Cisco 300-410  Implementing Cisco Enterprise Advanced Routing and Services (ENARSI) Exam  Dumps and Practice Test Questions Set 2 Q 21 -40

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Question 21:

Which EIGRP feature allows the protocol to achieve fast convergence while maintaining loop-free paths?

A) Successor and Feasible Successor
B) Split Horizon
C) Hold Timer
D) Route Summarization

Answer: A) Successor and Feasible Successor

Explanation:

A) Successor and Feasible Successor are core components of EIGRP’s loop-free routing and fast convergence mechanisms. A successor is the primary route to a destination, while a feasible successor is a backup route that satisfies the feasibility condition (its reported distance is less than the feasible distance of the current successor). By maintaining both successors and feasible successors in its topology table, EIGRP can immediately switch to the feasible successor if the primary route fails, avoiding downtime. This capability allows EIGRP to converge quickly without recalculating the entire topology, maintaining network stability and ensuring loop-free routing. The combination of successors and feasible successors allows EIGRP to provide both redundancy and rapid recovery, making it highly suitable for enterprise networks requiring high availability.

B) Split Horizon is a loop-prevention mechanism used in distance-vector protocols, including EIGRP. It prevents a route from being advertised back out the interface from which it was learned. While split horizon contributes to loop prevention, it does not by itself provide rapid convergence. It is a supporting mechanism rather than the main feature that enables immediate failover to a backup path.

C) Hold Timer defines the period a router waits before declaring a neighbor dead when no hello packets are received. While the hold timer is important for neighbor monitoring and convergence timing, it is not the mechanism that provides immediate loop-free backup paths. Convergence is affected by the hold timer, but the existence of feasible successors is what allows EIGRP to switch paths quickly without recalculating the topology.

D) Route Summarization aggregates multiple prefixes into a single advertisement to reduce routing table size and update overhead. Summarization optimizes network performance but does not directly provide fast convergence or loop-free backup paths. It is a tool for efficiency and scalability, not the mechanism for rapid path failover.

In conclusion, the combination of successor and feasible successor is the feature that enables EIGRP to maintain loop-free paths and achieve fast convergence. Split horizon, hold timers, and route summarization support EIGRP operation but do not provide the primary mechanism for rapid, loop-free failover. This makes successor and feasible successor the correct answer.

Question 22:

Which mechanism is used to control route advertisement between OSPF areas to reduce routing overhead?

A) Area Type (Stub, Totally Stubby)
B) Route Redistribution
C) Link-State Advertisement Flooding
D) SPF Algorithm

Answer: A) Area Type (Stub, Totally Stubby)

Explanation:

A) Area types, such as stub or totally stubby areas, are mechanisms in OSPF to control route advertisement and reduce routing overhead. In a stub area, external routes (Type 5 LSAs) are blocked, and only a default route is advertised from the ABR to the area. Totally stubby areas go further, blocking both external routes and inter-area routes (Type 3 LSAs), leaving only a default route to reach outside networks. These configurations minimize the number of LSAs within an area, reduce routing table size, and decrease processing overhead for routers within the area. By carefully choosing area types, network administrators can optimize OSPF performance and limit unnecessary route propagation, which is particularly important in large enterprise networks with many areas.

B) Route redistribution is the process of exchanging routes between different routing protocols or autonomous systems. While redistribution allows interoperability, it does not reduce routing overhead within OSPF areas. In fact, improper redistribution can increase routing overhead and introduce loops if not carefully controlled.

C) Link-State Advertisement (LSA) flooding is the mechanism by which OSPF routers distribute topology information. Flooding ensures all routers have consistent topology databases but can increase overhead if not limited. While controlling LSA types and frequency can impact overhead, flooding itself is not a mechanism to selectively reduce advertisement between areas.

D) SPF (Shortest Path First) algorithm calculates the best paths based on the link-state database. SPF is critical for OSPF path selection and loop-free routing but does not reduce the amount of routing information exchanged. It processes whatever information is already available but does not control the advertisement of routes to reduce overhead.

Area types (stub, totally stubby) are the correct mechanism because they directly control which LSAs are propagated into an area, reducing unnecessary routing information and optimizing router resources. The other mechanisms (redistribution, LSA flooding, SPF) are important for OSPF operation but do not selectively reduce route advertisement between areas.

Question 23:

 Which type of IPv6 address is automatically configured on all IPv6-enabled interfaces for communication with other nodes on the same link?

