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Question 81

Which EIGRP mechanism ensures that an alternate route is loop-free before it can become a feasible successor?

1. Split horizon
2. Feasibility condition
3. Route summarization
4. Hold timer

Correct Answer: 2

Explanation

The EIGRP feasibility condition is used to determine whether an alternate route can safely become a feasible successor. For a route to satisfy the feasibility condition, the reported distance advertised by the neighboring router must be less than the feasible distance of the current successor. This condition provides EIGRP with a way to identify loop-free backup paths before they are needed. If an alternate route does not satisfy the condition, EIGRP does not immediately consider it a feasible successor. The DUAL algorithm uses this information during route selection and convergence, helping EIGRP maintain loop-free routing while providing rapid recovery when possible.

Question 82

Which BGP command provides a concise overview of all configured BGP neighbors?

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

Correct Answer: 1

Explanation

The show ip bgp summary command provides a concise overview of configured BGP neighbors and the status of their sessions. The output typically includes the local BGP router ID, autonomous system information, neighbor addresses, remote autonomous systems, message counters, table version, and the number of prefixes received. It is one of the first commands administrators use when troubleshooting BGP because it quickly shows whether peers are established. For more detailed information about a specific neighbor, the show ip bgp neighbors command can be used. The summary command is particularly useful for quickly checking multiple BGP sessions on a router.

Question 83

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

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

Correct Answer: 3

Explanation

OSPF Type 4 LSAs, known as ASBR Summary LSAs, identify the location of an Autonomous System Boundary Router to routers in other OSPF areas. When an ASBR is located outside a router’s local area, the Type 4 LSA helps provide reachability information toward that ASBR. The actual external network information is carried by Type 5 LSAs. An ABR generates the Type 4 LSA when appropriate so that routers in other areas can determine how to reach the ASBR. Type 3 LSAs are used for inter-area network advertisements, while Type 2 LSAs describe multiaccess network segments. Understanding Type 4 LSAs helps troubleshoot external route reachability.

Question 84

Which EIGRP packet uses reliable delivery to acknowledge certain EIGRP messages?

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

Correct Answer: 2

Explanation

EIGRP uses acknowledgment packets to confirm the receipt of certain reliably delivered EIGRP messages. EIGRP uses a reliable transport mechanism for important routing information, including certain Update, Query, and Reply packets. An acknowledgment is essentially an EIGRP packet with an acknowledgment number and does not require a separate acknowledgment in return. Hello packets are normally used for neighbor discovery and maintenance and are not acknowledged in the same manner. Reliable delivery helps ensure that critical routing information reaches EIGRP neighbors and supports consistent topology information. Understanding acknowledgments can be useful when troubleshooting packet loss, delayed responses, or unreliable EIGRP neighbor communication.

Question 85

Which BGP attribute is used to provide information about the preferred entry point into an autonomous system?

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

Correct Answer: 2

Explanation

The Multi-Exit Discriminator, or MED, provides a neighboring autonomous system with information about which entry point into the advertising autonomous system may be preferred. When multiple links connect two autonomous systems, an organization can advertise different MED values to indicate a preference for one link over another. Lower MED values are generally preferred when MED is compared. MED is primarily intended to influence inbound traffic decisions made by a neighboring autonomous system. However, the receiving network may apply its own routing policies and comparison rules. Therefore, MED provides a routing suggestion rather than a guaranteed traffic-engineering mechanism across independent autonomous systems.

Question 86

Which OSPF state occurs immediately after a router receives a valid Hello packet from a neighbor but has not yet confirmed bidirectional communication?

1. Init
2. Full
3. Exchange
4. Loading

Correct Answer: 1

Explanation

The OSPF Init state occurs when a router receives a valid Hello packet from another OSPF router but has not yet confirmed two-way communication. The receiving router places the neighbor into the Init state while it checks whether its own router ID appears in the neighbor’s Hello packet. If the local router ID is present, communication is considered bidirectional and the neighbor can progress to the 2-Way state. If the required information is missing or parameters do not match, adjacency formation may stop. Understanding the Init state is useful when troubleshooting OSPF neighbors that are discovered but fail to progress through the normal adjacency process.

Question 87

Which EIGRP table contains information about all known EIGRP routes and potential paths?

