Cisco 300-410  Implementing Cisco Enterprise Advanced Routing and Services (ENARSI) Exam  Dumps and Practice Test Questions Set 6 Q101-120

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Question 101:

Which EIGRP feature allows the router to select multiple paths for traffic forwarding, even if their metrics are not identical?

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

Answer: B) Variance

Explanation:

A) Feasible Successor is a backup route maintained in EIGRP’s topology table. It satisfies the feasibility condition, meaning the neighbor’s reported distance is less than the current feasible distance. Feasible successors are loop-free and can immediately take over if the primary route fails. However, they do not enable traffic distribution across unequal-cost paths by themselves; they primarily serve as backup routes for rapid convergence.

B) Variance is the EIGRP feature specifically designed to allow unequal-cost load balancing. By default, EIGRP performs equal-cost load balancing across successor routes. When variance is configured, it multiplies the metric of the best path (successor) by a defined variance value, and any feasible successors with metrics less than this value become eligible for traffic forwarding. This allows traffic to be distributed across multiple paths with different costs, improving bandwidth utilization and redundancy. For example, in a network with diverse link speeds or redundant paths, variance ensures that higher-cost but still feasible routes can carry traffic, rather than leaving them idle. The combination of variance and feasible successors allows EIGRP to implement sophisticated traffic engineering strategies while maintaining loop-free routing, making variance the correct answer.

C) Route Summarization aggregates multiple network prefixes into a single advertisement to reduce routing table size. While summarization improves scalability and reduces SPF or routing table complexity, it does not allow traffic to flow over unequal-cost paths. Summarization affects advertisement and routing efficiency but is unrelated to path selection and load balancing.

D) Hold Timer is the interval a router waits before declaring a neighbor down when no hello messages are received. It affects convergence timing and neighbor stability but does not influence path selection or enable multiple paths.

Variance is correct because it directly allows multiple feasible paths, including unequal-cost routes, to carry traffic. Feasible successors provide backup but are not used for load sharing, route summarization optimizes table size, and hold timers govern neighbor detection.

Question 102:

Which OSPF feature allows redistribution of external routes into an NSSA while keeping them isolated from other areas?

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

Answer: C) Type 7 LSA

Explanation:

A) Type 3 LSAs summarize routes from one area to another. They are generated by ABRs and provide inter-area routing, but they do not carry redistributed external routes. Type 3 LSAs are purely for summarization of internal OSPF routes between areas and cannot inject routes from other protocols into the OSPF domain.

B) Type 5 LSAs carry external routes redistributed into OSPF, but they are blocked from entering NSSAs. Type 5 LSAs are used in standard OSPF areas for external connectivity but are inappropriate for external route injection within an NSSA.

C) Type 7 LSAs are specifically designed for NSSAs (Not-So-Stubby Areas). They allow the redistribution of external routes (from BGP, EIGRP, or static routing) into the OSPF domain while preventing flooding outside the NSSA. The ABR then translates Type 7 LSAs into Type 5 LSAs for distribution into other areas. Type 7 LSAs enable hierarchical OSPF design by isolating external route information to localized areas, reducing LSA flooding and SPF computation in other areas while maintaining controlled access to external networks. This makes Type 7 LSAs the correct answer.

D) Type 1 LSAs describe router links within an OSPF area. They are intra-area only and are not capable of carrying external routes.

Type 7 LSA is correct because it allows redistribution of external routes into an NSSA while maintaining isolation from other areas. Type 3 summarizes inter-area routes, Type 5 carries external routes outside NSSAs, and Type 1 is intra-area only.

Question 103:

 Which BGP attribute is used to enforce a preferred outbound 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 influence path selection only on the local router. It is the first criterion considered in the BGP best path selection process and does not propagate to other routers in the AS. By assigning a higher weight to a route, the local router prefers that path for outbound traffic, ensuring router-specific control. Weight provides fine-grained policy enforcement for individual routers without impacting global AS routing decisions, making it the correct answer.

