To keep the BGP routing table size manageable and below a specified threshold, the customer should consider enforcing routing policies with aggregation. Route aggregation reduces the number of individual routes advertised and stored by combining multiple routes into a summarized one.

Setting route metrics equal or advertising only a primary path does not reduce the number of routes as effectively.

Importing only the default route (0.0.0.0/0) is impractical for normal operations.

Thus, route aggregation is the best practice for controlling routing table size in merged BGP environments.