300-410 EIGRP Troubleshooting — Timed 40 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.

Answer

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

Answer

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.

Answer

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

Answer

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.

Answer

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.

Answer

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

Answer

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.

Answer

The EIGRP metric weights are different on the two routers.

Answer

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.

Answer

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

Answer

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.

Answer

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

Answer

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.

Answer

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

Answer

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.

Answer

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

Answer

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.

Answer

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

Answer

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

Question 11

A network engineer runs the following command on Router R1:

R1# show ip eigrp topology
EIGRP-IPv4 Topology Table for AS(100)/ID(192.168.1.1)
Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply,
       r - reply Status, s - sia Status

P 10.10.10.0/24, 1 successors, FD is 28160
         via 10.1.1.2 (28160/28160), GigabitEthernet0/0
P 10.20.20.0/24, 1 successors, FD is 28160
         via 10.2.2.2 (28160/28160), GigabitEthernet0/1
P 10.30.30.0/24, 1 successors, FD is 28160
         via 10.3.3.2 (28160/28160), GigabitEthernet0/2
A 10.40.40.0/24, 0 successors, FD is Infinity
         via 10.4.4.2 (Infinity/Infinity), GigabitEthernet0/3

Based on this output, what is the problem?

Accepted Answer

The route to 10.40.40.0/24 is stuck-in-active and may cause a network instability.. The topology table shows that the route to 10.40.40.0/24 is in Active state (A), meaning the router is actively querying for a successor. The FD is Infinity, indicating no feasible successor is available. This could be due to a network failure or a stuck-in-active condition.

Answer

The route to 10.40.40.0/24 is passive and stable.

Answer

The route to 10.30.30.0/24 has a feasible successor.

Answer

All routes are in a stable passive state.

Question 12

A network engineer runs the following command on Router R1:

R1# show ip eigrp interfaces
EIGRP-IPv4 Interfaces for AS(100)
                       Xmit Queue   Mean   Pacing Time   Multicast    Pending
Interface        Peers  Un/Reliable  SRTT   Un/Reliable   Flow Timer   Routes
Gi0/0              1       0/0       12       0/10         50           0
Gi0/1              1       0/0       15       0/10         50           0
Gi0/2              1       0/0       18       0/10         50           0
Gi0/3              1       0/0       20       0/10         50           0
Gi0/4              0       0/0        0       0/10         50           0

Based on this output, which statement is correct?

Accepted Answer

Interface Gi0/4 has no EIGRP neighbor, which may indicate a configuration issue or lack of connectivity.. The show ip eigrp interfaces command shows EIGRP-enabled interfaces and their statistics. Gi0/4 has 0 peers, meaning no EIGRP neighbor is formed on that interface. The other interfaces have 1 peer each, indicating a neighbor relationship.

Answer

All interfaces have at least one EIGRP neighbor.

Answer

The mean SRTT on Gi0/2 is 18 ms, which is too high and indicates a problem.

Answer

The pending routes count of 0 on all interfaces indicates a routing loop.

Question 13

A network engineer runs the following command on Router R1:

R1# show ip eigrp traffic
EIGRP-IPv4 Traffic Statistics for AS(100)
  Hellos sent/received: 5000/4995
  Updates sent/received: 150/148
  Queries sent/received: 10/8
  Replies sent/received: 8/10
  Acks sent/received: 300/298
  Input queue high water mark: 10
  Input queue drops: 0
  SIA-Queries sent/received: 0/0
  SIA-Replies sent/received: 0/0
  Hello process ID: 123
  PDM process ID: 124
  Socket queue: 0/2000/10/0 (current/max/highest/drops)
  Input queue: 0/2000/10/0 (current/max/highest/drops)

Based on this output, which statement is correct?

Accepted Answer

The EIGRP process is operating normally with no signs of issues.. The EIGRP traffic statistics show a balanced number of sent and received packets. There are no input queue drops, no SIA-Queries or SIA-Replies, indicating a healthy EIGRP process. The ratio of queries to replies is nearly balanced (10 sent vs 8 received, 8 sent vs 10 received), which is normal.

Answer

There is a problem because more queries were sent than replies received.

Answer

The input queue drops of 0 indicate that the router is not processing EIGRP packets.

Answer

The SIA-Queries count of 0 indicates that the network has experienced stuck-in-active events.

Question 14

A network engineer runs the following command on Router R1:

R1# show ip eigrp neighbors detail
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
   Version 12.0/2.0, Retrans: 0, Retries: 0, Restarts: 0
   Topology ids from peer: 0
   Passive interface: No
   Hello interval: 5
   Hold time: 15

Based on this output, what is the problem?

Accepted Answer

The neighbor is operating normally with no issues.. The detail output shows the neighbor is up with normal parameters. However, the 'Passive interface: No' indicates that the interface is not configured as passive, which is expected for forming neighbors. There is no problem evident; the neighbor is functioning correctly.

Answer

The interface is configured as passive, preventing neighbor formation.

Answer

The neighbor has a high number of retransmissions.

Answer

The hold time of 15 seconds is too short and may cause flapping.

Question 15

A network engineer runs the following command on Router R1:

R1# show ip eigrp topology 10.10.10.0/24
EIGRP-IPv4 Topology Entry for AS(100)/ID(192.168.1.1) for 10.10.10.0/24
  State: Passive, Reply status: 0, Originating router: 192.168.1.1
  Routing Descriptor Blocks:
  0.0.0.0 (Null0) from 0.0.0.0, Send flag: 0x0
      Composite metric: (2560000000/0), Route is Internal
      Vector metric:
        Minimum bandwidth: 100000 Kbit
        Total delay: 100 microseconds
        Reliability: 255/255
        Load: 1/255
        Minimum MTU: 1500
        Hop count: 0

Based on this output, what is the problem?

