Cisco 300-410  Implementing Cisco Enterprise Advanced Routing and Services (ENARSI) Exam  Dumps and Practice Test Questions Set 8 Q141-160

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Question 141:

Which EIGRP metric component determines the minimum capacity along a path to a destination?

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

Answer: A) Bandwidth

Explanation:

A) Bandwidth is the metric component in EIGRP that represents the minimum capacity along the path to a destination. EIGRP evaluates all links along a route and identifies the slowest link as the limiting factor. This ensures that the route selected is capable of handling the required traffic throughput. The minimum bandwidth along a path directly influences EIGRP’s composite metric calculation, which combines bandwidth and delay (along with optional load and reliability) to determine the overall route metric. Selecting a path based on minimum bandwidth ensures that traffic does not exceed the capacity of the bottleneck link, preventing congestion and packet loss. Bandwidth is expressed in kilobits per second, and EIGRP converts it into a metric value using the formula 10^7/minimum bandwidth. By prioritizing paths with higher minimum bandwidth, EIGRP ensures optimal network performance, particularly in enterprise networks where link capacities may vary. Bandwidth also impacts the selection of successors in the topology table, as paths with higher capacity are generally preferred. This makes bandwidth the correct answer because it directly reflects the limiting capacity along a route.

B) Delay measures the cumulative time required for a packet to traverse a path. While delay is important for latency-sensitive traffic and is included in EIGRP’s metric formula, it does not represent the maximum throughput a path can support. Delay is dynamic and affected by link speed, propagation time, and congestion, but it cannot identify the slowest link in terms of capacity.

C) Reliability measures historical stability of a link, tracking errors and link failures. While reliability ensures that unstable links are avoided, it does not quantify path capacity or influence throughput calculations. A highly reliable link may still have low bandwidth, making it unsuitable as a measure of capacity.

D) Load represents the current utilization of a link. While high load may indicate congestion and potential delay, load does not provide a static assessment of the maximum throughput a path can support. Load is dynamic and fluctuates with traffic patterns, making it unsuitable for determining minimum path capacity.

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

Question 142:

Which OSPF area type allows injection of external routes 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 LSAs to reduce routing table size and SPF computation, but they do not allow external routes to be redistributed into the area. Only inter-area Type 3 LSAs are allowed for connectivity, making stub areas unsuitable for scenarios where redistribution of external routes is required.

B) Totally Stubby Areas block both Type 3 and Type 5 LSAs, leaving only a default route for external connectivity. They cannot support external route redistribution, which limits functionality in areas that require localized external connectivity.

C) NSSA (Not-So-Stubby Area) provides a balance between stub and standard areas. NSSAs allow external routes to be redistributed using Type 7 LSAs, while blocking Type 5 LSAs from flooding the area. This ensures that external routes can enter the area without overloading the OSPF domain with external LSAs. The ABR translates Type 7 LSAs into Type 5 LSAs if wider propagation is needed. NSSAs are ideal for branch or edge areas where external connectivity is required without propagating external routes throughout the entire OSPF domain. They maintain hierarchical OSPF design, reduce SPF computation overhead, and provide controlled redistribution of external routes. This makes NSSA the correct answer.

D) Backbone Area (Area 0) allows propagation of all LSA types, including external routes via Type 5 LSAs. While it supports redistribution, it does not block Type 5 LSAs, so it cannot provide the controlled behavior of an NSSA.

NSSA is correct because it allows external route injection while restricting Type 5 LSAs. Stub and totally stubby areas do not permit external route injection, and the backbone area propagates all LSAs.

Question 143:

Which BGP attribute influences how traffic enters your autonomous system from neighbors?

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 locally on a router. It does not propagate to other routers and has no effect on how external ASes send traffic into your AS.

B) Local Preference is used to influence outbound path selection across all routers in an AS. While important for consistent path selection internally, it does not affect inbound traffic from external autonomous systems.

