Eigrp practice questions

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?

Trap 1: The OSPF route because metric 20 is lower than 30720

Comparing OSPF's metric of 20 to EIGRP's feasible distance of 30720 is invalid because each routing protocol uses a completely different metric calculation. OSPF calculates cost from interface bandwidth, whereas EIGRP uses a composite formula based on bandwidth and delay, so these numbers are not directly comparable. The router does not attempt to compare metrics across protocols; it first selects the route with the lowest administrative distance. Since EIGRP's AD of 90 is lower than OSPF's 110, the metric values are irrelevant to the final decision.

Trap 2: Both routes because ECMP is automatic across different protocols

Equal-cost multipath (ECMP) only applies when multiple routes have the same metric and are learned from the same routing protocol. Here, OSPF and EIGRP are different protocols with different administrative distances, so the router will not consider them for load balancing. Only the single route with the lowest AD is installed in the routing table, and traffic is forwarded along that one path. ECMP cannot occur across different protocols because they are not evaluated on an equal footing.

Trap 3: Neither route until one is redistributed into the other protocol

Redistribution is not required for a router to install a route learned via OSPF or EIGRP; each protocol independently builds its IP routing table and selects its best route. Redistribution is only used when injecting routes from one routing protocol into another for downstream routers, but it has no bearing on which of the two current routes is chosen for this router. The router simply compares the administrative distance of the two protocols and installs the one with the lower AD. Therefore, route installation and redistribution are separate processes.

A
The OSPF route because metric 20 is lower than 30720
Why wrong: Comparing OSPF's metric of 20 to EIGRP's feasible distance of 30720 is invalid because each routing protocol uses a completely different metric calculation. OSPF calculates cost from interface bandwidth, whereas EIGRP uses a composite formula based on bandwidth and delay, so these numbers are not directly comparable. The router does not attempt to compare metrics across protocols; it first selects the route with the lowest administrative distance. Since EIGRP's AD of 90 is lower than OSPF's 110, the metric values are irrelevant to the final decision.
B
The EIGRP route because its administrative distance is lower
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.
C
Both routes because ECMP is automatic across different protocols
Why wrong: Equal-cost multipath (ECMP) only applies when multiple routes have the same metric and are learned from the same routing protocol. Here, OSPF and EIGRP are different protocols with different administrative distances, so the router will not consider them for load balancing. Only the single route with the lowest AD is installed in the routing table, and traffic is forwarded along that one path. ECMP cannot occur across different protocols because they are not evaluated on an equal footing.
D
Neither route until one is redistributed into the other protocol
Why wrong: Redistribution is not required for a router to install a route learned via OSPF or EIGRP; each protocol independently builds its IP routing table and selects its best route. Redistribution is only used when injecting routes from one routing protocol into another for downstream routers, but it has no bearing on which of the two current routes is chosen for this router. The router simply compares the administrative distance of the two protocols and installs the one with the lower AD. Therefore, route installation and redistribution are separate processes.

Question 2mediummatching

Drag and drop the route types on the left to the correct administrative distance and use case descriptions on the right.

Drag a concept onto its matching description — or click a concept then click the description.

Concepts

Matches

AD 1; manually configured path

AD 5; backup route when primary fails

AD 1; catch-all for unknown destinations

AD 110; used for internal routing within an AS

AD 0; network directly attached to router interface

A
Connected routes: AD 0, directly connected networks
Connected routes are automatically injected into the routing table whenever an interface is configured with an IP address and is in the up/up state. Their administrative distance is 0, the lowest possible value, which means they are always preferred over static, EIGRP, OSPF, or any other route source for the same destination network. Because the network is directly attached to the router, no next-hop or dynamic protocol is needed, making this the correct answer to the question.
B
Static routes: AD 1, manually configured by an administrator
Static routes are indeed manually configured by an administrator and have a default administrative distance of 1. While this is extremely low and makes static routes highly trusted, it is not 0, so static routes are never preferred over directly connected routes if both exist for the same prefix. The question specifically asks for the route type with AD 0, which points to connected routes rather than static routes.
C
EIGRP internal routes: AD 90, used for routing within the same autonomous system
EIGRP internal routes for the same autonomous system have a default administrative distance of 90, which is lower than OSPF but still higher than both connected (0) and static (1) routes. This means an EIGRP-learned route will only be installed in the routing table if no connected or static route exists to that destination. Since the question requires an AD of 0, EIGRP internal routes cannot be the correct answer.
D
OSPF routes: AD 110, used for routing within the same autonomous system
OSPF routes within the same autonomous system use a default administrative distance of 110, making them less preferred than EIGRP internal routes (90), static routes (1), and especially connected routes (0). An OSPF route would be selected only when no lower-AD route is available for the same network. The AD of 110 clearly does not match the AD of 0 referenced in the correct option, so OSPF is not the answer.

