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Q241. Which OSPF area type allows external routes while still minimizing the amount of external routing information?

1) Stub area
2) Totally stubby area
3) NSSA
4) Backbone area

Correct Answer: 3) NSSA

Explanation:
An OSPF Not-So-Stubby Area (NSSA) is designed for situations where an area should limit external routing information but still needs to redistribute external routes into OSPF. Unlike a standard stub area, an NSSA permits an Autonomous System Boundary Router (ASBR) inside the area to introduce external routes. These routes are represented using Type 7 LSAs, which can be translated into Type 5 LSAs by an appropriate Area Border Router (ABR). A totally stubby area is even more restrictive because it suppresses most inter-area and external routes. Therefore, NSSA provides the appropriate balance when external route redistribution is required.

Q242. What is the primary purpose of an OSPF virtual link?

1) To connect an area to Area 0 through a transit area
2) To create a backup default route
3) To replace OSPF authentication
4) To establish an EIGRP adjacency

Correct Answer: 1) To connect an area to Area 0 through a transit area

Explanation:
An OSPF virtual link provides a logical connection to the OSPF backbone, Area 0, when a physical or normal logical connection is not available. OSPF requires every non-backbone area to have connectivity to Area 0 for proper inter-area routing. A virtual link is configured between two OSPF routers that share a common transit area, allowing the routers to logically extend the backbone through that area. It is generally considered a temporary or special-purpose solution rather than a preferred permanent design. Proper router IDs, area configuration, and transit-area connectivity are required for the virtual link to function correctly.

Q243. Which command allows an OSPF router to advertise a default route into an OSPF domain?

1) default-route advertise
2) default-information originate
3) ip ospf default-route
4) redistribute default-route

Correct Answer: 2) default-information originate

Explanation:
The default-information originate command is used under the OSPF routing process to advertise a default route into the OSPF domain. This allows other OSPF routers to use the originating router as a gateway for destinations that are not specifically present in their routing tables. By default, the router generally needs to have a default route in its routing table before advertising it. The always keyword can be used when the administrator wants OSPF to advertise the default route even if the router does not currently have one installed. This is particularly useful for internet-edge or centralized exit-router designs.

Q244. Which EIGRP metric component is primarily used to represent the delay associated with a route?

1) Bandwidth
2) Reliability
3) Delay
4) MTU

Correct Answer: 3) Delay

Explanation:
Delay is one of the traditional components used by EIGRP’s composite metric calculation. It represents the cumulative delay across the interfaces along a route. EIGRP considers both bandwidth and delay by default when calculating its metric, while reliability and load can be included in the formula but are normally not used because the default K values are zero for those components. Interface delay is configured independently of actual physical transmission delay and can be adjusted by administrators when appropriate. Because cumulative delay affects route selection, incorrect delay values can influence which path EIGRP considers the best successor.

Q245. What condition must be satisfied for an EIGRP route to be considered feasible and installed as a feasible successor?

1) The reported distance must be less than the feasible distance
2) The feasible distance must be zero
3) The neighbor must have a lower administrative distance
4) The route must pass through a different autonomous system

Correct Answer: 1) The reported distance must be less than the feasible distance

Explanation:
The EIGRP feasibility condition is an important mechanism that helps ensure a backup route is loop-free. A neighboring router can be considered a feasible successor when its reported distance (RD), also called advertised distance, is less than the current route’s feasible distance (FD). This condition guarantees that the neighbor is closer to the destination than the local router’s current known distance, providing confidence that the alternate path will not create a routing loop. EIGRP can then maintain that route as a feasible successor and quickly use it if the primary successor becomes unavailable.

Q246. What is a common symptom of an EIGRP Stuck-In-Active condition?

1) OSPF adjacency resets
2) An EIGRP route remains active while waiting for query responses
3) BGP removes every route from the RIB
4) MPLS labels disappear from the network

Correct Answer: 2) An EIGRP route remains active while waiting for query responses

Explanation:
An EIGRP route enters the Active state when the router loses its current successor and does not have a feasible successor available. The router then sends query messages to neighboring EIGRP routers asking whether they have a route to the destination. If a neighbor does not respond within the required time, the route can become stuck in active (SIA). SIA conditions can cause neighbor relationships to reset and may indicate excessive query propagation, unstable links, slow responses, or poor EIGRP topology design. Route summarization, EIGRP stub configuration, and careful network design can help reduce query scope and prevent widespread SIA problems.

Q247. Which EIGRP feature allows multiple routes to be summarized at an interface?

1) ip summary-address eigrp
2) ip route-summary eigrp
3) eigrp aggregate-route
4) ip eigrp summarize

Correct Answer: 1) ip summary-address eigrp

Explanation:
The ip summary-address eigrp command is used to configure EIGRP manual route summarization on an interface. Instead of advertising multiple specific prefixes individually, the router can advertise a summarized prefix toward its EIGRP neighbor. This reduces the size of routing tables and can also reduce the amount of routing information exchanged between routers. Summarization can improve network stability because changes to individual component routes may not need to propagate beyond the summarizing boundary. When configuring EIGRP summarization, administrators should carefully select the summary prefix and understand the automatically created summary route and its associated behavior.

