CCNA Eigrp Questions

MCQmedium

A router has learned a route to 10.10.10.0/24 from both OSPF and EIGRP. The OSPF route has a metric of 20, and the EIGRP route has a metric of 1000. Which route will be installed in the routing table, and why?

A.The EIGRP route, because EIGRP has a lower administrative distance (90) than OSPF (110).

B.The OSPF route, because OSPF has a lower administrative distance (110) than EIGRP (90).

C.Both routes are installed, and the router performs equal-cost multipathing.

D.The OSPF route, because its metric of 20 is lower than EIGRP's metric of 1000.

AnswerA

EIGRP has an administrative distance of 90, which is lower than OSPF's 110. When a router learns the same prefix from multiple routing protocols, it first compares administrative distance. The route with the lower administrative distance is installed in the routing table, regardless of the metric values.

Why this answer

When a router learns the same destination from multiple routing protocols, it uses administrative distance to select the best route. EIGRP's default administrative distance is 90, while OSPF's is 110. Because 90 is lower, the EIGRP route is installed in the routing table.

Metrics are only compared between routes from the same protocol.

Exam trap

The trap here is comparing metrics from different routing protocols, which is invalid because each protocol uses its own metric system.

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MCQhard

A router receives a destination prefix from EIGRP with administrative distance 90 and also from OSPF with administrative distance 110. The prefix length is identical. Which route source is preferred?

A.EIGRP

B.OSPF

C.Both equally

D.Neither, because route sources cannot overlap

AnswerA

EIGRP is the correct choice because its default administrative distance of 90 is lower than OSPF's default of 110 for the same destination prefix. When a router receives overlapping routes from multiple routing protocols, the protocol with the lowest administrative distance is deemed most trustworthy and installed in the routing table. The EIGRP route becomes the active route, while the OSPF route is kept as a backup or not installed at all.

Why this answer

The EIGRP route is preferred because its administrative distance is lower. In practical terms, once the prefix length is the same, the router compares the trustworthiness of the route source. Lower administrative distance wins. Since 90 is lower than 110, EIGRP is preferred over OSPF for that destination.

This is an administrative-distance comparison question, not a longest-prefix question. The key is that the prefix length is equal, so source preference becomes the deciding factor.

Exam trap

A frequent exam trap is to assume that OSPF routes might be preferred over EIGRP routes simply because OSPF is a widely used IGP or because of metric comparisons within OSPF. Candidates often confuse administrative distance with routing metrics, mistakenly thinking that the lower metric route is preferred regardless of protocol. However, administrative distance is the first criterion when routes come from different protocols.

Another trap is to think that routes from different protocols cannot overlap or that prefix length alone determines preference. The key is that when prefix lengths are equal, the router uses administrative distance to select the best route, so EIGRP’s lower AD of 90 always beats OSPF’s 110.

Why the other options are wrong

This option is incorrect because OSPF’s administrative distance of 110 is higher than EIGRP’s 90, so OSPF routes are less preferred when both advertise the same prefix length.

This option is incorrect because routers do not treat routes from different protocols with equal administrative distance; they prefer the route with the lower administrative distance, so both routes are not equally preferred.

This option is incorrect because routers can and often do receive overlapping routes from multiple routing protocols and must compare administrative distance to choose the best route.

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PBQhard

You are connected to R1. Configure R1 so that it uses a floating static route to reach the 203.0.113.0/24 network via R2 only when the primary route (learned via EIGRP) fails. The primary route has an administrative distance of 90. Currently, R1 has no route to 203.0.113.0/24 because EIGRP is down on the direct link. Ensure the floating static route is installed and used.

Network Topology

Hints

•The primary route would be learned via EIGRP with AD 90.
•A floating static route must have an AD higher than 90 to be less preferred.
•Use the 'ip route' command with an AD value between 91 and 255.