C) MED (Multi-Exit Discriminator) is the BGP attribute designed to influence inbound traffic from neighboring ASes. By advertising different MED values on multiple exit points, a network can indicate preferred paths into its AS. Lower MED values are considered more desirable by neighboring ASes. MED is a suggestion rather than a strict enforcement, but it is widely respected for multi-homed networks where precise control of incoming traffic distribution is required. It allows optimization of bandwidth, reduces congestion on certain links, and ensures predictable traffic flow into the AS. MED is particularly useful when an AS has multiple connections to another AS and wants to influence which entry point is used by external traffic. This makes MED the correct answer.

D) AS Path records the autonomous systems a route has traversed. While AS path prepending can influence inbound traffic indirectly by making a path appear longer, it is not precise and does not provide the controlled influence that MED offers.

MED is correct because it directly suggests preferred entry points for inbound traffic. Weight is local-only, local preference affects outbound traffic, and AS Path influences inbound traffic indirectly.

Question 144:

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 is the state in which a router forwards traffic for the HSRP virtual IP. The active router responds to ARP requests and handles data forwarding for hosts. It maintains hello messages to allow standby routers to monitor its status. Active is essential for maintaining uninterrupted gateway functionality, ensuring that hosts can access external networks without disruption.

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

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

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

Active is correct because it is the router currently responsible for forwarding traffic. Standby monitors the active router, listen is passive, and init is preliminary.

Question 145:

Which MPLS feature allows multiple VPNs to coexist on the same infrastructure while maintaining 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 exist on a single physical router. Each VRF maintains separate interfaces, routing tables, and forwarding paths. Combined with MPLS, VRFs provide complete traffic isolation between VPNs, even if they share the same physical links. VRFs also allow overlapping IP address spaces for different VPNs, enabling multi-tenant environments. This separation ensures that traffic from one VPN cannot reach another, maintaining security, scalability, and efficient use of resources. VRFs are fundamental in enterprise and service provider networks where multiple tenants or business units share physical infrastructure but require complete logical separation.

B) LDP (Label Distribution Protocol) distributes MPLS labels for forwarding along Label-Switched Paths. LDP enables MPLS functionality but does not provide VPN isolation or separate routing tables.

C) RSVP-TE establishes explicit LSPs with bandwidth reservation for traffic engineering. While useful for path optimization and predictable performance, it does not separate VPN traffic.

D) QoS (Quality of Service) prioritizes traffic, manages bandwidth allocation, and ensures service levels. QoS ensures performance but does not isolate traffic between VPNs.

VRF is correct because it allows multiple VPNs to share the same infrastructure securely. LDP, RSVP-TE, and QoS enhance MPLS operation but do not provide traffic separation.

Question 146:

 Which EIGRP metric component represents the cumulative time a packet takes to traverse a path?

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

Answer: B) Delay

Explanation:

A) Bandwidth measures the minimum capacity along a path. While it determines the maximum throughput achievable on a route, it does not reflect the actual time required for a packet to traverse the path. Bandwidth prioritizes paths capable of higher traffic throughput but ignores propagation, queuing, and processing delays. In EIGRP’s composite metric, bandwidth contributes to the overall metric calculation but is not an indicator of traversal time.

B) Delay represents the cumulative time for a packet to travel along a path, accounting for propagation delay, transmission delay, queuing delay, and processing time on each interface. EIGRP calculates delay in tens of microseconds per interface and sums the values for all interfaces along the path. This metric is crucial for latency-sensitive applications like VoIP or video conferencing, where minimizing traversal time is important. Delay is dynamic and can fluctuate depending on network congestion, interface speed, and topology changes. By including delay in its composite metric calculation, EIGRP can select the path that minimizes end-to-end latency, ensuring optimal network performance. Delay also works with bandwidth in the EIGRP metric formula to balance throughput and latency considerations. This makes delay the correct answer because it directly quantifies the time packets require to traverse a network path.

C) Reliability measures link stability and error rates. While highly reliable links reduce packet loss and retransmissions, reliability does not quantify traversal time. A highly reliable link may still introduce significant delay, so reliability alone cannot represent the total time a packet takes to travel along a route.

D) Load reflects the current utilization of a link. High load can contribute to queuing delays, but load is a transient, dynamic metric that fluctuates with traffic patterns. It does not provide a static measurement of traversal time, nor is it directly used to calculate EIGRP’s primary composite metric for path selection.

