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Question 1

Which routing protocol uses DUAL (Diffusing Update Algorithm) to calculate loop-free paths?

1. OSPF
2. EIGRP
3. IS-IS
4. BGP

Correct Answer: 2

Explanation

EIGRP uses the Diffusing Update Algorithm, commonly known as DUAL, to calculate loop-free paths and maintain efficient routing information. DUAL allows EIGRP routers to select a primary route called a successor and identify a backup route called a feasible successor when available. The algorithm helps EIGRP converge quickly when network topology changes. EIGRP calculates its default metric using bandwidth and delay, although other parameters can also be configured. The feasibility condition ensures that backup routes are loop-free before they can be used. This makes EIGRP particularly useful in enterprise networks that require reliable routing and relatively fast convergence.

Question 2

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

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

Correct Answer: 3

Explanation

OSPF Type 5 LSAs are used to advertise external routes that are introduced into an OSPF autonomous system through route redistribution. An Autonomous System Boundary Router, or ASBR, generates these LSAs when routes from another routing protocol or external source are redistributed into OSPF. Type 5 LSAs are normally flooded throughout the OSPF autonomous system, except in certain special area types such as stub areas. Type 1 LSAs describe router links, Type 2 LSAs describe transit networks, and Type 3 LSAs advertise networks between areas. Understanding different LSA types is important when troubleshooting OSPF route propagation and redistribution.

Question 3

Which BGP attribute is commonly used to influence outbound traffic from an autonomous system?

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

Correct Answer: 3

Explanation

BGP Local Preference is commonly used to influence outbound traffic within an autonomous system. When multiple external routes are available, routers generally prefer the route with the higher Local Preference value. This attribute is propagated among internal BGP peers, allowing administrators to influence the preferred exit point across the autonomous system. Local Preference is different from MED, which is generally used to influence inbound traffic from a neighboring autonomous system. Weight can also influence local Cisco router decisions, but it is Cisco-specific and is not propagated through BGP. Local Preference is therefore an important tool for controlling outbound routing behavior in enterprise and service-provider environments.

Question 4

Which command displays OSPF neighbors and their current adjacency states?

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

Correct Answer: 1

Explanation

The show ip ospf neighbor command displays information about OSPF neighbor relationships and their current states. The output can include the neighbor router ID, priority, state, dead timer, neighbor address, and local interface. Network administrators commonly use this command when troubleshooting OSPF adjacency problems. Depending on the network type, an adjacency may reach the FULL state or another appropriate state. If a neighbor does not establish correctly, this command can help identify the current condition. Other commands provide information about OSPF routes, the link-state database, or routing protocols, but show ip ospf neighbor is specifically designed to examine OSPF neighbor relationships.

Question 5

Which BGP attribute is used to prevent routing loops between autonomous systems?

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

Correct Answer: 4

Explanation

The AS Path attribute is an important BGP mechanism for preventing routing loops between autonomous systems. When a BGP route passes through an autonomous system, that autonomous system number is added to the AS Path. If a BGP router receives a route containing its own autonomous system number in the path, it normally rejects that route because accepting it could create a routing loop. The AS Path also influences BGP path selection because, all else being equal, a shorter AS Path is generally preferred over a longer one. This makes AS Path useful for both loop prevention and route selection across autonomous systems.

Question 6

Which OSPF area type blocks Type 5 LSAs and uses a default route for external destinations?

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

Correct Answer: 1

Explanation

A totally stubby OSPF area restricts external routing information and inter-area summary information while using a default route to reach destinations outside the area. This area type is commonly used to reduce the size of the link-state database and simplify routing information on routers that do not need detailed external routes. Type 5 LSAs are blocked from entering the area, and Type 3 LSAs are also generally restricted except for the default route generated by the ABR. Totally stubby areas are Cisco-specific OSPF implementations. They can reduce routing overhead and simplify configuration in branch or remote network environments.

Question 7

Which EIGRP metric component is primarily associated with the speed of an interface?

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

Correct Answer: 2

Explanation

Bandwidth is one of the primary components used by EIGRP when calculating its composite routing metric. By default, EIGRP considers bandwidth and delay when determining the best path. The bandwidth value represents the configured bandwidth of the interface and helps EIGRP estimate the capacity of the path. Delay represents the cumulative delay across the route. Reliability and load can also participate in EIGRP metric calculations when configured through the appropriate K values, but they are not used by default. Administrators should understand that the bandwidth value is a configured interface parameter and does not necessarily represent the actual measured traffic throughput of the link.