A.ip route 203.0.113.0 255.255.255.0 10.0.0.2 95

B.ip route 203.0.113.0 255.255.255.0 10.0.0.2 90

C.ip route 203.0.113.0 255.255.255.0 10.0.0.2 85

D.ip route 203.0.113.0 255.255.255.0 10.0.0.2

AnswerA

solution

! R1
ip route 203.0.113.0 255.255.255.0 10.0.0.2 95

Why this answer

The issue is that R1 has no route to 203.0.113.0/24 because EIGRP is not working (likely due to misconfiguration or link failure). A floating static route with an administrative distance greater than EIGRP's default AD of 90 is needed. By configuring a static route to 203.0.113.0/24 via next-hop 10.0.0.2 with AD 95, the static route will be used only when EIGRP is down (since 95 > 90, EIGRP is preferred when active).

The command 'ip route 203.0.113.0 255.255.255.0 10.0.0.2 95' accomplishes this.

Exam trap

Remember that floating static routes require an administrative distance higher than the primary route's AD. Do not use the default AD (1) or match the primary AD; always set a higher value.

Why the other options are wrong

The AD must be greater than 90 to ensure the static route is only used when EIGRP fails. An AD of 90 does not create a floating static route.

A floating static route must have a higher AD than the primary route. An AD of 85 is lower than 90, so it would be preferred over EIGRP.

The default AD for static routes is 1, which is lower than EIGRP's 90. Without specifying a higher AD, the static route will be preferred and not act as a floating static route.

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MCQmedium

A router learns 10.10.10.0/24 from OSPF and EIGRP at the same time. OSPF reports a metric of 20, and EIGRP reports a metric of 30720. Which route is installed in the routing table by default?

A.The OSPF route, because 20 is lower than 30720

B.The EIGRP route, because its administrative distance is lower

C.Both routes, because they point to the same prefix

D.Neither route, because the metrics are not comparable

AnswerB

Routers prioritise routes for the same destination using administrative distance (AD) before considering protocol metrics. EIGRP has a default administrative distance of 90, which is lower than OSPF's default of 110. Consequently, even though OSPF reports a numerically lower metric, the router will install the EIGRP route for 10.10.10.0/24 into its routing table because its superior administrative distance takes precedence.

Why this answer

When the same prefix is learned from different routing protocols, the router compares administrative distance first. EIGRP internal routes use AD 90, while OSPF uses AD 110, so the EIGRP route is preferred.

Exam trap

Remember, administrative distance is the first criterion for route selection between different protocols, not the metric.

Why the other options are wrong

Metrics from different routing protocols are not comparable because each protocol uses its own metric calculation (e.g., OSPF uses cost based on bandwidth, EIGRP uses composite metric based on bandwidth and delay). The router uses administrative distance to choose between routes from different protocols, not metric values.

A router installs only the best route to a destination in the routing table, unless equal-cost load balancing is configured. Since OSPF and EIGRP have different administrative distances, only the route with the lower AD is installed. Both routes cannot be installed simultaneously for the same prefix.

The router does compare routes from different protocols using administrative distance, not metrics. Since the metrics are from different protocols, they are not directly comparable, but the router still selects one route based on AD. Therefore, one route will be installed.

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MCQhard

A router learns the same destination prefix from OSPF and EIGRP. The prefix length is identical, and both routes are valid. Which route is preferred by default?

A.The EIGRP route

B.The OSPF route

C.Both routes are installed equally because the prefix length matches

D.Neither route is used because protocols cannot advertise the same prefix

AnswerA

The EIGRP route is preferred because EIGRP's default administrative distance (AD) of 90 is lower than OSPF's default AD of 110. When a router receives the same destination prefix from multiple routing protocols, it compares AD values and installs the route with the lowest AD into the routing table. Therefore, the EIGRP route wins this selection.

Why this answer

The EIGRP route is preferred by default because EIGRP has a lower default administrative distance than OSPF. In practical terms, once the prefix length is the same, the router compares source trust. Lower administrative distance wins. EIGRP’s default of 90 beats OSPF’s default of 110.

