routing table but does not reveal the LSA content. Option D), show running-config, shows configuration but not real-time LSA propagation.
ENARSI candidates must master this command to verify network topology, troubleshoot routing issues, and ensure OSPF design consistency. Examining LSAs helps identify misconfigurations, missing routes, or excessive LSA flooding that could impact performance.
Proper use of show ip ospf database allows engineers to confirm area type implementation, verify stub or NSSA configurations, and validate external route injection, which are crucial for enterprise network design and ENARSI exam scenarios. Misunderstanding LSA types or propagation can lead to routing loops, unreachable networks, and convergence delays, emphasizing the command’s importance in operational verification.
By mastering this command, candidates gain the ability to analyze OSPF operations in real time, troubleshoot complex topologies, and design reliable, scalable enterprise networks, aligning directly with the ENARSI 300-410 exam objectives.
Question 166
Which OSPF area type allows importing external routes using Type 7 LSAs?
A) Stub area
B) Totally stubby area
C) NSSA
D) Backbone area
Answer: C
Explanation:
An NSSA (Not-So-Stubby Area) is a specialized OSPF area type that combines characteristics of stub areas with the ability to import external routes into the OSPF domain using Type 7 LSAs. Unlike regular stub areas, which block all external Type 5 LSAs, NSSAs allow controlled redistribution from other routing protocols or external networks. This makes NSSAs particularly useful in branch offices or edge networks that need limited external connectivity while still reducing LSA flooding within the area.
Option C) is correct because NSSAs uniquely support Type 7 LSAs. Option A), stub areas, block external LSAs entirely. Option B), totally stubby areas, block both external and inter-area routes except a default route. Option D), backbone area, carries all LSAs and does not restrict external LSAs.
ENARSI candidates must understand NSSAs for designing scalable enterprise OSPF topologies where certain areas have restricted external route propagation but still require connectivity to external networks. Commands like area X nssa or area X nssa no-summary configure NSSAs and totally NSSAs, allowing the engineer to tune default route injection and summarization for the area.
Improper NSSA configuration can result in inaccessible networks, routing loops, or missing external connectivity, especially if external LSAs are expected but blocked by area settings. Properly leveraging NSSAs enables optimized SPF calculations, reduced memory and CPU usage, and controlled propagation of external routes, which is critical in large-scale enterprise deployments.
Understanding NSSA behavior also helps engineers plan hierarchical OSPF topologies, ensuring optimal area segmentation and scalability. Mastery of NSSAs, including Type 7 LSA conversion to Type 5 at the ABR, ensures predictable and reliable routing behavior, a vital topic for the ENARSI 300-410 exam. Candidates benefit by being able to balance performance, scalability, and external connectivity efficiently.
Question 167
Which BGP attribute is used to influence inbound traffic from external peers?
A) Weight
B) Local Preference
C) AS-path prepending
D) MED
Answer: C
Explanation:
AS-path prepending is a BGP technique used to influence inbound traffic from external peers by artificially lengthening the AS-path for a specific route. By adding multiple occurrences of its own AS number in the path, a BGP speaker makes that route appear less desirable to external autonomous systems, effectively controlling how external networks route traffic toward the enterprise.
Option C) is correct because AS-path prepending directly affects how other ASes perceive path length, influencing their route selection. Option A), Weight, is local-only and does not affect inbound traffic. Option B), Local Preference, applies only within the local AS. Option D), MED, provides entry preference hints to neighboring ASes but is less powerful than AS-path prepending for inbound traffic control.
ENARSI candidates must understand AS-path prepending because enterprises often have multi-homed BGP configurations where controlling inbound traffic is critical for load balancing, redundancy, and performance optimization. Proper use requires careful planning, as over-prepending can lead to underutilization of links, while insufficient prepending may not influence traffic effectively.
Tools like show ip bgp and show bgp summary provide visibility into AS-paths and allow engineers to verify the effect of prepending on advertised routes. Mismanagement of AS-path prepending can cause traffic asymmetry, congestion, or unintentional routing preferences, which can disrupt application performance.
