The summary automatic command enables the automatic aggregation for the locally imported routes.
The undo summary automatic command disables the automatic aggregation for the locally imported routes.
By default, the locally imported routes are not aggregated automatically.
Usage Scenario
BGP route aggregation is divided into manual aggregation and automatic aggregation. The command is applicable to the automatic aggregation. The preference of the automatic aggregation is lower than that of the manual aggregation.
After the summary automatic command is used, BGP aggregates routes according to the natural network segment (for example, 10.1.1.1/24 and 10.2.1.1/24 are aggregated to 10.0.0.0/8, a Class A address), and sends only the aggregated routes to peers. This reduces the amount of routing information.
After the summary automatic command is used, BGP cannot receive the sub-network routes advertised by an IGP. The amount of the routing information is therefore reduced.
Precautions
Automatic summarization is valid only for the routes imported through the import-route (BGP) command.