Cisco 300-410  Implementing Cisco Enterprise Advanced Routing and Services (ENARSI) Exam  Dumps and Practice Test Questions Set 10 Q181-200

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

Question 181:

 Which EIGRP metric component determines the path’s total latency?

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

Answer: B) Delay

Explanation:

A) Bandwidth represents the slowest link along a path, determining maximum throughput achievable. While important for capacity considerations, bandwidth does not provide information about latency or cumulative traversal time. A path with high bandwidth may still introduce significant latency if intermediate links have slow processing or propagation delays. Bandwidth ensures the network can handle traffic volume but does not quantify the time packets take to traverse a path.

B) Delay measures the total cumulative time for a packet to traverse a path, including transmission, propagation, queuing, and processing delays. In EIGRP, delay is expressed in tens of microseconds per interface and summed across all hops along the path. This makes delay the primary metric for evaluating latency. Delay is crucial for latency-sensitive applications such as VoIP, video conferencing, and online gaming. EIGRP uses both bandwidth and delay in its composite metric to balance throughput and latency. By selecting paths with lower cumulative delay, EIGRP ensures efficient end-to-end performance. Delay is particularly important when multiple paths exist with similar bandwidth but varying latencies, allowing EIGRP to choose the path that optimizes response time. This makes delay the correct answer.

C) Reliability measures historical stability and error rate of a link. While a stable link is desirable, reliability does not indicate the time required for packet traversal. A highly reliable link could still introduce significant latency if its propagation or processing delay is high.

D) Load reflects the current utilization of a link. High load can increase latency indirectly through queuing delays, but load is a dynamic metric and does not represent the inherent cumulative delay of a path.

Delay is correct because it directly measures total path latency. Bandwidth measures throughput, reliability measures stability, and load measures current utilization but does not quantify traversal time.

Question 182:

Which OSPF area type allows external route injection using Type 7 LSAs while blocking 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 LSAs and only allow Type 3 LSAs for inter-area routing. They reduce SPF computation and flooding overhead but cannot redistribute external routes. Stub areas are ideal for branch networks without external connectivity requirements.

B) Totally Stubby Areas block both Type 3 and Type 5 LSAs, allowing only a default route for inter-area connectivity. They minimize routing complexity but do not allow external route injection.

C) NSSA (Not-So-Stubby Area) allows external routes to be injected into OSPF using Type 7 LSAs. Type 7 LSAs remain localized within the NSSA but can be converted into Type 5 LSAs by the ABR for propagation to other areas. NSSAs provide controlled redistribution of external routes while maintaining the benefits of stub areas, such as reduced SPF calculation overhead. This design is ideal for branch networks needing connectivity to external routes without propagating Type 5 LSAs throughout the OSPF domain. NSSAs enhance scalability and maintain hierarchical OSPF structure by localizing external route management. This makes NSSA the correct answer.

D) Backbone Area (Area 0) supports all LSA types, including Type 5. It is used for inter-area routing but does not restrict external LSA flooding or provide localized injection mechanisms.

NSSA is correct because it allows Type 7 LSA injection while blocking Type 5 LSAs. Stub and Totally Stubby Areas restrict external routes, and the backbone area does not provide LSA restriction.

Question 183:

Which BGP attribute influences outbound traffic selection on a single router?

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

Answer: A) Weight

Explanation:

A) Weight is a Cisco-specific attribute used to influence outbound path selection locally on a router. Weight is evaluated first in the BGP best path selection process. Assigning a higher weight to a path ensures that the router prefers that path for outbound traffic. Weight does not propagate to other routers, making it ideal for router-specific traffic engineering. In multi-homed environments, weight allows deterministic path selection and predictable traffic distribution. Weight ensures that critical links are used preferentially and that less desirable paths are avoided locally, without affecting the routing behavior of the entire AS.

B) Local Preference affects outbound path selection across all routers in an AS and is propagated throughout the AS. While it influences which exit link is used, it cannot provide router-specific control like weight.

C) MED (Multi-Exit Discriminator) influences inbound traffic from external ASes rather than outbound traffic on the local router. MED indicates preferred entry points to neighboring ASes but does not control the router’s own outgoing traffic selection.

