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
Links:
https://networklessons.com/bgp/bgp-auto-summary
https://forum.networklessons.com/t/bgp-auto-summary/1236/16?u=lagapides