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Question 21

Which EIGRP packet type is used when a router needs additional information about a route after the route becomes unavailable?

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

Correct Answer: 3

Explanation

EIGRP uses Query packets when a router loses a successor route and does not have a feasible successor available. The router sends queries to its EIGRP neighbors asking whether they have an alternate path to the affected destination. Neighbors respond using Reply packets, providing information about their available routes. This process is part of EIGRP’s DUAL algorithm and helps the network determine a new loop-free path. Excessive query propagation can increase convergence time and network overhead, so EIGRP features such as route summarization and stub routing can help limit the query domain. Understanding Query and Reply packets is important for EIGRP troubleshooting.

Question 22

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

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

Correct Answer: 1

Explanation

OSPF Type 3 LSAs, also called Summary LSAs, are generated by Area Border Routers to advertise networks from one OSPF area into another area. They allow routers in different areas to learn about inter-area destinations without requiring the complete link-state database of every area. Type 3 LSAs contribute to OSPF’s hierarchical architecture and help limit the size of routing information within individual areas. Type 1 LSAs describe router links, Type 2 LSAs describe multiaccess network information, and Type 5 LSAs advertise external routes. Understanding Type 3 LSAs is important when troubleshooting inter-area route propagation and OSPF summarization.

Question 23

Which BGP attribute is Cisco-specific and has the highest priority in Cisco BGP path selection?

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

Correct Answer: 2

Explanation

BGP Weight is a Cisco-specific attribute used to influence path selection on an individual router. A higher Weight value is preferred over a lower value. Unlike Local Preference, Weight is not advertised to BGP neighbors, so its effect remains local to the router where it is configured. By default, routes originated locally can receive a higher Weight than routes learned from peers, depending on the configuration. Administrators can modify Weight using route maps or other BGP configuration methods to influence which path a particular Cisco router selects. Because Weight is local, it does not directly establish a network-wide outbound routing policy.

Question 24

Which command displays a summary of established BGP neighbor sessions?

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

Correct Answer: 3

Explanation

The show ip bgp summary command provides a concise overview of BGP neighbor relationships and session status. Its output commonly includes the local router ID, local autonomous system, neighbor IP addresses, remote autonomous systems, message counters, table version, and the current state or number of prefixes received from each neighbor. This command is one of the most commonly used BGP troubleshooting commands because it quickly indicates whether peer sessions are established. If a neighbor shows a state such as Active or Idle instead of an established prefix count, additional troubleshooting may be required to identify connectivity, configuration, authentication, or policy problems.

Question 25

Which OSPF state indicates that two routers have successfully synchronized their link-state databases?

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

Correct Answer: 4

Explanation

The OSPF Full state indicates that neighboring routers have completed their database synchronization and have matching link-state information for the relevant adjacency. During OSPF neighbor establishment, routers progress through several states, including Down, Init, 2-Way, ExStart, Exchange, Loading, and Full. The exact adjacency behavior depends on the OSPF network type and whether the routers need to form a full adjacency. On broadcast networks, some routers may remain in the 2-Way state with each other because only relationships involving the DR and BDR require full database synchronization. The Full state is therefore an important indicator of successful OSPF adjacency establishment.

Question 26

Which EIGRP command displays the EIGRP topology table?

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

Correct Answer: 1

Explanation

The show ip eigrp topology command displays information contained in the EIGRP topology table. This table includes routes learned through EIGRP and provides information such as feasible distance, reported distance, successors, and feasible successors. It is especially useful when troubleshooting EIGRP path selection because the topology table contains more information than the main IP routing table. The routing table normally displays only the routes selected for forwarding. By examining the EIGRP topology table, administrators can determine why a particular path was selected or why an alternate path did not become a feasible successor. This command is therefore valuable during EIGRP troubleshooting.

Question 27

Which BGP attribute describes the autonomous systems that a route has traversed?

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

Correct Answer: 2

Explanation

The AS Path attribute records the sequence of autonomous systems through which a BGP route has traveled. Each autonomous system normally adds its own AS number when advertising a route to an external BGP neighbor. BGP routers use this information to help prevent routing loops because a router can reject a route if its own autonomous system number already appears in the AS Path. AS Path length is also considered during BGP best-path selection, with shorter paths generally preferred when higher-priority attributes are equal. Network administrators can manipulate AS Path information through techniques such as AS-path prepending to influence how external networks select inbound paths.

