BGP uses BGP aggregates to reduce the size of the routing table. By advertising an aggregate instead of individual prefixes, BGP reduces the number of entries in the routing table, which saves memory and processing power.
BGP aggregates can be created in two ways:
1. Manual aggregation: A network administrator can manually create an aggregate by configuring BGP to advertise a summary route for a group of contiguous IP address blocks.
1. Automatic aggregation: BGP can automatically create aggregates based on the network topology. BGP examines its routing table and creates an aggregate if it finds multiple routes with the same network prefix.
When a BGP speaker receives an aggregate route, it examines its routing table to see if it has more specific routes for any subnets within the aggregate. If it does, it uses those more specific routes. Otherwise, it uses the aggregate route to forward traffic.
BGP aggregates also help to reduce the size of BGP update messages, which improves network efficiency. However, care must be taken to ensure that aggregates do not cause any subnets to become unreachable due to route summarization.
