Cisco 300-410  Implementing Cisco Enterprise Advanced Routing and Services (ENARSI) Exam  Dumps and Practice Test Questions Set 5 Q 81-100

Visit here for our full Cisco 300-410 exam dumps and practice test questions.

Question 81:

Which EIGRP feature allows unequal-cost load balancing across multiple feasible paths?

A) Feasible Successor
B) Variance
C) Route Summarization
D) Hold Timer

Answer: B) Variance

Explanation:

A) Feasible Successor is a backup route in EIGRP’s topology table that satisfies the feasibility condition. Feasible successors provide immediate failover if the primary route fails. Although feasible successors can be used in combination with variance to distribute traffic, by themselves they do not enable unequal-cost load balancing. They only serve as loop-free backup paths.

B) Variance is an EIGRP feature that allows traffic to be forwarded across multiple paths with different metrics. By default, EIGRP performs equal-cost load balancing across successor routes. When variance is configured, feasible successors with a metric less than the primary route multiplied by the variance value are eligible for forwarding traffic. This enables network engineers to utilize higher-cost paths efficiently, increasing redundancy and overall bandwidth utilization. Variance is particularly valuable in scenarios with heterogeneous link speeds, as it allows traffic to leverage multiple links without creating routing loops. Feasible successors combined with variance ensure traffic is distributed across eligible backup routes, making variance the correct answer.

C) Route Summarization reduces the number of advertised routes and optimizes SPF calculations, but it does not control how traffic is distributed across multiple paths. Summarization improves scalability but is unrelated to unequal-cost load balancing.

D) Hold Timer is the interval a router waits before declaring a neighbor down if no hello messages are received. It affects convergence time but does not control traffic distribution or load balancing.

Variance is correct because it explicitly allows unequal-cost load balancing. Feasible successors provide eligible backup paths, but variance determines which paths can carry traffic. Route summarization and hold timers are unrelated to traffic distribution

Question 82:

Which OSPF LSA type allows external routes to be redistributed into a Not-So-Stubby Area (NSSA)?

A) Type 3
B) Type 5
C) Type 7
D) Type 1

Answer: C) Type 7

Explanation:

A) Type 3 LSAs are summary LSAs generated by ABRs to advertise networks from one OSPF area into another. They are used for inter-area routing but cannot carry external routes from redistribution. Type 3 LSAs do not provide external connectivity within NSSAs.

B) Type 5 LSAs carry external routes redistributed into OSPF. However, in NSSAs, Type 5 LSAs from external sources are blocked. Type 5 LSAs are used in normal areas for external route propagation but cannot be used within NSSAs.

C) Type 7 LSAs are specifically designed for NSSAs to carry redistributed external routes. Routers inside an NSSA can generate Type 7 LSAs to advertise routes from other protocols (like EIGRP, BGP, or static routes) into the OSPF domain without flooding the entire network. The ABR eventually converts Type 7 LSAs into Type 5 LSAs for propagation outside the NSSA. Type 7 LSAs allow controlled external route injection while maintaining hierarchical scalability, making them the correct answer.

D) Type 1 LSAs describe a router’s links within an OSPF area. They are strictly intra-area and do not carry external route information.

Type 7 LSAs are correct because they enable external routes to be injected into an NSSA without affecting the entire OSPF domain. Type 3 summarizes inter-area routes, Type 5 propagates external routes only outside NSSAs, and Type 1 is intra-area topology.

Question 83

Which BGP attribute influences how other autonomous systems select entry points into your network?

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

Answer: C) MED

Explanation:

A) Weight is a Cisco-proprietary attribute used to control outbound traffic locally on a single router. It is not propagated to other routers or external autonomous systems and does not affect how neighbors select paths into your network.

B) Local Preference is propagated within an autonomous system to control outbound path selection network-wide. It does not influence how external ASes choose entry points, so it is irrelevant for inbound traffic engineering.

