EIGRP – old routing protocol.
Old routing protocol – Classful!
Auto-summary – Classful
No auto-summary – Classless
Auto-summary is active by default.
R1, R2 and R3 are configured like this:
R1 - show running-config eigrp section router eigrp 10 auto-summary - ACTIVE BY DEFAUT network 10.10.1.0 0.0.0.0.255 network [interco-R1-R2] R2 - running-config show eigrp section router eigrp 10 auto-summary - ACTIVE BY DEFAUT network [interco-R1-R2] network [interco-R2-R3] R3 show running-config eigrp section router eigrp 10 auto-summary - ACTIVE BY DEFAUT network 10.10.3.0 0.0.0.0.255 network [interco-R2-R3]
In the era of australopithecus…
IP address ranges functioned according to their classes, and sub-network masks did not exist!
If we had an IP address in a Class A, B or C network, it was because it was our set! As a result, EIGRP was acting on.
What's going to happen:
– R1 has the 10.10.1.0 network.
– 10.10.1.0 is part of Class A: 10.0.0.0 /8
– R1 concludes that the Class A 10.0.0.0/8 network has been assigned to it
– R1 broadcasts the network 10.0.0.0 /8
– R3 owns the 10.10.3.0 network.
– 10.10.3.0 is part of Class A: 10.0.0.0 /8
– R3 concludes that the Class A 10.0.0/8 network has been assigned to it
– R3 broadcasts the network 10.0.0.0 /8
EIGRP routing pollution
R2 learns the 10.0.0.0/8 network of R1 and R3…
R2 show ip road eigrp D 10.0.0.0/8 [90/XXXXXX]via R1 [90/XXXXXX] via R3
We have a Metric at equal cost for the network 10.0.0.0 /8 ??
Wooohoooo !!!! I'm going to do load-balancing!
In short, it's anything …
To avoid any nonsense, let's take the reflex to disable the self-summary tooooooout time!8
R1 (config) - router eigrp X R1 (config-rtr) no auto-summary
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