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

Correct Answer: 3

Explanation

The EIGRP topology table contains information about routes learned through EIGRP, including the successor and potentially feasible successors. It provides information such as feasible distance, reported distance, and neighboring routers associated with available paths. The main IP routing table contains only the routes selected for forwarding, while the EIGRP neighbor table records established EIGRP peer relationships. The topology table is therefore particularly useful when analyzing EIGRP path selection and convergence. Administrators can use commands such as show ip eigrp topology to inspect this information and determine why a route was selected, why another path was not installed, or whether a feasible successor exists.

Question 88

Which BGP attribute has the highest preference when using Cisco’s standard best-path selection process?

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

Correct Answer: 2

Explanation

Cisco BGP’s standard best-path selection process considers Weight before the other commonly discussed BGP path attributes. A higher Weight is preferred. Weight is Cisco-specific and applies only to the local router, meaning it is not advertised to BGP neighbors. This makes it useful when an administrator wants to influence path selection on a particular router. Local Preference is considered after Weight and is normally used for autonomous-system-wide outbound policy through iBGP. The exact best-path process includes additional checks and platform-specific details, but understanding Weight’s high priority is important when troubleshooting why a Cisco router selects one BGP path over another.

Question 89

Which OSPF command displays routes that were learned through OSPF and installed in the routing table?

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

Correct Answer: 2

Explanation

The show ip route ospf command filters the IPv4 routing table to display routes learned through OSPF. OSPF routes normally appear with the routing code O for intra-area and inter-area routes, while external routes can appear with codes such as O E1 or O E2 depending on the external metric type. This command is useful when verifying whether OSPF routes have actually been installed in the forwarding table. The OSPF database command provides LSA information, while the neighbor command focuses on adjacency relationships. Comparing the OSPF database with the routing table can help determine whether a learned route was excluded during route calculation or installation.

Question 90

Which EIGRP metric component is used to represent the slowest bandwidth along a path?

1. Minimum bandwidth
2. Total delay
3. Reliability
4. Load

Correct Answer: 1

Explanation

EIGRP uses the minimum bandwidth along a route as part of its default composite metric calculation. Rather than adding the bandwidth of every interface, EIGRP identifies the lowest configured bandwidth value along the complete path. This represents the limiting bandwidth of that route. EIGRP also accumulates delay values across all interfaces on the path. By default, bandwidth and delay are the primary metric components used by EIGRP. Reliability and load can be included through different K-value configurations, although changing these values is uncommon. Understanding minimum bandwidth is important when troubleshooting unexpected EIGRP path selection and comparing routes with different link characteristics.

Question 91

Which BGP attribute is commonly used to influence outbound routing decisions throughout an autonomous system?

1. AS Path
2. MED
3. Local Preference
4. Router ID

Correct Answer: 3

Explanation

Local Preference is commonly used to influence outbound routing decisions throughout an autonomous system. A higher Local Preference value is generally preferred, allowing administrators to designate which external connection should be used when multiple paths are available. Because Local Preference is propagated through internal BGP, the policy can affect multiple routers rather than only one device. For example, an organization with two Internet providers can assign a higher Local Preference to routes received from its preferred provider. This allows internal routers to consistently select that provider for outbound traffic. Local Preference therefore provides a scalable mechanism for controlling outbound path selection within an autonomous system.

Question 92

Which OSPF network type normally uses multicast communication and elects a DR and BDR?

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

Correct Answer: 2

Explanation

The OSPF broadcast network type is commonly used on Ethernet networks and uses multicast communication for OSPF neighbor discovery and protocol exchanges. Because multiple routers can share the same Ethernet segment, OSPF elects a Designated Router and Backup Designated Router to reduce the number of full adjacencies required. The DR represents the multiaccess network in the OSPF topology through a Type 2 Network LSA. Point-to-point networks do not require a DR or BDR because only two routers are connected. Understanding the broadcast network type is important when configuring OSPF on Ethernet interfaces and troubleshooting DR elections or neighbor relationships.

Question 93

Which EIGRP route is installed in the routing table when it has the lowest feasible distance among available successors?

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

Correct Answer: 1

Explanation

The EIGRP successor is the route selected as the best path to a destination and is normally installed in the routing table. DUAL compares available EIGRP paths and determines the route with the lowest feasible distance as the successor. If another path satisfies the feasibility condition, it may be retained as a feasible successor for fast failover. The distinction between these two roles is important because the successor is the active forwarding path, while the feasible successor is a qualified backup. If the successor fails and no feasible successor exists, EIGRP may need to query neighbors and perform additional calculations before selecting another valid route.

Question 94

Which BGP message is used to notify a peer about a serious protocol error?