C) MED (Multi-Exit Discriminator) is used to influence the selection of entry points for neighboring autonomous systems. By advertising a lower MED for preferred entry paths and higher MEDs for less preferred paths, a network can guide external ASes to choose specific paths for inbound traffic. MED is communicated to neighbors, enabling controlled inbound traffic engineering, congestion management, and optimal utilization of multiple links. This makes MED the correct answer because it allows predictable and policy-driven control of how external networks reach your AS.

D) AS Path records the autonomous systems traversed by a route and is used for loop prevention and shortest-path selection. AS path prepending can indirectly influence inbound traffic by making a path appear longer, but it is less precise and predictable than MED.

MED is correct because it directly influences inbound traffic selection by external ASes. Weight, local preference, and AS path influence local or outbound routing rather than controlled inbound selection.

Question 84:

Which HSRP state monitors hello messages and is ready to assume the active role if needed?

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

Answer: B) Standby

Explanation:

A) Active state occurs when a router is currently forwarding traffic for the virtual IP. Active routers respond to ARP requests for the VIP and handle all traffic, so they are not waiting to take over.

B) Standby is the state in which a router monitors hello messages from the active router and is prepared to take over traffic forwarding if the active router fails. The standby router maintains backup state information and ensures near-instantaneous failover to maintain uninterrupted network connectivity. This readiness to assume control makes standby the correct answer.

C) Listen is an intermediate state where the router is aware of the HSRP group and receives hello messages but is not actively participating in election or forwarding. It is preparatory rather than an active backup state.

D) Init is the initial state where the router has started HSRP but has not yet received hello messages from neighbors. Init cannot forward traffic or participate in standby election.

Standby is correct because it represents the router actively monitoring and ready to assume control. Active forwards traffic, listen is passive monitoring, and init is initialization.

Question 85:

Which MPLS feature provides logical separation of multiple VPNs on a shared infrastructure?

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

Answer: A) VRF

Explanation:

A) VRF (Virtual Routing and Forwarding) allows multiple independent routing tables to exist on the same physical router, providing complete separation of VPNs. Each VRF instance maintains its own interfaces, routing table, and forwarding information. When combined with MPLS labels, VRFs ensure that traffic from one VPN cannot reach another, even over the same physical links. VRFs support overlapping IP addresses and isolated routing for multiple customers, making VRF the correct answer.

B) LDP (Label Distribution Protocol) distributes MPLS labels to enable forwarding along FECs. LDP is critical for MPLS operation but does not provide VPN isolation or separate routing tables.

C) RSVP-TE establishes explicit label-switched paths with bandwidth reservation to optimize network performance. While RSVP-TE ensures predictable path selection and resource allocation, it does not provide logical separation of VPNs.

D) QoS prioritizes traffic, manages bandwidth, and guarantees performance for applications. QoS enhances network efficiency but does not provide isolated routing or separation of multiple VPNs.

VRF is correct because it allows multiple VPNs to share the same physical infrastructure while keeping routing and traffic logically separate. LDP, RSVP-TE, and QoS enhance MPLS forwarding and performance but do not isolate VPN traffic.

Question 86:

Which EIGRP metric component represents the sum of delays along a path?

A) Bandwidth
B) Delay
C) Reliability
D) Load

Answer: B) Delay

Explanation:

A) Bandwidth in EIGRP is a metric component that represents the minimum bandwidth along a path. It is calculated based on the slowest link in the route. Bandwidth heavily influences the composite EIGRP metric and is weighted in the calculation formula to favor high-throughput paths. While bandwidth reflects the capacity of the path, it does not account for time-based characteristics such as propagation delay, queuing delay, or processing delay. Therefore, bandwidth is not the correct component when considering cumulative delay along a path.

B) Delay is the metric component that measures the sum of delays along a path. In EIGRP, delay is expressed in tens of microseconds and is calculated as the total sum of the configured delays for all interfaces along the route. Delay incorporates transmission delay, propagation delay, queuing, and processing times, making it a comprehensive measure of end-to-end latency. When combined with bandwidth in EIGRP’s composite metric formula, delay influences path selection by favoring routes with lower cumulative delay. Routes with smaller delay values are preferred when calculating the overall metric, ensuring that traffic is sent over faster paths in terms of latency rather than just raw throughput. Delay is particularly important in networks carrying latency-sensitive applications such as VoIP or video conferencing. This makes delay the correct answer because it directly represents the sum of delays along a path and is essential in determining EIGRP’s route preference.

