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Q141. Which OSPF feature allows a router to advertise a summarized route for multiple networks?

1) Route tagging
2) Route summarization
3) Split horizon
4) Passive interface

Correct Answer: 2) Route summarization

Explanation: OSPF route summarization combines multiple contiguous network prefixes into a single summarized prefix. This can reduce the size of routing tables and decrease the amount of routing information that needs to be propagated throughout the network. In OSPF, summarization can be configured at an Area Border Router (ABR) for inter-area routes or at an Autonomous System Boundary Router (ASBR) for redistributed external routes. Proper summarization can improve scalability and reduce unnecessary routing updates. Route tagging is used to identify routes, split horizon is associated with distance-vector routing behavior, and passive interfaces control routing protocol participation.

Q142. An administrator wants OSPF to prefer one path over another when both paths exist. Which value can be manipulated to influence the OSPF path selection?

1) OSPF interface cost
2) Ethernet MTU
3) MAC address
4) DNS priority

Correct Answer: 1) OSPF interface cost

Explanation: OSPF uses a cost value to determine the best path to a destination. The total cost of an OSPF route is calculated by adding the costs of the interfaces along the path. By changing the OSPF interface cost, an administrator can influence which path OSPF selects when multiple paths are available. A lower total OSPF cost is preferred. The cost can be configured directly with the appropriate interface command or influenced by bandwidth settings. Ethernet MTU can affect adjacency formation, but it is not the normal metric used to select the preferred OSPF path.

Q143. Which BGP attribute is normally preferred when selecting the outbound path from an autonomous system?

1) MED
2) Local Preference
3) Origin code
4) Router ID

Correct Answer: 2) Local Preference

Explanation: BGP Local Preference is used to influence the preferred exit point from an autonomous system. A higher Local Preference value is preferred, making it useful when an organization has multiple connections to external networks and wants to control which connection is used for outbound traffic. Local Preference is propagated to other iBGP peers within the autonomous system. MED, in contrast, is generally used to influence how neighboring autonomous systems enter a network. The BGP origin code and router ID also participate in route selection, but they do not serve the same primary purpose as Local Preference for controlling outbound traffic.

Q144. Which BGP attribute is generally used to influence how external networks enter an autonomous system?

1) Local Preference
2) Weight
3) MED
4) Router ID

Correct Answer: 3) MED

Explanation: The Multi-Exit Discriminator (MED) is a BGP attribute that can be used to suggest a preferred entry point into an autonomous system when multiple links exist between two autonomous systems. A lower MED is generally preferred when comparing otherwise eligible routes from the same neighboring autonomous system. MED is commonly used to influence inbound traffic, although the neighboring AS ultimately controls whether and how it honors the received MED. Local Preference is primarily used inside an AS to influence outbound traffic, while Cisco Weight is locally significant to one router. Router ID is primarily used as a tie-breaking attribute.

Q145. Which EIGRP feature prevents a router from installing a route that could create a routing loop?

1) Feasible condition
2) Broadcast replication
3) NAT overload
4) BGP synchronization

Correct Answer: 1) Feasible condition

Explanation: EIGRP uses the feasibility condition to determine whether a reported route can safely be considered a loop-free backup path. A neighboring router must advertise a feasible distance that is lower than the local router’s feasible distance for the route. When this condition is satisfied, the neighbor can become a feasible successor. This allows EIGRP to maintain a loop-free alternate route that can be used quickly if the successor fails. NAT overload and BGP synchronization are unrelated to EIGRP loop prevention. Understanding the feasibility condition is important when troubleshooting EIGRP convergence and backup paths.

Q146. Which command can be used to display EIGRP neighbors on a Cisco router?

1) show ip eigrp neighbors
2) show ip bgp summary
3) show ospf database
4) show ip nat statistics

Correct Answer: 1) show ip eigrp neighbors

Explanation: The show ip eigrp neighbors command displays information about EIGRP neighbor relationships. The output can include the neighbor’s address, interface, hold time, uptime, sequence information, and other details useful for troubleshooting. If an expected neighbor does not appear, administrators can investigate issues involving interface configuration, network statements, authentication, AS numbers, timers, or connectivity. show ip bgp summary is used for BGP neighbor information, while OSPF database commands examine OSPF link-state information. NAT statistics provide information about address translation. Therefore, the EIGRP neighbor command is the appropriate troubleshooting command.

Q147. Which technology allows a router to maintain multiple routing tables containing separate routing information?

1) STP
2) VRF
3) LLQ
4) EtherChannel

Correct Answer: 2) VRF

Explanation: Virtual Routing and Forwarding (VRF) allows a single router or Layer 3 device to maintain multiple independent routing tables. Each VRF can contain its own interfaces, routes, and forwarding information, allowing overlapping IP address spaces to coexist while remaining logically isolated. VRFs are commonly used by service providers to separate customer routing environments and are a fundamental component of MPLS Layer 3 VPN architectures. STP provides Layer 2 loop prevention, LLQ is a QoS mechanism, and EtherChannel combines multiple physical links into a logical interface. Therefore, VRF is the technology that provides independent routing tables.