A) Global Unicast
B) Link-Local
C) Unique Local
D) Multicast

Answer: B) Link-Local

Explanation:

A) Global Unicast addresses are globally routable IPv6 addresses that are equivalent to public IPv4 addresses. They are used for end-to-end communication across the internet and are not automatically assigned to interfaces for local link communication. While necessary for global reachability, they are not the default mechanism for immediate link-level communication between devices.

B) Link-local addresses are automatically configured on all IPv6-enabled interfaces and are required for basic IPv6 functions such as neighbor discovery, routing protocol operations (e.g., OSPFv3, EIGRP for IPv6), and local communication. They always begin with the prefix FE80::/10 and exist independently of global or unique local addresses. Link-local addresses are used to communicate between devices on the same link without requiring any manual configuration or external address assignment. Every IPv6 interface must have a link-local address, making them essential for IPv6 operation. This is the correct answer.

C) Unique Local addresses (ULA) are private IPv6 addresses used for communication within an organization. While they provide routable internal addresses without being globally routable, they are not automatically assigned to interfaces. ULAs require manual configuration or DHCPv6 assignment, so they cannot be relied upon for automatic link-level communication.

D) Multicast addresses are used for one-to-many communication and include well-known addresses such as FF02::1 for all nodes on a link. While multicast facilitates communication to groups of devices, multicast addresses are not automatically assigned to individual interfaces for default communication. Multicast complements link-local addresses but does not replace them for basic local node communication.

Link-local addresses are the correct answer because they are automatically assigned, universally present on all IPv6 interfaces, and essential for communication between devices on the same link. Other address types (global unicast, ULA, multicast) serve different purposes and do not fulfill the automatic local communication requirement.

Question 24

Which mechanism in HSRP ensures a higher-priority router can take over as the active router when it becomes available?

A) Preemption
B) Priority
C) Hello Timer
D) IP Address

Answer: A) Preemption

Explanation:

A) Preemption is the HSRP feature that allows a higher-priority router to assume the active role when it comes online, even if a lower-priority router is currently active. When preemption is enabled, the router with the configured highest priority takes over the active role, ensuring that the most capable router manages traffic. Preemption is critical for network stability because it allows administrators to control which router is responsible for forwarding traffic while maintaining redundancy and failover. Without preemption, a lower-priority router could remain active indefinitely, potentially underutilizing network resources or failing to take advantage of a more optimal router.

B) Priority determines which router is preferred to become active in an HSRP group. The router with the highest priority becomes active initially. While priority influences which router should be active, preemption is required to allow a higher-priority router to take over after the group has already elected a different active router. Priority alone does not force a failover if a higher-priority router comes online later.

C) Hello Timer specifies how frequently HSRP routers send hello messages to each other. Hello timers affect the detection of router failures and convergence times but do not control which router can preempt the active role. While hello timers are important for maintaining the active/standby relationship, they do not enable preemption behavior.

D) IP Address is used as a tiebreaker if two routers have equal priority. While important in rare cases of tie-breaking, it is not a mechanism to allow higher-priority routers to take over when they become available. Preemption is required to achieve that behavior.

Preemption is the correct answer because it explicitly allows a higher-priority router to assume the active role dynamically, ensuring optimal failover and traffic management. The other mechanisms (priority, hello timer, IP address) influence election or communication but do not enable dynamic takeover after initial election.

Question 25:

Which feature of BGP allows a network engineer to filter routes and control routing policies effectively?

A) Route Maps
B) AS Path
C) MED
D) Weight

Answer: A) Route Maps

Explanation:

A) Route maps are a powerful feature in BGP that allow network engineers to filter, modify, and control route advertisement and acceptance. Using route maps, administrators can match routes based on prefixes, AS paths, communities, or other attributes, and then apply policies such as setting local preference, MED, or next-hop modification. Route maps provide granular control over routing decisions, ensuring that traffic flows according to business requirements, security policies, and performance considerations. They are essential in complex BGP deployments where multiple policies must be enforced simultaneously. Route maps enable flexible traffic engineering, selective route filtering, and the manipulation of BGP attributes to influence routing decisions.

B) AS Path is a BGP attribute that records the sequence of autonomous systems a route has traversed. While AS Path is used for loop prevention and basic path selection, it is not as flexible as route maps for detailed policy enforcement. AS Path filtering can influence route acceptance, but it does not allow complex attribute modifications or conditional policies like route maps do.