This is not a longest-prefix question. The prefix is identical, so the decision is about source preference rather than specificity.

Exam trap

A frequent exam trap is believing that when two routing protocols advertise the same prefix with identical prefix lengths, the router installs both routes equally or performs load balancing. This misconception ignores the role of administrative distance, which is the primary factor in route preference when prefix lengths match. Another trap is thinking that OSPF is always preferred because it is a widely used IGP, but Cisco routers prioritize routes based on AD values, not protocol popularity.

Misunderstanding this can lead to incorrect answers about route selection in multi-protocol environments.

Why the other options are wrong

This option is incorrect because OSPF’s default administrative distance (110) is higher than EIGRP’s (90), making OSPF routes less preferred when both advertise the same prefix.

This option is incorrect because equal prefix length does not cause routers to install both routes equally; administrative distance determines which route is preferred and installed.

This option is incorrect because routers can receive and compare the same prefix from multiple routing protocols; they do not reject prefixes simply because they come from different sources.

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PBQhard

You are connected to R1 via the console. R1 is a Cisco ISR 4321 router running IOS-XE. The network team has recently changed the routing protocol from EIGRP to OSPF, but some routes are missing from the routing table. You need to analyze the OSPF neighbor states and LSDB to identify the issue.

Network Topology

Hints

•Check if OSPF neighbors are in FULL state.
•Look for mismatched OSPF network types or hello intervals.
•Verify that both routers are in area 0.

A.Use 'show ip ospf neighbor' to check neighbor state; if not FULL, examine 'show ip ospf interface' for mismatched hello/dead intervals or network type.

B.Use 'show ip route ospf' to verify OSPF routes; if missing, re-enter the OSPF process and redistribute connected routes.

C.Use 'debug ip ospf events' to monitor OSPF packets; if no packets are seen, reconfigure OSPF router ID and clear the OSPF process.

D.Use 'show ip protocols' to verify OSPF process configuration; if incorrect, delete and recreate the OSPF process with the correct network statements.

AnswerA

solution

! R1
show ip ospf neighbor
show ip ospf interface gigabitethernet0/0
show ip route ospf

! R2
show ip ospf neighbor
show ip ospf interface

Why this answer

When OSPF routes are missing, the first diagnostic step is to verify adjacency formation with 'show ip ospf neighbor'; a state other than FULL (e.g., EXSTART, EXCHANGE, or 2-WAY) points to a Layer 2/3 or parameter mismatch. The most common culprits are mismatched hello/dead intervals, area IDs, authentication, MTU, or network type, which are all visible via 'show ip ospf interface'. This methodical approach isolates whether the problem is adjacency or LSDB/route calculation.

Exam trap

200-301 often tests whether candidates jump to configuration changes (redistribution, router ID, process recreation) instead of first verifying OSPF neighbor state and interface parameters, which is the correct diagnostic sequence.

Why the other options are wrong

The specific factual error is that 'show ip route ospf' shows only existing OSPF routes, not neighbor states. Redistribution is not needed for directly connected interfaces in the same OSPF area.

The specific factual error is that debugging is not the initial diagnostic step; it should be used after verifying neighbor states and interface parameters. Changing the router ID is unnecessary unless there is a duplicate router ID issue.

The specific factual error is that 'show ip protocols' does not display per-interface OSPF parameters. The problem is likely at the interface level, not the process level.

MCQhard

A router has the following routes in its routing table: a static route to 10.1.1.0/24 with administrative distance 1, an OSPF route to 10.1.1.0/24 with administrative distance 110, and an EIGRP route to 10.1.1.0/24 with administrative distance 90. A packet arrives destined for 10.1.1.50. Which route will the router use to forward the packet?