Q148. In an MPLS Layer 3 VPN, which component uniquely identifies a route within a provider’s routing infrastructure?

1) Route Distinguisher
2) Default gateway
3) VLAN ID
4) MAC address

Correct Answer: 1) Route Distinguisher

Explanation: A Route Distinguisher (RD) is used in MPLS Layer 3 VPN environments to make customer routes unique within the provider’s VPNv4 or VPNv6 routing tables. Different customers may use identical private address ranges, such as 10.0.0.0/8. The RD allows these otherwise overlapping routes to be represented as unique VPN routes. The RD provides uniqueness but does not determine which VPN receives the route. Route Targets are used to control VPN route import and export policies. VLAN IDs and MAC addresses operate at lower layers and do not perform the same function as an MPLS VPN Route Distinguisher.

Q149. Which MPLS VPN attribute determines which VRFs import or export specific VPN routes?

1) Route Target
2) Router ID
3) Administrative distance
4) OSPF cost

Correct Answer: 1) Route Target

Explanation: Route Targets (RTs) are extended BGP communities used in MPLS Layer 3 VPNs to control the import and export of VPN routes between VRFs. When a PE router exports a customer route, it attaches one or more Route Targets. Another VRF can import routes carrying a matching Route Target. This mechanism allows service providers to implement flexible connectivity policies between customer sites. The Route Distinguisher provides route uniqueness, while the Route Target controls membership and route distribution policy. OSPF cost and administrative distance are routing-selection concepts and do not perform the VPN import/export function.

Q150. Which command is useful for verifying the IPsec security associations on a Cisco router?

1) show ip ospf neighbor
2) show crypto ipsec sa
3) show ip eigrp topology
4) show spanning-tree

Correct Answer: 2) show crypto ipsec sa

Explanation: The show crypto ipsec sa command displays information about IPsec Security Associations. Administrators can use the output to verify whether IPsec is establishing security associations and whether encrypted and decrypted packet counters are increasing. These counters can be particularly useful when troubleshooting site-to-site VPN connectivity. If IKE negotiation succeeds but IPsec traffic is not passing, examining the IPsec SA information can help identify the problem. The other commands are associated with OSPF, EIGRP, and Spanning Tree Protocol respectively. Therefore, show crypto ipsec sa is the appropriate command for examining IPsec security associations.

Q151. Which IPsec protocol provides encryption, integrity, authentication, and anti-replay protection for IP traffic?

1) ESP
2) ARP
3) ICMP
4) DHCP

Correct Answer: 1) ESP

Explanation: Encapsulating Security Payload (ESP) is an IPsec protocol that can provide confidentiality through encryption as well as integrity, authentication, and anti-replay protection. ESP is widely used in modern IPsec VPN implementations because it can protect the actual payload of IP packets. Authentication Header (AH) can provide integrity and authentication but does not provide encryption. ARP resolves IPv4 addresses to MAC addresses, ICMP supports network control and diagnostic messaging, and DHCP provides address configuration. Therefore, ESP is the appropriate answer when the requirement includes encryption along with integrity and authentication for IP traffic.

Q152. Which BFD characteristic makes it useful for dynamic routing protocols?

1) It provides faster detection of forwarding-path failures
2) It assigns IPv6 addresses
3) It encrypts routing updates
4) It replaces all routing protocols

Correct Answer: 1) It provides faster detection of forwarding-path failures

Explanation: Bidirectional Forwarding Detection (BFD) is designed to provide rapid detection of failures in the forwarding path between network devices. Routing protocols may rely on relatively long timers to detect neighbor failures, which can delay convergence. BFD can operate with much faster detection intervals and notify supported routing protocols when a forwarding path fails. This allows routing protocols such as OSPF, EIGRP, and BGP to react more quickly. BFD does not assign IP addresses, encrypt routing updates, or replace routing protocols. Instead, it complements routing protocols by providing efficient and rapid failure detection.

Q153. Which route-map feature allows an administrator to identify routes so that they can later be treated differently during redistribution?

1) Route tagging
2) Port security
3) VLAN pruning
4) NAT overload

Correct Answer: 1) Route tagging

Explanation: Route tagging allows administrators to attach a numeric tag to routes so that those routes can later be identified and handled differently. This is particularly useful in redistribution scenarios where routing information may move between multiple routing protocols. For example, an administrator can tag routes redistributed from one protocol and then use a route map to prevent those same routes from being redistributed back into the original protocol, helping prevent routing loops. Route tagging does not modify the destination network itself. Port security protects switch access ports, VLAN pruning controls VLAN propagation, and NAT overload translates addresses.

Q154. What is the main purpose of route redistribution?

