Route summarization
Merging several specific network prefixes into one larger one ("supernet") in routing advertisements. It shrinks routing tables and hides instability — if one of the underlying links flaps, it isn't visible outside the summary.
Example: instead of advertising 10.1.0.0/24, 10.1.1.0/24, 10.1.2.0/24, and 10.1.3.0/24 separately, advertise 10.1.0.0/22 (which covers all four). Wins: smaller routing tables (less memory/CPU, faster lookups), stability (a flapping inner link doesn't change the summary → no constant updates outward), and simpler design. Requirement: the addressing must be planned hierarchically and contiguously (continuous blocks) to be summarized cleanly — one of the main reasons to plan IP addressing carefully. Done at area/AS boundaries (OSPF ABR, BGP aggregation). It builds on CIDR and prefix math. A cornerstone of scalable network design. Related to prefix-list and default route.