Bgp

Aggregation replaces a set of adjacent prefixes with one covering announcement, so every peer downstream stores one entry instead of dozens and stops processing updates for each component. The table gets smaller, and the churn of a flapping edge stops propagating outward. ...

BGP is the only protocol that stitches tens of thousands of independently operated networks into one forwarding table. It carries reachability, but what it really carries is policy: each network says which prefixes it originates, which neighbours it learned them from, and — through filters — which ones it is willing to pass on. ...