Cisco 300-410  Implementing Cisco Enterprise Advanced Routing and Services (ENARSI) Exam  Dumps and Practice Test Questions Set 9 Q161-180

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Question 161:

 Which EIGRP metric component is used to measure the cumulative time for a packet to traverse a path?

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

Answer: B) Delay

Explanation:

A) Bandwidth measures the minimum link capacity along a path. It is essential in determining the maximum throughput achievable for a route but does not reflect the time required for a packet to traverse the path. Bandwidth is static, calculated based on the slowest link on the route, and affects the EIGRP metric but does not account for latency caused by propagation, queuing, or interface processing delays. While bandwidth ensures the route can handle traffic, it does not guarantee low traversal time.

B) Delay represents the total cumulative time a packet requires to traverse a network path. It is measured in tens of microseconds per interface in EIGRP and summed for all interfaces along the route. Delay accounts for propagation delay, transmission delay, queuing delay, and processing delay. It is a critical metric for latency-sensitive applications such as VoIP, video conferencing, and online collaboration tools. EIGRP uses delay in its composite metric calculation along with bandwidth to balance throughput and latency. Unlike reliability or load, which are dynamic and historical metrics, delay provides a deterministic measure of end-to-end traversal time. By selecting paths with lower cumulative delay, EIGRP ensures efficient and responsive network performance. This makes delay the correct answer.

C) Reliability indicates the historical stability of a link, tracking errors and uptime. While a highly reliable link is less likely to fail, reliability does not quantify traversal time or latency. A stable link could still introduce significant delay due to interface speeds or network congestion.

D) Load reflects the current utilization of a link. Load can affect delay indirectly through queuing, but it is a dynamic metric that fluctuates with traffic. Load does not provide a static measure of the cumulative time for packets to traverse a path.

Delay is correct because it directly measures the traversal time for packets. Bandwidth measures throughput, reliability measures stability, and load measures utilization, but none quantify total delay.

Question 162:

 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 to reduce SPF calculation overhead but do not allow external route injection. Only Type 3 LSAs summarizing inter-area routes are permitted. Stub areas cannot redistribute external routes and are not suitable for branch networks requiring external connectivity.

B) Totally Stubby Areas block both Type 3 and Type 5 LSAs, allowing only a default route for external connectivity. They provide minimal SPF processing but cannot accommodate external route injection, making them unsuitable for scenarios requiring redistributed routes.

C) NSSA (Not-So-Stubby Area) allows external routes to be injected into the OSPF domain using Type 7 LSAs. These LSAs are localized within the NSSA and are converted to Type 5 LSAs by the ABR if external propagation is required. NSSAs provide controlled redistribution of external routes while maintaining the benefits of stub areas, such as reduced SPF calculation and minimized LSA flooding. This makes NSSA ideal for branch or edge networks where external route redistribution is required without propagating Type 5 LSAs throughout the OSPF domain. NSSAs maintain hierarchical OSPF design and improve scalability. This makes NSSA the correct answer.

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

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

Question 163:

Which BGP attribute can be used to control outbound path selection on a specific router?

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

Answer: A) Weight

Explanation

A) Weight is a Cisco-proprietary attribute that influences outbound path selection locally on a router. It is evaluated first in the BGP best path selection process. Assigning a higher weight to a path ensures that the local router prefers that path for outbound traffic, regardless of other attributes such as local preference or AS path length. Weight does not propagate to other routers, making it ideal for router-specific traffic engineering. In multi-homed networks, weight allows precise control over which exit link is used for outbound traffic, ensuring predictable performance and effective load distribution. Weight provides deterministic path selection without affecting the broader AS.

B) Local Preference affects outbound path selection across all routers in the AS. It is propagated throughout the AS and cannot provide router-specific control.

C) MED (Multi-Exit Discriminator) is used to influence inbound traffic from external ASes. It does not affect outbound path selection on the local router.

