Simple definition
BGP route aggregation advertises summarized prefixes to reduce routing table size while preserving intended reachability.
Purpose and use
BGP aggregation combines multiple prefixes into a less-specific advertisement to simplify route announcements and selected policies.
How does it work?
The summary covers a larger address range. Requirements for contributing routes depend on device configuration.
Example and verification
Before advertising a summary, verify reachability to intended subnets and ensure missing destinations cannot loop between routers.
Points to watch
A summary may remain visible while part of its range is unreachable. More-specific advertisements can also change the selected path.
In short
Fewer advertisements still require checks of actual coverage, appropriate discard routes and propagation policy.