Question 3mediummultiple choice

Why is a default route often called a route of last resort?

Trap 1: Because it always has the lowest bandwidth.

This is wrong because the default route is not defined by bandwidth.

Trap 2: Because it must be learned from OSPF only.

This is wrong because default routes can come from several sources, including static configuration.

Trap 3: Because it is more specific than every other route.

This is wrong because the default route is the least specific route.

A
Because it is used only when no more specific route matches the destination.
This is correct because the default route is a fallback path.
B
Because it always has the lowest bandwidth.
Why wrong: This is wrong because the default route is not defined by bandwidth.
C
Because it must be learned from OSPF only.
Why wrong: This is wrong because default routes can come from several sources, including static configuration.
D
Because it is more specific than every other route.
Why wrong: This is wrong because the default route is the least specific route.

Question 4hardmultiple choice

A router shows the following routing table entries for the same destination:

O    10.10.50.0/24 [110/20] via 192.168.12.2, GigabitEthernet0/0
D    10.10.50.0/24 [90/30720] via 192.168.13.2, GigabitEthernet0/1

Which route will become the active route in the routing table?

Trap 1: The OSPF route, because its metric is lower

This is the classic wrong answer because the OSPF metric looks smaller. The mistake is treating metric values from different protocols as if they mean the same thing. They do not. The router first compares administrative distance when choosing between route sources such as OSPF and EIGRP, and only then uses metrics within a single protocol's own logic.

Trap 2: Both routes, because the prefixes are identical

Routers do not automatically install both routes just because the prefix is identical. When the entries come from different routing protocols, the router chooses the source with the best administrative distance first. Only after that, and usually within the same protocol, do equal-cost load-balancing rules come into play.

Trap 3: Neither route, because the metrics use different scales

It is true that the metrics use different scales, but that does not mean the router rejects both routes. Cisco routers solve that comparison problem by using administrative distance first. In this case they still choose one route, and it is the EIGRP route.

A
The OSPF route, because its metric is lower
Why wrong: This is the classic wrong answer because the OSPF metric looks smaller. The mistake is treating metric values from different protocols as if they mean the same thing. They do not. The router first compares administrative distance when choosing between route sources such as OSPF and EIGRP, and only then uses metrics within a single protocol's own logic.
B
The EIGRP route, because its administrative distance is lower
EIGRP is selected because Cisco routers use administrative distance (AD) as the primary trust metric when multiple routing protocols propose the same prefix. The default AD for EIGRP internal routes is 90, while OSPF's default AD is 110; the lower AD wins, so the EIGRP route is installed in the routing table. The metric values from different protocols are never compared against each other—the router first chooses the protocol with the best AD, and only then uses that protocol's metric for path selection. Therefore, even though OSPF may report a numerically smaller cost, EIGRP's lower AD takes precedence.
C
Both routes, because the prefixes are identical
Why wrong: Routers do not automatically install both routes just because the prefix is identical. When the entries come from different routing protocols, the router chooses the source with the best administrative distance first. Only after that, and usually within the same protocol, do equal-cost load-balancing rules come into play.
D
Neither route, because the metrics use different scales
Why wrong: It is true that the metrics use different scales, but that does not mean the router rejects both routes. Cisco routers solve that comparison problem by using administrative distance first. In this case they still choose one route, and it is the EIGRP route.

Question 5mediummultiple choice

Why is RIP rarely chosen for large modern enterprise networks?

Trap 1: It does not support IPv4

RIPv1 and RIPv2 are both IPv4 routing protocols: RIPv1 uses broadcast updates and classful addressing, while RIPv2 adds classless prefixes, VLSM, and multicast updates to 224.0.0.9. RIP is entirely compatible with IPv4, and in fact the original RIP was designed specifically for IPv4, so claiming it lacks IPv4 support is incorrect.

Trap 2: It cannot run on routers and only works on switches

RIP is a traditional distance-vector routing protocol that runs on routers, including enterprise routers and integrated services routers; it can also run on Layer 3 switches, but it is by no means restricted to switch hardware. The idea that RIP cannot run on routers is simply backwards — routers are its primary platform, while switches typically use RIP only if they support Layer 3 routing.