Mastering AS-path prepending empowers ENARSI candidates to implement effective BGP traffic engineering, optimize inbound traffic distribution, and maintain enterprise connectivity, making it a key topic for the 300-410 exam.
Question 168
Which EIGRP feature enables unequal-cost load balancing?
A) Successor route
B) Feasible successor
C) Variance command
D) Stub routing
Answer: C
Explanation:
The Variance command in EIGRP allows unequal-cost load balancing by enabling multiple feasible routes to a destination to be installed in the routing table, even if their metric is higher than the primary route. By default, EIGRP only uses successor routes with the lowest metric for routing, but the variance command multiplies the lowest metric by a factor (the variance value) to determine which routes qualify for load balancing.
Option C) is correct because Variance explicitly permits unequal-cost load balancing. Option A), Successor route, represents the primary active path. Option B), Feasible successor, provides precomputed backup routes but does not automatically enable traffic sharing unless used with variance. Option D), Stub routing, limits routing updates for branch networks but does not affect load balancing.
ENARSI candidates must understand variance because unequal-cost load balancing improves bandwidth utilization, redundancy, and traffic distribution in enterprise networks. Commands like show ip eigrp topology and show ip route allow engineers to verify that multiple paths are installed and actively used.
Improper configuration of variance may result in loops, suboptimal routing, or traffic congestion, especially in large-scale WANs with multiple EIGRP paths. Using variance alongside feasible successors ensures loop-free, efficient routing, providing enterprise networks with resilient, high-performance routing capabilities.
Mastery of the variance command is essential for ENARSI candidates to design robust, high-availability EIGRP topologies that maximize network resource utilization while maintaining predictable convergence and fault tolerance, aligning directly with 300-410 exam objectives.
Question 169
Which OSPF command verifies adjacency states with neighbors?
A) show ip ospf database
B) show ip ospf neighbor
C) show ip route ospf
D) show running-config
Answer: B
Explanation:
The show ip ospf neighbor command is used to verify OSPF neighbor relationships and adjacency states. OSPF relies on establishing neighbor adjacencies to exchange LSAs and maintain accurate topology information. This command provides details such as neighbor ID, priority, state (e.g., Full, 2-Way), and interface information, which are crucial for troubleshooting OSPF issues.
Option B) is correct because it directly displays neighbor adjacency states. Option A), show ip ospf database, displays LSAs but does not indicate neighbor states. Option C), show ip route ospf, shows routes but not adjacency information. Option D), show running-config, shows configured interfaces and OSPF settings but not real-time adjacency data.
ENARSI candidates must master this command to troubleshoot OSPF adjacency problems, identify interface or authentication issues, and ensure proper area connectivity. Misconfigurations in OSPF, such as mismatched hello/dead intervals, area mismatches, or interface errors, can prevent adjacencies from forming, leading to network segmentation or incomplete routing information.
By using show ip ospf neighbor, engineers can confirm whether routers achieve Full state adjacencies required for LSA exchange and verify that OSPF areas are fully converged. Mastery of neighbor verification ensures predictable routing behavior, stable network topology, and successful enterprise OSPF deployments, all of which are critical topics for the 300-410 ENARSI exam.
Question 170
Which BGP command displays path selection and attribute values?
A) show ip bgp summary
B) show ip bgp
C) show running-config
D) show ip route
Answer: B
Explanation:
The show ip bgp command is fundamental for verifying BGP routing and understanding path selection based on attributes. This command displays prefixes, next hops, AS-path, local preference, MED, weight, and origin, providing visibility into how BGP selects the best path to each destination. This insight is essential for traffic engineering, troubleshooting, and confirming that policies such as route maps or prefix-lists are functioning correctly.
Option B) is correct because it directly displays BGP routes and their associated attributes. Option A), show ip bgp summary, provides an overview of peers and session states but not detailed path attributes. Option C), show running-config, shows configuration but not real-time BGP path selection. Option D), show ip route, shows the active routing table but does not include full BGP attribute information.
ENARSI candidates must use show ip bgp to validate route propagation, troubleshoot unexpected path selection, and verify policy enforcement. Misinterpretation of path attributes can lead to routing loops, suboptimal traffic paths, or failed failover mechanisms, particularly in enterprise networks with multi-homed BGP connections.