C) MED (Multi-Exit Discriminator) is an optional BGP attribute used to influence how external autonomous systems choose among multiple entry points into your AS. While MED affects path selection for inbound traffic, it does not provide the granular filtering, policy control, or attribute manipulation offered by route maps.

D) Weight is a Cisco-specific BGP attribute used to prefer a path locally within a router. It is not propagated to other routers and only influences outbound routing from that specific router. Weight cannot provide comprehensive filtering or multi-condition policy enforcement.

Route maps are the correct answer because they provide comprehensive control over route filtering, manipulation, and policy enforcement. While AS Path, MED, and Weight are useful attributes for influencing BGP behavior, they lack the flexibility and granularity that route maps provide for enterprise-scale routing policy management.

Question 26:

Which OSPF LSA type is used by an ASBR to advertise external routes into an OSPF area?

A) Type 1
B) Type 2
C) Type 5
D) Type 7

Answer: C) Type 5

Explanation:

A) Type 1 LSAs, also called Router LSAs, are generated by every OSPF router to describe its local links and interface states within a specific area. These LSAs are only propagated within a single area and do not carry information about external networks. They are fundamental to OSPF topology calculation, but they are not used to advertise routes learned from external sources. Therefore, Type 1 LSAs are irrelevant for external route advertisement.

B) Type 2 LSAs, or Network LSAs, are generated by Designated Routers on multi-access networks to advertise the set of routers attached to a segment. They only exist within an OSPF area and describe which routers are reachable on a broadcast or non-broadcast network. Type 2 LSAs are internal and do not contain external routing information, making them unsuitable for advertising external routes.

C) Type 5 LSAs, or External LSAs, are explicitly used by Autonomous System Boundary Routers (ASBRs) to inject external routes (learned from other routing protocols like BGP or EIGRP) into an OSPF area. Type 5 LSAs contain information about the external network prefix, the metric assigned to it, and the type of route (E1 or E2). These LSAs are flooded throughout the OSPF domain, except into stub or totally stubby areas where external LSAs are blocked. Type 5 LSAs allow OSPF routers to learn external routes while maintaining loop-free routing within the OSPF domain. This makes Type 5 LSAs the correct answer.

D) Type 7 LSAs are used in Not-So-Stubby Areas (NSSA) to advertise external routes originating within the NSSA. These LSAs are similar to Type 5 LSAs but are specifically designed for NSSA areas, allowing external routes to be advertised while still blocking Type 5 LSA flooding. While Type 7 LSAs eventually get converted into Type 5 LSAs by the ABR for propagation outside the NSSA, they are not the general mechanism for external route advertisement in standard areas.

In Type 5 LSAs are the standard OSPF mechanism for an ASBR to advertise external routes across non-stub areas. Type 1 and Type 2 LSAs are internal-only, while Type 7 LSAs are specific to NSSA areas and eventually translated into Type 5 for inter-area propagation.

Question 27:

Which MPLS feature allows service providers to isolate customer traffic across a shared backbone?

A) VRF
B) LDP
C) RSVP
D) QoS

Answer: A) VRF

Explanation:

A) VRF (Virtual Routing and Forwarding) is the mechanism in MPLS that allows multiple instances of routing tables to exist on the same router, effectively isolating customer traffic. Each VRF maintains its own routing table, interface assignments, and routing policies. With VRFs, overlapping IP address spaces across different customers can be supported without conflict, ensuring complete traffic separation. When combined with MPLS labels, VRF enables service providers to transport multiple customers’ traffic across a shared backbone while maintaining logical separation, privacy, and independent routing. This makes VRF the correct answer.

B) LDP (Label Distribution Protocol) is used to distribute MPLS labels between routers. LDP enables label-based forwarding but does not inherently provide traffic separation for different customers. While LDP assigns labels to Forwarding Equivalence Classes (FECs), traffic isolation relies on VRFs to segregate routing and labels for different customers.

C) RSVP (Resource Reservation Protocol) is used in MPLS-TE (Traffic Engineering) to establish explicit label-switched paths with specific bandwidth or QoS guarantees. While RSVP allows traffic engineering and path reservation, it does not provide isolation of multiple customers’ traffic across the shared backbone. RSVP focuses on path optimization rather than VPN separation.

D) QoS (Quality of Service) prioritizes traffic based on classification, marking, and policies to ensure predictable performance. QoS manages bandwidth and latency but does not separate routing tables or isolate traffic at a network layer. QoS can operate within VRFs but cannot replace the VRF’s role in isolating multiple customer routes.