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

Weight is correct because it allows precise outbound path control on a single router. Local Preference is AS-wide, MED affects inbound traffic, and AS Path only indirectly influences inbound routing.

Question 164:

 Which HSRP state monitors the active router and is ready to take over forwarding if needed?

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 ensures connectivity but does not serve a monitoring or backup role.

B) Standby monitors hello messages from the active router and is prepared to take over traffic forwarding 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 being ready to assume forwarding duties immediately. Standby ensures uninterrupted access to the gateway for hosts in the subnet, providing fault tolerance in enterprise networks. The standby router constantly monitors the active router, allowing rapid transition in milliseconds to seconds. This makes standby the correct answer.

C) Listen is a preparatory state in which the router receives hello messages but does not forward traffic or participate in failover.

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 165:

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) allows multiple independent routing and forwarding instances to exist on a single physical router. Each VRF maintains separate interfaces, routing tables, and forwarding paths. In MPLS environments, VRFs ensure complete traffic isolation between VPNs, even when sharing the same physical links. VRFs also allow overlapping IP address spaces for different VPNs, enabling multi-tenant networks. By maintaining separate routing tables and forwarding domains, VRFs prevent traffic from one VPN reaching another, ensuring security, scalability, and efficient use of resources. VRFs are widely used in enterprise and service provider networks to support multiple customers or departments on the same infrastructure. This makes VRF the correct answer.

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

C) RSVP-TE establishes explicit label-switched paths with bandwidth reservation for traffic engineering. While RSVP-TE optimizes path selection and reliability, it does not segregate VPN traffic.

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

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

Question 166:

 Which EIGRP metric component measures the historical stability and error rate of a link?

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

Answer: C) Reliability

Explanation:

A) Bandwidth represents the minimum capacity along a path. While it determines the maximum traffic throughput achievable on a route, it does not provide any information regarding the stability or historical performance of the link. Bandwidth ensures traffic can traverse a path without bottlenecking but cannot predict link flaps, errors, or packet loss, making it irrelevant for measuring link reliability.

B) Delay represents the cumulative time a packet takes to traverse a path, including propagation, queuing, and processing delays. Delay is essential for latency-sensitive applications but is unrelated to historical stability or error rates. A low-delay link could still be unreliable due to frequent errors or interface flaps.

C) Reliability measures the historical stability and error rate of a link. In EIGRP, reliability is represented as a value between 0 and 255, with higher values indicating a more stable and dependable link. EIGRP uses reliability in its composite metric to prefer paths that have a proven history of stability, avoiding links prone to packet loss or frequent failures. Reliability is critical in enterprise and service provider networks where uptime and consistent performance are essential. A link with high bandwidth and low delay may still be undesirable if its reliability is poor, highlighting the importance of this metric. By incorporating reliability into the metric calculation, EIGRP ensures that paths selected for traffic forwarding are both high-performing and dependable, reducing the likelihood of route flaps or network outages. This makes reliability the correct answer.

D) Load reflects the current utilization of a link. Load is a dynamic, real-time metric and fluctuates depending on traffic patterns. While high load may indicate potential congestion, it does not provide a historical measure of link stability. A highly utilized link could still be reliable over time, making load unsuitable for evaluating reliability.

Reliability is correct because it quantifies historical link stability and error rates, ensuring dependable path selection. Bandwidth measures capacity, delay measures traversal time, and load measures current utilization but does not reflect historical performance.

Question 167:

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

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

Answer: C) Type 3

Explanation:

A) Type 1 LSAs describe router links within an OSPF area. They provide intra-area topology information and list directly connected networks. Type 1 LSAs do not summarize routes for inter-area routing; they only provide local area link states.

B) Type 2 LSAs describe network links for broadcast and non-broadcast multi-access networks, generated by the Designated Router (DR). These LSAs provide intra-area network topology information but are not used for inter-area route summarization.