Mastery of this command allows engineers to analyze all BGP attributes affecting path selection, confirm best-path calculations, and optimize routing policies. Understanding weight, local preference, AS-path, and MED in real-world network scenarios is critical for scalable, reliable enterprise routing, aligning directly with 300-410 ENARSI exam objectives.
Question 171
Which EIGRP mechanism prevents routing loops using feasible successors?
A) Successor route
B) Feasibility condition
C) Split horizon
D) Stub routing
Answer: B
Explanation:
The feasibility condition is a fundamental EIGRP mechanism that prevents routing loops while allowing rapid convergence. EIGRP maintains a topology table containing all feasible routes to a destination. A feasible successor is a backup route that satisfies the feasibility condition, meaning its reported distance is less than the feasible distance of the primary successor route. This guarantees that the backup route is loop-free because it originates from a router closer to the destination than the current router itself.
Option B) is correct because the feasibility condition is specifically designed to ensure loop-free backup paths. Option A), Successor route, is the primary active path but does not itself prevent loops. Option C), Split horizon, prevents updates from being sent back on the same interface but is not the EIGRP-specific loop prevention mechanism. Option D), Stub routing, restricts route advertisement but does not inherently provide loop-free backup routes.
Understanding the feasibility condition is crucial for ENARSI candidates because EIGRP is widely deployed in enterprise networks where fast convergence and loop avoidance are vital. The feasibility condition allows EIGRP to use feasible successors immediately upon loss of the primary route without waiting for recomputation, resulting in sub-second convergence.
Practical scenarios include multi-homed branch offices or redundant WAN links, where feasible successors ensure network reliability and minimal traffic disruption. Commands like show ip eigrp topology and show ip route eigrp allow engineers to observe successor and feasible successor routes and verify that the feasibility condition is met. Misunderstanding this mechanism can lead to routing loops, suboptimal traffic paths, or delayed convergence, all of which impact enterprise network performance.
Mastery of the feasibility condition enables engineers to design scalable, resilient EIGRP networks that leverage both primary and backup paths efficiently. It also provides insight into EIGRP metric calculations, route preference, and topology stability, critical for passing the 300-410 ENARSI exam and implementing robust enterprise routing designs.
Question 172
Which HSRP command sets a router’s virtual IP address?
A) standby ip
B) standby priority
C) standby preempt
D) interface ip address
Answer: A
Explanation:
In HSRP (Hot Standby Router Protocol), the standby ip command assigns the virtual IP address that hosts use as the default gateway. The virtual IP is shared among a group of routers, with one router acting as the active router and another as the standby router. This configuration ensures gateway redundancy: if the active router fails, the standby router automatically assumes the active role, maintaining uninterrupted connectivity for hosts.
Option A) is correct because standby ip defines the virtual IP address that routers share. Option B), standby priority, determines which router becomes active when multiple routers are configured. Option C), standby preempt, allows a higher-priority router to take over the active role automatically. Option D), interface ip address, configures the physical interface IP, not the shared virtual IP.
ENARSI candidates must understand HSRP commands for designing redundant, high-availability enterprise networks. Misconfiguring virtual IP addresses can result in traffic blackholing or host connectivity loss, while incorrect priority or preempt settings may prevent the desired router from becoming active. Commands like show standby and show running-config are used to verify the HSRP configuration and ensure active/standby roles are correctly assigned.
Understanding HSRP behavior is essential for enterprises that require gateway redundancy and fast failover in LAN environments. Engineers must be able to implement HSRP across VLANs, verify redundancy, and troubleshoot convergence issues. Mastery of standby ip and related commands equips ENARSI candidates to maintain reliable, resilient, and scalable network topologies, fulfilling key objectives of the 300-410 exam.
Question 173
Which OSPF LSA type describes external routes imported into the OSPF domain?
A) Type 1
B) Type 2
C) Type 5
D) Type 3
Answer: C
Explanation:
Type 5 LSAs in OSPF are used to describe external routes that are redistributed into the OSPF domain from other routing protocols, such as EIGRP, BGP, or RIP. Type 5 LSAs are generated by Autonomous System Boundary Routers (ASBRs) and propagated throughout the OSPF domain, except into stub or totally stubby areas, which block these LSAs to reduce routing table size and minimize LSA flooding.
