EIGRP Auto summary command..

[kishorganbas]

Dear All,

Please help in understand,

1] why we use "no auto summary" command in eigrp configuration

2] what will happen if someone doesn't give this command?

please assist me with an example..

Thanks in advance,

Kishore

[daniel.dib]

Hi,

Auto summary was the default until more recent releases. When it's enabled networks are automatically summarized when crossing major network boundaries. This behavior is usually not wanted in modern networks.

If a router has an interface with 10.0.0.1/24 on one interface towards a LAN and an interface with 172.16.0.1/24 on an interface towards another router it is peering with. Then the 10.0.0.0/24 network will be automatically summarized to 10.0.0.0/8 when crossing the major network of 172.16.0.0/16.

If the routers were instead peering with 10.0.1.0/24 network then the 10.0.0.0/24 network would not be summarized since it is not crossing a major network boundary.

Daniel Dib
CCIE #37149

[rosaho]

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