C) Reliability measures the stability of a link based on error rates. It is calculated based on historical data over a period of time and is expressed as a fraction of 255 (with 255 being 100% reliable). While reliability can influence route selection, it does not measure cumulative delay. A highly reliable link may still have significant transmission or queuing delays, so reliability alone cannot represent path latency. Reliability is therefore not the correct metric for the sum of delays along a path.

D) Load is a dynamic metric representing the current utilization of the link. It ranges from 1 to 255, with higher values indicating higher utilization. Load is a measure of congestion rather than inherent transmission or propagation delay. While a highly loaded link may introduce queuing delays, load itself is not used to calculate the static sum of delays for metric purposes. EIGRP can optionally consider load, but it is not the principal component for determining the cumulative path delay.

Delay is correct because it measures the sum of all delays along the path, affecting EIGRP’s route selection for latency-sensitive traffic. Bandwidth measures throughput, reliability measures error rates, and load measures dynamic congestion, none of which directly reflect cumulative path delay.

Question 87:

Which OSPF area type allows external routes via Type 7 LSAs but blocks Type 5 LSAs from entering the area?

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

Answer: C) NSSA

Explanation:

A) Stub areas block Type 5 external LSAs, preventing external routes from being advertised into the area. They allow Type 3 summary LSAs from other areas but do not allow injection of external routes within the area. This makes stub areas unsuitable for scenarios where external routes must be redistributed into OSPF, as they are designed to simplify routing tables and reduce LSA flooding.

B) Totally stubby areas block both Type 3 and Type 5 LSAs, leaving only a default route for connectivity outside the area. While they reduce SPF computation and routing table size, totally stubby areas do not allow external route injection, so they cannot accommodate external routes via Type 7 LSAs.

C) NSSA (Not-So-Stubby Area) is specifically designed to allow the controlled injection of external routes into OSPF while limiting flooding across the network. NSSA routers can redistribute routes from other protocols such as EIGRP, BGP, or static routes into OSPF using Type 7 LSAs. Type 7 LSAs are only propagated within the NSSA, and the ABR eventually converts them into Type 5 LSAs for dissemination into the broader OSPF domain. This allows organizations to maintain hierarchical OSPF scalability while providing localized redistribution of external routes. NSSAs are particularly useful at the network edge where redistribution of external routes is needed without overwhelming the entire OSPF domain with external LSAs. This makes NSSA the correct answer.

D) Backbone Area (Area 0) is the central OSPF area through which all inter-area traffic passes. It carries all LSA types and does not block any LSAs. While the backbone connects areas and propagates routes, it is not used to restrict flooding or allow selective redistribution via Type 7 LSAs.

NSSA is correct because it allows localized redistribution of external routes via Type 7 LSAs while blocking Type 5 LSAs from flooding the area. Stub areas block external LSAs entirely, totally stubby areas block more than required, and the backbone area does not restrict LSA flooding.

Question 88:

Which BGP attribute is used to prefer a specific path locally without affecting other routers in the AS?

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

Answer: A) Weight

Explanation:

A) Weight is a Cisco-proprietary BGP attribute used to control path selection on a single router. It is the first criterion evaluated in BGP best path selection and is not propagated to other routers in the autonomous system. A higher weight ensures that the route is selected locally for outbound traffic, providing fine-grained control over routing decisions without impacting other routers. This makes weight the correct answer for local router-specific path preference.

B) Local Preference is propagated throughout the autonomous system and affects outbound path selection across all routers. While it is important for AS-wide policy, it cannot enforce router-specific control without affecting other routers.

C) MED (Multi-Exit Discriminator) is used to influence inbound path selection from external autonomous systems. It does not control local outbound traffic preference within the AS.

D) AS Path records the sequence of autonomous systems a route traverses. AS path manipulation, such as prepending, can indirectly influence external peers’ routing choices but is not a local mechanism for controlling outbound traffic on a specific router.

