Refer to the exhibit. Which single design aspect should be configured on the ABRs to reduce the impact of WAN upgrades for spoke routers on the core of the network?

When an ABR summarizes spoke router prefixes into a single aggregate before advertising into the core OSPF area, individual route flaps caused by spoke WAN upgrades do not trigger LSA flooding in the backbone. The summary route remains stable in the core even as specific spoke routes go up and down, significantly reducing topology change events and SPF recalculations. This directly reduces the operational impact of spoke-side WAN upgrades on core devices.

A stub area blocks Type 5 external LSAs from entering an area but does not prevent intra-area or inter-area LSA flooding caused by spoke router route changes during upgrades.

Route filtering can suppress specific routes but does not aggregate changes into a stable summary, so route flaps from spoke upgrades would still propagate individually toward the core.

A not-so-stubby area (NSSA) allows limited external route redistribution into a stub-like area but does not address the impact of spoke route instability on the core during WAN upgrades.