C) Type 3 LSAs are summary LSAs generated by Area Border Routers (ABRs) to advertise routes from one area to another. They allow an ABR to summarize multiple networks within its area into a single LSA, reducing routing table size and SPF computation overhead in other areas. For example, an ABR connecting Area 1 to Area 0 (backbone) would summarize Area 1’s networks into Type 3 LSAs for other areas. Type 3 LSAs ensure efficient inter-area routing, enabling hierarchical OSPF design and improved scalability. By providing aggregated routing information rather than individual network LSAs, Type 3 LSAs reduce flooding and SPF calculation time, making OSPF more efficient in large networks. This makes Type 3 the correct answer.

D) Type 5 LSAs carry external routes redistributed from other protocols into OSPF. They are not used for inter-area summarization but rather for propagating external routes across standard areas.

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

Question 168:

Which BGP attribute influences outbound traffic selection locally 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 influences path selection on the local router. It is evaluated first in the BGP best path selection process and does not propagate to other routers. A higher weight ensures that the local router prefers a particular path for outbound traffic, providing deterministic control in multi-homed environments. Weight allows administrators to control traffic distribution for specific routers without impacting the entire AS. It is ideal for optimizing performance and balancing traffic across multiple links.

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

C) MED (Multi-Exit Discriminator) influences inbound traffic by suggesting to neighboring ASes which entry point is preferred. It does not affect outbound traffic on the local router.

D) AS Path records the autonomous systems traversed by a route. AS path prepending can influence inbound traffic by making a path appear longer but does not control outbound traffic locally.

Weight is correct because it allows precise outbound path control on the local router. Local Preference is AS-wide, MED influences inbound traffic, and AS Path is indirect.

Question 169:

Which HSRP state monitors the active router and is ready to assume 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. It responds to ARP requests and ensures network connectivity but does not serve as a backup or monitoring node.

B) Standby monitors hello messages from the active router and is prepared to take over traffic forwarding immediately if the active router fails. Standby routers maintain all necessary state information to ensure seamless failover with minimal disruption. They do not forward traffic under normal operation but provide high availability and fault tolerance by being ready to assume forwarding duties instantly. Standby routers are critical in enterprise networks where uninterrupted gateway access is necessary. The standby router continuously monitors the active router, allowing rapid transition in milliseconds to seconds depending on configuration. This makes standby the correct answer.

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

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.

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 170:

 Which MPLS feature allows multiple VPNs to coexist securely on shared infrastructure?

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

Answer: A) VRF

Explanation:

A) VRF (Virtual Routing and Forwarding) allows multiple independent routing and forwarding instances to coexist on a single physical router. Each VRF maintains its own interfaces, routing tables, and forwarding domains. In MPLS networks, VRFs provide complete isolation between VPNs, even when sharing the same physical links. They also support overlapping IP address spaces for different VPNs, enabling multi-tenant deployments. By maintaining separate routing and forwarding instances, VRFs prevent traffic leakage between VPNs and ensure security, scalability, and efficient resource usage. VRFs are widely implemented in enterprise and service provider networks to support multiple customers or business units on the same infrastructure. This makes VRF the correct answer.

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

C) RSVP-TE establishes explicit label-switched paths with bandwidth reservations for traffic engineering. While it optimizes path selection and ensures predictable performance, RSVP-TE does not segregate VPN traffic.

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

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

Question 171:

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

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

Answer: A) Bandwidth

Explanation:

A) Bandwidth represents the minimum capacity along a network path. EIGRP calculates its composite metric based on both bandwidth and delay, among other factors, but bandwidth specifically identifies the slowest link along the route. This ensures the selected path can sustain the required traffic load without being bottlenecked by a single low-capacity interface. EIGRP converts the minimum bandwidth along the path into a metric value using the formula 10^7 / minimum bandwidth (in Kbps). By focusing on the slowest link, the routing protocol avoids paths that may appear optimal in other respects but are limited by one underperforming segment. Bandwidth is a static metric based on interface configuration and speed; it does not fluctuate with traffic conditions or errors, unlike load or reliability. This makes bandwidth the correct answer for identifying the limiting link along a path.

