300-410 EIGRP Troubleshooting — Timed 10 Questions

Question 1

A network engineer is troubleshooting an EIGRP adjacency issue between two directly connected routers, R1 and R2. Both routers are configured with the same autonomous system number, but the adjacency fails to come up. The engineer checks the interfaces and verifies that they are up/up. On R1, the output of 'show ip eigrp neighbors' shows nothing. What is the most likely cause of this problem?

Accepted Answer

The interfaces are configured with IP addresses from different subnets.. EIGRP requires that the primary IP addresses of the interfaces on the same link belong to the same subnet. If the subnet masks do not match, the routers will not form an adjacency because they will consider the other router to be on a different network.

Answer

The EIGRP process is shut down on one of the routers.

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The passive-interface default command is configured under the EIGRP process.

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The EIGRP router ID is the same on both routers.

Question 2

A network engineer is troubleshooting a routing issue in an EIGRP network. Router R1 is not learning a specific route from its neighbor R2, even though R2 has the route in its routing table. The engineer checks the EIGRP topology table on R1 and does not see the route. The output of 'show ip eigrp neighbors' shows that R1 and R2 are adjacent. What should the engineer check next?

Accepted Answer

Check if a distribute-list in or out is applied under the EIGRP process on R1.. If the neighbor adjacency is up but the route is not in the topology table, the issue is likely that the route is being filtered by a distribute-list configured under the EIGRP process on the receiving router.

Answer

Check if the route is being summarized on R2.

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Check if the EIGRP metric for the route is too high.

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Check if the route is a connected route on R2.

Question 3

An engineer is troubleshooting an EIGRP convergence issue. After a link failure, the network takes an unusually long time to converge. The engineer notices that the EIGRP hello and hold timers are set to the default values. The network has many routers in a hub-and-spoke topology. What is the most likely cause of the slow convergence?

Accepted Answer

The hub router has too many EIGRP neighbors, causing CPU overload and dropped hello packets.. In a hub-and-spoke topology, if the hub router has a large number of neighbors, the default EIGRP timers may cause slow convergence because the hub must process many updates. Increasing the hello and hold timers on the hub can help reduce the load, but the issue here is that the timers are default, which can be too fast for a large number of neighbors, causing the hub to drop packets and reset adjacencies.

Answer

The EIGRP stub feature is not enabled on the spoke routers.

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The EIGRP variance command is configured, causing unequal-cost load balancing.

Answer

The EIGRP router ID is not configured, so it defaults to the highest loopback IP.

Question 4

A network engineer is troubleshooting an EIGRP issue where a route is flapping in and out of the routing table. The engineer checks the logs and sees messages indicating that the route is being learned from two different neighbors, but the metric keeps changing. The route is a summary route. What is the most likely cause of the flapping?

Accepted Answer

The summary route is being advertised by multiple routers with different metrics.. If a summary route is being learned from two different neighbors, and the metric changes, it could be because one of the neighbors is advertising the summary route with a different metric, causing the router to constantly switch between the two paths. However, the most common cause is that the summary route is being originated by multiple routers, and the metric is not consistent, leading to instability.

Answer

The EIGRP stub feature is configured on one of the neighbors.

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The passive-interface command is applied to the interface receiving the summary route.

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The EIGRP router ID is the same on both neighbors.

Question 5

An engineer is troubleshooting an EIGRP issue where a router is not learning any routes from a neighbor, but the neighbor adjacency is up. The engineer checks the EIGRP topology table on the local router and sees that the neighbor is listed, but no routes from that neighbor are present. The engineer also verifies that the neighbor has routes to advertise. What is the most likely cause?

Accepted Answer

The neighbor is configured as an EIGRP stub router.. If the adjacency is up but no routes are received, the issue is likely that a distribute-list is filtering incoming routes, or the neighbor is configured as a stub router. In this case, the most common cause is that the neighbor is configured as a stub router, which restricts the routes it advertises.

Answer

The local router has a distribute-list out applied to the neighbor.

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The EIGRP metric weights are different on the two routers.

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The local router has a route-map applied to the EIGRP process that is filtering all routes.

Question 6

A network engineer is troubleshooting an EIGRP issue where a router is not installing a route in the routing table, even though the route is present in the EIGRP topology table. The route is a feasible successor, but it is not being used. What is the most likely reason for this?