Delay is correct because it reflects the cumulative traversal time. Bandwidth affects throughput, reliability affects stability, and load reflects utilization but does not directly quantify the time taken for packets to reach their destination.

Question 147:

Which OSPF area type blocks Type 5 LSAs but allows external route injection?

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

Answer: C) NSSA

Explanation:

A) Stub areas block Type 5 LSAs, reducing routing table size and SPF computation, but do not allow the injection of external routes. Only inter-area routes via Type 3 LSAs are permitted, making stub areas unsuitable when external redistribution is needed.

B) Totally Stubby Areas block both Type 3 and Type 5 LSAs, leaving only a default route for external connectivity. They cannot accommodate redistributed external routes, so they are limited in scenarios requiring external connectivity beyond a default path.

C) NSSA (Not-So-Stubby Area) allows external route injection using Type 7 LSAs while blocking Type 5 LSAs from flooding the area. The ABR can translate Type 7 LSAs into Type 5 LSAs for propagation outside the NSSA. This allows branch or edge areas to redistribute external routes into the OSPF domain without propagating them unnecessarily throughout all areas. NSSA maintains hierarchical OSPF design, limits SPF computation overhead, and ensures scalability. It is particularly useful for enterprise edge networks or remote branches that need to inject external routes into OSPF while maintaining control over LSA propagation. This makes NSSA the correct answer.

D) Backbone Area (Area 0) allows all LSA types, including Type 5, and does not block external LSAs. While it supports redistribution, it cannot restrict Type 5 flooding as an NSSA does.

NSSA is correct because it allows localized redistribution of external routes while blocking Type 5 LSAs. Stub and totally stubby areas restrict external redistribution, and the backbone propagates all LSAs.

Question 148:

Which BGP attribute influences inbound traffic from neighboring autonomous systems?

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

Answer: C) MED

Explanation:

A) Weight is a local-only attribute that affects path selection on a single router. It does not influence how neighboring autonomous systems send traffic into your AS and is irrelevant for inbound traffic engineering.

B) Local Preference controls outbound path selection within your AS. It is propagated to all routers in the AS but does not influence how external ASes choose entry points.

C) MED (Multi-Exit Discriminator) is the BGP attribute used to influence inbound traffic from neighbors. By advertising different MED values across multiple exit points, an AS can suggest to external ASes which entry point is preferable. Lower MED values are considered more desirable, while higher values indicate less preferred paths. Although MED is a suggestion rather than an enforcement, neighboring ASes typically respect it. MED is particularly useful for multi-homed networks, where optimizing inbound traffic distribution reduces congestion, balances link utilization, and ensures predictable performance. This precise influence on inbound routing makes MED the correct answer.

D) AS Path records the sequence of ASes a route has traversed. AS path prepending can influence inbound traffic indirectly by making certain paths appear longer, but it is less precise and lacks the direct control provided by MED.

MED is correct because it directly affects how traffic enters your AS. Weight is local-only, local preference affects outbound paths, and AS Path only indirectly affects inbound routing.

Question 149:

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

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

Answer: A) Active

Explanation:

A) Active is the state in which a router forwards traffic for the HSRP virtual IP. The active router handles ARP requests, maintains the virtual IP, and ensures connectivity for hosts in the subnet. It sends hello messages to allow standby routers to monitor its status. Active is essential for uninterrupted gateway functionality, providing continuous access to external networks. This makes active the correct answer because it represents the router currently performing forwarding duties.

B) Standby monitors the active router and is ready to take over if the active router fails. 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 yet received hello messages and cannot forward traffic or participate in failover.

Active is correct because it is the router currently responsible for forwarding traffic. Standby monitors, listen is passive, and init is preliminary.

Question 150:

Which MPLS feature allows multiple VPNs to share the same 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 logical routing and forwarding instances to exist on a single physical router. Each VRF maintains separate interfaces, routing tables, and forwarding paths. When combined with MPLS, VRFs ensure complete traffic isolation between VPNs even if they share the same physical links. They also support overlapping IP address spaces for different VPNs, enabling secure multi-tenant environments. By maintaining independent routing tables and forwarding paths, VRFs prevent traffic from one VPN reaching another, ensuring privacy, security, and scalability. VRFs are widely used in service provider and enterprise networks to support multiple customers or departments on the same infrastructure. This makes VRF the correct answer.

