The IT Stuff

Internal Router :All interfaces of the router are in single area. It does not mean that area has to be Area 0

Backbone Router: At least 1 interface in area 0.A router can be both an Internal and Backbone router if all its interfaces are in Area 0.

Area Border Router: has interfaces in multiple areas.at least [...]

A stub router is one that is connected to no more than two neighbors and should never be a transit router.The Enhanced Interior Gateway Routing Protocol (EIGRP) Stub Routing provides

improves network stability,
reduces resource utilization,
and simplifies stub router configuration.
The stub router has one exit path from the routing domain and forwards all traffic to a central [...]

EIGRP Summarization:

EIGRP Auto-summarization done when redistributing cannot be disabled.
EIGRP Auto-summarization done at class boundary and should be disabled with a “no auto-summary” when dealing with discontiguous networks.
EIGRP Will not automatically summarize external routes.
Automatic summarization can disabled using the following command:
Router(config-router)#no auto-summary
TO configure a summary route out a particular interface using the ip summary-address eigrp [...]

show ip route:  To inspect the routing table.
show ip route eigrp: To filter the routing table and show only the routes learned from EIGRP.
show ip protocols:  Verifies autonomous system, timer values, identified networks, and EIGRP neighbors (routing information sources).
show ip eigrp topology: Shows the EIGRP topology table and identifies successors and feasible successors.
show ip eigrp [...]

EIGRP’s has 5 Packet Types:

Hello packets:

Used to discover & form adjacencies with neighbors
To discover & establish adjacencies with neighbor routers
Serves as a keepalive mechanism

Update packets:

Used to propagate routing information

Acknowledgment packets:

Used to acknowledge receipt of update, query & reply packets

Query & Reply packets:

Used by DUAL for searching for networks
Query packets Can use

Unicast
Multicast

Reply packet
Use only unicast

EIGRP is [...]