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Question 121

Which EIGRP feature allows a router to advertise a summary route instead of multiple specific routes?

1. Variance
2. Route summarization
3. Split horizon
4. Stub routing

Correct Answer: 2

Explanation

EIGRP route summarization allows a router to advertise a single summary prefix instead of multiple more-specific routes. This reduces the amount of routing information exchanged between routers and can make routing tables smaller and easier to manage. Manual summarization can be configured on an interface where EIGRP routes are advertised. Summarization also helps reduce query propagation because downstream routers can work with the summary instead of needing every individual subnet. Careful address planning is important when designing summaries because an overly broad summary can potentially create undesirable routing behavior. On modern Cisco networks, manual summarization provides more predictable control than legacy automatic summarization.

Question 122

Which BGP attribute is used to identify the next-hop router that should be used to reach a BGP destination?

1. Next Hop
2. Origin
3. MED
4. AS Path

Correct Answer: 1

Explanation

The BGP Next Hop attribute identifies the IP address that a router should use as the next hop when forwarding traffic toward a BGP destination. The behavior of the Next Hop attribute differs depending on whether routes are exchanged through eBGP or iBGP. For example, an eBGP router normally advertises itself as the next hop when advertising routes to an external peer. With iBGP, the original next hop may be preserved unless the next-hop-self feature is configured. If the next-hop address is unreachable, the BGP route may not be installed in the routing table even though the BGP session itself is established. Therefore, next-hop reachability is important during BGP troubleshooting.

Question 123

Which OSPF packet is used to discover neighbors and maintain OSPF adjacencies?

1. Database Description
2. Link-State Update
3. Hello
4. Link-State Request

Correct Answer: 3

Explanation

OSPF Hello packets are used to discover neighboring OSPF routers and maintain neighbor relationships. Hello packets are periodically transmitted through OSPF-enabled interfaces and contain information such as the router ID, area ID, hello interval, dead interval, and other parameters. Certain values must match between neighbors for an adjacency to form successfully. On multiaccess networks, Hello packets also support the DR and BDR election process. If a router stops receiving Hellos from a neighbor within the configured dead interval, it can remove that neighbor from the adjacency table. Therefore, Hello packets are fundamental to both OSPF neighbor discovery and adjacency maintenance.

Question 124

Which EIGRP table stores information about neighboring EIGRP routers?

1. Routing table
2. Neighbor table
3. Topology table
4. ARP table

Correct Answer: 2

Explanation

The EIGRP neighbor table stores information about routers with which the local router has established EIGRP adjacencies. It contains details such as the neighbor’s IP address, interface, hold time, uptime, and sequence information. The neighbor table is different from the EIGRP topology table, which stores route and path information. The IP routing table contains routes selected for forwarding and does not specifically represent EIGRP neighbor relationships. Administrators commonly use the show ip eigrp neighbors command to verify whether expected EIGRP peers are present. If a neighbor is missing, troubleshooting should include interface configuration, EIGRP autonomous system numbers, authentication, timers, and network statements.

Question 125

Which BGP attribute is normally preferred when comparing routes with different values for Local Preference?

1. Higher Local Preference
2. Lower Local Preference
3. Higher MED
4. Longer AS Path

Correct Answer: 1

Explanation

BGP generally prefers a higher Local Preference value when comparing otherwise eligible paths. Local Preference is designed to influence outbound traffic selection within an autonomous system. For example, an administrator can assign a higher Local Preference to routes learned through a preferred external connection. Internal BGP routers can then use that policy when choosing their exit point toward external destinations. Local Preference is normally considered before AS Path in the standard Cisco BGP best-path process, although Cisco’s Weight attribute is considered before Local Preference. Because BGP path selection includes multiple attributes and policy controls, Local Preference should always be evaluated within the complete best-path selection process.

Question 126

Which OSPF LSA type is used by an ABR to advertise networks from one area into another area?

1. Type 5
2. Type 2
3. Type 3
4. Type 1

Correct Answer: 3

Explanation

An OSPF Type 3 LSA, also called a Summary LSA, is generated by an Area Border Router to advertise networks from one OSPF area into another. Type 3 LSAs allow routers in different areas to learn about inter-area destinations without requiring every router to maintain the complete topology database of every area. The ABR uses Type 3 LSAs to summarize and advertise networks across area boundaries. Type 1 LSAs describe individual routers within an area, Type 2 LSAs represent multiaccess networks, and Type 5 LSAs advertise external routes. Understanding Type 3 LSAs is particularly important when troubleshooting missing inter-area routes in multi-area OSPF deployments.

Question 127

Which EIGRP packet is sent in response to an EIGRP Query?