B) LDP (Label Distribution Protocol) distributes MPLS labels for packet forwarding along label-switched paths. While LDP enables MPLS operation, it does not provide traffic isolation between VPNs.

C) RSVP-TE establishes explicit label-switched paths with bandwidth reservation for traffic engineering purposes. While RSVP-TE optimizes path selection and performance, it 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 provide traffic separation between VPNs.

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

Question 151:

Which EIGRP metric component reflects historical link stability and error rate?

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

Answer: C) Reliability

Explanation:

A) Bandwidth measures the minimum capacity along a path, determining the maximum traffic throughput. While important for selecting high-capacity routes, it does not reflect the stability or error history of a link. Bandwidth ensures traffic can traverse without being bottlenecked but does not guarantee the reliability of that path over time.

B) Delay represents the cumulative time for a packet to traverse a path, including propagation, queuing, and processing delays. Delay is critical for latency-sensitive traffic but does not provide historical information about link stability or error rates. High-speed links may have low delay yet be unreliable due to frequent errors or flapping interfaces.

C) Reliability tracks the historical performance of a link based on error counts and uptime. EIGRP measures reliability as a value between 0 and 255, with higher values indicating more reliable links. Reliability is used to influence routing decisions, ensuring that routes selected have a history of stable operation. Links with low reliability are less preferred because they may experience packet loss, flapping, or failures. Reliability is particularly important in enterprise networks where uptime and consistent performance are critical. By considering reliability in the composite EIGRP metric, the protocol avoids unstable paths even if they have high bandwidth or low delay. Reliability provides network engineers with a way to prioritize consistent links over less predictable ones. This makes reliability the correct answer.

D) Load represents current link utilization. While high load may indicate potential congestion, it does not reflect the historical stability of a link. Load is dynamic and fluctuates with traffic patterns, making it unsuitable for evaluating the long-term reliability of a route.

Reliability is correct because it reflects historical link stability and error rates, which are critical for choosing stable and dependable paths. Bandwidth measures capacity, delay measures traversal time, and load measures current utilization, but none indicate historical performance or stability.

Question 152:

Which OSPF LSA type is used to summarize inter-area routes?

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 a single OSPF area. They provide intra-area topology information and list connected networks and link states. Type 1 LSAs are not designed for inter-area summarization and do not carry external or summarized routing information.

B) Type 2 LSAs describe network links for broadcast and non-broadcast multi-access networks, generated by the Designated Router (DR). They are specific to the area’s network topology and are not used for summarizing inter-area routes.

C) Type 3 LSAs are summary LSAs generated by Area Border Routers (ABRs) to advertise routes from one area to another. They summarize multiple internal routes within an area into a single advertisement, reducing the size of routing tables and minimizing SPF computation in other areas. Type 3 LSAs ensure efficient inter-area routing by conveying aggregated routing information without flooding the backbone with individual intra-area routes. For example, an ABR connecting Area 1 and Area 0 would generate Type 3 LSAs summarizing Area 1 networks for other areas. This reduces the complexity of the OSPF domain and improves scalability. Type 3 LSAs are the correct answer because their primary function is to summarize internal routes for inter-area propagation.

D) Type 5 LSAs carry external routes redistributed into OSPF from other protocols. They are not used for summarizing inter-area OSPF routes, and they propagate external routes throughout standard OSPF areas.

Type 3 is correct because it summarizes inter-area routes. Type 1 and Type 2 are intra-area LSAs, and Type 5 carries external routes.

Question 153:

Which BGP attribute is primarily used to control outbound traffic on a router?

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

Answer: A) Weight

Explanation:

A) Weight is a Cisco-proprietary BGP attribute that determines outbound path selection on a single router. It is the first criterion in the BGP best path selection process and does not propagate to other routers. Assigning a higher weight to a route ensures the local router prefers that path for outbound traffic, regardless of other attributes. This allows fine-grained traffic engineering on multi-homed routers, controlling which exit point is used for outgoing traffic. Weight is particularly useful in scenarios where different exit links have varying capacities, costs, or performance characteristics. It guarantees deterministic outbound traffic behavior at the router level without affecting the rest of the AS.