B) Delay represents the cumulative time required for a packet to traverse a path. While important for latency-sensitive traffic, delay does not indicate the slowest link in terms of throughput. A path may have low delay yet include an interface with limited capacity that would bottleneck traffic.

C) Reliability tracks the historical stability and error rates of a link. Reliability ensures that unstable or error-prone links are avoided but does not provide information about the slowest link in terms of data transfer capacity.

D) Load reflects the current utilization of a link. Load is dynamic and fluctuates with traffic patterns. While high load can temporarily affect performance, it does not define the inherent capacity of a link, making it unsuitable for identifying the slowest link.

Bandwidth is correct because it identifies the limiting capacity of a path. Delay measures latency, reliability measures stability, and load measures current utilization but not the maximum achievable throughput.

Question 172:

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 OSPF area. They provide information about directly connected networks, router interfaces, and link states. They are intra-area LSAs and do not carry external routes, making them irrelevant for redistributed external connectivity.

B) Type 3 LSAs summarize routes between OSPF areas. Generated by Area Border Routers (ABRs), Type 3 LSAs carry internal OSPF networks from one area to another but do not carry external routes redistributed from other protocols.

C) Type 5 LSAs are used to carry external routes redistributed into OSPF from other protocols such as BGP, EIGRP, or static routes. Type 5 LSAs are flooded throughout all standard OSPF areas, except stub areas and NSSAs, to inform routers about external destinations. They include a metric that can be of type E1 (internal plus external) or E2 (external only), which influences path selection in OSPF. By propagating external routes via Type 5 LSAs, OSPF routers gain connectivity to destinations outside the OSPF autonomous system. Type 5 LSAs are essential for integrating OSPF with other routing protocols and for providing consistent external reachability across the network. This makes Type 5 the correct answer.

D) Type 7 LSAs are used only in NSSAs (Not-So-Stubby Areas) to carry external routes locally. Type 7 LSAs can be converted into Type 5 LSAs by the ABR if the routes need to be advertised to the rest of the OSPF domain. They are not used in standard areas for external redistribution.

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 specific to NSSAs.

 

Question 173:

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-specific attribute used for outbound path selection on a single router. It does not affect how external autonomous systems select paths into your AS, so it cannot influence inbound traffic.

B) Local Preference is propagated within an AS and influences the path selection for outbound traffic across all routers. It is irrelevant for inbound traffic because external ASes do not consider local preference values when choosing their exit points.

C) MED (Multi-Exit Discriminator) is designed specifically to influence inbound traffic from neighboring autonomous systems. By advertising different MED values for multiple exit points, an AS can indicate preferred entry points for external ASes. Lower MED values are more desirable, while higher values are less preferred. MED provides predictable inbound traffic distribution, which is critical in multi-homed networks for load balancing and congestion management. Although MED is a suggestion rather than an enforcement, most external ASes honor it, making it a precise tool for inbound traffic engineering. This makes MED the correct answer.

D) AS Path lists the autonomous systems that a route has traversed. AS path prepending can indirectly influence inbound traffic by making a route appear longer, but it is less precise and less reliable than MED for controlling incoming traffic distribution.

MED is correct because it directly influences which paths external ASes use to enter your network. Weight is local-only, Local Preference is for outbound traffic, and AS Path prepending is an indirect method.

Question 174:

Which HSRP state monitors the active router and is ready to take over forwarding if it 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, maintains connectivity, and does not monitor other routers or serve as a backup.

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 required state information to ensure seamless failover with minimal network 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 for hosts, enabling rapid failover in milliseconds to seconds depending on configuration. This makes standby the correct answer.

C) Listen is an initial state where the router receives hello messages but does not participate in forwarding or actively monitor the active router.