Question 8

Which BGP message is exchanged between established BGP peers to maintain the session?

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

Correct Answer: 3

Explanation

BGP Keepalive messages are periodically exchanged between established BGP peers to confirm that the session is still operational. BGP uses a Hold Timer to determine how long it should wait for a valid message from the neighbor. If the Hold Timer expires without receiving an appropriate message, the BGP session can be considered failed. Keepalive messages help prevent unnecessary session termination when there are no routing updates to exchange. The Open message is used during session establishment, Update messages advertise or withdraw routes, and Notification messages report errors and terminate the session. Keepalive communication is therefore important for maintaining stable BGP peer relationships.

Question 9

Which OSPF router role connects one OSPF area to another OSPF area?

1. ASBR
2. ABR
3. DR
4. BDR

Correct Answer: 2

Explanation

An Area Border Router, or ABR, is an OSPF router that has interfaces in multiple OSPF areas and connects those areas to each other. ABRs maintain separate link-state databases for the areas to which they are connected and can generate Type 3 summary LSAs to advertise networks between areas. An ABR is normally connected to the OSPF backbone area, Area 0, when following the standard hierarchical design. An ASBR has a different role because it connects OSPF to external routing domains through redistribution. DR and BDR are roles used on certain multiaccess OSPF network segments to reduce adjacency requirements.

Question 10

Which BGP attribute is normally preferred when its value is higher during BGP best-path selection?

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

Correct Answer: 1

Explanation

Local Preference is a BGP path attribute where a higher value is generally preferred during the BGP best-path selection process. It is primarily used within an autonomous system to influence which exit point should be selected for outbound traffic. Because Local Preference is shared with internal BGP peers, administrators can establish a consistent outbound routing policy across multiple routers. For example, one Internet connection can be assigned a higher Local Preference than another connection, causing routers to prefer the higher-valued path. This attribute differs from MED, where a lower value is generally preferred. Local Preference is therefore an important policy-control mechanism in BGP networks.

Question 11

Which protocol is used by OSPF to establish neighbor relationships and exchange routing information?

1. TCP
2. UDP
3. IP
4. SCTP

Correct Answer: 3

Explanation

OSPF operates directly over IP and uses IP protocol number 89. Unlike BGP, OSPF does not rely on TCP for communication between routing peers. OSPF uses different packet types, including Hello, Database Description, Link-State Request, Link-State Update, and Link-State Acknowledgment packets. Hello packets are particularly important for discovering neighbors and maintaining neighbor relationships. OSPF routers use multicast addresses on appropriate network types to communicate with neighboring routers. Understanding that OSPF operates directly over IP is useful when troubleshooting connectivity and filtering issues because administrators must account for IP protocol 89 rather than TCP or UDP port numbers.

Question 12

Which EIGRP packet type is used to discover and maintain neighbor relationships?

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

Correct Answer: 2

Explanation

EIGRP Hello packets are used to discover neighboring routers and maintain EIGRP neighbor relationships. Routers periodically send Hello packets through enabled EIGRP interfaces. When another EIGRP router receives these packets and the required parameters match, a neighbor relationship can be established. Hello packets do not carry complete routing information; instead, they primarily provide neighbor discovery and keepalive functionality. EIGRP also uses Update, Query, Reply, and Acknowledgment packets for other routing operations. If EIGRP neighbors are not forming, administrators can check interface configuration, autonomous system settings, K values, network reachability, and authentication parameters along with the Hello packet exchange.

Question 13

Which BGP attribute is generally preferred when its value is lower during best-path selection?

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

Correct Answer: 3

Explanation

The Multi-Exit Discriminator, or MED, is a BGP attribute where a lower value is generally preferred during the relevant stages of BGP path selection. MED can be used to communicate a preference to a neighboring autonomous system about which entry point should be selected when multiple links exist between the two autonomous systems. MED is not normally propagated throughout multiple autonomous systems. Its comparison behavior can also depend on configuration and whether the routes originate from the same neighboring autonomous system. Administrators should therefore understand both the MED value and the surrounding BGP topology before using it to influence traffic flow.

Question 14

Which OSPF packet type is used to exchange summaries of the link-state database between neighbors?