D) AS Path is a list of autonomous systems traversed by a route. AS path prepending can influence inbound traffic indirectly but does not control outbound traffic selection locally.

Weight is correct because it allows precise, local control of outbound path selection. Local Preference is AS-wide, MED influences inbound routing, and AS Path is indirect.

Question 184:

Which HSRP state monitors the active router 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 router currently forwarding traffic for the HSRP virtual IP. It responds to ARP requests and maintains connectivity but does not monitor other routers for failover.

B) Standby monitors hello messages from the active router and is prepared to take over forwarding duties immediately if the active router fails. Standby routers maintain all state information necessary to ensure seamless failover with minimal disruption. They do not forward traffic under normal conditions but provide high availability and fault tolerance. In enterprise networks, the standby router ensures uninterrupted gateway access, allowing applications and services to function without disruption. The standby router continuously monitors the active router, enabling failover in milliseconds to seconds, which is critical for maintaining high availability in production networks. This makes standby the correct answer.

C) Listen is an intermediate state where the router receives hello messages but does not actively monitor the active router or forward traffic.

D) Init is the initial state during HSRP startup, where the router has not received hello messages and cannot forward traffic or participate in failover.

Standby is correct because it monitors the active router and is ready for immediate takeover. Active forwards traffic, Listen is passive, and Init is preliminary.

Question 185:

 Which MPLS feature allows multiple VPNs to share infrastructure while maintaining complete isolation?

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

Answer: A) VRF

Explanation:

A) VRF (Virtual Routing and Forwarding) enables multiple independent routing and forwarding instances to exist on a single physical router. Each VRF maintains separate interfaces, routing tables, and forwarding domains. In MPLS networks, VRFs allow multiple VPNs to share the same physical infrastructure while maintaining complete isolation. VRFs also support overlapping IP address spaces, enabling multi-tenant deployments. By keeping routing and forwarding separate, VRFs prevent traffic from one VPN from reaching another, ensuring security, scalability, and predictable network performance. VRFs are widely used in enterprise and service provider networks to allow multiple customers or business units to coexist on shared infrastructure securely. This makes VRF the correct answer.

B) LDP (Label Distribution Protocol) distributes labels in MPLS networks to enable label-switched path forwarding. While critical for MPLS operations, LDP does not provide VPN isolation.

C) RSVP-TE (Resource Reservation Protocol – Traffic Engineering) establishes explicit LSPs with bandwidth reservation to optimize performance. RSVP-TE enhances MPLS efficiency but does not segregate VPN traffic.

D) QoS (Quality of Service) prioritizes traffic and manages bandwidth for critical applications. QoS ensures predictable performance but does not enforce isolation between VPNs.

VRF is correct because it provides secure multi-VPN operation on shared infrastructure. LDP, RSVP-TE, and QoS enhance MPLS functionality and performance but do not enforce traffic separation.

Question 186:

Which EIGRP metric component is most critical for latency-sensitive applications such as VoIP?

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

Answer: B) Delay

Explanation:

A) Bandwidth measures the slowest link along a path and determines the maximum amount of traffic that can traverse that path. While bandwidth ensures sufficient capacity for high-volume data transfers, it does not guarantee minimal latency. A network with high bandwidth could still have significant delays due to interface processing, propagation, or queuing, which can negatively affect latency-sensitive applications such as VoIP or video conferencing. Therefore, bandwidth alone is insufficient to determine path suitability for low-latency traffic.

B) Delay measures the cumulative time a packet takes to traverse a network path, including propagation, transmission, processing, and queuing delays. EIGRP calculates the sum of delays across all interfaces on a path and incorporates this value into its composite metric. Delay is particularly important for latency-sensitive applications because it directly affects user experience. In a network with multiple paths of similar bandwidth, EIGRP will prefer the path with the lowest cumulative delay, ensuring optimal performance for voice, video, or interactive applications. Unlike bandwidth, which represents capacity, or reliability, which reflects historical stability, delay provides a real-time measure of traversal time and is directly correlated with responsiveness. For applications where milliseconds matter, such as VoIP, selecting a path with minimal delay is crucial to maintaining call quality and preventing jitter or packet loss.

C) Reliability represents historical link stability and error rates. Although highly reliable links are desirable for ensuring consistent connectivity, reliability does not provide a direct measure of latency. A reliable link may still introduce significant delays if processing or propagation time is high, which could degrade performance for latency-sensitive traffic.