B) Local Preference is used to influence outbound path selection across all routers in an AS. It is propagated throughout the AS, so changes affect all routers and cannot provide router-specific control.

C) MED (Multi-Exit Discriminator) influences inbound traffic by suggesting preferred entry points to neighboring ASes. MED does not affect outbound traffic.

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

Weight is correct because it provides precise control over outbound traffic at the local router level. Local Preference is AS-wide, MED affects inbound traffic, and AS Path influences inbound paths indirectly.

Question 154:

 Which HSRP state monitors hello messages and is ready to take over forwarding?

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. Active routers respond to ARP requests and maintain the virtual IP. They are not in a monitoring or backup state.

B) Standby is the router that monitors hello messages from the active router and is prepared to assume traffic forwarding if the active router fails. Standby routers maintain state information, ensuring seamless failover with minimal disruption. They do not forward traffic during normal operation but are fully ready to take over immediately, providing high availability and fault tolerance. Standby is critical for enterprise networks where uninterrupted access to the gateway is essential. By maintaining a heartbeat with the active router, standby routers can detect failures quickly and transition to active state within milliseconds to seconds, depending on configuration. This makes standby the correct answer.

C) Listen is a preparatory state where the router receives hello messages but is not actively participating in forwarding or monitoring.

D) Init is the startup state 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 155:

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

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

Answer: A) VRF

Explanation:

A) VRF (Virtual Routing and Forwarding) allows multiple logical routing instances to exist on a single router. Each VRF maintains its own interfaces, routing table, and forwarding domain. In MPLS environments, VRFs provide complete traffic separation for multiple VPNs, even on shared physical infrastructure. VRFs also allow overlapping IP address spaces across VPNs, enabling multi-tenant networks. By maintaining independent forwarding paths and routing tables, VRFs prevent traffic leakage and ensure security, scalability, and efficient utilization of physical resources. VRFs are essential in enterprise and service provider networks supporting multiple customers or business units on the same hardware. This makes VRF the correct answer.

B) LDP distributes labels in MPLS networks to enable packet forwarding along label-switched paths. LDP is critical for MPLS operation but does not enforce VPN separation.

C) RSVP-TE establishes explicit LSPs with bandwidth reservations for traffic engineering. While it optimizes path selection and reliability, RSVP-TE does not separate VPN traffic.

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

VRF is correct because it allows multiple VPNs to coexist securely on shared infrastructure. LDP, RSVP-TE, and QoS enhance MPLS operation but do not enforce VPN separation.

Question 156:

Which EIGRP metric component determines the slowest link along a path?

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

Answer: A) Bandwidth

Explanation:

A) Bandwidth is the component in EIGRP metrics that represents the minimum capacity along a route. EIGRP evaluates all links along the path and identifies the slowest link as the limiting factor for throughput. This ensures that the selected path can handle the required traffic load without congestion at the bottleneck interface. Bandwidth is expressed in kilobits per second and converted into a metric value using the formula 10^7/minimum bandwidth. The slowest link along the path defines the maximum achievable throughput, and EIGRP uses this value to compare multiple paths. Bandwidth is a static metric based on interface speed and is combined with delay in the composite EIGRP metric to select optimal paths. By focusing on the slowest link, EIGRP avoids selecting paths that may fail under heavy traffic, ensuring stability and efficiency. This makes bandwidth the correct answer.

B) Delay measures the total traversal time for a packet along a path. While important for latency-sensitive applications, delay does not determine the maximum throughput or the limiting link capacity. A path with low delay could still have a slow interface, resulting in a bottleneck.

C) Reliability indicates link stability based on historical error counts and uptime. Although important for avoiding unstable links, reliability does not identify the slowest link in terms of throughput. A highly reliable link may still have limited bandwidth.

D) Load represents current utilization of a link. Load is dynamic and fluctuates with traffic, so it does not provide a static measure of the slowest link along a path.