D) Init is the startup state where the router has not yet 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 175:

 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) allows multiple independent routing and forwarding instances to exist on a single physical router. Each VRF maintains its own interfaces, routing table, and forwarding domain. In MPLS networks, VRFs ensure complete traffic isolation between multiple VPNs, even when using the same physical links. VRFs also allow overlapping IP address spaces across different VPNs, enabling multi-tenant deployments. By maintaining separate routing tables and forwarding paths, VRFs prevent traffic leakage between VPNs and guarantee security, scalability, and efficient resource utilization. VRFs are widely implemented in service provider and enterprise networks to allow multiple customers or business units to coexist on the same infrastructure while remaining fully isolated. This makes VRF the correct answer.

B) LDP (Label Distribution Protocol) distributes labels in MPLS networks to enable label-switched path forwarding. LDP is essential for MPLS operation but does not provide traffic isolation between VPNs.

C) RSVP-TE establishes explicit label-switched paths with bandwidth reservations for traffic engineering. While it ensures predictable performance and optimized routing, it does not enforce separation between VPNs.

D) QoS (Quality of Service) prioritizes traffic and manages bandwidth allocation for critical applications. QoS ensures service levels but does not isolate traffic 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 provide isolation.

Question 176:

Which EIGRP metric component represents the historical stability and error rate of a link?

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

Answer: C) Reliability

Explanation:

A) Bandwidth is a measure of the slowest link along a path and determines the maximum throughput achievable. While bandwidth is critical for ensuring that the network can handle the traffic load, it does not provide any information regarding the historical performance or stability of a link. A link can have high bandwidth but still experience frequent errors or flapping. Bandwidth is a static, pre-configured metric derived from interface capacity, making it unsuitable for tracking historical link stability or error rate.

B) Delay measures the total time a packet requires to traverse a path, including propagation, queuing, and processing delays. Delay is vital for latency-sensitive applications such as voice and video, but it does not account for the reliability of a link over time. A low-delay link may still fail frequently or drop packets, which could disrupt traffic despite minimal latency.

C) Reliability is a measure of historical link stability and error rate. In EIGRP, reliability is quantified on a scale from 0 to 255, where higher values indicate a more stable link. The protocol monitors the link’s error counts, uptime, and overall stability to compute this metric. Reliability ensures that unstable or error-prone links are avoided in path selection, even if those links have high bandwidth or low delay. For example, a link with intermittent outages or high packet loss would have low reliability, causing EIGRP to prefer an alternative path. Reliability is especially important in enterprise networks, where uptime is critical, as it prevents routing decisions that could lead to frequent disruptions. By incorporating reliability into the composite metric, EIGRP ensures that selected paths are both high-performing and dependable, balancing throughput, latency, and stability.

D) Load represents the current utilization of a link. Although a highly utilized link may experience congestion, load is a dynamic metric that fluctuates with traffic patterns. It does not reflect historical stability or error rate. A link with consistently high traffic may still be stable and error-free, making load an unsuitable metric for evaluating long-term reliability.

Reliability is correct because it reflects historical link stability and error rates, ensuring paths are dependable. Bandwidth measures capacity, delay measures traversal time, and load measures utilization but does not account for historical performance.

Question 177:

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, or router LSAs, describe a router’s interfaces and directly connected networks within a single area. They provide essential intra-area topology information but do not summarize or propagate routes to other areas. Each router in an area generates its own Type 1 LSAs, allowing all routers in the area to maintain a consistent link-state database. However, Type 1 LSAs are limited to the local area and do not facilitate inter-area routing, making them irrelevant for summarization.

B) Type 2 LSAs describe multi-access network links, such as broadcast or non-broadcast multi-access (NBMA) networks. Generated by the Designated Router (DR), Type 2 LSAs list all routers connected to the segment. These LSAs provide detailed intra-area topology information but are not used to summarize inter-area routes or advertise them beyond the local area.