Q248. Which BGP attribute is commonly manipulated with a route map to influence the preferred outbound path within an autonomous system?

1) MED
2) Local Preference
3) Origin
4) Atomic Aggregate

Correct Answer: 2) Local Preference

Explanation:
BGP Local Preference is commonly used to influence outbound path selection within an autonomous system. A higher Local Preference value is preferred, making it useful when an organization has multiple exit points and wants internal routers to favor one exit over another. The attribute is propagated throughout the local AS, unlike BGP Weight, which is Cisco-specific and locally significant to a single router. Route maps can be used to match specific prefixes and assign different Local Preference values. This allows administrators to implement granular routing policies and control which external connection is preferred for outbound traffic.

Q249. Which BGP command enables multiple equal-cost paths to be installed in the routing table?

1) maximum-paths
2) bgp multipath enable
3) maximum-routes
4) neighbor multipath

Correct Answer: 1) maximum-paths

Explanation:
The BGP maximum-paths command allows a router to install multiple BGP paths for the same destination when the paths meet the necessary multipath selection requirements. Normally, BGP selects a single best path, even when several paths may be available. Multipath configuration can improve traffic distribution and provide additional resiliency. The number specified with maximum-paths determines how many eligible paths can be installed. BGP multipath still requires the candidate routes to satisfy appropriate path-selection and multipath compatibility conditions. Therefore, simply configuring the command does not guarantee that every available BGP path will automatically be installed.

Q250. What must be true for a BGP route to be usable as a forwarding path?

1) The route must have a reachable next hop
2) The route must always have AS_PATH length zero
3) The route must originate from an IGP
4) The route must have a MED of zero

Correct Answer: 1) The route must have a reachable next hop

Explanation:
BGP can select a route as the best path only when the next-hop address is reachable through the routing table. BGP may learn a prefix successfully but still be unable to install it as a usable forwarding route if the next hop cannot be resolved. This is especially important in eBGP and iBGP environments where the BGP next-hop attribute may not automatically be changed as a route passes between routers. Commands such as show ip bgp and show ip route can help verify both the BGP path and next-hop reachability. The next-hop-self feature is often used to simplify iBGP next-hop resolution.

Q251. What is the main purpose of BGP route dampening?

1) Increase OSPF hello frequency
2) Suppress unstable routes that repeatedly flap
3) Encrypt BGP updates
4) Increase the MTU of BGP packets

Correct Answer: 2) Suppress unstable routes that repeatedly flap

Explanation:
BGP route dampening is designed to reduce the impact of routes that repeatedly become available and unavailable, a condition known as route flapping. Each flap contributes a penalty to the route. When the penalty reaches a configured suppression threshold, BGP can temporarily suppress the unstable route. Over time, the penalty decays, and the route can eventually become eligible for advertisement again. This helps reduce excessive routing updates and instability across large networks. However, aggressive dampening can sometimes suppress legitimate routes for too long, so administrators should use appropriate thresholds and understand the operational characteristics of the network before enabling the feature.

Q252. In an MPLS Layer 3 VPN, which device typically connects directly to the customer network?

1) P router
2) PE router
3) Route Reflector
4) LSR-only switch

Correct Answer: 2) PE router

Explanation:
In an MPLS Layer 3 VPN architecture, the Provider Edge (PE) router is the device that typically connects directly to the customer’s Customer Edge (CE) router. The PE maintains customer-specific VRF information and exchanges VPN routes with other PE routers using mechanisms such as MP-BGP. Provider (P) routers generally operate inside the service-provider core and forward MPLS-labeled traffic without maintaining individual customer VPN routing information. The separation between PE and P roles is important because it allows the provider core to remain scalable while PE routers handle customer-specific routing and VPN information.

Q253. What is the purpose of a Route Target in an MPLS Layer 3 VPN?

1) It identifies the physical interface speed
2) It controls VPN route import and export between VRFs
3) It replaces the MPLS label
4) It determines the OSPF router ID

Correct Answer: 2) It controls VPN route import and export between VRFs

Explanation:
Route Targets are extended BGP communities used in MPLS Layer 3 VPNs to control which VPN routes are imported into or exported from VRFs. When a PE advertises a VPN route, one or more export Route Targets can be attached to that route. Other PE routers use their configured import Route Targets to determine whether the route should be placed into a particular VRF. This provides flexible control over VPN topology. For example, different customers or sites can be configured for full-mesh communication, hub-and-spoke communication, or selective route sharing by appropriately configuring Route Target import and export policies.

Q254. What is Penultimate Hop Popping (PHP) used for in an MPLS network?

