EIGRP summarization

By default,Auto summarizing is enabled in EIGRP.Automatic summarization can be disabled using the following command:     
Router(config)#  router eigrp 100
Router(config-router)#  no auto-summary
"No auto-summary" command is needed because by default EIGRP will behave like a classfull routing protocol which means it won’t advertise the subnet mask along the routing information. For example 1.1.1.0/24 and 2.2.2.0/24 will be advertised as 1.0.0.0/8 and 2.0.0.0/8. Disabling auto-summary will ensure EIGRP sends the subnet mask along

Summaries can also be produced manually on any interface
Syntax:
Router(config)# interface < interface >
Router(config-if)# ip summary-address eigrp < as-no> <summarized_network_ip> <summarized_subnet_mask>
Example:

Router(config)#  interface fa 0/0
Router(config-if)#  ip summary-address eigrp 100 79.0.0.0 255.0.0.0
The manually-created summary route is not advertised as an internal EIGRP route, but instead is classified as an EIGRP summary route. An EIGRP summary route has an Administrative Distance of 5.

Labs


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