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

Correct Answer: 3

Explanation

OSPF Database Description packets, commonly called DBD packets, are used during adjacency establishment to exchange summaries of the link-state databases between neighboring routers. The DBD packets contain abbreviated information about LSAs rather than the complete LSA contents. After comparing the received information with its own database, a router can use Link-State Request packets to request specific LSAs that it does not have or that are more recent. Hello packets are used for neighbor discovery and maintenance, while Link-State Update packets carry LSAs. Understanding the DBD exchange is important when troubleshooting OSPF neighbors that become stuck during the database synchronization process.

Question 15

Which BGP table contains routes learned from BGP neighbors before the best path is selected?

1. BGP routing table
2. IP routing table
3. BGP neighbor table
4. ARP table

Correct Answer: 1

Explanation

The BGP table, often referred to as the BGP RIB, contains BGP routes learned from configured BGP peers before the router installs the selected best routes into the main IP routing table. BGP can receive multiple paths to the same destination, evaluate those paths using its path-selection process, and select the best available path. Only routes that meet the required conditions are generally considered for installation into the IP routing table. The IP routing table contains the routes ultimately selected for forwarding traffic, while the ARP table contains Layer 2 address mappings. Understanding the distinction between these tables helps troubleshoot BGP route-selection problems.

Question 16

Which OSPF network type automatically elects a DR and BDR?

1. Point-to-point
2. Broadcast
3. Loopback
4. Point-to-multipoint

Correct Answer: 2

Explanation

OSPF broadcast network types, commonly found on Ethernet segments, automatically elect a Designated Router and Backup Designated Router. The DR reduces the number of full OSPF adjacencies required on a shared multiaccess network. Instead of every router forming a full adjacency with every other router, routers establish their primary adjacency relationships through the DR and BDR. The election uses OSPF interface priority and router ID as important factors. Point-to-point networks do not require DR or BDR elections because only two routers are involved. Understanding DR and BDR behavior is important when designing and troubleshooting OSPF networks on Ethernet infrastructure.

Question 17

Which command can be used to verify the BGP routes received from a specific neighbor?

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

Correct Answer: 3

Explanation

The show ip bgp neighbors command provides detailed information about configured BGP neighbors and can be used to examine routes and routing information associated with a particular peer. Depending on the command options and IOS version, administrators can inspect received prefixes, advertised routes, session details, timers, capabilities, and policy information. The show ip bgp summary command provides a concise overview of BGP sessions, while show ip route bgp displays BGP routes installed in the IP routing table. When troubleshooting why a particular prefix is not being received or advertised, detailed neighbor information can provide valuable diagnostic information.

Question 18

Which EIGRP route type represents a backup path that satisfies the feasibility condition?

1. Successor
2. Feasible successor
3. Advertised distance
4. Reported distance

Correct Answer: 2

Explanation

A feasible successor is an EIGRP backup route that satisfies the feasibility condition and can be used as an alternative path when the current successor becomes unavailable. The feasibility condition helps EIGRP ensure that the backup path is loop-free. A feasible successor has a reported distance that is lower than the feasible distance of the current successor. When the successor fails, EIGRP can immediately use a valid feasible successor without performing a full route recomputation. This contributes to EIGRP’s rapid convergence. Not every alternate EIGRP path becomes a feasible successor because it must satisfy the required feasibility condition.

Question 19

Which BGP message is used to advertise new routes or withdraw previously advertised routes?

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

Correct Answer: 1

Explanation

BGP Update messages are used to advertise new routing information and withdraw routes that are no longer reachable. An Update message can contain Network Layer Reachability Information, path attributes, and withdrawn routes. BGP peers process these messages and update their routing information accordingly. Open messages are exchanged when establishing a BGP session and contain important session parameters. Keepalive messages maintain an established session, while Notification messages indicate errors and normally cause the BGP session to terminate. Understanding Update messages is essential for troubleshooting route advertisements, withdrawals, policy behavior, and changes in BGP routing information.

Question 20

Which OSPF area is responsible for connecting different OSPF areas in a hierarchical design?

1. Area 1
2. Area 10
3. Area 0
4. Area 100

Correct Answer: 3

Explanation

OSPF Area 0, also called the backbone area, provides the central connection between different OSPF areas in a hierarchical OSPF design. Inter-area routing information normally passes through the backbone, and other OSPF areas should have logical connectivity to Area 0. Area Border Routers connect non-backbone areas to the backbone and generate summary information between areas. A well-designed OSPF hierarchy helps reduce the size of link-state databases and limits the scope of certain routing changes. Although virtual links can provide connectivity in special situations, the preferred design is to maintain direct logical connectivity between non-backbone areas and the OSPF backbone.