CCNA IP Routing Practice Test 25 — 15 Questions

Question 1

Refer to the exhibit. A network administrator is troubleshooting an OSPF adjacency on R1's GigabitEthernet0/0 interface connected directly to R2. R2 is powered on and shows correct OSPF configuration, but the adjacency is stuck in the INIT or DOWN state. Based on the output, what is the most likely cause of the failure?

Choose an answer to begin — your selection is scored in the full session.

Accepted Answer

The OSPF passive-interface command has been applied to GigabitEthernet0/0, preventing hello packets from being sent.. The adjacency is stuck in INIT or DOWN state, which indicates that R1 is not receiving OSPF Hello packets from R2. The passive-interface command on GigabitEthernet0/0 prevents R1 from sending Hellos, so R2 never sees R1, and R1 may see R2's Hellos (stuck in INIT) or not (stuck in DOWN). This matches the symptom exactly, as passive-interface suppresses outgoing Hellos while still allowing the interface to be advertised.

Answer

The OSPF network type on R1's GigabitEthernet0/0 does not match the network type on R2.

Answer

The OSPF hello and dead timers on R1 do not match those configured on R2.

Answer

The GigabitEthernet0/0 interface on R1 has been assigned to a different OSPF area than R2's connected interface.

Question 2

A network engineer configures a static route: ip route 192.168.10.0 255.255.255.0 10.1.1.2. The next hop 10.1.1.2 is reachable via OSPF. Later, the engineer notices that the route to 192.168.10.0/24 has disappeared from the routing table. What is the most likely cause?

Accepted Answer

The OSPF route to 10.1.1.0/30 has been lost, making the next-hop address 10.1.1.2 unresolvable.. The static route to 192.168.10.0/24 uses 10.1.1.2 as the next-hop address. For a static route with a next-hop IP (rather than an exit interface) to be installed in the routing table, the next-hop must be reachable via a valid route in the routing table. If the OSPF route to the subnet containing 10.1.1.2 (e.g., 10.1.1.0/30) is lost, the next-hop becomes unreachable, and the static route is removed from the routing table. This is the most likely cause of the route disappearing.

Answer

The static route has a higher administrative distance than OSPF, so OSPF's route to 192.168.10.0/24 replaced it.

Answer

The static route uses a next-hop IP address that is not directly connected, which is unsupported on this platform.

Answer

A routing loop caused by recursive lookups has suppressed the static route to prevent loops.

Question 3

R1 loses its route to 192.168.20.0/24 whenever R2's GigabitEthernet0/0 interface flaps. The network engineer has configured a floating static route with an administrative distance of 200. The OSPF route has an AD of 110. After R2's G0/0 interface recovers, the floating static route appears in the routing table instead of the OSPF route. What should the technician do next?

Accepted Answer

Check the carrier delay timers on R2's GigabitEthernet0/0 interface.. When R2's GigabitEthernet0/0 interface flaps, the OSPF neighbor relationship goes down, causing R1 to lose the OSPF route. The floating static route (AD 200) then takes over. After the interface recovers, OSPF should re-establish and install its route (AD 110) over the static route. However, if the carrier delay timer on R2's interface is set too high, the interface may not come up quickly enough for OSPF to re-converge before the floating static route is already installed and preferred. Checking and adjusting the carrier delay timer ensures that the interface state change is propagated promptly, allowing OSPF to re-establish and replace the static route.

Answer

Adjust the administrative distance of the floating static route to 201.

Answer

Clear the IP routing table and reset the OSPF process on R1.

Answer

Verify that the MTU on R1 and R2's GigabitEthernet0/0 interfaces match.

Question 4

A network engineer adds a loopback interface Lo0 with IP address 172.16.0.1/32 to router R1. After restarting the OSPF process, the OSPF router-ID changes from 10.1.1.1 to 172.16.0.1, and the neighbor relationship with R2 resets. What should the technician do next to prevent this disruption the next time a loopback is added?