1) To exchange routing information between different routing protocols
2) To encrypt IP packets
3) To assign MAC addresses
4) To prevent Ethernet loops

Correct Answer: 1) To exchange routing information between different routing protocols

Explanation: Route redistribution allows routes learned through one routing protocol or routing source to be introduced into another routing protocol. This is useful when different parts of an organization use different routing protocols or when a network is migrating from one protocol to another. Redistribution must be designed carefully because routing protocols use different metrics, administrative distances, and route-selection behaviors. Route maps, filtering, route tagging, and metric manipulation can help control redistributed routes. Redistribution itself does not encrypt packets, assign MAC addresses, or prevent Layer 2 loops. Its primary purpose is to exchange routing information between different routing domains.

Q155. Which mechanism can prevent a routing loop when redistributing routes between EIGRP and OSPF?

1) Route tagging and filtering
2) Increasing Ethernet MTU
3) Disabling ARP
4) Changing the device hostname

Correct Answer: 1) Route tagging and filtering

Explanation: Route tagging and filtering can help prevent routing loops during redistribution between protocols such as EIGRP and OSPF. A route can be tagged when it enters one routing domain, and a route map can later match that tag to prevent the route from being redistributed back into its original domain. This creates a controlled redistribution policy and prevents routes from repeatedly circulating between routing protocols. Simply changing MTU, disabling ARP, or modifying the hostname does not provide routing-loop protection. Proper redistribution design should also consider metrics, administrative distance, summarization, and filtering.

Q156. Which OSPF LSA type is generated by an ASBR to advertise external routes?

1) Type 1
2) Type 2
3) Type 3
4) Type 5

Correct Answer: 4) Type 5

Explanation: OSPF Type 5 LSAs are autonomous system external LSAs used to advertise routes that originate outside the OSPF autonomous system. An Autonomous System Boundary Router (ASBR) generates Type 5 LSAs when external routes are redistributed into OSPF. These LSAs can then be propagated throughout appropriate OSPF areas. Type 1 LSAs describe router information within an area, Type 2 LSAs represent network information generated by a DR on broadcast or multiaccess networks, and Type 3 LSAs are summary LSAs generated by ABRs to advertise inter-area networks. Therefore, Type 5 is associated with external routes.

Q157. Which OSPF area type restricts certain external LSAs and uses Type 7 LSAs for external route information?

1) Backbone area
2) Stub area
3) NSSA
4) Standard area

Correct Answer: 3) NSSA

Explanation: A Not-So-Stubby Area (NSSA) provides stub-area characteristics while still allowing external routes to be introduced into the area. An ASBR inside an NSSA uses Type 7 LSAs to represent external routes. An appropriate OSPF router can translate Type 7 LSAs into Type 5 LSAs so the external information can be propagated outside the NSSA. This design is useful when an area needs to connect to an external routing domain while maintaining restrictions on certain external LSAs. Standard areas have fewer restrictions, while traditional stub areas do not normally permit an internal ASBR to redistribute external routes.

Q158. Which QoS mechanism places selected high-priority traffic into a low-latency queue?

1) LLQ
2) NAT
3) WRED
4) DHCP snooping

Correct Answer: 1) LLQ

Explanation: Low Latency Queuing (LLQ) provides strict priority treatment to selected traffic classes that require low delay and low jitter. It is commonly used for voice and other real-time applications where excessive delay can significantly affect performance. LLQ is implemented as a priority queue within a Modular QoS CLI policy. During congestion, priority traffic can be serviced before other classes, although policing mechanisms may be applied to prevent priority traffic from consuming all available bandwidth. WRED is a congestion-avoidance mechanism, NAT performs address translation, and DHCP snooping provides Layer 2 security.

Q159. What is the primary difference between traffic shaping and traffic policing?

1) Shaping buffers excess traffic, while policing can drop or remark excess traffic
2) Policing always encrypts traffic, while shaping decrypts it
3) Shaping operates only at Layer 2, while policing operates only at Layer 7
4) They are identical mechanisms with no operational difference

Correct Answer: 1) Shaping buffers excess traffic, while policing can drop or remark excess traffic

Explanation: Traffic shaping and traffic policing are both used to control traffic rates, but they handle excess traffic differently. Traffic shaping generally buffers excess packets and sends them later at a controlled rate, which can smooth traffic bursts. Traffic policing typically measures traffic against a configured rate and can drop or remark packets that exceed the permitted rate. Shaping therefore introduces buffering and can increase delay, while policing can immediately enforce the configured rate. Neither mechanism inherently provides encryption, and their operation is not limited to the simplistic Layer 2 or Layer 7 distinctions described in the other options.

Q160. Which command is commonly used to verify BGP neighbor relationships and session status?

1) show ip ospf interface
2) show ip bgp summary
3) show ip eigrp neighbors
4) show crypto isakmp sa

Correct Answer: 2) show ip bgp summary

Explanation: The show ip bgp summary command provides a concise overview of BGP configuration and neighbor relationships. It displays information such as the local BGP autonomous system, router identifier, configured neighbors, message counters, and the current BGP session state or number of prefixes received. This command is especially useful when troubleshooting BGP sessions because it quickly shows whether a neighbor relationship has reached the Established state. show ip ospf interface provides OSPF information, show ip eigrp neighbors displays EIGRP peers, and show crypto isakmp sa provides information about IKE security associations.