Option C) is correct because Type 5 LSAs carry external route information. Option A), Type 1, represents router LSAs detailing router links. Option B), Type 2, represents network LSAs describing multi-access networks. Option D), Type 3, represents summary LSAs that advertise inter-area routes within OSPF.
ENARSI candidates must understand the behavior of Type 5 LSAs because external route redistribution is common in enterprise networks with multi-protocol environments. Proper handling ensures that external routes are correctly advertised without creating routing loops or unnecessary LSA flooding. Commands such as show ip ospf database and show ip route ospf help verify that Type 5 LSAs are correctly propagated.
Misunderstanding Type 5 LSAs can lead to missing external connectivity, suboptimal routing, or routing loops, particularly when redistributing multiple protocols into OSPF. Engineers must consider area types, LSA flooding behavior, and summarization to optimize OSPF convergence and scalability. Mastery of Type 5 LSAs ensures that ENARSI candidates can design and troubleshoot OSPF networks that integrate external routing information efficiently, a critical requirement for the 300-410 exam.
Question 174
Which command redistributes BGP into OSPF with a specific metric?
A) redistribute ospf metric
B) redistribute bgp subnets metric
C) network bgp metric
D) route-map bgp ospf
Answer: B
Explanation:
Redistributing BGP into OSPF allows an enterprise to advertise BGP-learned routes into the OSPF domain. The command redistribute bgp subnets metric <value> is used to include BGP prefixes and assign a specific OSPF metric for proper route preference. The subnets keyword ensures that all BGP subnets are redistributed into OSPF.
Option B) is correct because it explicitly allows redistribution with metric assignment. Option A) is invalid because it is incomplete; OSPF redistribution requires specifying the source protocol and metric. Option C), network bgp metric, does not apply to redistribution but rather to route advertisement from a BGP process. Option D), route-map bgp ospf, may be used to filter routes but does not assign the metric by itself.
ENARSI candidates must understand redistribution because enterprise networks often combine BGP for WAN connectivity and OSPF for internal routing. Improper configuration can lead to routing loops, suboptimal paths, or unreachable networks, especially in complex, multi-area OSPF environments. Commands like show ip route ospf and show ip ospf database are critical for verifying correct route injection and metric assignment.
Proper metric assignment is essential because OSPF uses it to calculate the shortest path first (SPF). Without a metric, redistributed routes may be ignored or incorrectly prioritized. Understanding redistribution concepts enables engineers to maintain predictable, stable, and optimized routing, aligning with ENARSI exam objectives on advanced enterprise routing and integration scenarios.
Question 175
Which BGP attribute determines outbound path preference to external peers?
A) Local preference
B) Weight
C) AS-path
D) MED
Answer: B
Explanation:
The Weight attribute in BGP is a Cisco-specific attribute that controls outbound path preference on a local router. Unlike Local Preference, which affects all routers in an AS, weight is locally significant and only influences the BGP best-path selection on the router where it is configured. Higher weight values make a path more preferred for outbound traffic.
Option B) is correct because weight determines the path a router chooses for sending traffic to external peers. Option A), Local Preference, influences inbound traffic decisions across the AS. Option C), AS-path, is mainly used to influence inbound traffic by making paths appear longer or shorter. Option D), MED, provides a suggestion to external neighbors on preferred entry points but does not override weight on the local router.
ENARSI candidates must understand weight because controlling outbound traffic is vital in multi-homed BGP scenarios, ensuring that traffic leaves the enterprise network via the most optimal or preferred path. Commands like show ip bgp allow engineers to verify weight settings and confirm their effect on best-path selection.
Misconfigured weight can result in traffic congestion, underutilization of links, or routing asymmetry. By properly leveraging weight, engineers can optimize performance, achieve load balancing, and maintain predictable traffic engineering policies, which is a critical skill for the 300-410 exam. Weight, combined with other attributes like Local Preference, AS-path, and MED, allows complete BGP traffic engineering control, ensuring efficient enterprise routing and high network availability.