Weight is correct because it allows local path selection without influencing other routers in the AS. Local preference is network-wide, MED is inbound-focused, and AS path affects external routing.

 

Question 89:

Which HSRP state indicates that the router is ready to take over if the active router fails but is not currently forwarding traffic?

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

Answer: B) Standby

Explanation:

A) Active state occurs when a router is currently forwarding traffic for the HSRP virtual IP. Active routers respond to ARP requests and serve as the primary gateway for hosts, so they are already handling traffic.

B) Standby is the state in which a router monitors hello messages from the active router and is prepared to assume the active role if the primary router fails. The standby router maintains backup state information, ensuring minimal downtime during failover. This makes standby the correct answer because it is actively monitoring but not currently forwarding traffic.

C) Listen is an intermediate state where the router is aware of the HSRP group and receives hello messages but does not participate in forwarding or standby election. It is a preparatory state rather than a backup state ready for immediate takeover.

D) Init is the initial HSRP state during router startup, where no hello messages have been received from neighbors. Routers in init cannot forward traffic or participate in standby.

Standby is correct because it represents a router ready to assume control if the active router fails. Active forwards traffic, listen monitors only, and init is preliminary.

Question 90

 Which MPLS feature allows multiple VPNs to share the same physical network 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 logical routing tables on a single router, providing complete separation of VPNs. Each VRF maintains its own interfaces, routing table, and forwarding information. When combined with MPLS labels, VRFs ensure that traffic from one VPN cannot reach another, even over the same physical links. VRFs also support overlapping IP addresses, making them essential in enterprise and service provider networks for delivering secure and isolated VPN services. This makes VRF the correct answer.

B) LDP (Label Distribution Protocol) distributes MPLS labels for forwarding packets along FECs. While critical for MPLS operation, LDP does not provide isolation between VPNs or create separate routing tables.

C) RSVP-TE (Resource Reservation Protocol-Traffic Engineering) establishes explicit label-switched paths with bandwidth reservation to optimize traffic flows. RSVP-TE ensures predictable performance and load balancing but does not provide VPN separation or isolated routing tables.

D) QoS prioritizes traffic, manages bandwidth, and guarantees performance for applications. While QoS is important for service quality, it does not provide logical isolation or separate routing tables for VPNs.

VRF is correct because it enables multiple VPNs to share the same infrastructure while maintaining logical separation. LDP, RSVP-TE, and QoS enhance MPLS performance and forwarding but do not provide VPN isolation.

Question 91:

 Which EIGRP metric component is influenced by the slowest link along the path?

A) Bandwidth
B) Delay
C) Reliability
D) Load

Answer: A) Bandwidth

Explanation:

A) Bandwidth is a fundamental EIGRP metric component representing the minimum bandwidth along a path. The composite EIGRP metric calculation uses this value to influence route selection, with lower minimum bandwidth making a route less preferable. The protocol evaluates all interfaces along the path and identifies the slowest link, because the slowest link effectively limits the maximum throughput achievable along the route. This ensures that high-capacity paths are favored, which is particularly important in enterprise networks with heterogeneous link speeds. Using minimum bandwidth prevents EIGRP from selecting a route that contains a slow interface, thereby improving overall performance and avoiding congestion on suboptimal paths. Bandwidth is weighted heavily in the composite metric formula, making it one of the primary factors in path selection.

B) Delay is another metric component in EIGRP, but it represents the sum of transmission, propagation, and queuing delays along the path. While delay affects route selection and is important for latency-sensitive applications, it is independent of the slowest link. Delay is cumulative, whereas bandwidth identifies the single limiting factor on throughput.

C) Reliability reflects the stability of a link based on historical error rates. Although low reliability may reduce preference for a route, it does not directly measure the capacity or speed of the path. Reliability is used as a secondary metric in EIGRP and cannot replace the function of bandwidth in identifying the slowest link.

D) Load measures the current utilization of an interface, representing how busy a link is at any given moment. While high load may temporarily degrade performance, load is dynamic and does not indicate the inherent limiting capacity of a link. It is not used to determine the minimum bandwidth for EIGRP metric calculations.