Accepted Answer

Configure a static router-id using the router-id command under the OSPF process. The OSPF router-ID is dynamically selected based on the highest IP address of any loopback interface, or if none exist, the highest IP of any physical interface. Adding a new loopback with a higher IP than the current router-ID causes OSPF to reselect a new router-ID upon process restart, which resets all neighbor adjacencies. Configuring a static router-ID with the 'router-id' command under the OSPF process prevents this disruption by fixing the router-ID regardless of interface IP changes.

Answer

Configure passive-interface Lo0 under the OSPF process

Answer

Set a higher OSPF priority on the router’s interfaces

Answer

Configure the OSPF area as a stub area

Question 5

Refer to the exhibit. A network engineer notices that traffic from R1 to the 10.1.0.0/16 network is taking a longer path than expected despite OSPF being the only routing protocol. The engineer examines the OSPF LSDB on R1 to investigate. Based on the output, what is the most likely cause of the suboptimal routing?

Accepted Answer

The ABR is configured with the 'area 1 range 10.1.0.0 255.255.0.0 cost 1000' command.. The OSPF LSDB output shows that the route to 10.1.0.0/16 has a metric of 1000, which is unusually high for an intra-area or inter-area route. The 'area 1 range 10.1.0.0 255.255.0.0 cost 1000' command on the ABR sets a fixed cost for the summarized route, overriding the default OSPF cost calculation. This causes R1 to see a higher metric for the summarized route, leading to suboptimal routing if a lower-cost path exists via another area or router.

Answer

The reference bandwidth has been misconfigured on R1, causing the OSPF cost calculation to be inflated for some links.

Answer

The ABR is filtering the 10.1.0.0/16 route from Area 1 into Area 0, causing the router to recalculate the metric higher.

Answer

The metric-type for OSPF external routes has been set to type 2, causing the metric to be inflated to 1000 for the 10.1.0.0/16 prefix.

Question 6

A technician is troubleshooting an OSPF network. On a broadcast segment, R1 is the DR and R2 is the BDR. R1's interface GigabitEthernet0/0 is shut down for maintenance. The technician expects that R2 will assume the DR role, but instead a new DR election occurs and another router is elected DR. What is the most likely cause?

Accepted Answer

R2 has an OSPF priority of 0.. When the DR (R1) goes down, a new DR election occurs. R2 is the BDR, but if its OSPF priority is 0, it is ineligible to become the DR. Therefore, a new election takes place among the remaining routers with non-zero priorities, and another router wins the DR role.

Answer

The OSPF hello and dead intervals on R2 do not match those of other routers on the segment.

Answer

R2 has an OSPF priority of 255.

Answer

The OSPF network type on the segment was changed to point-to-point.

Question 7

After configuring a static discard route with the command 'ip route 0.0.0.0 0.0.0.0 Null0 254' on R1, a network engineer finds that traffic to destinations that are not in the routing table is still being forwarded out to the ISP instead of being dropped. What is the most likely cause?

Accepted Answer

The ISP static default route has an administrative distance of 1, which is lower than the administrative distance of 254 set for the Null0 route.. The static discard route with an administrative distance of 254 is less preferred than the ISP default route with an administrative distance of 1. Since the ISP route has a lower AD, it remains in the routing table and is used for forwarding traffic to unknown destinations, overriding the discard route. The Null0 route only becomes active if the ISP route is removed or fails, as the router always selects the route with the lowest administrative distance.

Answer

The Null0 interface is administratively shut down.

Answer

The address 0.0.0.0/0 is an invalid destination for a static route because it is not a real network.

Answer

The static discard route must include a next-hop IP address instead of specifying Null0 as the interface.

Question 8

A network technician is troubleshooting a router-on-a-stick configuration. R1 has sub-interface G0/0.10 with encapsulation dot1q 10 and IP 192.168.10.1/24, and sub-interface G0/0.20 with encapsulation dot1q 20 and IP 192.168.20.1/24. Hosts in VLAN 10 cannot reach hosts in VLAN 20. The physical interface G0/0 is up and no shutdown. Both sub-interfaces show up/up. What should the technician do next?