In VRFs are the cornerstone of MPLS VPN implementations for separating customer traffic. LDP and RSVP are control-plane mechanisms that support label distribution and traffic engineering, and QoS manages performance but does not provide logical separation.

Question 28:

Which HSRP state represents a router that is listening but neither forwarding traffic nor actively participating in the election process?

A) Active
B) Standby
C) Listen
D) Init

Answer: C) Listen

Explanation:

A) Active state in HSRP indicates that the router is currently forwarding traffic for the virtual IP address. The router actively participates in routing and responds to ARP requests for the HSRP VIP. This is not the correct answer because the question asks for a router that is not forwarding traffic and is only listening.

B) Standby state refers to a router that monitors the active router and is ready to take over if the active router fails. A standby router has elected itself to be next in line but is still not actively forwarding traffic. While it is not the active router, standby is considered part of the election process, which disqualifies it as the correct answer.

C) Listen state is the state where the router is initialized, aware of the HSRP group, and listening to HSRP hello messages from the active and standby routers. It is neither forwarding traffic nor actively participating in the election process. Listen is essentially a passive state before the router transitions to standby or active, making it the correct answer.

D) Init state occurs when HSRP is just starting and the router has not yet received hello messages from other routers in the HSRP group. The router is preparing to participate in HSRP but has not yet transitioned into listening or standby states. Init is a preliminary state and does not fit the description provided in the question.

Listen state is correct because it specifically represents a router that is aware of the HSRP group but is passive—neither forwarding traffic nor participating in election decisions. Active and standby are engaged in forwarding or backup duties, while init is the initial startup phase.

Question 29:

 Which BGP feature allows selective redistribution of routes into other routing protocols using policies?

A) Route Maps
B) MED
C) Weight
D) Local Preference

Answer: A) Route Maps

Explanation:

A) Route maps provide the most flexible mechanism in BGP and other routing protocols to selectively control route redistribution. Using route maps, administrators can match routes based on prefix lists, AS paths, community attributes, or other criteria, and then apply policies such as setting local preference, MED, or route filtering. Route maps are critical for implementing granular routing policies, controlling which routes are redistributed into other protocols, and shaping traffic in large enterprise networks. This level of control is essential when redistributing routes between BGP, OSPF, or EIGRP to prevent loops, enforce security policies, and optimize traffic paths, making route maps the correct answer.

B) MED (Multi-Exit Discriminator) is an optional BGP attribute that influences how external ASes select the preferred entry point into your network. MED is not used to control redistribution into other protocols. It only signals preference to external neighbors.

C) Weight is a Cisco-specific BGP attribute that affects outbound path selection locally on the router. Weight is not propagated to neighbors and does not control redistribution into other protocols.

D) Local Preference is used to influence outbound traffic from the AS and is propagated within the AS. While it helps choose preferred routes internally, it does not provide selective redistribution capabilities.

Route maps are the correct answer because they provide precise, policy-driven control over route redistribution. MED, Weight, and Local Preference influence routing decisions but do not enable conditional redistribution between protocols.

Question 30:

Which mechanism in OSPF allows summarization of multiple network prefixes into a single advertisement?

A) Type 1 LSA
B) Type 2 LSA
C) ABR Summary
D) NSSA LSA

Answer: C) ABR Summary

Explanation:

A) Type 1 LSAs are router LSAs used to advertise a router’s interfaces and directly connected networks within an area. They do not provide summarization capabilities; each prefix is advertised individually.

B) Type 2 LSAs are network LSAs generated by the DR on broadcast or NBMA networks to advertise attached routers. Type 2 LSAs exist only within the area and do not perform summarization of routes between areas.

C) ABR Summary is the feature where Area Border Routers (ABRs) summarize multiple network prefixes from one area into a single summary advertisement (Type 3 LSA) into another area. This reduces routing table size, optimizes LSA flooding, and improves scalability in large OSPF networks. ABR summarization is critical for hierarchical OSPF design, especially when dealing with large numbers of networks or prefixes in multiple areas. By aggregating prefixes, ABR summary minimizes memory usage, improves SPF calculation efficiency, and ensures network stability. This makes ABR summary the correct answer.

D) NSSA LSAs (Type 7) are used to advertise external routes within Not-So-Stubby Areas. While Type 7 LSAs allow external route injection, they are not the general mechanism for summarizing multiple prefixes across OSPF areas. They are specific to NSSA configurations.