A.The static route

B.The EIGRP route

C.The OSPF route

D.The router will load-balance between all three routes

AnswerA

The static route has an administrative distance of 1, which is lower than both OSPF (110) and EIGRP (90). When multiple routes to the same destination exist from different sources, the router prefers the route with the lowest administrative distance. Therefore, the static route is installed in the routing table and used to forward the packet.

Why this answer

Administrative distance is used to select the best route when multiple routing sources provide a route to the same destination. The static route has the lowest administrative distance (1), so it is preferred over EIGRP (90) and OSPF (110). The packet will be forwarded using the static route.

Exam trap

The trap here is assuming that the dynamic routing protocol with the lowest administrative distance among dynamic protocols is chosen, forgetting that a static route has an even lower distance.

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MCQmedium

A router learns the same prefix from both OSPF and EIGRP. Which route is installed by default?

A.The OSPF route because OSPF is link-state

B.The EIGRP route because it has the lower administrative distance

C.The route with the lower metric value regardless of protocol

D.Both routes are always installed

AnswerB

The EIGRP route is installed because EIGRP has an administrative distance of 90, while OSPF uses 110. When a router receives the same prefix from different routing protocols, the lower AD is selected as the best path. Protocol-specific metrics are never compared across protocols; AD is the first tie-breaker.

Why this answer

When identical prefixes are learned from different routing protocols, the router compares administrative distance first. EIGRP internal routes use AD 90, while OSPF uses AD 110.

Exam trap

Remember that lower administrative distance values indicate higher preference. Don't confuse protocol complexity with route preference.

Why the other options are wrong

The type of routing protocol (link-state vs. distance vector) does not determine route preference when comparing routes from different protocols. Route selection is based on administrative distance, not protocol characteristics.

Metrics are only comparable within the same routing protocol. Different protocols use different metrics (e.g., OSPF uses cost, EIGRP uses composite metric), so they cannot be directly compared. Administrative distance is used to choose between protocols.

By default, a router installs only the best route (lowest AD) for a given prefix into the routing table. Both routes are not installed unless features like equal-cost multipath or policy routing are configured, which is not the case here.

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MCQhard

A router learns the same destination from EIGRP and OSPF. The EIGRP route has a metric of 1000, and the OSPF route has a metric of 10. Which route is installed by default?

A.The OSPF route, because 10 is lower than 1000

B.The EIGRP route, because its source has a lower default administrative distance

C.Both routes automatically install for load balancing

D.Neither route installs until the administrator chooses manually

AnswerB

The EIGRP route is chosen because Cisco's default administrative distance for EIGRP is 90, while OSPF uses a default AD of 110. Since the router compares AD first to decide which protocol's route to trust, the lower AD of EIGRP makes it the preferred source for the destination, and OSPF's route is held as a backup only. The metric values, no matter how attractive, are not considered until the AD comparison is resolved, so EIGRP wins outright.

Why this answer

The EIGRP route is installed by default because route selection between different routing protocols is based on administrative distance before the protocol-specific metric is compared across sources. In plain language, the router does not compare an OSPF metric of 10 directly against an EIGRP metric of 1000 because those metrics come from different systems and are not numerically comparable in a meaningful cross-protocol way. Instead, the router first looks at the trustworthiness of the source.

By default, internal EIGRP routes have a lower administrative distance than OSPF routes, so EIGRP wins even though the OSPF metric value appears lower. This is a classic CCNA trap designed to catch people who compare metrics across different protocols without considering administrative distance first.

Exam trap

A common exam trap is to assume that the route with the numerically lowest metric is always preferred, regardless of the routing protocol. In this question, the OSPF route has a metric of 10, which looks better than the EIGRP metric of 1000. However, metrics from different protocols are not directly comparable.

The router first compares administrative distance, which rates the trustworthiness of the routing source. Since EIGRP’s default administrative distance (90) is lower than OSPF’s (110), the router installs the EIGRP route despite its higher metric. This trap tests your understanding of routing protocol preference, not just metric values.