Bandwidth is correct because it identifies the slowest link in a path, directly impacting EIGRP path selection. Delay, reliability, and load provide additional context for route evaluation but do not determine the minimum throughput.

Question 92:

Which OSPF LSA type is used to summarize routes between areas?

A) Type 1
B) Type 2
C) Type 3
D) Type 5

Answer: C) Type 3

Explanation:

A) Type 1 LSAs describe a router’s links within an area and are strictly intra-area. They are used to calculate the shortest path within an area but do not propagate routing information between areas. Type 1 LSAs help establish the internal topology but are irrelevant for summarization or inter-area communication.

B) Type 2 LSAs describe network links on broadcast or NBMA segments within an area. They are generated by the designated router on each segment and facilitate SPF calculations, but they are confined to a single area and do not summarize routes for other areas.

C) Type 3 LSAs, also called summary LSAs, are generated by Area Border Routers (ABRs) to advertise networks from one area into another. ABRs aggregate multiple routes into a single Type 3 LSA, reducing the size of routing tables in the receiving area and limiting SPF calculation overhead. Summary LSAs allow OSPF to scale efficiently in large networks, ensuring routers in other areas do not maintain detailed topology information for networks outside their area. This hierarchical structure reduces convergence time and improves stability. Type 3 LSAs also support route summarization, enabling network designers to aggregate contiguous prefixes into a single advertisement. This reduces unnecessary flooding of LSAs and helps maintain manageable routing tables, making Type 3 the correct answer.

D) Type 5 LSAs are external LSAs used to propagate routes redistributed from other protocols into OSPF. While they carry external information, they are not used for summarizing internal routes between areas.

Type 3 LSAs are correct because they allow ABRs to summarize routes and advertise them efficiently to other areas. Type 1 and Type 2 LSAs are intra-area, and Type 5 LSAs handle external routes.

Question 93:

Which BGP attribute allows consistent path selection for outbound traffic across an entire autonomous system?

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

Answer: B) Local Preference

Explanation:

A) Weight is a Cisco-specific attribute that influences path selection only on the local router. Weight does not propagate throughout the AS, so it cannot enforce consistent outbound traffic selection network-wide. It is ideal for fine-grained, router-specific control but is not suitable for AS-wide policy.

B) Local Preference is a well-known BGP attribute that propagates throughout an autonomous system to control outbound path selection. By assigning higher local preference to preferred routes, all routers in the AS will consistently select the same exit point for outbound traffic. This ensures predictable routing, optimizes bandwidth usage, and maintains policy consistency across multiple routers. Local preference is crucial in multi-homed environments where traffic engineering requires coordinated path selection. It provides a centralized mechanism to influence all routers without relying on individual configurations. This makes local preference the correct answer.

C) MED (Multi-Exit Discriminator) is used to influence the selection of entry points into an AS by neighboring autonomous systems. It affects inbound traffic and does not control outbound path selection within the AS.

D) AS Path records the sequence of autonomous systems a route has traversed and is used primarily for loop prevention and shortest path selection. Manipulating AS Path through prepending can influence inbound traffic indirectly but does not enforce uniform outbound path selection within the AS.

Local Preference is correct because it allows coordinated outbound path selection across all routers in the AS. Weight is local-only, MED is inbound-focused, and AS Path is external-focused.

Question 94:

Which HSRP state is active and forwarding traffic for the virtual IP?

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

Answer: A) Active

Explanation:

A) Active state occurs when a router is currently forwarding traffic for the HSRP virtual IP. The router responds to ARP requests for the VIP and serves as the primary gateway for hosts. Active routers maintain the primary routing function for the subnet, ensuring uninterrupted connectivity. Active is the correct answer because it directly represents the router performing forwarding duties for the HSRP group.

B) Standby is the backup router that monitors hello messages from the active router and is ready to take over in case of failure. Standby routers do not forward traffic unless the active router fails.

C) Listen is an intermediate state where the router is aware of the HSRP group and receives hello messages but is not participating in forwarding or standby election. It is a preparatory state and does not forward traffic.