Trap 3: It requires link-state advertisements

RIP is a distance-vector protocol that uses the Bellman-Ford algorithm to compute routes, exchanging periodic copies of its full routing table with directly connected neighbors. It does not build a network-wide topology map or send link-state advertisements; that behavior is characteristic of link-state protocols like OSPF and IS-IS, not RIP.

A
It does not support IPv4
Why wrong: RIPv1 and RIPv2 are both IPv4 routing protocols: RIPv1 uses broadcast updates and classful addressing, while RIPv2 adds classless prefixes, VLSM, and multicast updates to 224.0.0.9. RIP is entirely compatible with IPv4, and in fact the original RIP was designed specifically for IPv4, so claiming it lacks IPv4 support is incorrect.
B
It scales poorly due to slow convergence and hop-count limitations
RIP's maximum hop count of 15 (with 16 considered unreachable) makes it impossible to use in networks with paths longer than 15 routers, and its distance-vector algorithm relies on periodic full-table updates and split horizon, causing slow convergence that scales poorly as network diameter grows. In large enterprise networks, route propagation and reconvergence times become unacceptably slow, and the hop limit itself is a hard scalability barrier.
C
It cannot run on routers and only works on switches
Why wrong: RIP is a traditional distance-vector routing protocol that runs on routers, including enterprise routers and integrated services routers; it can also run on Layer 3 switches, but it is by no means restricted to switch hardware. The idea that RIP cannot run on routers is simply backwards — routers are its primary platform, while switches typically use RIP only if they support Layer 3 routing.
D
It requires link-state advertisements
Why wrong: RIP is a distance-vector protocol that uses the Bellman-Ford algorithm to compute routes, exchanging periodic copies of its full routing table with directly connected neighbors. It does not build a network-wide topology map or send link-state advertisements; that behavior is characteristic of link-state protocols like OSPF and IS-IS, not RIP.

Question 6hardmultiple choice

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?

Trap 1: The OSPF route, because 10 is lower than 1000

The claim that 10 is lower than 1000 incorrectly implies that metric values from OSPF and EIGRP can be directly compared, which is impossible because each protocol uses a distinct metric scale with no common baseline. Even if a numeric comparison were meaningful, routing logic first compares administrative distance—OSPF defaults to 110, while EIGRP uses 90—so the OSPF route would still lose regardless of its metric. The metric is only used as a tiebreaker between routes that already have the same AD, not across different protocols.

Trap 2: Both routes automatically install for load balancing

The router cannot install both routes from different routing protocols just because they reach the same destination. For load balancing to occur, the routes must have identical administrative distances and metrics, and typically originate from the same routing protocol or from a single source. Because EIGRP and OSPF have different ADs (90 and 110), only the EIGRP route will be placed in the routing table, so there is no automatic equal-cost load balancing across protocol boundaries.

Trap 3: Neither route installs until the administrator chooses manually

Routing decisions are fully automated by the router's control plane; there is no requirement for manual selection before a route is installed. When both EIGRP and OSPF advertise the same prefix, the router automatically applies its route-selection logic, comparing administrative distance first and then metric if AD is equal, and installs the winning route without administrator intervention. Manual override would require configuration such as a static route or specifically modifying the distance or using policy routing, but that is not the default behavior.

A
The OSPF route, because 10 is lower than 1000
Why wrong: The claim that 10 is lower than 1000 incorrectly implies that metric values from OSPF and EIGRP can be directly compared, which is impossible because each protocol uses a distinct metric scale with no common baseline. Even if a numeric comparison were meaningful, routing logic first compares administrative distance—OSPF defaults to 110, while EIGRP uses 90—so the OSPF route would still lose regardless of its metric. The metric is only used as a tiebreaker between routes that already have the same AD, not across different protocols.
B
The EIGRP route, because its source has a lower default administrative distance
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.
C
Both routes automatically install for load balancing
Why wrong: The router cannot install both routes from different routing protocols just because they reach the same destination. For load balancing to occur, the routes must have identical administrative distances and metrics, and typically originate from the same routing protocol or from a single source. Because EIGRP and OSPF have different ADs (90 and 110), only the EIGRP route will be placed in the routing table, so there is no automatic equal-cost load balancing across protocol boundaries.
D
Neither route installs until the administrator chooses manually
Why wrong: Routing decisions are fully automated by the router's control plane; there is no requirement for manual selection before a route is installed. When both EIGRP and OSPF advertise the same prefix, the router automatically applies its route-selection logic, comparing administrative distance first and then metric if AD is equal, and installs the winning route without administrator intervention. Manual override would require configuration such as a static route or specifically modifying the distance or using policy routing, but that is not the default behavior.

