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Question 141

Which EIGRP feature allows multiple equal-cost paths to be installed in the routing table?

1. Split horizon
2. Equal-cost load balancing
3. Route summarization
4. Stub routing

Correct Answer: 2

Explanation

EIGRP supports equal-cost load balancing by installing multiple paths that have the same metric and satisfy the routing requirements. When multiple equal-cost routes are available, the router can place them into the routing table and distribute traffic across them according to the configured switching method. This can improve bandwidth utilization and provide redundancy. The number of paths that can be installed is controlled by the maximum-paths configuration. EIGRP can also perform unequal-cost load balancing through the variance feature when additional conditions are satisfied. Equal-cost load balancing should not be confused with route summarization or stub routing, which serve different purposes in EIGRP network design.

Question 142

Which BGP attribute is used to identify the preferred path within a Cisco router when multiple BGP routes are available?

1. Weight
2. MED
3. Origin
4. Next Hop

Correct Answer: 1

Explanation

Weight is a Cisco-specific BGP attribute that can be used to influence path selection on an individual router. A higher Weight is preferred when comparing eligible BGP paths. Unlike Local Preference, Weight is not advertised to BGP peers, so its effect is limited to the local router. This makes it useful when an administrator wants to select a particular path locally without changing the routing policy of other routers in the autonomous system. Weight is considered before Local Preference in Cisco’s standard BGP best-path process. When troubleshooting BGP, checking Weight can explain why a router selects one path even when another route has a shorter AS Path.

Question 143

Which OSPF command displays the contents of the link-state database?

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

Correct Answer: 2

Explanation

The show ip ospf database command displays the OSPF link-state database maintained by the router. It can show different types of LSAs, including Router LSAs, Network LSAs, Summary LSAs, ASBR Summary LSAs, and external LSAs. The database represents the topology information that OSPF uses when running the SPF algorithm. This command is particularly useful when troubleshooting missing routes, unexpected topology information, or LSA propagation problems. The show ip ospf neighbor command instead displays adjacency states, while show ip route ospf shows routes that were actually installed in the routing table. Comparing the database with the routing table can help identify route calculation issues.

Question 144

Which EIGRP packet is normally sent periodically to maintain neighbor relationships?

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

Correct Answer: 3

Explanation

EIGRP Hello packets are used to discover neighbors and maintain established neighbor relationships. Routers periodically send Hello packets through EIGRP-enabled interfaces, allowing neighboring routers to verify that the remote device is still reachable and participating in EIGRP. The hold timer determines how long a router can wait without receiving expected EIGRP communication before declaring the neighbor unavailable. Hello packets are not primarily used to exchange complete routing information. Update packets carry route information, Query packets request alternate path information, and Reply packets respond to Queries. Proper Hello and hold-timer operation is therefore essential for stable EIGRP neighbor adjacencies.

Question 145

Which BGP attribute is normally used to influence route selection for traffic leaving an autonomous system?

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

Correct Answer: 1

Explanation

Local Preference is commonly used to influence outbound traffic within an autonomous system. A higher Local Preference is generally preferred, allowing administrators to select which external connection should serve as the preferred exit point. Because Local Preference is carried through internal BGP, the policy can influence multiple routers within the autonomous system. For example, an organization with two upstream providers can assign a higher Local Preference to routes learned from one provider. Weight can also influence outbound path selection, but its effect is limited to the local Cisco router. Local Preference provides a broader mechanism for implementing consistent outbound routing policy across an autonomous system.

Question 146

Which OSPF neighbor state indicates that two routers have established bidirectional communication but have not necessarily formed a full adjacency?

1. Init
2. 2-Way
3. Loading
4. Full

Correct Answer: 2

Explanation

The OSPF 2-Way state indicates that two routers have successfully established bidirectional communication. Each router has seen its own router ID in the neighbor’s Hello packet. On broadcast networks, routers that are not selected as the DR or BDR may remain in the 2-Way state with one another rather than forming full database synchronization. DR and BDR routers establish full adjacencies with the other routers on the segment. If an expected point-to-point neighbor remains in 2-Way instead of progressing toward Full, troubleshooting should include network type, priority, and configuration parameters. Understanding the 2-Way state helps distinguish normal behavior from adjacency problems.

Question 147

Which EIGRP command provides information about EIGRP-enabled interfaces and the number of peers using each interface?

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

Correct Answer: 1

Explanation

The show ip eigrp interfaces command provides information about interfaces participating in EIGRP. Depending on the IOS version and command options, the output can include the EIGRP process, interface, peers, packet statistics, timers, and other operational details. This command is useful when checking whether EIGRP is active on an expected interface and whether the interface has established peers. The neighbor command focuses specifically on adjacency information, while the topology command provides route and path details. When troubleshooting an EIGRP interface, administrators can use this command together with show ip eigrp neighbors and show ip protocols to obtain a more complete view of the configuration.