Why the other options are wrong

This option is incorrect because it assumes the router compares OSPF and EIGRP metrics directly. Metrics from different protocols are not comparable until administrative distance is considered, so the lower OSPF metric does not guarantee route installation.

This option is incorrect because load balancing occurs only when multiple equal-cost routes exist within the same routing protocol. Routes from different protocols are not automatically load-balanced simply because they reach the same destination.

This option is incorrect because the router automatically selects the best route using its decision process based on administrative distance and metric. Manual intervention is not required for route installation in this scenario.

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Multi-Selectmedium

A router learns a route to 172.16.0.0/16 via OSPF (administrative distance 110) and a route to 172.16.10.0/24 via EIGRP (administrative distance 90). No other overlapping routes exist. Which TWO statements about how the router handles these routes are correct?

Select 2 answers

A.The router installs only the EIGRP route because it has a lower administrative distance.

B.Both the OSPF and EIGRP routes are installed in the routing table.

C.Traffic to 172.16.10.100 is forwarded using the OSPF route.

D.The EIGRP route is used for all traffic destined to any address within 172.16.0.0/16.

E.The OSPF route is used for destinations within 172.16.0.0/16 that are not part of the 172.16.10.0/24 subnet.

AnswersB, E

Because 172.16.0.0/16 and 172.16.10.0/24 are not identical prefixes, the router treats them as separate destinations in the routing table. The RIB can hold a less-specific covering route and a more-specific route simultaneously, regardless of administrative distance. Longest-prefix matching during packet forwarding then determines which route is used for a given destination.

Why this answer

B is correct because the router installs both routes in the routing table when they have different prefix lengths. The EIGRP route to 172.16.10.0/24 (AD 90) is more specific than the OSPF route to 172.16.0.0/16 (AD 110). The router uses the longest prefix match rule for forwarding, so both routes coexist without conflict.

Exam trap

Cisco often tests the misconception that administrative distance alone determines which route is installed, ignoring the critical role of prefix length in the longest prefix match rule.

Why the other options are wrong

The router does not discard the OSPF route; it installs both /16 and /24 entries because they represent different network-specific entries.

The traffic matches the /24 route, not the /16, so it would be forwarded via the EIGRP next-hop.

The /24 is a subset; traffic outside 172.16.10.0/24 matches only the /16 OSPF route.

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PBQhard

You are connected to R1 via the console. The network currently uses EIGRP as its IGP, but you recently configured a static default route toward R2 (next-hop 203.0.113.2) to reach the Internet. However, traffic from R1 to the Internet is not taking the expected path. Examine the provided routing table and partial configuration, then fix the issue so that the static default route is used only when the EIGRP-learned default route is unavailable.

Network Topology

Hints

•Compare the administrative distances of the two default routes in the routing table.
•The static route currently has a lower AD (1) than EIGRP (90), so it is not acting as a backup.
•To make a static route a floating static, you need to configure an AD higher than the dynamic protocol's AD.

A.Configure the static route with an administrative distance of 100 using 'ip route 0.0.0.0 0.0.0.0 203.0.113.2 100'.

B.Remove the EIGRP default route by configuring 'no network 0.0.0.0' under the EIGRP process.

C.Increase the metric of the EIGRP default route to make it less preferred than the static route.

D.Configure the static route with a next-hop of 203.0.113.2 and a metric of 100.

AnswerA

solution

! R1
configure terminal
no ip route 0.0.0.0 0.0.0.0 203.0.113.2 10
ip route 0.0.0.0 0.0.0.0 203.0.113.2 100
end
write memory

Why this answer

The static default route was configured with an administrative distance (AD) of 10, which is lower than the EIGRP‑learned default route's AD of 90. This made the static route the preferred path, overriding the intended primary EIGRP route. To create a floating static route that only activates when the EIGRP route disappears, the static AD must be raised above 90—using 'ip route 0.0.0.0 0.0.0.0 203.0.113.2 100' ensures the EIGRP route is primary.