D) Init is the initial state during HSRP startup where no hello messages have been received from neighbors. Routers in init cannot forward traffic or participate in standby election.

Active is correct because it indicates the router is currently responsible for forwarding traffic for the VIP. Standby monitors for failover, listen is monitoring only, and init is initialization.

Question 95:

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 logical routing tables on a single router, providing complete separation of VPNs. Each VRF maintains its own interfaces, routing table, and forwarding information. When combined with MPLS labels, VRFs ensure that traffic from one VPN cannot reach another VPN, even over the same physical links. VRFs also support overlapping IP addresses and isolated routing for multiple customers, making them essential in enterprise and service provider environments. This makes VRF the correct answer.

B) LDP (Label Distribution Protocol) distributes MPLS labels to enable forwarding along FECs. LDP is essential for MPLS operations but does not isolate VPNs or create separate routing tables.

C) RSVP-TE establishes explicit label-switched paths with bandwidth reservation for traffic engineering. While RSVP-TE ensures predictable performance and efficient utilization of network resources, it does not provide logical separation of VPNs.

D) QoS prioritizes traffic, allocates bandwidth, and guarantees performance for applications. While QoS is critical for service quality, it does not provide VPN separation or isolated routing tables.

VRF is correct because it allows multiple VPNs to share the same infrastructure while maintaining logical separation. LDP, RSVP-TE, and QoS support MPLS performance and forwarding but do not provide isolation between VPNs.

Question 96:

Which EIGRP feature provides a precomputed backup route that can be used immediately if the primary route fails?

A) Feasible Successor
B) Variance
C) Route Summarization
D) Hold Timer

Answer: A) Feasible Successor

Explanation:

A) Feasible Successor is a route in the EIGRP topology table that satisfies the feasibility condition, which states that the reported distance from a neighbor must be less than the feasible distance of the current route. Feasible successors are loop-free backup routes precomputed and stored alongside the primary route (successor). When the primary route fails, EIGRP can immediately switch to the feasible successor without recalculating the topology. This ensures near-instantaneous convergence and minimizes traffic disruption. The feasibility condition guarantees that the backup route does not introduce loops, maintaining network stability. Feasible successors are particularly useful in large networks with multiple redundant paths because they allow traffic to continue flowing while EIGRP recalculates other possible paths in the topology. This makes feasible successor the correct answer.

B) Variance is an EIGRP feature used to enable unequal-cost load balancing. While it works with feasible successors to allow traffic over higher-cost paths, variance itself does not provide a precomputed backup route—it only determines which routes are eligible for load sharing.

C) Route Summarization aggregates multiple routes into a single advertisement to reduce routing table size. While summarization improves scalability and reduces SPF computation, it does not provide an immediate failover mechanism or backup path.

D) Hold Timer defines the interval a router waits before declaring a neighbor down if no hello messages are received. It affects convergence timing but does not create or maintain backup routes.

Feasible Successor is correct because it provides an immediately usable, loop-free backup path. Variance, route summarization, and hold timers serve different functions related to load balancing, scalability, and convergence timing, but they do not provide immediate failover.

Question 97:

Which OSPF area type blocks both Type 3 and Type 5 LSAs and receives only a default route?

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

Answer: B) Totally Stubby Area

Explanation:

A) Stub areas block Type 5 LSAs (external routes) but allow Type 3 summary LSAs. Stub areas are designed to reduce routing table size and SPF computation but still allow inter-area route propagation. They are unsuitable for scenarios requiring complete restriction of both external and inter-area LSAs.

B) Totally Stubby Areas block both Type 3 (inter-area) and Type 5 (external) LSAs. Routers within a totally stubby area receive only a default route from the ABR, which provides connectivity to all destinations outside the area. This design significantly reduces routing table size and SPF calculation overhead in edge areas with limited routers. Totally stubby areas are particularly useful for enterprise branch offices where detailed route knowledge is unnecessary and only default routing is sufficient for external connectivity. By using totally stubby areas, OSPF scales more efficiently while minimizing LSA flooding. This makes totally stubby area the correct answer.