B) Local Preference is propagated throughout the autonomous system to influence outbound traffic selection network-wide. While it ensures consistency across the AS, it is not suitable for router-specific decisions because any change affects all routers within the AS.

C) MED (Multi-Exit Discriminator) influences how neighboring ASes select entry points into your network. MED affects inbound traffic from external networks, not local outbound routing.

D) AS Path records the autonomous systems traversed by a route. AS path prepending can influence external path selection indirectly but does not provide local control for router-specific outbound paths.

Weight is correct because it allows local router-specific control over outbound traffic without affecting other routers. Local preference affects the entire AS, MED is inbound-focused, and AS path is external-focused.

Question 104:

Which HSRP state indicates that the router is actively forwarding traffic for the virtual IP?

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

Answer: A) Active

Explanation:

A) Active state is when a router is currently responsible for forwarding traffic for the HSRP virtual IP. The router responds to ARP requests for the virtual IP, maintains the primary gateway role for hosts in the subnet, and handles all data forwarding. Active is the correct answer because it directly represents the router performing the primary gateway function.

B) Standby is the backup router that monitors hello messages from the active router and is ready to take over in the event of a failure. Standby does not forward traffic under normal conditions.

C) Listen is an intermediate state in which a router receives hello messages and learns about the HSRP group but is not actively forwarding or participating in standby election. Listen is preparatory, not operational in traffic forwarding.

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

Active is correct because it indicates the router is performing its role as the primary traffic forwarder. Standby monitors for failover, listen is passive, and init is preliminary.

Question 105:

Which MPLS mechanism allows multiple VPNs to coexist on the same physical 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 independent routing tables on a single router. Each VRF maintains its own interfaces, routing table, and forwarding information. When combined with MPLS labels, VRFs ensure traffic isolation between multiple VPNs sharing the same physical infrastructure. VRFs also allow overlapping IP address spaces for different VPNs, making them crucial in enterprise and service provider environments. By maintaining separate routing tables and forwarding paths, VRFs prevent traffic from one VPN from reaching another, ensuring both security and logical separation. This makes VRF the correct answer.

B) LDP (Label Distribution Protocol) distributes MPLS labels for forwarding along FECs. While critical for MPLS operation, LDP does not isolate traffic between VPNs or maintain separate routing tables.

C) RSVP-TE establishes explicit label-switched paths with bandwidth reservation for traffic engineering. RSVP-TE optimizes network performance and path selection but does not provide logical separation of VPNs.

D) QoS (Quality of Service) prioritizes traffic, allocates bandwidth, and guarantees application performance. While QoS is important for service quality and traffic prioritization, it does not maintain isolation or separate routing for multiple VPNs.

VRF is correct because it provides multiple VPNs with isolated routing and forwarding environments on the same physical infrastructure. LDP, RSVP-TE, and QoS enhance MPLS performance and forwarding but do not provide VPN isolation.

Question 106:

Which EIGRP feature ensures loop-free backup paths are immediately available 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 critical EIGRP feature designed to maintain network stability and fast convergence. EIGRP stores all potential routes in its topology table, but only routes that satisfy the feasibility condition—meaning the neighbor’s reported distance is less than the feasible distance of the current successor—are eligible to be feasible successors. This condition guarantees loop-free paths. If the primary route fails, the router can immediately switch to the feasible successor, reducing downtime and avoiding the need for a full route recalculation. Feasible successors are particularly important in large, complex networks with multiple redundant paths. They help maintain traffic flow without requiring recomputation of the entire topology, thus significantly decreasing convergence time. The feasibility condition ensures that the backup route will never create a routing loop, which is a critical safety mechanism in EIGRP. Feasible successors are stored proactively in the topology table, unlike variance-based load-balancing paths, which are calculated on-demand. This makes feasible successor the correct answer for immediate, loop-free backup routes.

B) Variance is an EIGRP mechanism that enables traffic to use multiple paths with unequal metrics. While variance allows load balancing over feasible successors that meet the metric criteria, it does not inherently provide a precomputed backup. Variance is used for traffic distribution rather than immediate failover, so it is not the feature responsible for rapid, loop-free backup route availability.