Accepted Answer

Verify the switch port connected to R1 is configured as a trunk and allows VLANs 10 and 20.. The router-on-a-stick configuration requires the switch port connecting to R1 to be configured as a trunk port that permits VLANs 10 and 20. Even though the router sub-interfaces are correctly configured with encapsulation dot1q and IP addresses, if the switch port is in access mode or does not allow the specific VLANs, frames from VLAN 10 or 20 will be dropped by the switch, preventing inter-VLAN routing. The next logical step is to verify the switch port configuration with commands like 'show interfaces trunk' or 'show running-config interface <port>'.

Answer

Verify the encapsulation dot1Q numbers on the sub-interfaces match the VLAN assignments.

Answer

Verify the default gateway settings on hosts in VLANs 10 and 20.

Answer

Check the physical interface G0/0 for interface errors or duplex mismatches.

Question 9

A technician configures OSPF on R1 using the command network 10.0.0.0 0.0.0.255 area 0. R1's GigabitEthernet0/0 interface has IP address 10.0.0.1/30 and is included in the OSPF process. The technician confirms the interface is not passive using the show ip ospf interface GigabitEthernet0/0 command. However, R2 is not forming an OSPF adjacency with R1. What should the technician do next?

Accepted Answer

Verify the subnet mask configured on R2's connecting interface.. The OSPF network command 10.0.0.0 0.0.0.255 area 0 uses a wildcard mask that matches only the first 24 bits. The interface on R1 has a /30 mask (255.255.255.252), so its IP 10.0.0.1 falls within the 10.0.0.0/24 range. However, if R2's connecting interface has a different subnet mask (e.g., /24 or /28), the two interfaces will be in different subnets, preventing OSPF adjacency from forming. OSPF requires that interfaces on the same link share the same subnet prefix length to establish a neighbor relationship.

Answer

Check the OSPF hello and dead intervals on R1 and R2.

Answer

Verify the OSPF area ID configured on R2's interface.

Answer

Check whether R2's interface is configured as a passive interface.

Question 10

Refer to the exhibit. An engineer expects all traffic destined to the 10.10.10.0 network to be forwarded via 10.1.1.2. However, when testing connectivity to host 10.10.10.64, traffic is being sent to 10.2.2.2 instead. What is the most likely cause?

Accepted Answer

The router is using longest prefix matching; the /26 route is more specific, so traffic to 10.10.10.64 is forwarded via 10.2.2.2.. B is correct because routers use longest prefix matching to forward traffic. The route to 10.10.10.64/26 is more specific (longer prefix length) than the route to 10.10.10.0/24, so even though the /24 route may have a lower administrative distance, the /26 route is preferred for traffic destined to 10.10.10.64. This is a fundamental IP routing principle that overrides administrative distance when both routes exist in the routing table.

Answer

The static route to 10.10.10.0/24 has a higher administrative distance than the /26 route, making the /26 preferred.

Answer

The /26 static route was configured as a floating static route with an administrative distance of 5, overriding the /24 route.

Answer

The next-hop 10.1.1.2 for the /24 route is unreachable, causing the router to fall back to the /26 route.

Question 11

Refer to the exhibit. A network engineer is verifying OSPF routing on R1. All routers in the topology are expected to reside in OSPF area 0, and the network 172.16.0.0/16 should be advertised from R2 within the same area. The engineer issues the show ip route 172.16.0.0 command on R1 and sees the output in the exhibit. The engineer expected to see an intra-area route (O) instead of an inter-area route (O IA). What is the most likely cause of this discrepancy?

Accepted Answer

The destination network 172.16.0.0/16 is located in a different OSPF area.. The route 172.16.0.0/16 appears as O IA (inter-area) on R1, which means R1 learned it via a Type 3 LSA from an ABR. For the route to be intra-area (O), the destination network must reside in the same OSPF area (area 0) as R1. Since R2 is advertising this network, if it were truly in area 0, R1 would see an O route. The O IA designation indicates that the network is in a different area, likely because R2's interface connected to 172.16.0.0/16 is configured in a different OSPF area, or R2 is acting as an ABR.

Answer

R1 has a mismatched OSPF process ID compared to the ABR.

Answer

The network type on GigabitEthernet0/0 is configured as non-broadcast, preventing full adjacency.

Answer

The metric for the route is too high, causing OSPF to treat it as an inter-area route.