Question 28

Which OSPF LSA type represents the link-state information generated by an individual router?

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

Correct Answer: 3

Explanation

OSPF Type 1 LSAs are Router LSAs generated by every OSPF router within an area. They describe the router’s interfaces, connected links, and the state of those links within the local area. Every OSPF router maintains Type 1 information for the routers participating in its area. These LSAs form an important part of the link-state database used by OSPF’s Shortest Path First algorithm to calculate routes. Type 2 LSAs describe transit networks, Type 3 LSAs advertise inter-area networks, and Type 5 LSAs represent external routes. Understanding Type 1 LSAs helps administrators interpret OSPF database information during troubleshooting.

Question 29

Which routing protocol uses multicast address 224.0.0.10 for neighbor communication?

1. OSPF
2. EIGRP
3. BGP
4. RIP

Correct Answer: 2

Explanation

EIGRP uses the IPv4 multicast address 224.0.0.10 to communicate with EIGRP-capable routers on the local network. EIGRP Hello and other protocol packets can use this multicast address to reach neighboring EIGRP routers without requiring individual unicast destinations. OSPF uses different multicast addresses, including 224.0.0.5 for all OSPF routers and 224.0.0.6 for designated routers. BGP normally establishes sessions using TCP unicast connections, while RIP uses 224.0.0.9 for RIPv2. Knowing protocol multicast addresses can help network administrators troubleshoot multicast filtering, interface configuration, and routing protocol neighbor discovery problems.

Question 30

Which BGP path attribute is normally propagated to internal BGP peers and used to select an outbound exit point?

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

Correct Answer: 1

Explanation

Local Preference is propagated to internal BGP peers and is commonly used to determine the preferred exit point from an autonomous system. When multiple external paths are available, routers generally prefer the path with the highest Local Preference value. This allows administrators to establish consistent outbound routing policies across multiple routers within the same autonomous system. Local Preference is not normally advertised to external BGP neighbors. In contrast, MED is intended to communicate a preference between neighboring autonomous systems and is generally compared as a lower-is-better attribute. Proper use of Local Preference is therefore important when controlling outbound traffic across multiple external connections.

Question 31

Which OSPF network type does not require a DR or BDR election?

1. Broadcast
2. Nonbroadcast multiaccess
3. Point-to-point
4. Point-to-multipoint nonbroadcast

Correct Answer: 3

Explanation

OSPF point-to-point network types do not require a Designated Router or Backup Designated Router election because the network is designed to connect two OSPF routers directly. Both routers can form an adjacency without the additional DR and BDR mechanism required on multiaccess networks. Broadcast and nonbroadcast multiaccess networks can require DR and BDR elections because multiple routers share the same segment. Point-to-multipoint configurations also use different adjacency behavior depending on the implementation. Understanding OSPF network types is important because they affect neighbor discovery, adjacency formation, packet behavior, and the requirement for DR and BDR elections.

Question 32

Which EIGRP feature can reduce the scope of query propagation in a network?

1. Route redistribution
2. EIGRP stub routing
3. Split horizon disablement
4. Passive interfaces

Correct Answer: 2

Explanation

EIGRP stub routing can reduce the scope of query propagation by informing neighboring routers that a particular router should not be considered as a transit path for certain destinations. Stub routers are commonly used at branch locations where the router does not need to provide transit routing between other parts of the network. When a route becomes unavailable, this can help prevent unnecessary EIGRP queries from being propagated toward the stub router. Reducing query scope can improve convergence behavior and reduce routing protocol overhead. EIGRP stub configurations should be designed carefully so that the router advertises only the route types and networks appropriate for its role.

Question 33

Which BGP message is exchanged when a BGP session is first established?

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

Correct Answer: 4

Explanation

BGP peers exchange Open messages when establishing a BGP session. The Open message contains important parameters such as the BGP version, autonomous system number, BGP identifier, Hold Time, and optional capabilities. After two routers successfully exchange and accept Open messages, they use Keepalive messages to maintain the session and Update messages to exchange routing information. If a serious protocol error occurs, a Notification message can be sent and the session may be terminated. Understanding the BGP session establishment process helps administrators troubleshoot problems where peers remain in states such as Active or Idle instead of reaching the established state.

Question 34

Which OSPF mechanism allows an area to advertise external routes without using Type 5 LSAs inside the area?