D) Load reflects the current utilization of a link. While high load can cause queuing and increase latency, it is a dynamic metric that fluctuates with network traffic. Load alone cannot guarantee consistent performance for latency-sensitive applications because it provides only a snapshot of current conditions and does not account for inherent link characteristics.

Delay is correct because it directly measures cumulative latency along a path. Bandwidth ensures capacity, reliability ensures stability, and load indicates current usage, but only delay provides an accurate measure of traversal time, which is critical for applications requiring minimal latency.

Question 187:

Which OSPF area type is designed to allow external route injection while minimizing SPF overhead by blocking 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 LSAs and allow only Type 3 LSAs for inter-area routing. While this reduces SPF calculation and flooding overhead, stub areas cannot accommodate external route injection, making them unsuitable for networks requiring redistribution from external protocols. Stub areas are optimal for small branch networks where external connectivity is not needed.

B) Totally Stubby Areas block both Type 3 and Type 5 LSAs, allowing only a default route for inter-area communication. While minimizing SPF calculation further than stub areas, totally stubby areas are unable to inject external routes, limiting their usefulness in networks requiring redistributed external connectivity.

C) NSSA (Not-So-Stubby Area) allows controlled injection of external routes using Type 7 LSAs while still blocking Type 5 LSAs. Type 7 LSAs remain localized within the NSSA, but ABRs can convert them into Type 5 LSAs for propagation to other areas if needed. NSSAs provide a balance between minimizing SPF overhead and supporting external route redistribution, making them ideal for branch or edge networks that require external connectivity without flooding the entire OSPF domain with Type 5 LSAs. NSSAs maintain hierarchical OSPF design, scalability, and reduced SPF processing while allowing localized external route management. This ensures that critical external routes are available to routers in the NSSA without impacting the rest of the network. This makes NSSA the correct answer.

D) Backbone Area (Area 0) supports all LSA types, including Type 5, and is responsible for inter-area routing. While the backbone area can handle external route propagation, it does not restrict Type 5 LSAs, and its purpose is not to minimize SPF overhead or localize external route management.

NSSA is correct because it allows Type 7 LSA injection for external routes while minimizing SPF overhead and blocking Type 5 LSAs. Stub and totally stubby areas cannot inject external routes, and the backbone area does not limit LSA propagation.

Question 188:

Which BGP attribute is used to influence outbound traffic selection on a local 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 that affects BGP outbound path selection locally on a router. It is evaluated first in the BGP best path selection algorithm, and higher weights are preferred over lower ones. Weight allows administrators to control traffic distribution on a per-router basis without propagating changes to the rest of the AS. This is particularly useful in multi-homed networks where traffic must be directed through specific links for performance, cost, or policy reasons. Because weight does not propagate, it provides deterministic and localized control of outbound routing decisions, ensuring predictable traffic flows on the specific router where it is configured.

B) Local Preference is an AS-wide attribute propagated to all routers within the same autonomous system. While it influences outbound path selection, it is not router-specific and therefore cannot provide localized control like weight.

C) MED (Multi-Exit Discriminator) affects how neighboring autonomous systems choose the preferred entry point into your AS, influencing inbound traffic rather than outbound. MED cannot dictate the router-specific outbound path selection.

D) AS Path records the sequence of autonomous systems traversed by a route. AS path prepending can influence inbound traffic by making certain paths appear longer, but it does not control outbound path selection on a local router.

Weight is correct because it provides precise local control over outbound traffic selection. Local Preference is propagated AS-wide, MED influences inbound traffic, and AS Path is only an indirect method of inbound influence.

Question 189:

 Which HSRP state is responsible for monitoring the active router and ready to take over forwarding if failure occurs?

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

Answer: B) Standby

Explanation:

A) Active is the router currently responsible for forwarding traffic for the HSRP virtual IP address. It maintains connectivity, responds to ARP requests, and ensures the network gateway is operational. However, it does not monitor other routers for failover purposes, nor does it serve as a backup.