1. Update
2. Reply
3. Hello
4. Acknowledgment

Correct Answer: 2

Explanation

An EIGRP Reply packet is sent in response to an EIGRP Query. When a router loses its successor and does not have a feasible successor, DUAL may place the route into an active state and send Query packets to neighboring routers. Those neighbors respond with Reply packets indicating whether they have a valid path to the requested destination. The originating router waits for the required Replies before completing the route calculation. Excessive Query and Reply activity can indicate scalability or topology problems, particularly in large networks. EIGRP stub routers and route summarization can help limit unnecessary query propagation and improve convergence behavior.

Question 128

Which BGP command displays the BGP routes currently known by the router?

1. show ip bgp
2. show ip bgp summary
3. show ip route ospf
4. show ip protocols

Correct Answer: 1

Explanation

The show ip bgp command displays the BGP routing table maintained by the router. It can show prefixes learned through BGP, next-hop information, path attributes, route status, and the autonomous systems contained in the AS Path. The BGP table can contain multiple paths for the same destination even though only the selected best path may be installed in the IP routing table. The show ip route command can be used separately to verify which BGP routes were actually installed for forwarding. The show ip bgp summary command provides a concise overview of BGP neighbors and session status rather than detailed route information.

Question 129

Which OSPF network type does not elect a Designated Router or Backup Designated Router?

1. Broadcast
2. Non-broadcast multiaccess
3. Point-to-point
4. Ethernet

Correct Answer: 3

Explanation

OSPF point-to-point networks do not require a Designated Router or Backup Designated Router because only two routers participate on the logical link. Both routers can establish their adjacency directly without the additional DR election process used on multiaccess networks. Ethernet interfaces commonly operate as broadcast networks by default and therefore use DR and BDR elections when multiple OSPF routers share the same segment. Non-broadcast multiaccess networks can also use DR and BDR mechanisms. Understanding OSPF network types is important because the selected network type affects neighbor discovery, adjacency formation, multicast behavior, and DR/BDR elections.

Question 130

Which EIGRP command displays detailed topology information including successors and feasible successors?

1. show ip eigrp topology
2. show ip eigrp neighbors
3. show ip eigrp interfaces
4. show ip route

Correct Answer: 1

Explanation

The show ip eigrp topology command displays information stored in the EIGRP topology table. This includes destination networks, feasible distances, reported distances, successors, and qualifying alternate paths. It is particularly useful when troubleshooting EIGRP path selection because the administrator can determine why a route became the successor and whether a feasible successor is available. The neighbor command instead focuses on EIGRP adjacencies, while the interface command provides interface-related EIGRP information. By examining the topology table, administrators can better understand DUAL’s decisions and determine whether a backup route satisfies the feasibility condition before a network failure occurs.

Question 131

Which BGP attribute is used to influence inbound traffic by advertising different preferences to a neighboring AS?

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

Correct Answer: 2

Explanation

MED is commonly used to influence how a neighboring autonomous system selects among multiple entry points into the local autonomous system. A lower MED is generally preferred when MED is considered by the receiving BGP router. An organization can therefore advertise different MED values on multiple connections to suggest which link should receive inbound traffic. However, MED is only one part of BGP policy, and the neighboring autonomous system may use other attributes or local policies instead. Weight and Local Preference primarily affect path selection within the local autonomous system, while Router ID is used for BGP speaker identification and does not directly provide inbound traffic engineering.

Question 132

Which OSPF area type permits external route redistribution but represents those external routes using Type 7 LSAs?

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

Correct Answer: 3

Explanation

A Not-So-Stubby Area, or NSSA, allows external routes to be redistributed into the area while preventing normal Type 5 LSAs from entering the area from outside. External routes introduced by an ASBR inside the NSSA are represented using Type 7 LSAs. An appropriate ABR can translate Type 7 LSAs into Type 5 LSAs when advertising the external routes toward other areas. This provides a useful combination of stub-like behavior and controlled external redistribution. A standard stub area does not permit normal external route redistribution, while a totally stubby area imposes even stronger restrictions on inter-area information. NSSA design is therefore useful when limited external connectivity is required.

Question 133

Which EIGRP mechanism is primarily responsible for maintaining loop-free, rapid convergence?

1. DUAL
2. SPF
3. TCP
4. LSA flooding

Correct Answer: 1

Explanation

EIGRP uses the Diffusing Update Algorithm, or DUAL, to calculate loop-free paths and support rapid convergence. DUAL maintains successor and feasible successor information and evaluates alternate paths using the feasibility condition. When the active successor becomes unavailable, EIGRP can immediately use a qualified feasible successor if one exists. If no feasible successor is available, DUAL initiates a query process to discover another valid path. This approach allows EIGRP to converge without periodically recalculating the entire network topology in the same manner as a traditional link-state protocol. Understanding DUAL is central to understanding EIGRP route selection, backup paths, and convergence.

Question 134

Which BGP state indicates that the BGP session has been successfully established and routing updates can be exchanged?