Question 7hardmultiple choice

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?

Exhibit

R1# show ip route
D    10.10.10.0/24 [90/30720] via 192.0.2.2
O    10.10.10.0/24 [110/20] via 192.0.2.6

Destination being tested: 10.10.10.200

Trap 1: Because OSPF routes are never installed when EIGRP is present.

OSPF routes can absolutely be installed in the routing table when EIGRP is running, provided the OSPF path is the best route (e.g., if EIGRP is not advertising that prefix or has a higher AD). In this scenario, the OSPF route exists as a candidate but is not selected because EIGRP's AD is lower; however, it is still present in the RIB or topology table. The statement falsely claims an absolute prohibition, which is not how multi-protocol routing works; different protocols can coexist and the best route is chosen per prefix.

Trap 2: Because OSPF can be used only for IPv6 routes.

OSPFv2 is specifically designed for IPv4, while OSPFv3 handles IPv6; the claim that OSPF is only for IPv6 is factually incorrect. The destination 10.10.10.200 is an IPv4 address, so OSPF is absolutely a valid routing protocol for this traffic. This option fails because it misrepresents OSPF's protocol capabilities, not because of any routing decision logic.

Trap 3: Because EIGRP routes always have a smaller subnet mask than OSPF…

The subnet mask length advertised by a routing protocol is not an inherent property of the protocol itself; both EIGRP and OSPF can carry any valid IPv4 prefix length, from /8 to /32. In this exhibit, both routes are for 10.10.10.0/24, so the mask lengths are equal, not smaller for EIGRP. Routing preference is determined by administrative distance and metric, never by the protocol's typical mask length, making this option both false and irrelevant.

A
Because EIGRP has a lower administrative distance than OSPF for the same prefix length.
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.
B
Because OSPF routes are never installed when EIGRP is present.
Why wrong: OSPF routes can absolutely be installed in the routing table when EIGRP is running, provided the OSPF path is the best route (e.g., if EIGRP is not advertising that prefix or has a higher AD). In this scenario, the OSPF route exists as a candidate but is not selected because EIGRP's AD is lower; however, it is still present in the RIB or topology table. The statement falsely claims an absolute prohibition, which is not how multi-protocol routing works; different protocols can coexist and the best route is chosen per prefix.
C
Because OSPF can be used only for IPv6 routes.
Why wrong: OSPFv2 is specifically designed for IPv4, while OSPFv3 handles IPv6; the claim that OSPF is only for IPv6 is factually incorrect. The destination 10.10.10.200 is an IPv4 address, so OSPF is absolutely a valid routing protocol for this traffic. This option fails because it misrepresents OSPF's protocol capabilities, not because of any routing decision logic.
D
Because EIGRP routes always have a smaller subnet mask than OSPF routes.
Why wrong: The subnet mask length advertised by a routing protocol is not an inherent property of the protocol itself; both EIGRP and OSPF can carry any valid IPv4 prefix length, from /8 to /32. In this exhibit, both routes are for 10.10.10.0/24, so the mask lengths are equal, not smaller for EIGRP. Routing preference is determined by administrative distance and metric, never by the protocol's typical mask length, making this option both false and irrelevant.

Question 8mediummultiple choice

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

Trap 1: The OSPF route because OSPF is link-state

Selecting OSPF simply because it is link-state ignores how routing preference actually works. Link-state vs distance-vector describes how routes are computed, not which is preferred. Cisco routers compare administrative distance, not protocol type, so OSPF's higher AD (110) loses to EIGRP's 90 regardless of OSPF's link-state advantages.

Trap 2: The route with the lower metric value regardless of protocol

Lower metric never decides between OSPF and EIGRP because their metrics are not comparable — OSPF uses cost derived from bandwidth, while EIGRP uses a composite of bandwidth, delay, load, and reliability. Metrics only matter when comparing routes from the same protocol. A router first applies administrative distance to pick the protocol, then compares metrics only within that protocol.

Trap 3: Both routes are always installed

A router installs only the single best route for each prefix in its routing table, not every route learned from every protocol. Both OSPF and EIGRP may feed the RIB, but the one with the lowest AD is chosen; the other is kept in the topology table but not installed. Only equal-cost paths from the same protocol and same metric could both be installed.