Bandwidth is correct because it identifies the slowest link and dictates maximum throughput. Delay measures latency, reliability measures stability, and load measures utilization but not the limiting capacity.

Question 157:

Which OSPF LSA type carries 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 describe a router’s links within an area. They provide intra-area topology information and do not carry external routes.

B) Type 3 LSAs are summary LSAs used by ABRs to advertise inter-area routes. They summarize internal routes between areas but do not carry external routes redistributed from other protocols.

C) Type 5 LSAs carry external routes redistributed into OSPF from other routing protocols such as BGP or EIGRP. Type 5 LSAs are flooded throughout standard OSPF areas but are blocked from entering stub or NSSA areas to reduce SPF computation overhead. Type 5 LSAs allow OSPF routers to reach destinations outside the OSPF autonomous system by propagating external network information. They include a metric for external cost, which can be E1 (internal plus external) or E2 (external only) type. Type 5 LSAs ensure that external connectivity is known throughout the OSPF domain while maintaining area hierarchy. This makes Type 5 the correct answer.

D) Type 7 LSAs carry external routes into NSSAs. They are translated into Type 5 LSAs by the ABR if the routes need to propagate outside the NSSA. Type 7 is specific to NSSAs and does not apply to standard OSPF areas.

Type 5 is correct because it distributes external routes throughout standard areas. Type 1 is intra-area, Type 3 summarizes inter-area routes, and Type 7 is used only for NSSAs.

Question 158:

 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 on a local router. It does not influence how traffic enters an AS from neighbors and is irrelevant for inbound traffic engineering.

B) Local Preference affects outbound routing decisions across all routers within an AS. It is propagated to all routers in the AS but does not impact how external ASes choose entry points.

C) MED (Multi-Exit Discriminator) is designed to influence inbound traffic. By advertising different MED values for multiple exit points to a neighboring AS, a network can suggest the preferred entry path. Lower MED values are more desirable, and neighboring routers typically honor this preference. MED is particularly useful for multi-homed networks, providing predictable inbound traffic distribution and reducing congestion on specific links. Unlike AS Path prepending, MED allows precise control of which entry points are preferred by neighboring ASes. This attribute is a key tool for inbound traffic engineering and makes MED the correct answer.

D) AS Path records the autonomous systems a route traversed. AS path prepending can influence inbound traffic by making certain paths appear longer, but it is an indirect method and less precise than MED.

MED is correct because it directly influences inbound traffic. Weight is local-only, Local Preference affects outbound traffic, and AS Path prepending is an indirect method for influencing inbound routing.

Question 159:

Which HSRP state 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 handles ARP requests and traffic forwarding but is not in a monitoring or backup role.

B) Standby monitors hello messages from the active router and is ready to assume traffic forwarding immediately if the active router fails. Standby routers maintain state information to ensure seamless failover with minimal disruption. They do not forward traffic under normal operation but provide high availability by taking over without delay when the active router becomes unavailable. Standby is critical for maintaining uninterrupted gateway connectivity in enterprise networks. The standby router constantly monitors the active router’s status, allowing rapid failover in milliseconds to seconds depending on configuration. 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 is not actively participating in forwarding or monitoring.

D) Init is the initial startup state where the router has not yet received hello messages. Routers in init 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 160

 Which MPLS feature enables multiple VPNs to coexist on the same 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 fundamental MPLS feature that allows multiple independent routing and forwarding instances to coexist on a single physical router. Each VRF instance operates as a completely isolated routing domain, maintaining its own interfaces, routing table, forwarding information base (FIB), and associated network policies. This logical separation ensures that traffic from one VPN cannot traverse into another VPN, even when multiple VPNs share the same physical links. By creating independent routing and forwarding domains, VRFs enable secure, scalable, and multi-tenant network deployments on shared infrastructure.

In an MPLS network, VRFs are tightly integrated with MPLS labels. Each packet is tagged with an MPLS label that identifies the VRF to which it belongs. This ensures that packets are forwarded based on the correct VRF routing table, maintaining isolation between VPNs. Without VRFs, traffic from different VPNs could inadvertently mix, leading to potential security risks, data leakage, or misrouting. VRFs prevent these issues by keeping each VPN completely separate at the routing and forwarding layer.