C) Route Summarization is used to aggregate multiple contiguous routes into a single advertisement, reducing routing table size and improving scalability. While summarization enhances network efficiency, it does not provide immediate backup paths for failover. Summarization is related to advertisement efficiency, not convergence or backup path readiness.

D) Hold Timer determines the time a router waits before declaring a neighbor down if no hello packets are received. While the hold timer affects convergence time, it does not precompute backup paths or provide loop-free failover. It is simply a timer for neighbor monitoring and failure detection.

Feasible successor is correct because it maintains loop-free backup routes that are immediately available upon primary route failure. Variance distributes traffic, route summarization optimizes table size, and hold timer controls convergence timing but does not provide backup paths.

Question 107:

Which OSPF LSA type allows external routes to be injected into an NSSA without flooding the entire OSPF domain?

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

Answer: C) Type 7

Explanation:

A) Type 3 LSAs are used for inter-area route summarization. They are generated by Area Border Routers (ABRs) to advertise networks from one area into another. Type 3 LSAs carry only internal OSPF routes and are not capable of carrying external routes from other protocols. While they help reduce SPF calculations by summarizing inter-area routes, they do not allow redistribution of external networks into OSPF, so they are incorrect for this scenario.

B) Type 5 LSAs carry external routes redistributed into OSPF, such as routes from BGP or static configurations. However, Type 5 LSAs are blocked from entering NSSAs by design to prevent flooding of external information into stub-like areas. Therefore, Type 5 LSAs cannot be used to inject external routes specifically within NSSAs.

C) Type 7 LSAs are designed to allow external routes to be introduced into NSSAs. NSSA routers can redistribute external routes (like EIGRP, BGP, or static routes) into OSPF using Type 7 LSAs. These LSAs remain confined to the NSSA until the ABR translates them into Type 5 LSAs for propagation into other areas. This approach allows OSPF networks to maintain hierarchical design and limit LSA flooding while still enabling localized redistribution of external routes. Type 7 LSAs are essential in edge networks where redistribution is needed but full external propagation is undesirable. This makes Type 7 LSAs the correct choice because they provide a mechanism for external route injection while maintaining isolation from the rest of the OSPF domain.

D) Type 1 LSAs describe a router’s links within an area. They provide intra-area topology information but cannot carry external routes, making them unsuitable for NSSA redistribution scenarios.

Type 7 LSAs are correct because they allow controlled redistribution of external routes into an NSSA, limiting LSA propagation while maintaining OSPF hierarchy. Type 3 summarizes inter-area routes, Type 5 carries external routes outside NSSAs, and Type 1 is intra-area only

Question 108:

Which BGP attribute is used to influence outbound path selection locally on a router without affecting other routers in the autonomous system?

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

Answer: A) Weight

Explanation:

A) Weight is a Cisco-specific BGP attribute that only affects the local router’s path selection. It is the first criterion evaluated in BGP best path selection. By assigning higher weight to a route, a router can prefer that path for outbound traffic, regardless of what other routers in the autonomous system are configured to do. Weight does not propagate to neighbors, making it ideal for controlling router-specific outbound traffic policies. This is particularly useful in scenarios where different routers within the same AS have different preferred paths for redundancy or traffic engineering purposes. Weight ensures that even if multiple routes exist, the local router can enforce its own routing preference, providing granular control over outbound traffic.

B) Local Preference is propagated throughout the entire autonomous system to influence outbound routing decisions. While effective for AS-wide path selection, it does not provide router-specific control, which is why it is not the correct answer for this scenario.

C) MED (Multi-Exit Discriminator) influences how external ASes select entry points into your network. It is used for inbound traffic engineering and does not affect local outbound path selection.

D) AS Path records the sequence of ASes a route has traversed. While AS path prepending can indirectly influence inbound traffic by making a path appear longer, it does not provide local outbound control.

Weight is correct because it allows router-specific outbound path selection without influencing other routers in the AS. Local preference is network-wide, MED affects inbound traffic, and AS path indirectly influences external routing.