C) Type 3 LSAs, also known as summary LSAs, are generated by Area Border Routers (ABRs) to advertise networks from one area into another. They consolidate multiple internal routes into a single summary, reducing the size of the routing table and the amount of LSA flooding. For example, an ABR connecting Area 1 to the backbone Area 0 may summarize all Area 1 networks into one Type 3 LSA to advertise them to other areas. Type 3 LSAs enable hierarchical OSPF design, improve SPF calculation efficiency, and reduce CPU and memory usage on routers. They also allow network engineers to control route advertisement using summarization techniques, which minimizes routing complexity and enhances scalability in large networks.

D) Type 5 LSAs carry external routes redistributed into OSPF from other protocols. These LSAs propagate external destinations across the OSPF domain but are not intended for inter-area route summarization. Type 5 LSAs operate at the domain level and distribute external reachability rather than summarize intra-area networks.

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

Question 178:

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

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 outbound path selection locally on a router. Weight is evaluated first in the BGP best path selection process. By assigning a higher weight to a path, administrators can ensure that the local router prefers that path for outbound traffic. Weight does not propagate to other routers in the AS, making it ideal for precise, router-specific traffic engineering. In multi-homed environments, weight allows deterministic path selection and ensures predictable traffic patterns, preventing congestion or suboptimal routing on specific links. Weight is particularly useful when multiple exit points are available, and traffic must be routed according to specific performance or cost considerations.

B) Local Preference affects outbound path selection but is propagated across all routers within an AS. While it can influence which exit link is preferred for outbound traffic, it does not 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 suggests preferred entry points to neighboring ASes but does not control the router’s own outbound routing decisions.

D) AS Path is a cumulative list of autonomous systems that a route has traversed. AS Path prepending can influence inbound traffic by making certain paths appear longer, but it does not control outbound routing decisions on a local router.

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 179:

 Which HSRP state monitors the active router and is ready 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 forwarding traffic for the HSRP virtual IP. It responds to ARP requests, maintains connectivity, and does not monitor other routers for failover. Active routers are responsible for actual packet forwarding but are not in a monitoring or backup role.

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 necessary state information to ensure seamless failover. They do not forward traffic during normal operations but provide high availability and fault tolerance by being ready to assume forwarding instantly. In enterprise networks, the standby router ensures uninterrupted gateway access, allowing critical applications to function without disruption. Standby routers continuously monitor the active router, enabling failover in milliseconds to seconds, which is essential for network resiliency and service continuity. 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 for failover or forward traffic.

D) Init is the startup state during which 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 to assume forwarding immediately. Active forwards traffic, Listen is passive, and Init is preliminary.

Question 180

 Which MPLS feature allows multiple VPNs to coexist on shared 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 critical MPLS feature that allows multiple independent routing and forwarding instances to exist on a single router. Each VRF instance operates as a completely separate routing domain, with its own interfaces, routing table, and forwarding domain. This separation ensures that traffic from one VPN cannot traverse into another VPN, even when multiple VPNs share the same physical network infrastructure. VRFs create the logical equivalent of multiple routers within a single physical device, enabling secure multi-tenant operation without the need for dedicated hardware for each VPN or customer.

In MPLS networks, VRFs work closely with MPLS labels to maintain traffic separation. Each packet associated with a VRF is tagged with a label that identifies the VRF it belongs to. This allows routers along the MPLS path to forward traffic based on the VRF routing table, not just the IP header, ensuring that VPN traffic remains isolated. By maintaining distinct routing tables and forwarding domains, VRFs prevent traffic leakage, misrouting, and unauthorized access between different tenants, departments, or customers. This is especially critical in environments that host multiple clients, where the confidentiality and integrity of each VPN must be maintained at all times.

VRFs also enable overlapping IP address spaces, which is a common requirement in multi-tenant networks. Multiple VPNs can use identical private IP ranges, and VRFs ensure that these subnets remain isolated. For example, two customers might both use the 192.168.1.0/24 subnet. With VRFs, each subnet is bound to its own routing table, so there is no conflict or cross-traffic, allowing seamless coexistence. This feature significantly simplifies network design and reduces the operational complexity associated with renumbering or NAT when accommodating multiple tenants.