C) NSSA (Not-So-Stubby Area) allows the injection of external routes via Type 7 LSAs while blocking Type 5 LSAs from outside. However, NSSA does not block Type 3 summary LSAs; therefore, it does not restrict inter-area LSA flooding entirely and is not equivalent to a totally stubby area.

D) Backbone Area (Area 0) is central to OSPF and propagates all LSA types. It does not block any LSAs and is unsuitable for minimizing LSA flooding in edge areas.

Totally Stubby Area is correct because it blocks both inter-area and external LSAs, leaving only a default route. Stub, NSSA, and backbone areas either allow some LSA types or propagate all LSAs.

Question 98:

Which BGP attribute influences the entry point selection into your AS from neighboring ASes?

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

Answer: C) MED

Explanation:

A) Weight is a Cisco-specific attribute used to control path selection locally on a single router. It does not propagate to other routers and cannot influence how external ASes select routes into your network.

B) Local Preference is propagated within the AS and affects outbound path selection for all routers in the autonomous system. It does not affect inbound traffic from external ASes.

C) MED (Multi-Exit Discriminator) is the standard BGP attribute for influencing how neighboring autonomous systems select entry points into your AS. By advertising a lower MED for preferred paths and higher MED for less preferred paths, network engineers can guide inbound traffic through specific links. MED provides predictable and policy-driven inbound traffic control, optimizing link utilization and managing congestion. Unlike AS path prepending, which indirectly influences inbound traffic, MED allows precise control communicated directly to neighbors. This makes MED the correct answer.

D) AS Path records the sequence of autonomous systems a route traverses. While AS path prepending can influence inbound traffic, it is less precise than MED and cannot guarantee predictable routing behavior from external ASes.

MED is correct because it directly controls how external ASes choose entry points into your network. Weight is local-only, local preference is outbound-focused, and AS path is an indirect influence on inbound routing.

Question 99

Which HSRP state monitors hello messages and is ready to take over forwarding if the active router fails?
A) Active
B) Standby
C) Listen
D) Init

Answer: B) Standby

Explanation:

A) Active is the state in which a router is currently responsible for forwarding traffic for the HSRP virtual IP (VIP). Active routers handle all ARP requests for the VIP and serve as the default gateway for hosts in the subnet. Because they are already performing the primary forwarding function, they are not in a monitoring or backup role. Active routers continuously send hello messages to notify other routers in the HSRP group of their presence and current state, but they are not in standby monitoring mode—they are the ones being monitored by other routers.

B) Standby is the state in which a router is fully prepared to take over forwarding duties if the active router fails. Routers in the standby state continuously monitor hello messages from the active router to determine its health and availability. If the standby router detects a failure—such as missed hello messages exceeding the hold time—it immediately transitions to the active state, assuming responsibility for forwarding traffic for the VIP. Standby routers maintain backup information, including MAC addresses and other relevant HSRP state data, to ensure minimal disruption and seamless failover. This redundancy provides high availability in enterprise networks, ensuring that hosts maintain uninterrupted access to the gateway. Standby is the correct answer because it represents the router actively performing monitoring and is ready to take over the active role when necessary.

Routers in standby do not forward traffic under normal conditions. Instead, they remain in a ready state, continuously evaluating the health of the active router. This state ensures that failover occurs within milliseconds to seconds, preventing network downtime and minimizing packet loss. Standby routers are essential for high-availability environments, including data centers, campus networks, and service provider infrastructures, where uninterrupted gateway access is critical.

C) Listen is an intermediate state where a router is aware of the HSRP group and receives hello messages but is neither active nor standby. Routers in this state are only preparing to participate in HSRP but do not forward traffic or maintain a ready-to-failover status.

D) Init is the initial state during HSRP startup. Routers in this state have not yet received any hello messages from other group members and cannot participate in elections or forwarding. They are essentially in a preliminary configuration phase.

  Standby is correct because it represents a backup router actively monitoring the active router and ready to assume the active role immediately in case of failure. Active routers are already forwarding, listen routers are passive, and init routers are in the startup phase. The standby state is crucial for high availability, seamless failover, and uninterrupted network service.