Question 109:

 Which HSRP state indicates a router is ready to take over traffic forwarding 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. Since active routers are already handling traffic, they are not in a backup monitoring state.

B) Standby is the state in which a router monitors hello messages from the active router and is prepared to assume forwarding responsibilities if the active router fails. Standby routers maintain state information and are ready for immediate failover, ensuring uninterrupted network connectivity. The standby router does not forward traffic under normal conditions but is effectively the backup gateway. This makes standby the correct answer. Standby provides both monitoring and readiness functions, ensuring seamless failover without impacting network availability.

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 traffic forwarding or failover readiness. Listen is preparatory and does not provide immediate backup functionality.

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 failover.

Standby is correct because it monitors the active router and is ready to take over forwarding duties immediately. Active is forwarding, listen is passive monitoring, and init is initial setup.

 

Question 110:

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

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

Answer: A) VRF

Explanation:

A) VRF (Virtual Routing and Forwarding) is a mechanism that allows multiple logical routing and forwarding instances to coexist on a single physical router. Each VRF maintains its own interfaces, routing table, and forwarding information. When combined with MPLS, VRFs ensure that traffic from one VPN cannot reach another, even over the same physical links. VRFs also allow overlapping IP address spaces, making them essential in enterprise and service provider networks for delivering secure and isolated VPN services. By maintaining separate routing tables and forwarding paths, VRFs provide complete logical separation between multiple VPNs on shared infrastructure. This ensures security, isolation, and scalability, making VRF the correct answer.

B) LDP (Label Distribution Protocol) distributes MPLS labels to enable forwarding along FECs. While essential for MPLS operation, LDP does not provide VPN isolation or multiple independent routing tables.

C) RSVP-TE establishes explicit label-switched paths with bandwidth reservation for traffic engineering. While useful for optimizing network performance and path selection, RSVP-TE does not provide logical separation of VPNs.

D) QoS (Quality of Service) prioritizes traffic, allocates bandwidth, and ensures application performance. While QoS is critical for service quality, it does not provide isolation or separate routing for multiple VPNs.

VRF is correct because it allows multiple VPNs to share the same physical infrastructure while maintaining complete logical separation. LDP, RSVP-TE, and QoS enhance MPLS performance and traffic management but do not isolate VPN traffic.

Question 111:

Which EIGRP metric component reflects the time it takes for a packet to traverse a path?

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

Answer: B) Delay

Explanation:

A) Bandwidth is a metric component in EIGRP that represents the minimum capacity along a path. It is a measure of throughput, calculated based on the slowest link. While bandwidth influences the speed at which data can be transmitted, it does not account for the cumulative time a packet takes to traverse multiple links, so it does not directly represent delay. Bandwidth ensures the route selection favors higher-capacity paths, but it cannot provide latency information necessary for latency-sensitive traffic analysis.

B) Delay is the sum of all time-based components along a path, including transmission, propagation, queuing, and processing delays. EIGRP uses delay in its composite metric calculation to determine the fastest route in terms of packet traversal time, not just capacity. For example, a path with higher bandwidth but significant queuing delays may have a worse delay metric than a slightly lower-bandwidth path with minimal latency. Delay is expressed in tens of microseconds for each interface, and EIGRP sums these values for all interfaces along the path. Routes with lower cumulative delay are preferred for time-sensitive applications like VoIP or video conferencing. This makes delay the correct answer because it directly represents the traversal time along a path and is essential for EIGRP’s composite metric computation.

C) Reliability reflects the historical stability of a link, based on error rates over time. While reliability is important for long-term network stability and route preference, it does not measure how quickly a packet can traverse a path. A highly reliable link could still have high latency, making reliability unsuitable for representing cumulative traversal time.

D) Load indicates current link utilization. It is dynamic, reflecting congestion or active traffic on the interface at a given moment. While load can indirectly affect perceived delay through queuing, it is not a static component used in EIGRP’s metric calculations to represent path traversal time. Load fluctuates frequently, so it is not reliable for path selection based on consistent latency characteristics.