ABR Summary is correct because it provides hierarchical summarization, reduces routing table size, and optimizes OSPF operation across multiple areas. The other LSA types (Type 1, Type 2, NSSA/Type 7) serve other purposes but do not implement inter-area summarization.

Question 31:

Which feature in EIGRP allows a router to immediately use a backup path without recalculating the topology when the primary path fails?

A) Feasible Successor
B) Split Horizon
C) Hold Timer
D) Route Summarization

Answer: A) Feasible Successor

Explanation:

A) Feasible Successor is the core mechanism in EIGRP that enables fast convergence and loop-free backup. Each EIGRP router maintains a topology table containing the primary route, called the successor, and any feasible successors that satisfy the feasibility condition. The feasibility condition requires that the reported distance from a neighbor to a destination is less than the current feasible distance to that destination. When the primary successor fails, the router can immediately switch to the feasible successor without recomputing the entire topology. This ensures minimal downtime and rapid failover, which is essential in enterprise networks where high availability is required. Feasible successors are precomputed backup routes, allowing EIGRP to achieve convergence almost instantaneously.

B) Split Horizon is a technique used to prevent routing loops in distance-vector protocols, including EIGRP. It prevents a router from advertising a route back out the interface from which it was learned. While split horizon is important for loop prevention, it does not provide immediate failover to a backup path. It only restricts route advertisement to maintain loop-free operation.

C) Hold Timer defines the interval after which a neighbor is considered down if hello packets are not received. While the hold timer affects convergence timing, it does not enable instantaneous use of a backup route. Hold timers determine how quickly a neighbor is marked unavailable but do not precompute alternative paths.

D) Route Summarization aggregates multiple network prefixes into a single route advertisement, reducing routing table size and update overhead. While summarization improves efficiency and scalability, it does not directly provide a backup path or influence convergence speed. Summarization may indirectly affect convergence by reducing the number of updates, but it is not the mechanism that allows immediate path switching.

Feasible Successor is the correct answer because it is the only EIGRP feature that precomputes alternative loop-free paths, allowing instant failover without recalculating the topology. Split horizon, hold timers, and route summarization support network stability and efficiency but do not provide rapid backup path usage.

Question 32:

Which mechanism in OSPFv3 provides support for IPv6 routing while maintaining area-based hierarchy?

A) Type 7 LSA
B) Link-State Advertisements
C) OSPFv2 Compatibility Mode
D) Area Border Router (ABR)

Answer: D) Area Border Router (ABR)

Explanation:

A) Type 7 LSAs are used in Not-So-Stubby Areas (NSSA) to inject external routes into an OSPF area. While Type 7 LSAs allow external route distribution in NSSA, they are not the primary mechanism for maintaining hierarchical area structure or supporting IPv6 routing across the network. Type 7 LSAs are a specific exception mechanism rather than a core IPv6 OSPF feature.

B) Link-State Advertisements (LSAs) are the building blocks of OSPF routing, carrying topology information. LSAs are critical for OSPFv3 operation but do not inherently provide hierarchical support. LSAs flood within areas and provide detailed link information, but hierarchy management requires a router to connect multiple areas and summarize routes between them.

C) OSPFv2 Compatibility Mode does not exist as a feature in OSPFv3. OSPFv3 is designed natively for IPv6 with separate LSAs, area types, and support for multiple instances per link. Compatibility with OSPFv2 is not provided by a mode but through dual-stack deployment.

D) Area Border Routers (ABRs) connect multiple OSPF areas, including the backbone area (Area 0). ABRs maintain separate link-state databases for each area and generate summary LSAs to advertise networks from one area to another. In OSPFv3, ABRs perform the same function as in OSPFv2: they maintain hierarchical structure, isolate LSAs within areas, and summarize prefixes to reduce routing table size and LSA flooding. ABRs are essential for scaling OSPFv3 networks while supporting IPv6 routing. Without ABRs, OSPFv3 could not maintain a hierarchical area design, making ABR the correct answer.

In summary, ABRs are the key mechanism enabling hierarchical design in OSPFv3, while Type 7 LSAs and LSAs themselves provide details for routing but not hierarchy. Compatibility mode does not exist, confirming that ABR is the essential component for scalable IPv6 OSPF deployment.

Question 33:

Which BGP attribute is primarily used to prefer a path locally on a single router without affecting other routers?

