Route aggregation is a mechanism that combines multiple routes into one route. This mechanism allows a BGP device to advertise only the summarized route but not all the specific routes to peers, therefore reducing the size of the BGP routing table. If the aggregated route flaps, the network is not affected, so network stability is improved.

To prevent routing loops caused by route summarization, BGP uses the AS_Set attribute. The AS_Set attribute is an unordered set of all ASs that a route passes through. When the summarized route enters an AS in the AS_Set attribute again, BGP finds that the local AS number has been recorded in the AS_Set attribute of the route and discards this route to prevent a routing loop.

The following example command aggregates a range of addresses, such as 10.10.1.0/24, 10.10.2.0/24, 10.10.3.0/24 into the single prefix 10.10.0.0/16.