Question 12

Refer to the exhibit. A network engineer is troubleshooting connectivity to server 10.10.10.130. The routing table contains both a static route and an OSPF route for overlapping prefixes. The engineer examines the specific routing entry for 10.10.10.130. Based on the output, why does the router choose the route via 10.1.1.2 instead of the OSPF route via 10.2.2.2 (for 10.10.10.0/24)?

Accepted Answer

The static route has a longer prefix length (/26) than the OSPF route (/24), making it a more specific match.. The router selects the route via 10.1.1.2 because the static route has a prefix length of /26, which is longer (more specific) than the OSPF route's /24. When multiple routes to the same destination exist, the router uses the most specific match (longest prefix) regardless of administrative distance or metric. Since 10.10.10.130 falls within the 10.10.10.128/26 range, the /26 route is preferred over the /24 route.

Answer

The static route has a lower administrative distance (1) than the OSPF route (110).

Answer

The OSPF route is inactive because its next-hop 10.2.2.2 is down.

Answer

The router prefers the static route because it has a metric of 0, which is better than the OSPF metric.

Question 13

Refer to the exhibit. An administrator is troubleshooting connectivity from a branch router R1 to the internet. A ping to 8.8.8.8 from R1 fails. The output of the show ip route command is shown. What is the most likely cause?

Accepted Answer

The next-hop IP address for the default route is not reachable.. The ping to 8.8.8.8 fails because the default route (0.0.0.0/0) points to a next-hop IP address that is not reachable. The routing table shows the default route is present, but if the next-hop address is not in the routing table via a connected or static route, the router cannot resolve the Layer 2 adjacency and will not forward packets. This is confirmed by the fact that the default route exists but the ping fails, indicating a reachability issue with the next hop.

Answer

The default route is missing from the routing table.

Answer

The static route has an incorrect administrative distance.

Answer

The ip routing process has not been enabled.

Question 14

Refer to the exhibit. A network administrator is troubleshooting an OSPF adjacency on R1's GigabitEthernet0/0 interface connected directly to R2. R2 is powered on and shows correct OSPF configuration, but the adjacency is stuck in the INIT or DOWN state. Based on the output, what is the most likely cause of the failure?

Choose an answer to begin — your selection is scored in the full session.

Accepted Answer

The neighbor is a DROther and a full adjacency with another DROther is not required; adjacency is formed only with the DR and BDR.. In a multi-access broadcast OSPF network, only the Designated Router (DR) and Backup Designated Router (BDR) form full adjacencies with all other routers. DROthers (routers that are neither DR nor BDR) only form full adjacencies with the DR and BDR, and remain in the 2WAY state with other DROthers. The show ip ospf neighbor output on R1 shows neighbor 172.16.1.1 as 2WAY/DROTHER, which is normal behavior because both are DROthers and do not need to exchange LSAs directly.

Answer

The OSPF hello and dead timers are mismatched between R1 and neighbor 172.16.1.1.

Answer

The network type is configured as point-to-point on one side and broadcast on the other, causing a DR/BDR election failure.

Answer

The neighbor's router ID 172.16.1.1 is not reachable, preventing the completion of the adjacency process.

Question 15

Refer to the exhibit. A network engineer is troubleshooting a missing route on R1. The router R3 is configured to advertise network 192.168.30.0/24 via OSPF, but the route is not present in the OSPF routing table of R1 when issuing the show ip route ospf command. What is the most likely cause?

Accepted Answer

R3 has passive-interface default configured and has not issued the no passive-interface command on the interface facing the OSPF neighbor.. R3 has passive-interface default configured, which makes all interfaces passive by default, preventing OSPF hello packets from being sent. Without the no passive-interface command on the interface facing R1, R3 cannot form an OSPF adjacency, so R1 never learns the 192.168.30.0/24 route. This is a common misconfiguration when using passive-interface default to suppress OSPF on non-neighbor interfaces.

Answer

R3 has not enabled OSPF on the network 192.168.30.0/24 using the network command.

Answer

R1 has an inbound ACL applied to GigabitEthernet0/1 that blocks OSPF multicast traffic to 224.0.0.5 and 224.0.0.6.

Answer

R3's OSPF router ID is duplicated with another OSPF router, causing the SPF algorithm to drop routes.