Question 100

 Which MPLS feature enables multiple VPNs to coexist on the same physical infrastructure while maintaining traffic isolation?
A) VRF
B) LDP
C) RSVP-TE
D) QoS

Answer: A) VRF

Explanation:

A) VRF (Virtual Routing and Forwarding) is a critical MPLS feature that allows a single router to support multiple independent routing tables, effectively creating separate logical networks on the same physical infrastructure. Each VRF instance maintains its own interfaces, routing table, and forwarding information base (FIB), ensuring complete isolation of traffic between VPNs. This isolation guarantees that traffic from one VPN cannot traverse or interfere with another VPN, even though both use the same underlying physical network links. VRF also allows the reuse of overlapping IP address spaces, which is common in multi-tenant environments or when multiple customers use private IP ranges.

In MPLS networks, VRFs are combined with MPLS labels to identify the VPN associated with each packet. The MPLS label acts as a tag, instructing routers along the path which VRF forwarding table to use. This mechanism ensures that packets from different VPNs do not mix, preserving logical separation and security. For service providers, VRFs enable the delivery of Layer 3 VPN services (L3VPNs) over a shared backbone infrastructure, allowing multiple customers to securely share network resources without compromising privacy or performance. Enterprises can also leverage VRFs to segment internal departments, data centers, or business units while maintaining centralized physical infrastructure.

VRFs are particularly useful in multi-tenant or enterprise environments, where each tenant or department requires isolated routing domains to prevent accidental or malicious traffic leakage. By using VRFs, organizations can host multiple VPNs on a single router or switch, reducing hardware costs while maintaining strict separation of traffic. VRF instances can also be integrated with BGP (Border Gateway Protocol) for distributing routes between sites or service providers, enabling scalable and secure connectivity across geographically dispersed networks.

B) LDP (Label Distribution Protocol) is used to distribute MPLS labels and facilitate forwarding along Forwarding Equivalence Classes (FECs). While LDP is essential for MPLS packet switching and path establishment, it does not inherently provide logical isolation between VPNs. LDP ensures that MPLS routers know how to forward packets based on labels but does not create separate routing tables or prevent traffic from one VPN from reaching another. LDP operates at the MPLS forwarding layer, whereas VRF operates at the routing and forwarding table level, providing true VPN separation.

C) RSVP-TE (Resource Reservation Protocol – Traffic Engineering) allows network administrators to establish explicit Label Switched Paths (LSPs) and reserve bandwidth along these paths. RSVP-TE is valuable for optimizing network resource utilization, avoiding congestion, and guaranteeing performance for critical applications. However, RSVP-TE does not inherently separate multiple VPNs or create isolated routing domains. It focuses on traffic engineering, ensuring predictable packet delivery and efficient utilization of network resources, but it does not provide the multi-tenant isolation capabilities offered by VRFs.

D) QoS (Quality of Service) prioritizes traffic, enforces bandwidth limits, and ensures that latency-sensitive applications (such as voice or video) receive appropriate network resources. QoS is critical for network performance and user experience, but it does not create isolated routing tables or logically separate VPN traffic. While QoS can differentiate and prioritize traffic, it cannot prevent one VPN’s traffic from reaching another VPN, making it insufficient for secure multi-VPN deployments.

  VRF is the correct answer because it allows multiple VPNs to coexist securely on the same physical infrastructure while maintaining complete logical separation. By using separate routing tables for each VPN and combining them with MPLS labels, VRFs prevent traffic leakage and allow overlapping IP address spaces. LDP, RSVP-TE, and QoS enhance MPLS forwarding efficiency, path optimization, and traffic performance but do not provide the traffic isolation and multi-tenant routing separation that VRFs deliver.

In practice, VRFs are fundamental to service provider L3VPN offerings, enterprise segmentation, and multi-department or multi-tenant network design. They reduce hardware requirements, improve operational efficiency, and maintain security and privacy across all logical networks on a shared physical backbone. Correctly configuring VRFs, in combination with MPLS labels and proper routing policies, is essential for scalable, secure, and high-performing network infrastructures.