Option B is wrong because removing the EIGRP route eliminates the preferred path entirely, defeating the backup purpose. Option C fails because EIGRP metrics are irrelevant against a lower‑AD static route; AD dictates route source preference. Option D is incorrect because static routes do not accept a metric parameter—the trailing number sets the AD, not a metric.

Exam trap

Don't confuse administrative distance with metric. When comparing routes from different sources (static vs. EIGRP), AD is the deciding factor.

Also, remember that static routes use AD, not metric, to influence preference. The 'ip route' command syntax does not include a metric parameter.

Why the other options are wrong

The specific factual error: EIGRP does not use 'network 0.0.0.0' to advertise a default route; default routes are typically redistributed or generated via 'ip default-network' or redistribution. Removing the EIGRP default route would break the intended primary path.

The specific factual error: Administrative distance is the primary factor for route selection between different routing protocols or sources. Changing the EIGRP metric does not affect the comparison with a static route.

The specific factual error: The 'ip route' command syntax is 'ip route prefix mask {next-hop | interface} [distance] [name] [permanent] [tag tag]'. There is no metric parameter. The correct way to make a static route less preferred is to set a higher administrative distance.

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Multi-Selectmedium

Which three of the following are valid features of Enhanced Interior Gateway Routing Protocol (EIGRP)? (Choose three.)

Select 3 answers

.EIGRP maintains a topology table containing all routes learned from neighbors.

.EIGRP uses the Diffusing Update Algorithm (DUAL) to ensure loop-free paths.

.EIGRP supports unequal-cost load balancing using the 'variance' command.

.EIGRP is a link-state routing protocol similar to OSPF.

.EIGRP uses multicast address 224.0.0.5 for all neighbor communications.

.EIGRP automatically summarizes routes at classful boundaries by default on all interfaces.

Why this answer

All three statements are correct features of EIGRP. EIGRP maintains a topology table that stores all routes learned from directly connected neighbors, including feasible successors. It uses the Diffusing Update Algorithm (DUAL) to guarantee loop-free paths by performing a diffusing computation when a route is lost.

Additionally, EIGRP supports unequal-cost load balancing by using the 'variance' command, which allows traffic to be distributed across multiple paths with different metrics, as long as the metric of the alternate path is within the variance multiplier times the best metric.

Exam trap

Cisco often tests the distinction between EIGRP's topology table (which stores all learned routes) and its routing table (which stores only the best routes), and candidates may confuse the 'variance' command with equal-cost load balancing only, forgetting that it enables unequal-cost load balancing.

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MCQhard

A router has the following routes in its routing table: a static route to 10.60.4.16/28, an OSPF route to 10.60.4.0/24, and an EIGRP route to 10.60.0.0/16. Which route will be used for a packet destined to 10.60.4.17?

A.The static route to 10.60.4.16/28

B.The OSPF route to 10.60.4.0/24

C.The EIGRP route to 10.60.0.0/16

D.No route at all

AnswerA

The destination address 10.60.4.17 falls within all three advertised prefixes, but the router selects the route with the longest prefix match. The static route to 10.60.4.16/28 uses a 28-bit subnet mask, which is longer than the 24-bit OSPF route and the 16-bit EIGRP route. Because this /28 prefix provides the most specific match for the destination, it overrides the other less-specific entries in the routing table.

Why this answer

The route used will be the route with the longest matching prefix. In practical terms, 10.60.4.17 falls inside the /28 route shown, and that is more specific than the broader /24 and /16 alternatives. Because specificity comes first, the /28 route wins.

This is a clean route-table interpretation problem that mirrors actual exam-style thinking very closely.

Exam trap

Remember, the longest prefix match rule is crucial; don't assume broader prefixes are better.

Why the other options are wrong

This option is wrong because the OSPF route to 10.60.4.0/24 does not directly match the destination 10.60.4.17, which falls under the static route to 10.60.4.16/28. OSPF would not be preferred if a more specific static route exists.