Question 148

Which BGP attribute contains information about the original source of a route within the BGP routing process?

1. MED
2. Origin
3. Weight
4. Local Preference

Correct Answer: 2

Explanation

The BGP Origin attribute indicates how a route was introduced into the BGP routing system. Common Origin values include IGP, EGP, and Incomplete. Routes introduced using a BGP network statement generally receive an IGP origin, while routes introduced through redistribution commonly have an Incomplete origin. When BGP reaches the Origin comparison during its best-path process, an IGP origin is generally preferred over EGP, and EGP is preferred over Incomplete. Origin does not describe the physical source router or next-hop address. Instead, it provides information about how the prefix entered BGP, helping the routing process compare otherwise eligible paths.

Question 149

Which OSPF LSA type is used to advertise external routes throughout an OSPF autonomous system?

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

Correct Answer: 3

Explanation

OSPF Type 5 LSAs are used to advertise external routes that have been redistributed into OSPF by an ASBR. These LSAs normally flood throughout the OSPF autonomous system, except in area types that restrict external LSAs. Type 5 LSAs contain information about the external destination and its external metric. External routes can be represented as E1 or E2 routes depending on the selected external metric type. E2 is the default external metric type on many Cisco configurations, while E1 includes the internal OSPF cost when calculating the total path cost. Understanding Type 5 LSAs is important when troubleshooting redistribution and external route propagation.

Question 150

Which EIGRP metric component represents the accumulated delay across all interfaces in a route?

1. Bandwidth
2. Load
3. Reliability
4. Delay

Correct Answer: 4

Explanation

Delay is an EIGRP metric component that is accumulated across all interfaces along a route. Unlike bandwidth, which uses the minimum bandwidth value along the path, delay is added together for each interface. By default, EIGRP’s composite metric primarily uses bandwidth and delay. The configured delay value on an interface therefore influences the calculated EIGRP metric and can affect path selection. Administrators can inspect interface characteristics using commands such as show interfaces and examine EIGRP topology information to understand route metrics. Changing interface delay can influence routing decisions, but such changes should be carefully planned because they can alter the preferred paths across the network.

Question 151

Which BGP message is used to establish the parameters of a BGP session?

1. Open
2. Update
3. Keepalive
4. Notification

Correct Answer: 1

Explanation

The BGP Open message is used to establish the parameters of a BGP session after the underlying TCP connection has been established. It contains information such as the BGP version, autonomous system number, hold time, and BGP identifier. Both peers exchange Open messages and verify that the session parameters are acceptable. After successful negotiation, the peers exchange Keepalive messages and can transition to the Established state, where Update messages are exchanged. Notification messages are used when serious protocol errors occur. Understanding the Open message is useful when troubleshooting sessions that fail during the early stages of BGP establishment.

Question 152

Which OSPF router is responsible for representing a broadcast multiaccess network in the OSPF topology?

1. ABR
2. ASBR
3. DR
4. Internal router

Correct Answer: 3

Explanation

The Designated Router, or DR, represents a broadcast multiaccess network in the OSPF topology. On Ethernet networks with multiple OSPF routers, electing a DR reduces the number of full adjacencies required. The DR generates a Type 2 Network LSA that describes the shared network segment and identifies the routers connected to it. A Backup Designated Router is also elected to provide a replacement if the DR fails. ABRs connect different OSPF areas, while ASBRs connect OSPF to external routing domains. Understanding the DR role is important when troubleshooting OSPF adjacency behavior and LSA generation on shared Ethernet segments.

Question 153

Which EIGRP feature allows a router to use an unequal-cost path for load balancing?

1. Stub
2. Variance
3. Split horizon
4. Summarization

Correct Answer: 2

Explanation

The EIGRP variance feature allows the router to install certain unequal-cost paths into the routing table for load balancing. By default, EIGRP favors equal-cost paths, but variance can permit additional paths when their metrics fall within the configured variance multiplier of the best path. The alternate path must also satisfy the feasibility condition before it can be used. This allows networks with links of different capacities to distribute traffic across multiple valid paths. Variance should be configured carefully because it directly affects path selection and traffic distribution. The feature is especially useful when network links have different bandwidth or delay characteristics but both can safely carry traffic.

Question 154

Which BGP attribute is generally preferred when the value is lower and can influence inbound traffic from another autonomous system?