Accepted Answer

The route is a local summary route pointing to Null0, which is normal for EIGRP summarization.. The route to 10.10.10.0/24 is a local summary or null0 route (via Null0). This is typical for a summary route or a route to a directly connected network. The composite metric of 2560000000/0 indicates a very high metric, which is normal for a null0 route. There is no problem; this is a common configuration.

Answer

The route has a metric of 2560000000, indicating a network failure.

Answer

The hop count of 0 means the route is not reachable.

Answer

The route is in Active state, indicating a problem.

Question 16

A network engineer runs the following command on Router R1:

R1# show ip eigrp topology all-links
EIGRP-IPv4 Topology Table for AS(100)/ID(192.168.1.1)
Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply,
       r - reply Status, s - sia Status

P 10.10.10.0/24, 1 successors, FD is 28160, Qos: 0
     via 10.1.1.2 (28160/28160), GigabitEthernet0/0
     via 10.2.2.2 (28672/28160), GigabitEthernet0/1
P 10.20.20.0/24, 1 successors, FD is 28160, Qos: 0
     via 10.2.2.2 (28160/28160), GigabitEthernet0/1
     via 10.3.3.2 (28672/28160), GigabitEthernet0/2

Based on this output, which statement is correct?

Accepted Answer

The network has redundant paths with feasible successors for both routes.. The all-links output shows all known routes, including feasible successors. For 10.10.10.0/24, there is a successor via 10.1.1.2 and a feasible successor via 10.2.2.2 (since its reported distance of 28160 is less than the FD of 28160). For 10.20.20.0/24, there is a successor via 10.2.2.2 and a feasible successor via 10.3.3.2. This indicates good redundancy.

Answer

The route to 10.20.20.0/24 has no feasible successor.

Answer

The FD for 10.10.10.0/24 is 28672.

Answer

The route to 10.10.10.0/24 is in Active state.

Question 17

A network engineer runs the following command on Router R1:

R1# show ip eigrp interfaces detail Gi0/0
EIGRP-IPv4 Interfaces for AS(100)
Interface: GigabitEthernet0/0
  Peers: 1
  Xmit Queue Un/Reliable: 0/0
  Mean SRTT: 12
  Pacing Time Un/Reliable: 0/10
  Multicast Flow Timer: 50
  Pending Routes: 0
  Hello interval: 5
  Hold time: 15
  Split horizon: Enabled
  Next multicast: 0.0.0.0
  Next broadcast: 0.0.0.0

Based on this output, what is the problem?

Accepted Answer

Split horizon is enabled, which is a normal and expected configuration.. The detail output shows split horizon is enabled on the interface. Split horizon is a loop prevention mechanism that prevents routes from being advertised out the interface they were learned on. This is normal and expected. There is no problem.

Answer

Split horizon is disabled, which could cause routing loops.

Answer

The hold time of 15 seconds is too short and may cause instability.

Answer

The interface has no peers, indicating a problem.

Question 18

A network engineer runs the following command on Router R1:

R1# show ip eigrp topology 10.50.50.0/24
EIGRP-IPv4 Topology Entry for AS(100)/ID(192.168.1.1) for 10.50.50.0/24
  State: Active, Reply status: 0, Originating router: 192.168.1.1
  Routing Descriptor Blocks:
  10.1.1.2 (GigabitEthernet0/0), from 10.1.1.2, Send flag: 0x0
      Composite metric: (4294967295/4294967295), Route is Internal
      Vector metric:
        Minimum bandwidth: 100000 Kbit
        Total delay: 100 microseconds
        Reliability: 255/255
        Load: 1/255
        Minimum MTU: 1500
        Hop count: 1

Based on this output, what is the problem?

Accepted Answer

The route is in Active state with an infinite metric, indicating that the router has lost the route and is querying for a new path.. The route to 10.50.50.0/24 is in Active state, meaning the router is actively querying for a successor. The composite metric is 4294967295 (Infinity), indicating that the route is unreachable. This is a problem because the router has lost the route and is trying to find an alternative path.

Answer

The route is passive and stable.

Answer

The metric of 4294967295 is normal for a summary route.

Answer

The hop count of 1 indicates the route is one hop away and reachable.

Question 19

Consider the following EIGRP configuration on Router R1:

router eigrp 100
 network 10.0.0.0
 passive-interface default
 no passive-interface GigabitEthernet0/0

What is the effect of this configuration?

Accepted Answer

EIGRP will form neighbor adjacencies only on GigabitEthernet0/0.. The configuration sets all interfaces to passive by default, then re-enables EIGRP on GigabitEthernet0/0. This means only GigabitEthernet0/0 will send and receive EIGRP hello packets and form adjacencies; all other interfaces will only advertise networks without forming neighbors.

Answer

EIGRP will form neighbor adjacencies on all interfaces.

Answer

EIGRP will not form any neighbor adjacencies.

Answer

EIGRP will form neighbor adjacencies on all interfaces except GigabitEthernet0/0.

Question 20

Given the following EIGRP configuration on Router R2:

router eigrp 200
 network 192.168.1.0
 network 10.0.0.0
 no auto-summary

Which statement is true about the operation of EIGRP?

Accepted Answer

EIGRP will advertise 192.168.1.0/24 and 10.0.0.0/8 as exact prefixes.. The no auto-summary command disables automatic summarization at classful boundaries, so EIGRP will advertise subnets exactly as configured under the network statements.

Answer

EIGRP will automatically summarize 192.168.1.0 to 192.168.0.0/16.

Answer

EIGRP will only advertise the classful networks 192.168.0.0/16 and 10.0.0.0/8.

Answer

EIGRP will not form neighbor adjacencies due to missing network mask.