Most recently EIGRP Multiple choice Questions and Answers pdf

11. Explain Unequal Cost Load Balancing in EIGRP?
By default, EIGRP will automatically load-balance across equal-metric routes. EIGRP also supports load-balancing across routes with an unequal metric. Unequal cost load balancing in EIGRP is the concept by which load sharing can take place on paths that does not have the equal metric. In EIGRP variance is used for Unequal cost load balancing. Variance is specified as an integer in the range of 1 through 128. The router then multiplies the variance by the successor route’s FD (metric of the best route to reach that subnet). Any Feasible Successor route whose metric is less than or equal to the product of the variance by the successors FD are considered to be equal routes and can be placed into the routing table for load sharing.
Router(config)# router eigrp 100
Router(config-router)# variance 2
In this case variance is 2.

12. Explain Split Horizon?
The Split Horizon feature prevents a route learned on one interface from being advertised back out of that same interface. It is used to prevent loop in EIGRP.

13. Explain Null Zero?
It is a loop avoidance mechanism entry stored in routing table only in case of summarization (auto & manual). It terminates or flush unwanted packets, if any traffic goes towards null0 it will be drop by eigrp.

14. What is Active State and Passive State?
Routes for which the successor route fails and no feasible successor routes exist moves to an active state forcing the EIGRP to send out query packets and reconverge.
A route is in passive state for which the router has a successor route, and no failure has yet occurred. A stable EIGRP network will have all routes in a Passive state.

15. Explain Stuck in Active?
When for a certain prefix, successor route fails and no feasible successor route exists than the router begins a process of finding any loop-free alternative routes to reach that prefix by sending Query messages to all of its neighbors requesting path to lost prefix. If the neighbor routers does not have information about the lost prefix, they will forward the query message to further routers. Within a large network, particularly when routers exist several router hops away, the number of Queries might not only be large, but there also might be a string of routers that all must wait on multiple Reply messages before they can, in turn, issue a Reply. To deal with this long time problem, Cisco IOS first sets a limit on how long it should take to receive all such replies. This timer is called the active timer and is set to 3 minutes by default. Routes for which a router does not receive a Reply within the active timer are considered to be Stuck-in-Active (SIA) routes. Router sends an SIA-Query (Stuck-in-Active Query) EIGRP message to each neighbor that has yet to send back a Reply. The purpose of the message is to either get an SIA-Reply back indicating that the neighbor really is still waiting for replies to its own queries meaning the neighbor is alive and still working & there is no need to kill the neighborship or to get nothing in reply meaning neighbor was not able to reply, so the action of failing the neighborship is reasonable.

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