B) Standby monitors hello messages from the active router and is ready to take over forwarding duties immediately if the active router fails. Standby routers maintain all state information required for seamless failover, ensuring minimal disruption to traffic. They do not forward traffic during normal operation but are crucial for high availability and redundancy. The standby router continuously monitors the active router and transitions to active within milliseconds to seconds upon detecting failure. This guarantees uninterrupted network access for critical applications and services. The standby router is an essential component of HSRP deployments in enterprise networks where continuous gateway availability is required. This makes standby the correct answer.

C) Listen is a transitional state in which the router is aware of the HSRP group but does not actively monitor the active router or forward traffic.

D) Init is the initial state where the router has not yet received hello messages and cannot participate in forwarding or failover.

Standby is correct because it monitors the active router and is ready for immediate failover. Active forwards traffic, Listen is passive, and Init is preliminary.

Question 190:

Which MPLS feature allows multiple VPNs to coexist securely on shared infrastructure while maintaining complete traffic separation?

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 router. Each VRF maintains its own interfaces, routing tables, and forwarding domains. In MPLS networks, VRFs provide full traffic isolation for multiple VPNs sharing the same physical infrastructure. VRFs also support overlapping IP address spaces across VPNs, enabling multi-tenant deployments without risking traffic leakage. By keeping routing and forwarding separate, VRFs ensure security, scalability, and predictable performance. VRFs are essential for service provider and enterprise networks where multiple customers or departments share the same infrastructure. They allow centralized management of routing instances and maintain traffic segregation while enabling efficient resource utilization.

B) LDP (Label Distribution Protocol) distributes MPLS labels to enable label-switched path forwarding. While critical for MPLS functionality, LDP does not provide logical isolation between VPNs.

C) RSVP-TE (Resource Reservation Protocol – Traffic Engineering) establishes explicit LSPs with bandwidth reservation. RSVP-TE enhances performance, reliability, and path optimization but does not segregate VPN traffic.

D) QoS (Quality of Service) prioritizes traffic and manages bandwidth allocation for specific applications. QoS ensures predictable performance but does not enforce VPN isolation.

VRF is correct because it enables secure, isolated multi-VPN operation on shared infrastructure. LDP, RSVP-TE, and QoS enhance MPLS functionality and performance but do not enforce traffic separation.

Question 191:

 Which EIGRP metric component represents the minimum bandwidth along a path?

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

Answer: A) Bandwidth

Explanation:

A) Bandwidth is the metric component in EIGRP that identifies the slowest link along a path, representing the minimum transmission capacity. This is crucial for determining the maximum throughput that a path can support. EIGRP calculates its composite metric by taking into account the minimum bandwidth across all interfaces along the route. The rationale behind using minimum bandwidth is that a single bottleneck link can limit overall performance, regardless of the capacity of the other links. For example, if a path contains multiple high-speed links but one slow interface, the throughput achievable on that path is constrained by the slowest link. This is why EIGRP uses the minimum bandwidth in its metric calculation. By considering the slowest link, EIGRP ensures that traffic is routed along paths that can sustain the required throughput. Bandwidth is measured in kilobits per second and converted to a metric using the formula 10^7 / minimum bandwidth (in Kbps). This ensures consistency and comparability among multiple routes.

B) Delay measures the cumulative time required for a packet to traverse all interfaces along a path. Delay is important for latency-sensitive applications but does not determine the path’s maximum throughput. Even if a path has minimal delay, a slow interface can limit traffic, making delay insufficient for evaluating bottlenecks.

C) Reliability measures historical stability and error rate of a link. Reliability ensures stable connectivity but does not quantify the slowest or limiting link in terms of throughput. A highly reliable link may still be slow, which could restrict traffic flow.

D) Load indicates the current utilization of a link. Load is a dynamic metric that reflects how busy a link is at a given time. While high load can temporarily affect performance, it does not provide an intrinsic measurement of link capacity and cannot identify bottleneck links consistently.

Bandwidth is correct because it identifies the slowest link, which is critical for throughput calculations. Delay measures latency, reliability measures historical stability, and load measures current utilization but does not determine path capacity.

Question 192:

Which OSPF LSA type carries information about external routes redistributed into the OSPF domain?

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

Answer: C) Type 5

Explanation:

A) Type 1 LSAs, also called router LSAs, describe the router’s own interfaces, links, and states within an area. They are essential for intra-area routing and maintaining an accurate link-state database but do not carry external route information. Type 1 LSAs help routers understand the internal topology of the area but do not propagate routes from external sources.