A) Weight
B) Local Preference
C) MED
D) AS Path

Answer: A) Weight

Explanation:

A) Weight is a Cisco-specific BGP attribute used to influence path selection locally on the router where it is configured. It is not advertised to other routers and allows administrators to prefer one route over others for outbound traffic from that specific router. Weight is applied first in the BGP best path selection process, making it the most powerful tool for local path control. By assigning higher weight to a preferred route, the router will always select it over others regardless of other attributes, ensuring predictable routing decisions for local traffic.

B) Local Preference is used to influence path selection within an autonomous system and is propagated to all routers in the AS. While local preference is effective for internal traffic control, it is not local to a single router. Changes to local preference affect all routers, which differs from the router-specific scope of weight.

C) MED (Multi-Exit Discriminator) is an optional BGP attribute used to influence how external ASes choose entry points into your network. MED is shared with external neighbors and is used for inbound traffic engineering, not local router path preference.

D) AS Path records the autonomous systems a route has traversed and is used primarily for loop prevention and path selection. While prepending AS numbers can influence path selection externally, it does not provide a mechanism to control routing locally on a single router without affecting others.

Weight is the correct answer because it is the only attribute applied locally and not propagated, making it ideal for controlling path selection at a single router. Local preference, MED, and AS Path either affect multiple routers or external peers.

Question 34:

Which MPLS mechanism is used to signal label-switched paths for traffic engineering purposes?

A) LDP
B) RSVP-TE
C) VRF
D) MPLS Forwarding Table

Answer: B) RSVP-TE

Explanation:

A) LDP (Label Distribution Protocol) is used to distribute labels between MPLS routers automatically. It maps Forwarding Equivalence Classes (FECs) to labels for normal MPLS forwarding but does not provide traffic engineering capabilities or explicit path control. LDP is a simpler, default-label signaling protocol without support for QoS or bandwidth reservation.

B) RSVP-TE (Resource Reservation Protocol – Traffic Engineering) is designed specifically for establishing MPLS Label-Switched Paths (LSPs) with explicit path control, bandwidth reservation, and QoS. RSVP-TE allows network engineers to define LSPs based on available resources and topology constraints, optimizing traffic flow across the MPLS backbone. By signaling LSPs with RSVP-TE, routers can reserve bandwidth, avoid congested links, and meet SLA requirements. This makes RSVP-TE the correct answer for traffic-engineered MPLS deployments.

C) VRF (Virtual Routing and Forwarding) is used to maintain separate routing tables for different customers or traffic domains. While VRFs provide traffic separation and support MPLS VPNs, they do not signal LSPs or control traffic engineering. VRFs focus on logical segmentation, not path optimization.

D) MPLS Forwarding Table contains the mapping of labels to outgoing interfaces and next-hop labels. It is part of the data-plane forwarding mechanism and does not signal or establish LSPs. MPLS forwarding tables depend on signaling protocols like LDP or RSVP-TE but do not themselves perform path selection or bandwidth reservation.

RSVP-TE is the correct answer because it allows the signaling of explicit LSPs with traffic engineering considerations, whereas LDP handles default label distribution, VRF provides isolation, and MPLS forwarding tables handle packet forwarding.

Question 35:

Which OSPF feature allows summarization of networks from one area into another to reduce routing table size?

A) ABR Summary
B) Stub Area
C) Type 1 LSA
D) Type 2 LSA

Answer: A) ABR Summary

Explanation:

A) ABR Summary is the mechanism in OSPF where Area Border Routers (ABRs) summarize multiple network prefixes from one area into a single summary advertisement (Type 3 LSA) for another area. This reduces the size of routing tables, decreases LSA flooding, and improves convergence efficiency. By aggregating routes, ABR summarization ensures that routers in other areas do not maintain individual prefixes for every subnet, improving scalability in large networks. This makes ABR summary the correct answer.

B) Stub areas are OSPF areas that limit the advertisement of external routes (Type 5 LSAs). While they reduce routing overhead by blocking external LSAs, stub areas do not perform summarization of multiple prefixes between areas. Stub areas are more restrictive but do not provide hierarchical summarization.

C) Type 1 LSAs describe a router’s interfaces and links within a single area. Type 1 LSAs are essential for OSPF operation but do not summarize multiple networks or reduce routing table size between areas.

D) Type 2 LSAs are generated by the DR on multi-access networks to advertise the set of routers attached to a segment. They exist only within an area and do not summarize routes across areas.