Delay is correct because it represents the total time for packets to traverse a path. Bandwidth measures throughput, reliability measures stability, and load measures utilization, none of which reflect cumulative packet traversal time.

Question 112:

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

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

Answer: C) NSSA

Explanation

A) Stub areas block Type 5 external LSAs to reduce routing table size and SPF calculation overhead. However, stub areas do not allow injection of external routes via Type 7 LSAs. Stub areas are suitable for minimizing LSA flooding but cannot redistribute external routes within the area.

B) Totally Stubby Areas block both Type 3 and Type 5 LSAs, leaving only a default route for connectivity outside the area. They do not allow external routes through Type 7 LSAs, making them unsuitable for scenarios requiring external redistribution within the area.

C) NSSA (Not-So-Stubby Area) is specifically designed to provide a middle ground between stub areas and standard OSPF areas. NSSA allows the redistribution of external routes using Type 7 LSAs while blocking Type 5 LSAs from entering the area. Type 7 LSAs carry external routes from other protocols such as BGP or EIGRP and are converted to Type 5 LSAs by the ABR for propagation into the rest of the OSPF domain. This ensures external routes are isolated within the NSSA but can still reach the backbone or other areas after conversion. NSSAs are ideal for edge networks that require external connectivity without propagating all external routes into the entire OSPF domain, maintaining hierarchical OSPF scalability. This makes NSSA the correct answer.

D) Backbone Area (Area 0) carries all LSA types and propagates both inter-area and external routes. It does not restrict external route flooding, making it unsuitable for controlled redistribution of external routes in a localized area.

NSSA is correct because it allows external routes via Type 7 LSAs while blocking Type 5 LSAs from flooding the area. Stub areas restrict external routes entirely, totally stubby areas restrict both internal and external LSAs, and the backbone area propagates everything.

Question 113:

Which BGP attribute ensures that a specific path is preferred on a single router 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 attribute used to influence path selection locally on a single router. It is the first criterion evaluated in the BGP best path selection process. By assigning a higher weight to a route, the local router will prefer that path for outbound traffic. Weight is not propagated to other routers in the AS, making it ideal for router-specific traffic engineering. This allows network engineers to control outbound traffic behavior precisely on individual routers without impacting global routing policies. Weight ensures that even if multiple paths exist in the BGP table, the preferred route will be chosen locally first, which is especially useful in scenarios involving multi-homed routers or redundant connections.

B) Local Preference is propagated throughout the autonomous system and affects outbound path selection on all routers in the AS. While useful for AS-wide policy enforcement, it is unsuitable for router-specific control because any change impacts the entire AS.

C) MED (Multi-Exit Discriminator) influences how neighboring ASes choose entry points into your AS. It affects inbound traffic from external peers but does not control local outbound routing.

D) AS Path records the sequence of autonomous systems traversed by a route. AS path manipulation, such as prepending, can indirectly influence inbound traffic but does not allow local router-specific outbound control.

Weight is correct because it provides local, router-specific path preference without affecting other routers. Local preference is AS-wide, MED is inbound-focused, and AS path only indirectly influences routing decisions.

Question 114:

Which HSRP state indicates a router is ready to take over traffic forwarding 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 is the state in which a router is currently forwarding traffic for the HSRP virtual IP. Active routers handle ARP requests and serve as the primary gateway. They are not in a backup monitoring state, so they are unsuitable for representing failover readiness.

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 failure occurs. Standby routers maintain backup state information and are ready for immediate failover, ensuring high availability. They do not forward traffic under normal operation but are actively monitoring the active router and maintaining readiness. Standby provides seamless failover in case of primary router failure, ensuring minimal disruption in connectivity. This 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 does not participate in forwarding or standby election. Listen is preparatory, not operational for failover.

D) Init is the initial state during HSRP startup where no hello messages have been received. Routers in init cannot forward traffic or participate in failover, making them unsuitable for representing standby readiness.