B) Type 3 LSAs, or summary LSAs, are generated by ABRs to summarize networks between OSPF areas. They help reduce the size of routing tables and minimize SPF recalculation within other areas. However, Type 3 LSAs only carry internal OSPF information, not routes redistributed from external protocols.

C) Type 5 LSAs are external LSAs used to advertise routes redistributed into OSPF from other protocols, such as BGP, EIGRP, or static routes. Type 5 LSAs are flooded throughout all standard areas except stub and totally stubby areas. They include a metric type (E1 or E2) that influences path selection: E1 includes both external cost and internal area cost, while E2 only considers external cost. Type 5 LSAs allow OSPF routers to learn about destinations outside the OSPF domain, ensuring full connectivity and interoperability with other routing protocols. They are essential for integrating OSPF with other parts of the network and maintaining reachability to external networks. This makes Type 5 the correct answer.

D) Type 7 LSAs are specific to NSSAs and allow external routes to be advertised locally within the NSSA. They can be converted into Type 5 LSAs by ABRs for propagation outside the NSSA but are not used in standard areas for external route advertisement.

Type 5 is correct because it propagates external routes throughout standard areas. Type 1 is intra-area, Type 3 is inter-area summary, and Type 7 is specific to NSSAs.

Question 193:

Which BGP attribute is used to influence inbound traffic from external autonomous systems?

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

Answer: C) MED

Explanation:

A) Weight is a Cisco-proprietary attribute that affects outbound path selection on a single router. It does not influence how neighboring autonomous systems choose entry points into your AS, so it cannot control inbound traffic.

B) Local Preference is propagated throughout an AS and influences outbound path selection. It does not affect how external ASes route traffic toward your network, making it irrelevant for inbound traffic management.

C) MED (Multi-Exit Discriminator) is specifically designed to influence inbound traffic by suggesting preferred entry points to neighboring autonomous systems. Lower MED values are more desirable, signaling to external ASes which exit path into your network is preferred. MED provides controlled inbound traffic distribution, enabling multi-homed networks to manage incoming traffic efficiently, balance load across multiple links, and avoid congestion. MED is a non-binding attribute, meaning that while most neighbors honor it, they are not required to. It allows network engineers to shape inbound traffic flows without affecting internal routing decisions or outbound traffic. MED is particularly useful when multiple interconnections exist between ASes, allowing precise control over which links external traffic uses. This makes MED the correct answer.

D) AS Path is a cumulative list of autonomous systems traversed by a route. AS path prepending can indirectly influence inbound traffic by making a path appear longer, discouraging use, but it is less precise and less reliable than MED. AS Path is a passive method and cannot provide guaranteed inbound traffic control.

MED is correct because it directly influences how external ASes enter your network. Weight controls local outbound traffic, Local Preference affects AS-wide outbound traffic, and AS Path is an indirect inbound influence.

Question 194:

Which HSRP state monitors the active router and is ready to assume forwarding if failure occurs?

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

Answer: B) Standby

Explanation

A) Active is the router currently responsible for forwarding traffic for the HSRP virtual IP. While it maintains connectivity and responds to ARP requests, it does not monitor other routers or serve as a backup for failover purposes.

B) Standby monitors hello messages from the active router and is prepared to take over immediately if the active router fails. Standby routers maintain all necessary state information, ensuring seamless failover with minimal disruption. They do not forward traffic during normal operation but provide redundancy, high availability, and fault tolerance. The standby router is crucial in enterprise environments, where uninterrupted gateway access is required for mission-critical applications. By continuously monitoring the active router, the standby router ensures rapid failover, often in milliseconds, which prevents service interruption and maintains network reliability. This makes standby the correct answer.

C) Listen is a preparatory state where the router is aware of the HSRP group but does not actively monitor or forward traffic.

D) Init is the initial state where the router has not yet received hello messages and cannot participate in forwarding or failover.

Standby is correct because it monitors the active router and can immediately assume forwarding duties. Active forwards traffic, Listen is passive, and Init is preliminary.