ABR Summary is correct because it directly addresses inter-area route aggregation, reducing routing table entries and improving OSPF efficiency. Stub areas and LSAs serve supporting roles but do not provide the summarization function.

Question 36:

Which IPv6 routing protocol supports equal and unequal-cost load balancing while providing fast convergence?

A) RIPng
B) OSPFv3
C) EIGRP for IPv6
D) BGP

Answer: C) EIGRP for IPv6

Explanation:

A) RIPng is the IPv6 version of RIP. It is a distance-vector protocol that uses hop count as its metric and has a maximum limit of 15 hops. While it supports basic routing and equal-cost load balancing, RIPng does not support unequal-cost load balancing. Its convergence is relatively slow because it relies on periodic updates, timers, and hop count increments. This makes RIPng unsuitable for enterprise networks that require fast recovery and flexible load balancing.

B) OSPFv3 is a link-state routing protocol for IPv6 that uses Dijkstra’s SPF algorithm. OSPFv3 provides equal-cost load balancing by allowing multiple routes with the same cost to be installed in the routing table. However, it does not support unequal-cost load balancing natively. Convergence is fast relative to distance-vector protocols, but for unequal-cost distribution of traffic across multiple paths, OSPFv3 alone cannot accomplish this.

C) EIGRP for IPv6 is a Cisco-proprietary routing protocol that supports both equal and unequal-cost load balancing using the variance command. By calculating feasible successors and evaluating metrics such as bandwidth, delay, reliability, and load, EIGRP can distribute traffic across multiple paths even if they have different costs. EIGRP maintains a topology table and uses the DUAL algorithm to ensure loop-free paths while providing fast convergence when a primary route fails. This combination of unequal-cost load balancing and rapid failover makes EIGRP for IPv6 the correct answer for enterprise scenarios requiring high availability and optimized traffic distribution.

D) BGP is a path-vector protocol designed primarily for inter-domain routing. While BGP can manipulate path selection using attributes like AS Path, MED, and Weight, it does not perform unequal-cost load balancing in the way EIGRP does. BGP convergence is slower because path selection is based on policy and attribute comparison rather than immediate topology recalculation. It is not designed for internal IPv6 LAN/WAN load balancing scenarios.

In EIGRP for IPv6 is the only protocol among the options that provides both fast convergence and the capability to perform unequal-cost load balancing, making it ideal for enterprise networks. RIPng and OSPFv3 are limited to equal-cost load balancing, and BGP is not suitable for internal IPv6 load balancing.

Question 37:

Which OSPF area type blocks Type 5 LSAs but allows inter-area routes?

A) Stub Area
B) Totally Stubby Area
C) NSSA
D) Backbone Area

Answer: A) Stub Area

Explanation:

A) Stub areas are designed to reduce routing overhead by blocking external routes (Type 5 LSAs) while allowing inter-area routes (Type 3 LSAs) to be propagated into the area. The ABR injects a default route into the stub area so that routers can reach external destinations without learning all external prefixes. This design minimizes routing table size and processing overhead while still allowing communication between areas. The stub area is particularly useful for edge areas where external routing details are not required, making it the correct answer.

B) Totally stubby areas take stub functionality further by blocking both Type 5 (external routes) and Type 3 LSAs (inter-area routes), leaving only a default route to reach both internal and external destinations. While this reduces routing table size even more, it prevents inter-area routes, which is contrary to the requirement specified in the question.

C) NSSA (Not-So-Stubby Area) allows Type 7 LSAs, which carry external route information from within the NSSA, to be injected into the OSPF network. NSSA is designed for areas that need external connectivity while still limiting Type 5 LSA flooding. However, NSSA is not a simple stub area; it is a hybrid mechanism and can carry external routes internally. The question specifically asks about an area type that blocks Type 5 LSAs while allowing inter-area routes, making the traditional stub area the best fit.

D) Backbone Area (Area 0) is the central area to which all other areas connect in OSPF. The backbone area carries all types of LSAs, including Type 1, 2, 3, and 5, and does not provide blocking of external LSAs. Its purpose is to ensure hierarchical routing and connectivity between areas, not to restrict external LSA flooding.

Stub area is correct because it blocks Type 5 LSAs to reduce routing overhead while still allowing inter-area (Type 3 LSA) propagation. Totally stubby, NSSA, and backbone areas either block more than required or allow all LSAs, making them unsuitable for this specific scenario.

Question 38:

Which HSRP feature allows a router to assume the active role immediately if it has higher priority than the current active router?