A
The OSPF route because OSPF is link-state
Why wrong: Selecting OSPF simply because it is link-state ignores how routing preference actually works. Link-state vs distance-vector describes how routes are computed, not which is preferred. Cisco routers compare administrative distance, not protocol type, so OSPF's higher AD (110) loses to EIGRP's 90 regardless of OSPF's link-state advantages.
B
The EIGRP route because it has the lower administrative distance
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.
C
The route with the lower metric value regardless of protocol
Why wrong: Lower metric never decides between OSPF and EIGRP because their metrics are not comparable — OSPF uses cost derived from bandwidth, while EIGRP uses a composite of bandwidth, delay, load, and reliability. Metrics only matter when comparing routes from the same protocol. A router first applies administrative distance to pick the protocol, then compares metrics only within that protocol.
D
Both routes are always installed
Why wrong: A router installs only the single best route for each prefix in its routing table, not every route learned from every protocol. Both OSPF and EIGRP may feed the RIB, but the one with the lowest AD is chosen; the other is kept in the topology table but not installed. Only equal-cost paths from the same protocol and same metric could both be installed.

Question 9hardmultiple choice

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?

Trap 1: The OSPF route

The OSPF route is not installed because its default administrative distance of 110 is higher than EIGRP's default AD of 90. Administrative distance acts as a preference rating for routing protocol sources, and OSPF's higher value makes it less trustworthy than EIGRP for the same prefix. Even though OSPF is a valid routing protocol, the lower-AD EIGRP route takes precedence.

Trap 2: Both routes are installed equally because the prefix length matches

Equal prefix length alone does not make routes equally preferred; longest-prefix matching only applies when comparing routes with different subnet masks. Since both OSPF and EIGRP advertise the same prefix and mask, the router must use administrative distance as the next tiebreaker. The route with the lower AD—EIGRP's 90 versus OSPF's 110—is selected exclusively.

Trap 3: Neither route is used because protocols cannot advertise the same…

A router absolutely can receive the same destination prefix from multiple routing protocols; this is a common scenario in networks running both OSPF and EIGRP. Routing protocols do not prohibit overlapping route advertisements, and the router simply selects the best one using administrative distance. Thus, neither route is ignored; the EIGRP route is chosen and placed in the routing table.

A
The EIGRP route
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.
B
The OSPF route
Why wrong: The OSPF route is not installed because its default administrative distance of 110 is higher than EIGRP's default AD of 90. Administrative distance acts as a preference rating for routing protocol sources, and OSPF's higher value makes it less trustworthy than EIGRP for the same prefix. Even though OSPF is a valid routing protocol, the lower-AD EIGRP route takes precedence.
C
Both routes are installed equally because the prefix length matches
Why wrong: Equal prefix length alone does not make routes equally preferred; longest-prefix matching only applies when comparing routes with different subnet masks. Since both OSPF and EIGRP advertise the same prefix and mask, the router must use administrative distance as the next tiebreaker. The route with the lower AD—EIGRP's 90 versus OSPF's 110—is selected exclusively.
D
Neither route is used because protocols cannot advertise the same prefix
Why wrong: A router absolutely can receive the same destination prefix from multiple routing protocols; this is a common scenario in networks running both OSPF and EIGRP. Routing protocols do not prohibit overlapping route advertisements, and the router simply selects the best one using administrative distance. Thus, neither route is ignored; the EIGRP route is chosen and placed in the routing table.

Question 10easymulti select

A company wants all routers and switches to use a common time source so log timestamps line up during incident review. Which two statements about NTP are correct?

Trap 1: It advertises Layer 3 reachability between routers

NTP is transported over IP, but it does not exchange routing information or build neighbor adjacency for Layer 3 reachability. Routing protocols — such as OSPF, EIGRP, and BGP — are responsible for discovering paths and populating the routing table, while NTP merely carries time-sync packets. Therefore, NTP cannot serve as a substitute for a routing protocol.

Trap 2: It encrypts data traffic between endpoints by default

NTP is strictly a time synchronization protocol, so it does not encrypt or protect data-plane traffic by default. Its messages carry time information, not user payloads, and any confidentiality on the wire is an optional enhancement such as NTP authentication, which only verifies packet integrity, not encrypt traffic. Encryption of endpoints is handled by separate protocols like IPsec, TLS, or SSH, not by NTP itself.