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

Correct Answer: 1

Explanation

A Not-So-Stubby Area, or NSSA, allows an OSPF area to contain an ASBR and introduce external routes while restricting Type 5 LSAs from entering the area. The ASBR inside the NSSA generates Type 7 LSAs to represent external routes. These Type 7 LSAs can then be translated into Type 5 LSAs by an appropriate ABR when the routes need to be advertised outside the NSSA. This design provides a balance between limiting external routing information and allowing redistribution within the area. NSSA is useful in branch or special network designs where external connectivity is required without making the entire area a standard OSPF area.

Question 35

Which command displays routes learned through EIGRP in the IPv4 routing table?

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

Correct Answer: 2

Explanation

The show ip route eigrp command filters the IPv4 routing table to display routes learned through EIGRP. EIGRP routes in the routing table are normally identified by the code D for internal EIGRP and D EX for external EIGRP. This command is useful when administrators need to quickly verify whether EIGRP routes have been installed in the forwarding table. The EIGRP neighbor and topology commands provide additional information about peer relationships and available paths, but they do not directly show the filtered routing table view. When troubleshooting route installation, administrators can compare the EIGRP topology table with the actual IP routing table.

Question 36

Which BGP attribute is used to indicate where a route originated?

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

Correct Answer: 3

Explanation

The BGP Origin attribute indicates how a route was introduced into BGP. It has three commonly recognized values: IGP, EGP, and Incomplete. An IGP origin generally indicates that the network was introduced using a network statement, while Incomplete commonly indicates that the route was redistributed into BGP. The Origin attribute is considered during BGP best-path selection after several higher-priority attributes. In general, an IGP origin is preferred over an EGP origin, and an EGP origin is preferred over an Incomplete origin. Understanding the Origin attribute can help explain why BGP selects one route over another when other path attributes are equal.

Question 37

Which OSPF LSA type is used to advertise the location of an ASBR to routers in other areas?

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

Correct Answer: 1

Explanation

OSPF Type 4 LSAs, known as ASBR Summary LSAs, are generated by an Area Border Router to provide information about the location of an Autonomous System Boundary Router in another OSPF area. This information allows routers in other areas to determine how to reach the ASBR when they need to use externally originated routes. Type 4 LSAs are different from Type 5 LSAs, which contain the external network information itself. Type 3 LSAs advertise inter-area network information, while Type 1 and Type 2 LSAs describe topology within an area. Understanding Type 4 LSAs is particularly useful when troubleshooting external route reachability across multiple OSPF areas.

Question 38

Which EIGRP route is identified as the primary route selected by DUAL?

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

Correct Answer: 2

Explanation

The EIGRP successor is the primary route selected by the DUAL algorithm for a destination. It represents the best available path that EIGRP places into the routing table. If a feasible successor exists, it can provide an immediate backup path if the current successor fails. EIGRP evaluates routes using its composite metric and applies the feasibility condition when determining whether an alternate path can safely be considered a feasible successor. If no feasible successor exists after a successor failure, EIGRP may need to enter an active state and send queries to neighbors. Understanding successor and feasible successor roles is essential for analyzing EIGRP convergence.

Question 39

Which BGP attribute is used to influence how external networks select an entry point into an autonomous system?

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

Correct Answer: 3

Explanation

The Multi-Exit Discriminator, or MED, can be used to influence how a neighboring autonomous system selects an entry point into another autonomous system when multiple connections are available. A lower MED value is generally preferred when MED is compared. MED is carried in BGP updates and provides neighboring autonomous systems with information about the preferred path for entering the advertising autonomous system. Its behavior can depend on configuration and comparison rules, so administrators should understand the BGP topology before relying on MED for traffic engineering. Local Preference, by contrast, is mainly used internally to influence outbound path selection within an autonomous system.

Question 40

Which protocol is commonly used to redistribute routes between different routing domains?

1. OSPF
2. EIGRP
3. BGP
4. Route redistribution

Correct Answer: 4

Explanation

Route redistribution is the mechanism used to exchange routing information between different routing protocols or routing domains. For example, an administrator can redistribute routes from OSPF into EIGRP or from EIGRP into OSPF. Redistribution requires careful policy control because different protocols use different metrics, route-selection processes, and administrative characteristics. Route maps, prefix lists, distribute lists, and metric configuration can be used to control which routes are redistributed. Improper redistribution can introduce routing loops, suboptimal paths, or excessive routing information. Therefore, redistribution should normally be designed with clear route filtering and metric policies to maintain predictable network behavior.