Question 195:

 Which MPLS feature enables multiple VPNs to securely share 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) allows multiple independent routing and forwarding instances to coexist on a single physical router. Each VRF maintains separate routing tables, interfaces, and forwarding domains. In MPLS networks, VRFs enable multiple VPNs to share the same physical infrastructure while remaining fully isolated. VRFs also support overlapping IP address spaces across different VPNs, which is critical for multi-tenant deployments. By maintaining independent routing and forwarding, VRFs prevent traffic leakage, ensure security, and provide predictable performance. They are widely used in enterprise and service provider networks to allow multiple customers or departments to coexist on shared hardware without compromising privacy or network integrity. VRFs also simplify network management by enabling centralized configuration of routing instances, while maintaining strict separation between VPNs.

B) LDP (Label Distribution Protocol) distributes labels to create label-switched paths in MPLS networks. While essential for MPLS operation, LDP does not provide logical separation between VPNs.

C) RSVP-TE (Resource Reservation Protocol – Traffic Engineering) establishes explicit LSPs with bandwidth reservation. RSVP-TE enhances network efficiency and reliability but does not enforce isolation between VPNs.

D) QoS (Quality of Service) prioritizes traffic and manages bandwidth for critical applications. QoS ensures predictable performance but does not segregate traffic between VPNs.

VRF is correct because it provides secure, isolated operation of multiple VPNs on shared infrastructure. LDP, RSVP-TE, and QoS enhance MPLS functionality and performance but do not enforce traffic separation.

Question 196:

Which EIGRP metric component ensures selection of paths with the most stable link history?

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

Answer: C) Reliability

Explanation:

A) Bandwidth measures the slowest link along a path and determines the maximum traffic capacity. While it is critical for throughput calculations, bandwidth does not account for the historical stability of a link. A link may have high bandwidth but experience frequent errors or flapping, which could disrupt traffic. Therefore, relying solely on bandwidth does not guarantee selection of stable paths.

B) Delay measures the cumulative time for packets to traverse a path. It is important for latency-sensitive applications, such as VoIP or video conferencing, but does not reflect long-term link stability. A path with minimal delay could still experience frequent outages, making delay insufficient for selecting stable paths.

C) Reliability quantifies the historical stability and error rate of a link. EIGRP tracks errors, uptime, and overall performance over time, assigning a value on a scale from 0 to 255. A higher reliability value indicates a stable, error-free link. When multiple paths exist, EIGRP prefers routes that are not only high-performance but also dependable. Reliability ensures that frequently failing or error-prone links are avoided, maintaining consistent connectivity. For enterprise networks with critical applications, reliability is essential in path selection because it prevents interruptions due to unstable interfaces. By considering reliability alongside bandwidth and delay, EIGRP can select paths that balance performance, latency, and stability. This makes reliability the correct answer.

D) Load measures the current utilization of a link. While excessive load can temporarily affect performance, it is a dynamic metric that fluctuates with traffic conditions. Load does not represent historical stability and cannot ensure that a path is consistently reliable.

Reliability is correct because it reflects historical stability and error rates. Bandwidth measures capacity, delay measures latency, and load measures current usage but not long-term stability.

Question 197:

 Which OSPF LSA type summarizes routes between areas?

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

Answer: C) Type 3

Explanation:

A) Type 1 LSAs, also called router LSAs, describe a router’s interfaces and directly connected networks within an area. They provide intra-area topology information but do not summarize routes between areas. Type 1 LSAs are generated by every router in an area to allow all routers to maintain a consistent view of the local topology. They are crucial for intra-area routing but cannot carry information about networks in other areas.

B) Type 2 LSAs describe multi-access links, such as broadcast or NBMA networks, and are generated by the Designated Router (DR). Type 2 LSAs list all routers connected to a multi-access segment, providing detailed intra-area topology information. However, they do not summarize inter-area routes.

C) Type 3 LSAs, or summary LSAs, are generated by Area Border Routers (ABRs) to advertise routes from one OSPF area into another. Type 3 LSAs consolidate multiple internal routes into a single summary, reducing routing table size and minimizing SPF computation. For example, an ABR connecting Area 1 to the backbone Area 0 can summarize all Area 1 networks into a single Type 3 LSA for advertisement to other areas. Type 3 LSAs improve OSPF scalability, reduce CPU and memory usage, and allow network administrators to control route advertisement using summarization techniques. This makes Type 3 the correct answer.