Another significant benefit of VRFs is centralized management and policy enforcement. Network administrators can configure routing policies, access control, and monitoring per VRF. Each VPN can have distinct security rules, Quality of Service (QoS) policies, and routing preferences, all managed centrally through MPLS-enabled devices or BGP policy configurations. This ensures consistency across the network and allows granular control of traffic, making VRFs invaluable for both enterprise segmentation and service provider deployments.

VRFs also enhance scalability. Enterprises and service providers can support hundreds or even thousands of VPNs on the same infrastructure without requiring additional routers. This maximizes hardware utilization, reduces capital expenditure, and allows network operators to scale services efficiently. VRFs are fully compatible with BGP and MP-BGP (Multiprotocol BGP) for route distribution between VRFs and core network routers. MP-BGP enables secure and isolated route propagation between VPNs and the provider backbone, maintaining separation while allowing controlled connectivity where needed. This combination of VRFs and BGP is the backbone of large-scale MPLS VPN deployments.

B) LDP (Label Distribution Protocol) is a protocol used in MPLS networks to distribute labels for forwarding along Label-Switched Paths (LSPs). LDP ensures that routers know which labels to use to forward packets efficiently across the MPLS network. While LDP is fundamental for MPLS packet forwarding, it does not provide VPN isolation or independent routing domains. LDP’s primary function is to facilitate efficient label-based forwarding, not to segregate traffic between multiple tenants or departments. Therefore, while it is critical for MPLS operation, LDP cannot replace VRFs in providing secure, multi-tenant network segmentation.

C) RSVP-TE (Resource Reservation Protocol – Traffic Engineering) is used to establish explicit LSPs with bandwidth reservations to optimize traffic flows and network performance. RSVP-TE allows network operators to engineer traffic paths to avoid congestion, provide predictable latency, and ensure efficient bandwidth utilization. While RSVP-TE is important for performance optimization and reliability, it does not inherently create separate routing tables or isolate VPN traffic. RSVP-TE is primarily concerned with traffic engineering, not the logical separation of multiple VPNs on shared infrastructure.

D) QoS (Quality of Service) manages traffic prioritization, bandwidth allocation, and performance guarantees for critical applications like voice, video, and transactional data. QoS ensures that high-priority traffic receives appropriate resources and that performance metrics are maintained under network congestion. However, QoS does not enforce traffic isolation between VPNs. Traffic from different VPNs may share a QoS-enabled link, but QoS cannot prevent one VPN from affecting the routing or security of another. QoS enhances network performance but does not address multi-tenant separation or logical isolation, which are critical requirements in shared infrastructures.

 VRF is the correct answer because it provides complete logical separation of multiple VPNs on the same physical infrastructure. Each VRF instance has independent interfaces, routing tables, and forwarding domains, ensuring that traffic cannot cross between VPNs. VRFs also support overlapping IP addresses, centralized policy management, security enforcement, and scalable multi-tenant deployment.

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

Furthermore, VRFs enable flexible service deployment models. Enterprises can create VRFs for different departments, applications, or projects, each with independent routing, security policies, and performance parameters. Service providers can host multiple clients on the same core network while maintaining compliance with SLAs, privacy, and security standards. VRFs also allow for incremental network growth, as new VPNs can be added without affecting existing services.

In large-scale deployments, VRFs are critical for operational efficiency, high availability, and fault isolation. If a routing or configuration issue occurs in one VRF, it is contained within that VRF and does not affect other VPNs. This containment reduces troubleshooting complexity and increases network resilience. VRFs are, therefore, indispensable in modern MPLS networks, where multiple VPNs or tenants share the same infrastructure but require strict isolation, predictable performance, and centralized management.