Which design solution decreases CAPEX when designing an enterprise campus involving many small Sites?

Summarization on data center distribution routers optimizes internal data center routing but does not reduce hardware costs or routing table sizes at the many small remote sites.

Summarization on routed access layers affects only local site internal routing scope and does not meaningfully reduce the routing overhead seen by WAN-facing infrastructure or remote site hardware.

Core router summarization reduces backbone routing table size but does not directly lower the hardware requirements or costs at the small remote sites where CAPEX savings are targeted.

WAN edge routers aggregate and advertise routes from all remote small sites across the WAN; applying route summarization at this boundary minimizes the number of prefixes that remote site routers must maintain, enabling deployment of lower-cost routers with smaller routing tables and reduced memory requirements at each small site, directly reducing capital expenditure across the enterprise.