The EIGRP route to 10.60.0.0/16 is not used for the destination 10.60.4.17 because it does not match the more specific subnet of 10.60.4.16/28, which is preferred in routing decisions.

This option is wrong because there is a valid static route to the destination 10.60.4.17 via the static route to 10.60.4.16/28, making it reachable. Therefore, stating 'no route at all' is incorrect in this context.

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MCQmedium

A router learns 172.16.40.0/24 from OSPF with AD 110 and metric 20. It also learns the same prefix from EIGRP with AD 90 and feasible distance 30720. Which route is installed?

A.The OSPF route because metric 20 is lower than 30720

B.The EIGRP route because its administrative distance is lower

C.Both routes because ECMP is automatic across different protocols

D.Neither route until one is redistributed into the other protocol

AnswerB

The EIGRP route is installed because Cisco routers compare administrative distance (AD) before any metric when two different routing protocols advertise the same prefix. OSPF has a default AD of 110, while EIGRP's default AD is 90, making EIGRP more trustworthy. Since the router selects the route with the lowest AD, the EIGRP route wins regardless of its metric value. Metrics are only compared among routes from the same protocol.

Why this answer

When the same prefix is learned from different routing protocols, the router compares administrative distance first. EIGRP internal routes have AD 90, which beats OSPF AD 110, so the EIGRP path goes into the table.

Exam trap

A frequent exam trap is assuming that the route with the lower metric value is always preferred, regardless of the routing protocol. In this question, the OSPF route has a metric of 20, which seems better than EIGRP's feasible distance of 30720. However, Cisco routers do not compare metrics across different protocols.

Instead, they rely on administrative distance to choose the best route. Mistaking metric comparison for cross-protocol route selection can lead to choosing the wrong answer and misunderstanding how Cisco routing decisions work.

Why the other options are wrong

This option incorrectly assumes that the router compares OSPF metric 20 directly against EIGRP feasible distance 30720 to select the route. Cisco routers do not compare metrics across different routing protocols; they use administrative distance first. Therefore, this option is incorrect.

This option incorrectly claims that both routes are installed due to automatic ECMP across different protocols. Cisco routers do not perform equal-cost load balancing between different routing protocols without explicit redistribution or configuration, so this is false.

This option incorrectly states that neither route is installed until redistribution occurs. Redistribution is not necessary for a router to install a route learned from a routing protocol. The router installs the route with the lowest administrative distance immediately, so this option is incorrect.

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MCQhard

Why is traffic to 10.10.10.200 using the EIGRP route instead of the OSPF route, given that both routes have the same prefix length?

A.Because EIGRP has a lower administrative distance than OSPF for the same prefix length.

B.Because OSPF routes are never installed when EIGRP is present.

C.Because OSPF can be used only for IPv6 routes.

D.Because EIGRP routes always have a smaller subnet mask than OSPF routes.

AnswerA

Both EIGRP and OSPF have learned routes to 10.10.10.0/24, so the prefix lengths are identical, meaning longest-match selection does not break the tie. Cisco's default administrative distance for internal EIGRP is 90, while OSPF's is 110; since lower AD is preferred, the EIGRP route is installed in the routing table. This is the correct explanation of why traffic to 10.10.10.200 uses the EIGRP path.

Why this answer

When two routes have the same prefix length, the router uses administrative distance to choose the route with the lowest value. EIGRP has a default administrative distance of 90, while OSPF uses 110. Therefore, the EIGRP route is preferred.

Exam trap

A common mistake is to assume that OSPF routes always have a lower administrative distance than EIGRP routes.

Why the other options are wrong

OSPF routes are installed when EIGRP is present; routing protocols coexist and the route with the lowest AD is selected.

OSPF supports both IPv4 and IPv6; it is not limited to IPv6.

EIGRP routes do not always have a smaller subnet mask; prefix length is determined by the network design, not the routing protocol.

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