Route summarization: turn many routes into a few

Smaller routing tables converge faster and fail less. Route summarization (aggregation) replaces a run of specific prefixes with one covering prefix, so your neighbours carry one entry instead of many.

Contiguous blocks collapse

Four consecutive /24s, 10.0.0.0/24 through 10.0.3.0/24, share the same first 22 bits. That means they summarize exactly to 10.0.0.0/22 - one advertisement covering all four, with no extra address space.

10.0.0.0/24
10.0.1.0/24   ->  10.0.0.0/22
10.0.2.0/24
10.0.3.0/24

The over-advertise trap

A summary must not cover address space you do not own or route. If 10.0.2.0/24 lives somewhere else, advertising 10.0.0.0/22 draws its traffic to you and blackholes it. Summarize only contiguous blocks you actually own - and confirm the aggregate covers exactly them, nothing more.