Standby is correct because it represents a router ready to take over traffic if the active router fails. Active is forwarding, listen is passive, and init is preliminary.

Question 115:

Which MPLS feature allows multiple VPNs to share the same physical 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 independent routing and forwarding instances to exist on a single physical router. Each VRF maintains its own interfaces, routing table, and forwarding information. Combined with MPLS, VRFs ensure that traffic from one VPN cannot reach another VPN, even over the same physical links. VRFs also allow overlapping IP addresses between VPNs, making them essential for enterprise and service provider environments. By providing isolated routing tables and forwarding domains, VRFs ensure logical separation, secure multi-tenancy, and scalability. This makes VRF the correct answer for maintaining VPN isolation while sharing the same infrastructure.

B) LDP (Label Distribution Protocol) distributes MPLS labels for forwarding packets along FECs. While LDP is critical for MPLS functionality, it does not provide VPN isolation or independent routing tables.

C) RSVP-TE establishes explicit label-switched paths for traffic engineering purposes, optimizing network performance and bandwidth utilization. While useful for performance and path control, RSVP-TE does not separate traffic between multiple VPNs.

D) QoS (Quality of Service) manages traffic prioritization, bandwidth allocation, and performance guarantees. While QoS is crucial for service quality, it does not provide logical separation or isolated routing domains between VPNs.

VRF is correct because it allows multiple VPNs to coexist securely on the same physical infrastructure while maintaining complete isolation. LDP, RSVP-TE, and QoS enhance MPLS performance but do not enforce VPN separation.

Question 116:

Which EIGRP metric component represents the minimum capacity along the path?

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

Answer: A) Bandwidth

Explanation:

A) Bandwidth is a key component of EIGRP’s composite metric and represents the minimum bandwidth along the path to a destination. EIGRP evaluates every link along a route and identifies the slowest link as the limiting factor. This ensures that routes are selected based on the capacity of the bottleneck, preventing the selection of routes with insufficient throughput for efficient traffic handling. Bandwidth is critical because EIGRP combines it with delay in a weighted formula to determine the composite metric used for route selection. A higher minimum bandwidth makes a path more desirable, particularly in enterprise environments with links of varying speeds, as it ensures higher-capacity paths are preferred. The calculation considers each interface’s bandwidth and identifies the minimum value along the route, which directly influences EIGRP’s successor selection and overall traffic engineering.

B) Delay measures the cumulative time required for a packet to traverse a path, including propagation, transmission, and queuing delays. Delay is essential for latency-sensitive applications but does not reflect throughput limitations. While delay is part of the composite metric, it represents speed rather than the maximum capacity that the path can support.

C) Reliability represents the historical stability of a link, measured by error rates. It ensures that unstable links are avoided in route selection. However, reliability does not define the maximum throughput of a link, so it is unrelated to identifying the minimum capacity along a path.

D) Load indicates the current utilization of a link. High load may temporarily degrade performance, but it is dynamic and not used in EIGRP’s calculation of the minimum bandwidth. Load affects perceived congestion but does not provide a static measure of path capacity.

Bandwidth is correct because it identifies the slowest link along a path, which dictates the maximum achievable throughput. Delay, reliability, and load provide important supplemental metrics but do not define the path’s minimum capacity.

Question 117:

Which OSPF LSA type is generated by an ABR to advertise summary routes between areas?

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

Answer: C) Type 3

Explanation:

A) Type 1 LSAs are router LSAs that describe a router’s links within an area. They provide intra-area topology information used for SPF calculations but do not propagate routes between areas. Type 1 LSAs remain confined to a single area and are not used for summarization or inter-area advertisement.

B) Type 2 LSAs are network LSAs generated by the designated router (DR) on broadcast or NBMA segments. They describe the segment’s attached routers and facilitate SPF computation for routers within an area. Type 2 LSAs are intra-area and do not summarize routes between areas.