A) Preemption
B) Priority
C) Hello Timer
D) Track Interface

Answer: A) Preemption

Explanation:

A) Preemption is the HSRP mechanism that allows a router with higher priority to take over the active role as soon as it becomes available. Without preemption, a lower-priority router could remain active even when a better router comes online. Preemption ensures that the most capable router controls forwarding for the virtual IP, maintaining optimal network performance. Enabling preemption is critical in enterprise networks to guarantee redundancy and make full use of router capabilities.

B) Priority determines which router is preferred during the election process. While it influences which router should become active initially, it does not automatically allow a higher-priority router to take over once a lower-priority router is already active. Priority must be combined with preemption for dynamic takeover.

C) Hello Timer defines how often routers send hello messages to monitor HSRP neighbors. It affects the speed of failover detection but does not allow a higher-priority router to assume the active role dynamically. Hello timers are essential for convergence timing but not for preemptive election.

D) Track Interface allows HSRP to adjust router priority based on the state of an interface. While tracking can influence priority, it alone does not allow preemption to occur. It is a supporting mechanism for dynamic adjustments rather than a direct preemption feature.

Preemption is the correct answer because it explicitly enables a higher-priority router to take control immediately upon availability. Priority, hello timers, and tracking support HSRP operation but do not provide automatic takeover.

Question 39:

Which MPLS feature allows multiple VPNs to share the same infrastructure while keeping traffic isolated?

A) VRF
B) LDP
C) RSVP-TE
D) QoS

Answer: A) VRF

Explanation:

A) VRF (Virtual Routing and Forwarding) allows multiple customers or VPNs to maintain separate routing tables on the same physical device. By using VRFs in combination with MPLS, traffic for each VPN can be logically separated, even when sharing the same underlying infrastructure. VRFs ensure overlapping IP addresses can coexist safely, and MPLS labels provide path isolation, ensuring packets from one VRF cannot accidentally leak into another. This combination of VRF and MPLS is widely used in service provider networks for scalable and secure multi-customer deployments, making VRF the correct answer.

B) LDP (Label Distribution Protocol) is used to distribute MPLS labels for standard forwarding. While LDP enables label switching, it does not inherently provide traffic separation for multiple VPNs. LDP simply ensures that labels are understood and mapped between routers.

C) RSVP-TE establishes explicit label-switched paths with traffic engineering and bandwidth guarantees. While it helps optimize network usage and avoid congestion, it does not separate customer routing tables or VPN traffic. Traffic isolation is not the purpose of RSVP-TE.

D) QoS (Quality of Service) manages bandwidth, prioritization, and latency, ensuring predictable performance. QoS does not create separate logical routing tables and cannot isolate VPN traffic on its own. QoS can operate within VRFs but is not a mechanism for multi-VRF separation.

VRF is correct because it provides logical separation of routing tables and traffic, enabling multiple VPNs to share the same MPLS infrastructure without interference. LDP, RSVP-TE, and QoS do not provide this type of isolation.

Question 40:

 Which BGP attribute is used to influence outbound traffic from a router within a single autonomous system?

A) Weight
B) Local Preference
C) AS Path
D) MED

Answer: B) Local Preference

Explanation:

A) Weight is a Cisco-specific BGP attribute used to influence path selection locally on a single router. While it affects outbound traffic from that specific router, it is not propagated to other routers in the AS. Weight is suitable for local decisions but does not allow a coordinated path preference across the AS.

B) Local Preference is a BGP attribute that is propagated throughout the autonomous system. It allows network engineers to influence which exit path is preferred for outbound traffic for the entire AS. A higher local preference ensures that all routers within the AS select the specified path as the preferred route for traffic leaving the AS. Local preference is critical in multi-homed environments to control outbound traffic efficiently and is widely used in enterprise and service provider networks. This makes Local Preference the correct answer.

C) AS Path is primarily used for loop prevention and for selecting the best path based on the shortest AS path length. While AS Path affects path selection, it is mostly relevant for incoming traffic and inter-AS routing, not controlling outbound traffic within the AS.

D) MED (Multi-Exit Discriminator) is used to influence how external neighbors choose the preferred entry point into the AS. It is not propagated internally and is used for inbound traffic engineering rather than controlling outbound traffic within the AS.

Local Preference is correct because it is the only attribute that allows coordinated control of outbound traffic across all routers in the AS. Weight, AS Path, and MED serve other purposes but do not provide AS-wide outbound traffic control.