D) Type 5 LSAs carry external routes redistributed into OSPF from other protocols. They are used to propagate external destinations across the OSPF domain but do not summarize intra-area routes between areas.

Type 3 is correct because it summarizes routes between areas. Type 1 and Type 2 provide intra-area information, and Type 5 carries external routes.

Question 198:

Which BGP attribute is primarily used to influence inbound traffic from external autonomous systems?

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

Answer: C) MED

Explanation:

A) Weight is a Cisco-specific attribute that controls outbound path selection locally on a router. It does not influence how neighboring autonomous systems select paths into your AS, so it cannot manage inbound traffic.

B) Local Preference is propagated throughout an AS and influences outbound path selection. It does not affect how external ASes route traffic toward your network, making it irrelevant for inbound traffic engineering.

C) MED (Multi-Exit Discriminator) is specifically designed to influence inbound traffic from neighboring autonomous systems. By advertising different MED values on multiple interconnections, an AS can indicate its preferred entry points to external ASes. Lower MED values are more desirable, while higher values are less preferred. MED allows controlled inbound traffic distribution, ensuring efficient load balancing, congestion management, and predictable entry points. It is particularly useful in multi-homed networks where traffic engineering is critical. Although MED is non-binding, meaning neighbors are not required to honor it, most networks respect MED values for traffic optimization. MED provides a precise and reliable mechanism for shaping inbound traffic flows, unlike AS Path prepending, which is indirect. This makes MED the correct answer.

D) AS Path lists the autonomous systems a route traverses. AS path prepending can influence inbound traffic by making a route appear longer, discouraging use, but it is less precise and less reliable than MED.

MED is correct because it directly influences how external ASes select entry points into your network. Weight affects local outbound traffic, Local Preference is AS-wide outbound, and AS Path prepending is indirect.

Question 199:

Which HSRP state monitors the active router and is prepared to assume forwarding if the active fails?

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

Answer: B) Standby

Explanation

A) Active is the router currently responsible for forwarding traffic for the HSRP virtual IP. It maintains connectivity and responds to ARP requests but does not monitor other routers for failover.

B) Standby monitors hello messages from the active router and is ready to take over immediately if the active router fails. Standby routers maintain all state information required for seamless failover, ensuring minimal disruption. They do not forward traffic during normal operation but provide redundancy, high availability, and fault tolerance. Standby routers are essential in enterprise networks where uninterrupted gateway access is required for critical applications. By continuously monitoring the active router, standby routers can transition to active within milliseconds to seconds, maintaining service continuity and network reliability. This makes standby the correct answer.

C) Listen is a transitional state where the router is aware of the HSRP group but does not actively monitor or forward traffic.

D) Init is the initial state during startup, where the router has not received hello messages and cannot participate in forwarding or failover.

Standby is correct because it monitors the active router and can immediately assume forwarding duties. Active forwards traffic, Listen is passive, and Init is preliminary.

Question 200

Which MPLS feature enables multiple VPNs to coexist securely on shared infrastructure while maintaining full 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 independent routing and forwarding instances to exist on a single physical router or switch. Each VRF maintains its own routing table, interfaces, and forwarding domain, effectively creating a distinct logical router within the physical device. This separation ensures that traffic from one VPN cannot traverse into another VPN, even when multiple VPNs share the same underlying infrastructure. VRFs are essential for multi-tenant environments, whether in enterprise networks with multiple departments or in service provider networks serving multiple customers.

The primary function of VRF is to provide full traffic isolation between VPNs. When a packet is received, the router consults the routing table associated with the VRF to determine the appropriate forwarding path. This prevents traffic from leaking between VPNs, protecting sensitive data, maintaining compliance, and enforcing organizational security policies. Each VRF instance operates independently, allowing overlapping IP address spaces for different VPNs. This capability is critical for scenarios where multiple tenants or customers use private IP ranges that would otherwise conflict. For example, two separate departments or customers might each use the 10.0.0.0/24 network. VRFs allow both networks to coexist without conflict by associating each with a separate routing table.

