eigrp scenario based interview questions and answers

We are discussing about EIGRP Scenario based question -  

Scenario 1 - 

EIGRP neighbor not coming up -

1.AS number mismatch between neighbors.
2.K value mismatch between routers.
3.IP is on different subnets
4.Primary and secondary address on interface mismatch between routers.
5.layer 2 switch/hub connecting different subnet devices in the same VLAN. For example, VLAN leaking from vlan 1 to vlan2 by using back to back cable. 
6. Access-list blocking EIGRP multicast packets on interface.

CLI  Command - Show ip eigrp neighbors

Solution of the Above question --

1- Make sure same AS number is in use.
2- Make sure same K value is in use.
3- Make sure same IP subnets on both side.
4- Make sure Primary to Primary address match on both side and secondary to secondary.
5- Make sure there is no leaking

Scenario 2 - 

EIGRP neighbor is established but not exchanging routes and getting reset -

1. Mismatch mask between the neighbor.
2. Hold time getting expired
3. Retry limit exceeded.
4. Vlan  leak is happening or cross VLAN domain due to some redundant link or wrong cabling

Cli command - Show ip eigrp neighbors.

Solution of the Above question --

1- Make sure there is no mismatch mask between neighbors.
2- Make sure there is no packet loss on ports (End-CPU to End-End CPU)
3- Make sure Unicast rechability is available and can ping end to end.
4- Make sure there is no access-list blocking the communication unicast communication between neighbors.
5- Make sure COPP is not blocking the unicast packet between neighbors.
6-Make sure there is no MTU mismatch between the neighbors.
7- Make sure EIGRP neigobors on the same subnet and no VLAN are leaking to other subnets.

Note - Mismatch mask causes the routing loop in the network

Scenario 3 - 

Router stuck in active -

    1.Bad or congested links
    2.Low router resources, such as low memory or high CPU on the router
    3.Long query range
    4.Excessive redundancy
    5. Access-list /Copp blocking the unicast packet between neighbors.

CLI command -

 show ip eigrp topology active

 Show ip eigrp neigbors

Solution of the Above question --

1- Use summarization.
 2- Use eigrb stub
  3- Use Hierarchy design.

Scenario 4 - 

Routes not advertising to neigbor -

1.Access-list with distribute list is misconfigured.
2.Routers has discontigous network.
3.EIGRP split horizon is enabled

Cli cmd - Debug ip eigrp

Solution of the Above question --

1- Make sure access-list allow the networks in distribute list.
2- Make sure "no auto summary" is enabled.
3- Make sure EIGRP split is disabled on Hub router in Hub/spoke topology.
4- OR Use sub-interface with different subnet between Hub/Spoke.