C) Type 3 LSAs, also called summary LSAs, are generated by ABRs to advertise routes from one area into another. They summarize multiple networks into a single advertisement, reducing routing table size and LSA flooding in other areas. Type 3 LSAs allow OSPF to maintain hierarchical scalability by limiting detailed topology knowledge outside an area. ABRs can perform route summarization when generating Type 3 LSAs, further reducing the size of routing tables in remote areas. Type 3 LSAs are essential for efficient route propagation between areas and are the correct answer for inter-area summarization.

D) Type 5 LSAs carry external routes redistributed into OSPF from other protocols. They propagate external routes throughout the OSPF domain but are not used for summarizing internal routes between areas.

Type 3 LSAs are correct because they allow ABRs to summarize and advertise inter-area routes efficiently. Type 1 and Type 2 LSAs are confined to a single area, and Type 5 LSAs handle external route distribution.

Question 118:

Which BGP attribute controls how incoming traffic enters your autonomous system?

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

Answer: C) MED

Explanation:

A) Weight is a Cisco-proprietary attribute that influences path selection only on the local router. It does not propagate to other routers and does not affect how external ASes choose entry points into your network. Weight only controls local outbound traffic preferences.

B) Local Preference is propagated throughout the AS to control outbound path selection. It ensures consistent path selection for all routers in the AS but does not influence how neighboring ASes send traffic into your network.

C) MED (Multi-Exit Discriminator) is the standard BGP attribute used to influence inbound traffic from neighboring autonomous systems. By advertising lower MED values on preferred entry links and higher values on less desirable links, an AS can suggest to its neighbors which paths are optimal for traffic entering the AS. MED does not enforce policy; it is a suggestion to neighboring ASes. MED allows network engineers to control incoming traffic patterns, optimize link utilization, and manage congestion. It is particularly useful in multi-homed scenarios to ensure predictable routing behavior for inbound traffic. This makes MED the correct answer.

D) AS Path records the autonomous systems traversed by a route. AS path prepending can influence inbound traffic indirectly by making a path appear longer, but it does not provide precise control over which external ASes select a particular entry point.

MED is correct because it directly influences inbound traffic selection by neighboring ASes. Weight is local-only, local preference controls outbound traffic, and AS path is an indirect factor for inbound selection.

Question 119:

 Which HSRP state is responsible for 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. Active routers respond to ARP requests for the VIP and handle all data forwarding for the subnet. Being the primary gateway, the active router ensures uninterrupted connectivity for hosts. The active router maintains hello messages to allow standby routers to monitor its status. Active is the correct answer because it is the router performing the forwarding duties in normal operation.

B) Standby is the backup router that monitors hello messages from the active router. It is prepared to take over forwarding duties if the active router fails, but it does not forward traffic during normal operation.

C) Listen is a preparatory state where the router is aware of the HSRP group and receives hello messages but does not actively participate in forwarding or standby functions.

D) Init is the initial state during HSRP startup. Routers in init have not received hello messages and cannot forward traffic or participate in failover.

Active is correct because it represents the router currently responsible for forwarding traffic. Standby is monitoring, listen is passive, and init is initial setup.

Question 120

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

Answer: A) VRF

Explanation:

A) VRF (Virtual Routing and Forwarding) is a foundational feature in MPLS networks that enables multiple logical routing and forwarding tables to exist simultaneously on the same physical router. Each VRF instance is fully independent, maintaining its own interfaces, routing table, and forwarding information base (FIB). This separation ensures that traffic belonging to one VPN cannot access, traverse, or interfere with traffic in another VPN, even if both VPNs share the same physical network infrastructure. VRF, in combination with MPLS labels, provides a mechanism for maintaining strict logical isolation, which is critical for both enterprise networks and service provider environments supporting multiple tenants or customers.

By using VRF, organizations can implement multi-tenancy on a single infrastructure. This capability is especially important for service providers who host multiple VPNs for different clients over the same core backbone network. Each VRF functions as a completely independent routing domain, with its own routing policies, BGP peering sessions, and forwarding logic. From the perspective of each VPN, it appears as if it has its own dedicated router, even though the physical resources are shared. This approach allows operators to reduce hardware costs while maintaining high levels of security and isolation.