1. Active
2. OpenSent
3. Established
4. Connect

Correct Answer: 3

Explanation

The Established state indicates that a BGP session has successfully completed the required session establishment process and that the peers can exchange routing updates. Before reaching Established, BGP progresses through states such as Idle, Connect, Active, OpenSent, and OpenConfirm. In Established state, the routers exchange Update messages containing routing information and periodically exchange Keepalive messages to maintain the session. If a BGP neighbor remains in Active or another earlier state, the session has not completed successfully. Administrators can use show ip bgp summary and show ip bgp neighbors to identify the current state and investigate connectivity, configuration, authentication, or policy problems.

Question 135

Which OSPF command can be used to display the OSPF process ID, router ID, area information, and timers?

1. show ip ospf
2. show ip ospf neighbor
3. show ip route ospf
4. show ip ospf database

Correct Answer: 1

Explanation

The show ip ospf command provides general information about the OSPF routing process. Depending on the Cisco IOS version and configuration, the output can include the OSPF process ID, router ID, areas, SPF statistics, timers, and other process-level information. This makes it useful when verifying basic OSPF operation and identifying configuration details that may affect adjacency formation or route calculation. The show ip ospf neighbor command focuses on neighbor relationships, while show ip ospf database displays LSAs. The show ip route ospf command focuses on OSPF routes installed in the routing table. Each command therefore provides a different troubleshooting perspective.

Question 136

Which EIGRP route type has an administrative distance of 170 by default?

1. Internal EIGRP
2. External EIGRP
3. Static route
4. OSPF route

Correct Answer: 2

Explanation

External EIGRP routes have a default administrative distance of 170 on Cisco routers. External EIGRP routes are routes that have entered EIGRP through redistribution or another external routing source rather than being learned as native EIGRP internal routes. Internal EIGRP routes have a lower default administrative distance of 90. Because administrative distance determines the preference between routes learned from different routing sources, the higher value for external EIGRP makes it less preferred than internal EIGRP when competing routes have the same destination. Understanding the distinction between internal and external EIGRP is important when troubleshooting redistribution and route installation.

Question 137

Which BGP attribute is evaluated to determine whether a route was learned through an IGP, EGP, or redistribution?

1. Origin
2. Weight
3. Local Preference
4. Next Hop

Correct Answer: 1

Explanation

The BGP Origin attribute identifies how a route was introduced into BGP. Its common values are IGP, EGP, and Incomplete. A route advertised using a BGP network statement normally receives an IGP origin code. Routes introduced through redistribution generally receive an Incomplete origin code. During the BGP best-path selection process, IGP origin is preferred over EGP, and EGP is preferred over Incomplete when this attribute is reached in the comparison sequence. Origin should not be confused with the AS Path, which identifies the autonomous systems through which the route has traveled. Together, these attributes provide important information for BGP path selection and troubleshooting.

Question 138

Which OSPF LSA is used to describe a multiaccess network and the routers connected to that network?

1. Type 4
2. Type 2
3. Type 5
4. Type 3

Correct Answer: 2

Explanation

OSPF Type 2 LSAs are Network LSAs generated by the Designated Router on broadcast and certain other multiaccess network types. The LSA represents the shared network segment and lists the OSPF routers connected to that segment. This approach reduces the amount of information needed to represent a multiaccess network in the link-state database. Type 1 Router LSAs describe individual routers, Type 3 LSAs advertise networks between areas, and Type 4 LSAs provide reachability information for ASBRs. Type 5 LSAs are used for external routes. Type 2 LSAs therefore play an important role in accurately representing multiaccess segments within an OSPF area.

Question 139

Which EIGRP feature can limit the scope of Query packets and improve scalability?

1. EIGRP stub routing
2. Weight
3. MED
4. DR election

Correct Answer: 1

Explanation

EIGRP stub routing helps limit Query propagation by identifying routers that should not be used as transit routers for certain EIGRP destinations. A typical stub router is connected to a limited portion of the network, such as a branch office, and does not need to receive or process every possible Query. When properly configured, the stub relationship tells neighboring routers that the stub router has limited routing information and should not be queried for routes beyond its advertised capabilities. This can reduce unnecessary Query propagation and improve convergence scalability. EIGRP stub routing is especially useful in hub-and-spoke network designs with many remote branches.

Question 140

Which BGP attribute is used to specify the autonomous system through which a route was learned and helps prevent routing loops?

1. MED
2. Weight
3. AS Path
4. Local Preference

Correct Answer: 3

Explanation

The AS Path attribute records the sequence of autonomous systems through which a BGP route has passed. When an eBGP router advertises a route to another autonomous system, its own AS number is normally added to the AS Path. This information allows receiving routers to identify potential routing loops. If a router sees its own autonomous system number in the AS Path of a received route, it normally rejects the route. AS Path also influences BGP best-path selection, where shorter paths are generally preferred when higher-priority attributes do not determine the result. Administrators can additionally use AS-path prepending to influence inbound traffic by making selected paths appear longer.