Question 176
Which routing protocol supports route tagging for redistribution control?
A) OSPF
B) EIGRP
C) BGP
D) RIP
Answer: B
Explanation:
Route tagging is an essential mechanism in advanced enterprise routing environments, particularly when managing multi-protocol redistribution scenarios. Enterprise networks often employ multiple routing protocols, such as EIGRP, OSPF, and BGP, to handle different network segments, failover paths, and connectivity to external peers. In such situations, route loops can occur if redistribution is performed indiscriminately. Route tags serve as identifiers that mark routes with a specific numerical value, allowing administrators to track, filter, and control the redistribution of routes between protocols efficiently.
EIGRP provides robust support for route tagging through its redistribution configuration. When redistributing routes from another protocol into EIGRP or redistributing EIGRP routes into a different protocol, engineers can apply tags to ensure that previously redistributed routes are not reintroduced, preventing routing loops and potential instability. For instance, if an OSPF route is redistributed into EIGRP, tagging it with a unique value allows future redistribution operations to recognize the route as already processed, thereby avoiding duplicate entries and path flapping.
Option B) is correct because EIGRP supports route tagging natively in redistribution scenarios, providing granular control over route propagation. Option A), OSPF, uses redistribution but does not inherently leverage route tagging in the same granular way as EIGRP; instead, OSPF relies on area types and LSA filtering. Option C), BGP, primarily uses attributes like AS-path, MED, and local preference to influence route selection and propagation but does not natively use tags in the context of multi-protocol redistribution in the same manner as EIGRP. Option D), RIP, is a simpler protocol without sophisticated tagging capabilities, making it unsuitable for advanced loop prevention in complex enterprise environments.
From an ENARSI exam perspective, understanding route tagging is crucial because enterprise networks often have branch-to-branch connectivity, multiple WAN links, and hybrid protocol designs. Misconfiguration can result in routing loops, duplicate advertisements, or unpredictable path selection, leading to packet loss or network downtime. Practical commands such as redistribute ospf 1 metric 100 tag 2000 in EIGRP enable engineers to assign tags effectively. Verification can be done with show ip route and show ip eigrp topology to confirm that tagged routes are correctly applied and propagated.
Furthermore, route tagging allows complex traffic engineering, as engineers can apply route maps to selectively redistribute traffic, prioritize certain paths, or implement policy-based routing (PBR). It is particularly critical in environments that interconnect multiple enterprise sites, cloud connections, or service provider backbones, where controlling redistribution pathways ensures loop-free, efficient, and predictable routing. Mastery of route tagging allows ENARSI candidates to design scalable and resilient enterprise networks while passing exam objectives related to advanced EIGRP and redistribution scenarios.
Question 177
Which command verifies MPLS LDP neighbor relationships?
A) show mpls ldp neighbor
B) show ip route mpls
C) show ldp bindings
D) show mpls forwarding-table
Answer: A
Explanation:
In MPLS (Multiprotocol Label Switching) networks, establishing and verifying Label Distribution Protocol (LDP) neighbor relationships is fundamental for ensuring that labels are correctly distributed among routers. LDP is the protocol responsible for mapping FECs (Forwarding Equivalence Classes) to labels, which are then used by routers to forward packets efficiently without relying solely on routing tables. LDP neighbors form over TCP sessions between directly connected routers and exchange label mapping messages to maintain label consistency across the MPLS domain.
Option A) is correct because show mpls ldp neighbor directly displays the state of LDP neighbor relationships, including the neighbor IP, state, uptime, and discovery transport address. This command allows engineers to quickly identify if LDP sessions are established, idle, or in an error state. Without active LDP neighbor relationships, MPLS cannot forward labeled packets, resulting in blackholed traffic or routing failures.
Option B), show ip route mpls, displays routes with MPLS labels but does not provide information about neighbor establishment or LDP session states. Option C), show ldp bindings, shows label-to-FEC mappings but does not verify connectivity with neighbors. Option D), show mpls forwarding-table, shows the label-forwarding table used for packet forwarding but does not indicate neighbor session states.