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

Correct Answer: 3

Explanation

BGP Notification messages are used to report serious protocol errors to a BGP peer. When a Notification message is sent, the BGP session is normally terminated. The message includes an error code and subcode that can help identify the reason for the failure, such as an incorrect message type, malformed attribute, or configuration-related issue. Open messages establish the BGP session, Keepalive messages maintain the session, and Update messages exchange routing information. During troubleshooting, administrators can examine BGP logs and detailed neighbor output to determine whether Notification messages are being generated and identify the underlying error that caused the session to terminate.

Question 95

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

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

Correct Answer: 3

Explanation

An Autonomous System Boundary Router generates Type 5 LSAs to advertise external routes that have been redistributed into an OSPF domain. These routes may originate from another routing protocol, a static route, or another external source. Type 5 LSAs contain information about the external destination and associated external metric. They are normally flooded throughout the OSPF autonomous system, although special area types such as stub areas can restrict their propagation. Type 1 and Type 2 LSAs describe internal topology, while Type 3 LSAs advertise networks between OSPF areas. Understanding Type 5 LSAs is essential when troubleshooting route redistribution and external route propagation.

Question 96

Which EIGRP feature allows unequal-cost load balancing across multiple paths?

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

Correct Answer: 1

Explanation

EIGRP supports unequal-cost load balancing using the variance feature. By default, EIGRP generally selects equal-cost paths for load balancing, but variance allows certain additional paths to be installed when their metrics fall within the configured variance multiplier of the best path. The alternate route must also satisfy the EIGRP feasibility condition before it can be used. This provides greater flexibility for networks where available links have different bandwidth or delay characteristics. Administrators can configure variance on an EIGRP router and then verify the resulting paths in the routing and topology tables. Proper configuration can distribute traffic across links with different capacities.

Question 97

Which BGP attribute is used to identify the source of a route within BGP?

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

Correct Answer: 2

Explanation

The BGP Origin attribute identifies how a route was introduced into the BGP routing system. The three commonly recognized values are IGP, EGP, and Incomplete. Routes introduced through a BGP network statement normally receive an IGP origin, while redistributed routes commonly receive an Incomplete origin. During best-path selection, BGP generally prefers IGP over EGP and EGP over Incomplete when reaching the relevant stage of comparison. The Origin attribute is only one factor in the overall BGP selection process, so it does not automatically determine the final path when other attributes have higher priority. Understanding Origin helps explain differences between otherwise similar BGP routes.

Question 98

Which OSPF state is associated with exchanging Database Description packets?

1. Loading
2. Exchange
3. Full
4. Init

Correct Answer: 2

Explanation

The OSPF Exchange state is the stage during which neighboring routers exchange Database Description packets containing summaries of their link-state databases. Each router compares the information received from its neighbor with its own database and determines which LSAs it needs. Routers can then use Link-State Request packets to request missing or newer LSAs, followed by Link-State Update packets containing the requested information. After the required database information has been synchronized, the adjacency can progress to the Full state. If a router becomes stuck in Exchange, administrators should investigate MTU mismatches, packet loss, filtering, or other configuration problems affecting database synchronization.

Question 99

Which BGP attribute can be modified to make a route appear longer to external BGP neighbors?

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

Correct Answer: 3

Explanation

The AS Path can be modified using AS-path prepending to make a route appear to traverse more autonomous systems than it actually does. An administrator can add multiple copies of the local AS number to an outbound BGP advertisement. External networks may then see the path as longer and potentially prefer another available route when their other path-selection attributes are equal. This technique is commonly used to influence inbound traffic toward an organization. However, the result depends on the routing policies of external networks because they may prioritize other BGP attributes. AS-path prepending should therefore be viewed as a policy tool rather than an absolute traffic-control mechanism.

Question 100

Which OSPF component determines the best path based on the shortest cumulative cost?

1. DUAL
2. SPF algorithm
3. BGP decision process
4. EIGRP feasibility condition

Correct Answer: 2

Explanation

OSPF uses the Shortest Path First algorithm to calculate the best paths through the network based on cumulative OSPF interface costs. Each router builds a shortest path tree using the topology information contained in its link-state database. The cost of each link is considered when calculating the total cost toward a destination, and the path with the lowest cumulative cost is generally selected. OSPF’s link-state design allows every router within an area to independently calculate paths from the same topology information. This differs from EIGRP, which uses DUAL, and BGP, which uses a path-selection process based on multiple attributes and routing policies.