BGP - auto-summary feature

Auto-summary is a feature of BGP that changes the way the network command functions under the BGP router configuration.

Normally when you advertise a network in BGP you have to type in the exact network and subnet mask that you want to advertise or it won’t be placed in the BGP table.

With auto-summary enabled, you can advertise a classful network and you don’t have to add the mask parameter. BGP will automatically advertise the classful network if you have the classful network or a subnet of this network in your routing table.

The auto-summary feature is disabled by default on all Cisco IOS devices