For ENARSI candidates, understanding LDP neighbor verification is essential for designing and troubleshooting MPLS-based enterprise WANs. Common issues include mismatched LDP configuration parameters, interface misconfigurations, or TCP connectivity issues between routers. Commands like ping, traceroute, and show mpls ldp neighbor allow engineers to isolate problems and verify that all routers can exchange labels efficiently. Proper LDP operation ensures fast packet forwarding, loop-free label paths, and support for traffic-engineered MPLS solutions such as LSPs (Label Switched Paths).
Additionally, LDP plays a role in advanced enterprise designs where QoS, TE tunnels, and MPLS VPNs are implemented. A thorough understanding of the neighbor relationship and session establishment helps engineers anticipate network convergence behaviors, verify redundancy, and maintain service-level guarantees. Mastering LDP neighbor verification prepares candidates for the ENARSI exam topics on MPLS fundamentals, LDP troubleshooting, and high-performance enterprise routing.
Question 178
Which OSPF feature prevents routing table growth in branch offices?
A) Totally stubby area
B) NSSA
C) Virtual link
D) Route summarization
Answer: A
Explanation:
OSPF offers several mechanisms to optimize routing in large enterprise networks, particularly in branch office deployments where resource constraints and limited router memory can be critical. One of the most effective features to control routing table growth is the Totally Stubby Area (TSA), a concept developed by Cisco. TSAs prevent the propagation of external routes (Type 5 LSAs) and inter-area routes (Type 3 LSAs) into the area, allowing only a default route to reach destinations outside the area. This dramatically reduces routing table size and SPF calculation overhead on branch routers.
Option A) is correct because Totally Stubby Areas are specifically designed to minimize routing information in small branch routers. Option B), NSSA (Not-So-Stubby Area), allows limited redistribution of external routes but does not achieve the same level of routing table minimization as TSA. Option C), Virtual link, connects non-backbone areas to the backbone but does not reduce routing table size. Option D), Route summarization, reduces inter-area routes but still allows Type 5 external routes into the area, which can increase table size compared to a TSA.
For ENARSI candidates, understanding TSAs is essential because enterprise networks frequently include many branch offices with limited processing resources. By designating branch areas as TSAs, engineers can reduce OSPF overhead, speed up SPF calculations, and ensure routers remain stable and responsive under load. Configuring TSAs involves using the area x stub no-summary command on all area routers. Verification can be performed using show ip ospf database and show ip route ospf, confirming that only default routes and intra-area routes are present.
TSAs also enhance network stability, as fewer LSAs are processed by branch routers, reducing the risk of SPF recalculation storms during network topology changes. When combined with route summarization at area borders, TSAs provide a robust mechanism for controlling OSPF growth and maintaining predictable performance in large, hierarchical enterprise networks. Knowledge of TSAs is crucial for exam scenarios that test advanced OSPF design, inter-area optimization, and resource-efficient routing, which are critical objectives of the 300-410 ENARSI exam.
By strategically implementing TSAs, engineers can optimize WAN connectivity, reduce CPU load on branch routers, and maintain fast convergence, ensuring that enterprise networks remain resilient, scalable, and aligned with business requirements. This deep understanding of TSAs demonstrates mastery of OSPF area design, traffic engineering, and enterprise routing optimization—all fundamental skills for passing the ENARSI exam.
Question 179
Which BGP attribute controls outbound route preference to multiple neighbors?
A) Local preference
B) MED
C) AS-path
D) Community
Answer: A
Explanation:
In Border Gateway Protocol (BGP), controlling route selection and preference is critical when managing multiple external peers or internal route reflectors in large enterprise networks. One of the most significant attributes used for this purpose is Local Preference (Local Pref). Local Preference is an internally propagated BGP attribute, meaning it influences route selection only within an Autonomous System (AS) and is not advertised to external BGP peers.
Local Preference allows network engineers to define which exit point or neighbor should be preferred for outbound traffic. For example, if an enterprise connects to two ISPs, the Local Preference attribute can be adjusted so that traffic destined for the internet primarily exits through the preferred provider, ensuring optimized routing, predictable traffic flow, and policy compliance.