1. Local Preference
2. Weight
3. MED
4. Origin

Correct Answer: 3

Explanation

The Multi-Exit Discriminator, or MED, is generally preferred when it has a lower value during the appropriate stage of BGP path selection. MED can be used when two autonomous systems have multiple connections and one network wants to suggest which connection should be preferred for incoming traffic. For example, an organization can advertise a lower MED on one external link than another. The neighboring autonomous system may then prefer the lower-MED route, depending on its own BGP policies and configuration. MED should not be confused with Local Preference, which primarily influences outbound traffic inside an autonomous system and generally prefers higher values.

Question 155

Which OSPF mechanism calculates the shortest path tree from the link-state database?

1. DUAL
2. SPF
3. BGP best-path selection
4. Split horizon

Correct Answer: 2

Explanation

OSPF uses the Shortest Path First algorithm, based on Dijkstra’s algorithm, to calculate the shortest path tree from the link-state database. Each OSPF router builds a representation of the topology within its area and independently calculates the best paths using interface costs. The resulting shortest path tree determines which routes are installed in the routing table. When topology changes occur, OSPF can update its link-state database and run SPF again as necessary. DUAL is associated with EIGRP, while BGP uses a policy-based path-selection process. Understanding SPF helps explain OSPF convergence, route costs, and how topology changes affect routing decisions.

Question 156

Which EIGRP route is considered the primary path and is normally installed in the routing table?

1. Feasible successor
2. Successor
3. Query
4. Reported route

Correct Answer: 2

Explanation

The EIGRP successor is the primary route selected by DUAL and is normally installed in the routing table. It represents the best available path to a destination based on EIGRP’s metric calculation. A feasible successor is a qualifying backup path that satisfies the feasibility condition and can potentially replace the successor immediately if the primary path fails. If no feasible successor exists after a failure, EIGRP may need to send Query packets and perform additional calculations. The distinction between successor and feasible successor is important when troubleshooting EIGRP convergence and understanding why some alternate routes are available for immediate failover while others are not.

Question 157

Which BGP command displays a concise summary of BGP neighbors, their AS numbers, and session states?

1. show ip bgp neighbors
2. show ip bgp
3. show ip bgp summary
4. show ip route bgp

Correct Answer: 3

Explanation

The show ip bgp summary command provides a concise overview of BGP neighbor relationships. The output normally includes the local BGP router ID, local autonomous system, neighbor addresses, remote AS numbers, message counters, and current session state. It also provides information about the number of prefixes received from each neighbor. This command is particularly useful as an initial troubleshooting step because it quickly identifies whether BGP peers are in the Established state. For detailed information about a specific neighbor, show ip bgp neighbors should be used. The BGP routing table itself can be examined with show ip bgp to investigate individual prefixes and their path attributes.

Question 158

Which OSPF LSA provides information about the location of an ASBR in another area?

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

Correct Answer: 3

Explanation

OSPF Type 4 LSAs, known as ASBR Summary LSAs, provide information that allows routers in other areas to reach an ASBR. An ABR generates the Type 4 LSA when an ASBR needs to be reachable from outside its local area. Type 5 LSAs carry the actual external route information originated by the ASBR. The Type 4 LSA therefore provides the path toward the ASBR, while the Type 5 LSA describes the external destination. Type 1 and Type 2 LSAs describe internal routers and multiaccess networks. Understanding the relationship between Type 4 and Type 5 LSAs is useful when troubleshooting external route reachability across multiple OSPF areas.

Question 159

Which EIGRP mechanism prevents a router from advertising a route back through the same interface from which it learned that route?

1. Variance
2. Split horizon
3. Feasibility condition
4. Summarization

Correct Answer: 2

Explanation

EIGRP split horizon prevents a router from advertising a route back through the same interface from which that route was learned. This behavior helps reduce the possibility of routing loops in distance-vector-style routing environments. For example, if a router learns a network from a neighbor through one interface, it normally does not advertise that same network back to that neighbor through the same interface. Split horizon is enabled by default on many EIGRP interfaces, although there are specific network designs where administrators may disable it. Disabling split horizon should be done carefully because it can affect routing behavior and potentially contribute to routing loops.

Question 160

Which BGP attribute is added by an eBGP router to identify the autonomous system through which a route was advertised?

1. AS Path
2. Weight
3. MED
4. Origin

Correct Answer: 1

Explanation

The AS Path attribute records the autonomous systems through which a BGP route has passed. When an eBGP router advertises a route to another autonomous system, it normally adds its own AS number to the AS Path. This provides valuable information for both loop prevention and BGP path selection. If a receiving router detects its own AS number in the path, it normally rejects the route to prevent a routing loop. AS Path can also be modified using AS-path prepending to influence how external networks perceive the length of a route. Because BGP uses multiple attributes, AS Path is considered as part of a larger best-path selection process.