Accepted Answer

The feasible successor has a higher metric than the current successor.. EIGRP only installs the best route (successor) into the routing table. If a route is in the topology table as a feasible successor but not installed, it means that the feasible distance for that route is higher than the current successor's metric, so it is not the best path.

Answer

The route is a summary route that is being suppressed.

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The route is being filtered by a distribute-list in.

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The EIGRP variance command is set to 1, preventing unequal-cost load balancing.

Question 7

An engineer is troubleshooting an EIGRP issue where a router is not forming an adjacency with a neighbor over a Frame Relay point-to-point subinterface. The physical interface is up/up, and the subinterface is configured with an IP address. The engineer checks the EIGRP configuration and sees that the network statement includes the subnet of the subinterface. What is the most likely cause of the adjacency failure?

Accepted Answer

The subinterface is configured as multipoint instead of point-to-point.. On Frame Relay point-to-point subinterfaces, the default interface type is non-broadcast, and EIGRP by default uses multicast hellos. If the interface is not configured as a point-to-point type, or if the multicast capability is not enabled, EIGRP will not send hellos, and adjacency will not form.

Answer

The subinterface is not configured with the 'frame-relay interface-dlci' command.

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The EIGRP hello timer is set to 0 on the subinterface.

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The IP address on the subinterface is not in the same subnet as the neighbor.

Question 8

A network engineer is troubleshooting an EIGRP issue where a router is not learning any routes from a neighbor, but the neighbor adjacency is up. The engineer checks the EIGRP topology table and sees that the neighbor is listed, but no routes are present. The engineer also checks the interface configuration and sees that the interface is configured as a passive interface under the EIGRP process. What is the most likely cause of the issue?

Accepted Answer

The neighbor is configured with a distribute-list that filters all routes.. If an interface is configured as passive under EIGRP, the router will not send or receive hello packets on that interface, which prevents adjacency formation. However, if the adjacency is up, the passive-interface command is not the issue. In this case, the adjacency is up, so passive-interface is not the cause.

Answer

The passive-interface command is preventing the router from sending updates, but not receiving them.

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The EIGRP process is configured with the 'no auto-summary' command.

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The router ID is not configured, so EIGRP is using the highest loopback IP.

Question 9

An engineer is troubleshooting an EIGRP issue where a router is not learning a specific route from a neighbor, but other routes from the same neighbor are being learned. The engineer checks the EIGRP topology table and sees that the route is not present. The engineer also checks the neighbor's routing table and confirms that the route exists. What is the most likely cause?

Accepted Answer

A distribute-list in is applied on the local router that filters the specific route.. If only one route is missing from a neighbor, the issue is likely that the route is being filtered by a distribute-list or route-map on the receiving router. Since other routes are received, the filter is specific to that route.

Answer

The neighbor is configured as a stub router.

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The route is a summary route that is being suppressed by the 'summary-address' command.

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The EIGRP metric for the route is too high, so it is not considered feasible.

Question 10

A network engineer runs the following command on Router R1:

R1# show ip eigrp neighbors
EIGRP-IPv4 Neighbors for AS(100)
H   Address                 Interface       Hold Uptime   SRTT   RTO  Q  Seq
                                           (sec)         (ms)       Cnt Num
0   10.1.1.2                Gi0/0            13 00:12:34   12   200  0  45
1   10.2.2.2                Gi0/1            12 00:10:20   15   200  0  32
2   10.3.3.2                Gi0/2            14 00:08:15   18   200  0  28
3   10.4.4.2                Gi0/3            13 00:06:10   20   200  0  22

Based on this output, which statement is correct?

Accepted Answer

All four EIGRP neighbors are in the established state and exchanging routes.. The show ip eigrp neighbors command displays all EIGRP neighbors. The 'H' column shows the order in which neighbors were learned. The 'Hold' column shows the remaining hold time in seconds. All neighbors are in a stable state with low SRTT and RTO values, and no outstanding packets (Q Cnt = 0). The output indicates that all four neighbors are fully operational.

Answer

Neighbor 10.4.4.2 has a high SRTT of 20 ms, indicating a slow link.

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The Q Cnt of 0 means that there are 0 packets queued for retransmission, but this could indicate a problem.

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The neighbor on Gi0/3 has the lowest uptime, so it may be flapping.