Option A) is correct because Local Preference is applied within the AS and propagates through iBGP peers, allowing all routers in the AS to consistently prefer the designated path. Option B), MED (Multi-Exit Discriminator), influences inbound traffic from external neighbors, not outbound preference. Option C), AS-path, influences route selection based on the shortest AS sequence and is used primarily to avoid longer paths but does not provide granular outbound control. Option D), Community, is a tagging mechanism that allows policy control, but by itself, it does not directly dictate outbound path preference.
BGP policy design often combines Local Preference with route maps to apply granular control over multiple prefixes. For instance, a company may prefer routes learned from ISP1 for high-priority services while routes from ISP2 are used only as backup. Local Preference is configured with commands like set local-preference 200 in route maps, and verification can be done using show ip bgp.
Understanding Local Preference is essential for the ENARSI exam, as enterprise networks frequently implement multiple BGP sessions for redundancy, load balancing, and traffic engineering. Misconfiguring Local Preference can result in suboptimal traffic patterns, asymmetric routing, and potential SLA violations. Engineers must consider interaction with other attributes such as AS-path, MED, and communities, particularly in complex scenarios involving hybrid cloud connectivity or MPLS VPNs.
Additionally, Local Preference is a foundational tool for influencing outbound routing, which is more controllable than inbound routing because external neighbors determine inbound traffic based on AS-path, MED, or policies. Candidates should also understand how Local Preference interacts with route reflectors in iBGP designs, ensuring consistent routing decisions across all routers in the AS. Mastery of Local Preference enables ENARSI candidates to design predictable, scalable, and policy-compliant BGP environments that align with enterprise routing requirements, prevent routing loops, and support high availability architectures.
Question 180
Which feature prevents OSPF route flooding in hierarchical networks?
A) Route summarization
B) Stub area
C) SPF throttling
D) Virtual link
Answer: B
Explanation:
OSPF (Open Shortest Path First) is widely used in enterprise networks for its scalability, fast convergence, and hierarchical design. One of the key challenges in large OSPF networks is controlling the amount of link-state advertisement (LSA) flooding, particularly to branch routers or areas with limited processing and memory capacity. Excessive LSAs can overwhelm routers, increase SPF calculation time, and impact overall network stability.
Option B), Stub Area, is designed specifically to reduce LSA propagation. In a stub area, Type 5 external LSAs—which represent routes redistributed from other protocols—are not allowed. Instead, routers in the stub area use a default route to reach external destinations, significantly reducing the routing table size and minimizing unnecessary flooding. This makes stub areas ideal for branch offices, WAN edge routers, or resource-constrained devices.
Option A), Route summarization, reduces inter-area LSAs (Type 3 LSAs) but does not inherently prevent external LSA flooding within the area. Option C), SPF throttling, slows down SPF recalculation after topology changes but does not prevent LSA flooding itself. Option D), Virtual link, connects non-backbone areas to the backbone and maintains OSPF connectivity but does not limit LSA propagation.
Configuring a stub area requires the area x stub command on all routers within the area and optionally no-summary for a Totally Stubby Area. Verification is performed using show ip ospf database and show ip route ospf, which confirm that only necessary intra-area and inter-area LSAs are present, along with a default route. By preventing unnecessary LSAs, stub areas improve network convergence, reduce CPU utilization, and enhance overall OSPF stability.
For the ENARSI exam, understanding stub areas is essential when designing hierarchical OSPF networks with multiple branches, as misconfigurations can lead to routing table bloat, convergence delays, and intermittent connectivity issues. In large networks, combining stub areas with route summarization at ABRs (Area Border Routers) allows for optimal OSPF performance, predictable SPF computation, and resource-efficient design.
Mastery of OSPF stub areas equips candidates to implement scalable, resilient enterprise networks, minimize flooding, and maintain predictable behavior during topology changes or link failures. Additionally, knowing how stub areas interact with Totally Stubby Areas (TSA) or Not-So-Stubby Areas (NSSA) provides flexibility in designing enterprise hierarchies that optimize memory usage, routing efficiency, and convergence performance, directly addressing ENARSI objectives.