A
It helps synchronize device clocks
NTP uses a hierarchical stratum model to distribute UTC time from authoritative sources down to client routers and switches, typically over UDP port 123. Each device adjusts its local clock gradually to eliminate drift and jitter, converging on a mutually consistent time reference. This is the core synchronization mechanism that makes a common time base possible across all networking devices.
B
Consistent time improves correlation of syslog and other event data
When syslog entries, interface counters, RADIUS/TACACS+ records, and access logs carry trustworthy, synchronized timestamps, administrators can sequence security-related and operational events across multiple devices. If each device ticks to a different clock, a single incident can appear as unrelated entries, and reconstructing the exact order of a DDoS attack or unauthorized access becomes nearly impossible. A common time base enables correlated analysis and accurate forensic timelines.
C
It advertises Layer 3 reachability between routers
Why wrong: NTP is transported over IP, but it does not exchange routing information or build neighbor adjacency for Layer 3 reachability. Routing protocols — such as OSPF, EIGRP, and BGP — are responsible for discovering paths and populating the routing table, while NTP merely carries time-sync packets. Therefore, NTP cannot serve as a substitute for a routing protocol.
D
It encrypts data traffic between endpoints by default
Why wrong: NTP is strictly a time synchronization protocol, so it does not encrypt or protect data-plane traffic by default. Its messages carry time information, not user payloads, and any confidentiality on the wire is an optional enhancement such as NTP authentication, which only verifies packet integrity, not encrypt traffic. Encryption of endpoints is handled by separate protocols like IPsec, TLS, or SSH, not by NTP itself.

Question 11mediummulti select

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?

Trap 1: The router installs only the EIGRP route because it has a lower…

Administrative distance is only compared when two routes have the exact same prefix length and network address. Here, OSPF's 172.16.0.0/16 and EIGRP's 172.16.10.0/24 differ in prefix length, so they are treated as different destinations. The router installs both routes; the lower AD of EIGRP does not disqualify the OSPF route.

Trap 2: Traffic to 172.16.10.100 is forwarded using the OSPF route.

Packet forwarding uses longest-prefix match, not administrative distance. The address 172.16.10.100 falls inside the 172.16.10.0/24 subnet, so the EIGRP route with the 24-bit mask is the most specific match and is selected. The OSPF /16 route would only be considered if no longer prefix matched, but here the /24 always wins for addresses within its range.

Trap 3: The EIGRP route is used for all traffic destined to any address…

The EIGRP route covers only the 172.16.10.0/24 subnet, not the entire 172.16.0.0/16 range. Traffic to addresses such as 172.16.11.1 or 172.16.20.1 does not match that /24 prefix, so those packets use the OSPF /16 route instead. The EIGRP route only affects destinations inside its specific /24 subnet, leaving the aggregate route active for everything else.

A
The router installs only the EIGRP route because it has a lower administrative distance.
Why wrong: Administrative distance is only compared when two routes have the exact same prefix length and network address. Here, OSPF's 172.16.0.0/16 and EIGRP's 172.16.10.0/24 differ in prefix length, so they are treated as different destinations. The router installs both routes; the lower AD of EIGRP does not disqualify the OSPF route.
B
Both the OSPF and EIGRP routes are installed in the routing table.
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.
C
Traffic to 172.16.10.100 is forwarded using the OSPF route.
Why wrong: Packet forwarding uses longest-prefix match, not administrative distance. The address 172.16.10.100 falls inside the 172.16.10.0/24 subnet, so the EIGRP route with the 24-bit mask is the most specific match and is selected. The OSPF /16 route would only be considered if no longer prefix matched, but here the /24 always wins for addresses within its range.
D
The EIGRP route is used for all traffic destined to any address within 172.16.0.0/16.
Why wrong: The EIGRP route covers only the 172.16.10.0/24 subnet, not the entire 172.16.0.0/16 range. Traffic to addresses such as 172.16.11.1 or 172.16.20.1 does not match that /24 prefix, so those packets use the OSPF /16 route instead. The EIGRP route only affects destinations inside its specific /24 subnet, leaving the aggregate route active for everything else.
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.
The OSPF 172.16.0.0/16 route is a covering route for the whole major network, but it is not used when the destination matches the more-specific 172.16.10.0/24. For any address within 172.16.0.0/16 that does not fall within the /24 subnet, the router finds only the OSPF /16 match, so that route is used. This is the standard behavior that allows a summary route to coexist with a more-specific child route.