A key advantage of VRFs is their ability to support overlapping IP address spaces. Multiple customers or departments may use identical private IP ranges, but because each VRF maintains a separate routing table, there is no conflict or traffic leakage. For example, two separate departments might both use the 10.0.0.0/24 subnet. With VRFs, packets from one department are forwarded exclusively within its assigned VRF, and packets from the other department remain isolated in a separate VRF. This eliminates the need for renumbering or complex NAT configurations while providing true logical separation.

In addition to isolation, VRFs facilitate scalability and operational efficiency. Service providers can deploy hundreds or thousands of VPNs on the same backbone network without requiring dedicated physical routers for each customer. Enterprise networks can segment multiple business units, departments, or applications over the same core infrastructure while maintaining strict separation of traffic, security policies, and routing domains. VRFs integrate seamlessly with BGP (Border Gateway Protocol), allowing route distribution between sites while maintaining isolation. Multi-protocol BGP (MP-BGP) is often used to exchange routes between VRFs and core routers, ensuring secure connectivity for each VPN while supporting overlapping IP addresses.

VRF implementation also provides enhanced security and policy control. By isolating traffic at the routing table level, organizations can enforce separate firewall rules, access control policies, and monitoring for each VPN. This ensures that misconfigurations or security breaches in one VRF do not impact other VPNs. VRFs also allow network operators to implement differentiated services, route policies, and traffic engineering independently for each VPN. This level of granularity is critical for service-level agreements (SLAs) in multi-tenant environments.

B) LDP (Label Distribution Protocol) is a protocol used to distribute MPLS labels, allowing packets to be forwarded along Label-Switched Paths (LSPs). LDP is essential for basic MPLS operation, enabling efficient forwarding and label-based routing, but it does not inherently provide logical separation of VPN traffic or create independent routing tables for multiple tenants. LDP ensures that MPLS routers can forward traffic along the correct path, but it cannot enforce isolation between different VPNs or tenants on a shared infrastructure.

C) RSVP-TE (Resource Reservation Protocol – Traffic Engineering) allows network administrators to establish explicit LSPs with bandwidth guarantees and path constraints. RSVP-TE is extremely useful for optimizing network resource utilization, avoiding congestion, and providing predictable performance for critical applications. However, while RSVP-TE enables path control and traffic engineering, it does not isolate multiple VPNs on the same infrastructure. RSVP-TE is primarily focused on path optimization and performance guarantees rather than logical separation of tenant or customer traffic.

D) QoS (Quality of Service) provides mechanisms to prioritize traffic, manage bandwidth, and ensure performance for critical applications such as voice, video, and transactional systems. QoS is essential for maintaining network efficiency and service quality, particularly in congested or high-volume environments. However, QoS does not provide independent routing tables or isolate traffic between VPNs. While it can ensure that one type of traffic is prioritized over another, it does not prevent one VPN from accessing or affecting the traffic of another VPN.

 VRF is the correct answer because it enables multiple VPNs to share the same physical infrastructure while maintaining complete logical and traffic isolation. Each VRF has independent routing tables, forwarding information, and interfaces, preventing traffic from crossing between VPNs even if they share the same links. VRF supports overlapping IP addresses, multi-tenancy, scalable network design, security policy enforcement, and flexible routing for enterprise and service provider networks.

LDP, RSVP-TE, and QoS enhance MPLS operation by enabling label-based forwarding, path optimization, and traffic prioritization, respectively. However, none of these features provide true logical separation between multiple VPNs. In contrast, VRF ensures that VPNs operate as fully isolated, independent networks on shared physical resources, making it essential for secure, scalable, and multi-tenant network architectures.

By leveraging VRFs, service providers can deliver secure Layer 3 VPN services, enterprises can segment internal traffic for multiple business units, and operators can maintain consistent security and routing policies across complex, multi-customer, or multi-department networks without additional hardware. VRFs are therefore fundamental to modern MPLS design and large-scale network deployments where isolation, scalability, and multi-tenancy are priorities.