1) Encrypting MPLS packets
2) Removing the MPLS label before the packet reaches the egress router
3) Adding multiple VPN labels
4) Assigning IP addresses to PE routers

Correct Answer: 2) Removing the MPLS label before the packet reaches the egress router

Explanation:
Penultimate Hop Popping, or PHP, allows the router immediately before the MPLS egress router to remove the top MPLS label from a packet. This reduces the label-processing workload on the egress router because it receives the packet without that outer label. In many MPLS designs, the egress router advertises an implicit-null label for certain destinations, causing the penultimate router to perform the pop operation. PHP is particularly useful for improving efficiency in MPLS forwarding. It does not provide encryption and should not be confused with VPN label operations used to identify customer-specific forwarding information.

Q255. Which DMVPN phase allows spoke-to-spoke tunnels to be dynamically established using NHRP?

1) Phase 1
2) Phase 2
3) Phase 3
4) Phase 0

Correct Answer: 2) Phase 2

Explanation:
DMVPN Phase 2 allows spokes to establish dynamic spoke-to-spoke tunnels using NHRP while retaining the original destination information needed to select the remote spoke. This can reduce unnecessary traffic through the hub. In Phase 1, spoke traffic generally travels through the hub, while Phase 2 introduces direct spoke-to-spoke communication when routing conditions support it. Phase 3 further improves scalability by allowing NHRP redirects and shortcuts, helping spokes dynamically learn more efficient paths. Understanding these phases is important when designing DMVPN networks because routing behavior and NHRP operation differ significantly between them.

Q256. Which QoS mechanism reserves bandwidth for different traffic classes while using a class-based queueing model?

1) CBWFQ
2) WRED
3) FIFO
4) Policing

Correct Answer: 1) CBWFQ

Explanation:
Class-Based Weighted Fair Queuing (CBWFQ) allows administrators to classify traffic into different classes and allocate a minimum amount of bandwidth to selected classes. It uses class maps to identify traffic and policy maps to define how each class should be treated. CBWFQ is useful when applications have different bandwidth requirements and administrators need predictable service levels. Unlike simple FIFO, CBWFQ provides differentiated treatment for traffic classes. LLQ can be incorporated into a class-based QoS policy when low-latency traffic, such as voice, requires strict priority treatment. Proper classification and bandwidth allocation are essential for effective CBWFQ operation.

Q257. What happens when a QoS policer detects traffic exceeding its configured rate?

1) Excess traffic is always queued indefinitely
2) Excess traffic may be dropped or remarked
3) The interface speed automatically increases
4) The routing protocol changes the next hop

Correct Answer: 2) Excess traffic may be dropped or remarked

Explanation:
QoS policing monitors traffic against a configured rate and takes action when traffic exceeds the permitted level. Depending on the policy, excess traffic can be dropped, remarked, or otherwise handled according to the configured exceed and violate actions. Unlike shaping, policing does not normally buffer excess traffic for later transmission. Shaping smooths traffic by storing excess packets in a queue and transmitting them later when bandwidth becomes available. Policing is therefore useful when strict traffic-rate enforcement is required, but excessive policing can cause packet loss if applications regularly transmit above the configured threshold.

Q258. Which feature can automatically change a static route’s availability based on the status of a tracked object?

1) HSRP only
2) IP SLA with object tracking
3) OSPF virtual link
4) BGP route reflection

Correct Answer: 2) IP SLA with object tracking

Explanation:
IP SLA combined with object tracking can provide dynamic control over static routes and other network decisions. An IP SLA operation can test reachability to a remote destination, such as an upstream gateway or server. The result can then be associated with a tracked object. A static route can reference that tracked object so that the route is removed from the routing table when the tracked condition fails and restored when the condition becomes healthy again. This is commonly used for primary and backup WAN connectivity. It provides a simple mechanism for improving path availability without requiring a dynamic routing protocol.

Q259. Which HSRP feature allows the active router to change when a tracked interface or object fails?

1) Interface tracking
2) Route reflection
3) NHRP registration
4) MPLS PHP

Correct Answer: 1) Interface tracking

Explanation:
HSRP interface or object tracking allows an HSRP router to reduce its priority when an important interface or tracked condition fails. If the priority becomes lower than the priority of another HSRP router, the standby router can become active, provided the relevant preemption behavior is configured. This improves gateway redundancy because the HSRP active role can reflect the actual availability of upstream connectivity. Without tracking, a router could remain the active default gateway even after losing its primary WAN or uplink. Proper priority values and preemption settings should therefore be considered when implementing HSRP tracking.

Q260. Which IPv6 mechanism allows a router to advertise network prefix information to hosts on a local link?

1) DHCPv4
2) ARP
3) Router Advertisement
4) NHRP

Correct Answer: 3) Router Advertisement

Explanation:
IPv6 Router Advertisement (RA) messages are part of Neighbor Discovery and allow routers to provide hosts with important network configuration information. RA messages can advertise IPv6 prefixes, indicate whether hosts should use Stateless Address Autoconfiguration (SLAAC), and provide other parameters such as default-router information. IPv6 does not use ARP; instead, Neighbor Discovery Protocol performs address-resolution and related functions using ICMPv6. Router Advertisements are therefore fundamental to IPv6 host configuration and communication. Administrators troubleshooting IPv6 should verify that RA messages are being generated and received correctly, particularly when hosts are expected to automatically configure their addresses.