In MPLS networks, VRFs integrate closely with MPLS labels to enforce isolation. Each packet is tagged with a label corresponding to the VRF, ensuring that intermediate routers forward it according to the correct VRF table. This mechanism guarantees that even when multiple VPNs traverse the same physical links, their traffic remains logically separated. VRFs combined with MP-BGP (Multiprotocol BGP) allow secure propagation of routing information for each VPN across the provider network while maintaining strict separation. MP-BGP carries VPN-specific routes, ensuring that only the intended VRF can access them, which prevents accidental or malicious cross-VPN routing.

VRFs also enable centralized policy enforcement and security controls. Each VRF can have distinct access control lists (ACLs), routing policies, firewall rules, and Quality of Service (QoS) parameters. This allows administrators to customize security and performance settings per VPN without impacting other tenants or business units. By managing policies on a per-VRF basis, network operators can ensure compliance with internal standards, regulatory requirements, and service-level agreements (SLAs).

Scalability is another significant advantage of VRFs. Enterprises and service providers can host hundreds or thousands of VPNs on the same physical infrastructure, maximizing hardware utilization and minimizing operational costs. VRFs allow the addition of new VPNs without the need for dedicated routers, simplifying network expansion and reducing complexity. This makes VRFs a cost-effective solution for organizations requiring secure, segmented networks at scale.

B) LDP (Label Distribution Protocol) is used to distribute MPLS labels for creating label-switched paths (LSPs) across the network. LDP ensures that routers know which labels to use for forwarding packets efficiently along MPLS paths. While LDP is essential for MPLS operations and enables high-speed forwarding, it does not create independent routing tables or provide traffic isolation between VPNs. LDP alone cannot prevent data from one VPN from reaching another, which makes it insufficient for multi-tenant security.

C) RSVP-TE (Resource Reservation Protocol – Traffic Engineering) is a protocol that establishes explicit label-switched paths with reserved bandwidth for predictable network performance. RSVP-TE allows traffic to take optimized paths, avoiding congestion and ensuring performance guarantees for critical applications. While RSVP-TE enhances network reliability and efficiency, it does not isolate traffic between VPNs. RSVP-TE focuses on performance optimization and traffic engineering rather than creating separate routing domains for multiple tenants or customers.

D) QoS (Quality of Service) prioritizes traffic, manages bandwidth allocation, and ensures that critical applications receive appropriate network resources. QoS is vital for maintaining application performance and avoiding congestion in high-traffic networks. However, QoS does not segregate VPN traffic or enforce security boundaries between multiple tenants. While QoS can enhance the performance of traffic within a VPN, it cannot prevent one VPN from interfering with another or provide the logical isolation needed in multi-tenant networks.

 VRF is the correct answer because it allows secure, isolated operation of multiple VPNs on shared infrastructure. Each VRF instance maintains independent routing tables, interfaces, and forwarding domains, ensuring that traffic from one VPN cannot reach another. VRFs enable overlapping IP addresses, centralized policy enforcement, and scalable multi-tenant network deployment. They are widely deployed in enterprise WANs, data centers, and service provider networks where multiple customers or business units share physical infrastructure but require strict traffic separation.

LDP, RSVP-TE, and QoS enhance MPLS forwarding, performance, and traffic engineering but do not enforce logical separation between VPNs. LDP provides label distribution for efficient MPLS forwarding, RSVP-TE ensures optimized paths with bandwidth reservation, and QoS guarantees performance and prioritization. None of these features replace VRF when secure multi-tenant separation is required.

VRFs also provide operational benefits, including fault isolation. If a routing or configuration issue occurs in one VRF, it does not impact other VRFs on the same device. This containment reduces troubleshooting complexity, increases resilience, and ensures that services in one VPN remain unaffected by failures in another. Furthermore, VRFs support incremental deployment, allowing organizations to gradually add new VPNs without disrupting existing services.

In large-scale networks, VRFs are essential for service providers offering MPLS VPN services, enabling multiple clients to share the same backbone while maintaining full isolation. Enterprises also use VRFs internally to separate departments, projects, or applications, providing enhanced security, compliance, and operational control. By combining VRFs with MPLS labels and MP-BGP route distribution, networks can achieve secure, scalable, and highly efficient multi-VPN deployments on shared infrastructure, ensuring that traffic is fully isolated, predictable, and manageable.