A significant advantage of VRFs is their ability to support overlapping IP address spaces. In many enterprise or multi-tenant environments, different customers or departments may use the same private IP ranges. VRFs allow these identical subnets to exist concurrently without conflicts because each VRF maintains a separate routing table. For example, two customers may both use the 10.1.1.0/24 subnet. By associating each subnet with a distinct VRF, the network ensures complete isolation between customers, allowing simultaneous operation without IP conflicts. This capability is especially valuable in service provider environments, where multiple clients or tenants share the same physical infrastructure.

VRFs also facilitate centralized policy management and security enforcement. Each VRF can have its own set of access control lists (ACLs), firewall rules, and quality-of-service policies. This allows network administrators to enforce specific security, performance, and routing policies for each VPN independently. If a security incident occurs in one VRF, it does not affect other VRFs or the shared infrastructure. This level of isolation enhances both security and operational resilience, reducing the risk of cascading failures across multiple tenants or business units.

In addition, VRFs improve scalability and resource utilization. Organizations can deploy multiple VRFs on the same physical router or switch without requiring additional hardware for each tenant or department. This reduces operational costs, simplifies network design, and maximizes utilization of network resources. VRFs also enable multi-site VPN connectivity using BGP (Border Gateway Protocol) or MP-BGP (Multiprotocol BGP) for distributing routes between VRFs and core network routers. MP-BGP ensures secure and isolated route propagation while maintaining scalable VPN connectivity across geographically dispersed networks.

B) LDP (Label Distribution Protocol) is used to distribute MPLS labels to routers for forwarding along Label-Switched Paths (LSPs). LDP ensures that routers know how to forward packets using MPLS labels, enabling fast and efficient packet forwarding. While LDP is essential for MPLS operation, it does not create separate routing tables or provide traffic isolation between VPNs. LDP focuses on label distribution and packet forwarding along the MPLS network, not on separating multi-tenant traffic or maintaining VPN-specific policies.

C) RSVP-TE (Resource Reservation Protocol – Traffic Engineering) is used to establish explicit LSPs with bandwidth reservation for optimized path selection and guaranteed performance. RSVP-TE allows network administrators to engineer network paths to avoid congestion, optimize utilization, and provide predictable application performance. However, while RSVP-TE enhances network reliability and performance, it does not isolate traffic between different VPNs. RSVP-TE is primarily focused on traffic engineering, not on providing independent routing or forwarding domains for multiple VPNs.

D) QoS (Quality of Service) manages traffic prioritization, bandwidth allocation, and ensures performance for critical applications like voice, video, or real-time data streams. QoS is crucial for maintaining application performance and preventing congestion, especially in high-traffic networks. While QoS ensures predictable performance, it does not provide isolation between VPNs. Traffic from multiple VPNs may share the same QoS-enabled link, and QoS does not prevent one VPN’s traffic from impacting another’s routing or forwarding path.

 VRF is the correct answer because it provides complete logical separation of multiple VPNs on the same physical infrastructure. Each VRF instance maintains independent interfaces, routing tables, and forwarding domains, ensuring that traffic from one VPN cannot reach another. VRFs enable overlapping IP addresses, multi-tenant scalability, security policy enforcement, and centralized management.

LDP, RSVP-TE, and QoS enhance MPLS network performance, efficiency, and traffic engineering but do not enforce VPN separation or logical isolation. VRFs are essential for service providers hosting multiple clients, enterprises segmenting internal departments, and any environment requiring secure, multi-tenant routing on shared infrastructure. By combining VRFs with MPLS labels and BGP route distribution, networks can achieve secure, scalable, and operationally efficient multi-VPN deployment without additional physical hardware.

Proper VRF deployment allows organizations to maintain high availability, predictable routing, and isolated traffic domains while using shared network infrastructure. VRFs are widely used in large-scale enterprise WANs, data centers, and service provider networks to support hundreds or even thousands of logically separated VPNs. They are foundational for modern MPLS designs and critical for maintaining security, operational resilience, and compliance in multi-tenant networks.