ITsurecert engineer has chosen to use EIGRP for their network routing protocol.
Which three statements are true regarding EIGRP? (Select three)

A. By default, EIGRP uses the Dijkstra algorithm to determine the best path to a
destination network based on bandwidth and delay.
B. To speed convergence, EIGRP attempts to maintain a successor and feasible successor
path for each destination.
C. EIGRP uses hellos to establish neighbor relationships.
D. By default, EIGRP performs auto-summarization across classful network boundaries.
E. EIGRP uses an area hierarchy to increase network scalability.
Answer: B, C, D

Explanation:
EIGRP routers establish adjacencies with neighbor routers by using small hello packets.
Hellos are sent by default every five seconds. An EIGRP router assumes that as long as it
is receiving hello packets from known neighbors, those neighbors (and their routes)
remain viable.
By forming adjacencies, EIGRP routers do the following:
1. Dynamically learn of new routes that join their network
2. Identify routers that become either unreachable or inoperable
3. Rediscover routers that had previously been unreachable

 EIGRP routers keep route and topology information readily available in RAM so they
can react quickly to changes. Like OSPF, EIGRP keeps this information in several tables,
or databases.
* Successor - A successor is a route selected as the primary route to use to reach a
destination. Successors are the entries kept in the routing table. M ultiple successors for a destination can be
retained in the routing table.
* Feasible successor - A feasible successor is a backup route. These routes are selected
at the same time the successors are identified, but are kept in the topology table. Multiple
feasible successors for a destination can be retained in the topology table.
EIGRP automatically summarizes routes at the classful boundary, the boundary where
the network address ends as defined by class-based addressing. In most cases, auto summarization
is a good thing, keeping the routing tables as compact as possible
In the presence of discontiguous subnetworks, automatic summarization must be disabled
for routing to work properly.
To turn off auto-summarization, use the following command:
Router(config-router)#no auto-summary

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