Which solution best fits: simplify deployment for 100+ branches, enable branch-to-branch connectivity, be cost-effective, and provide strong encryption?

DMVPN (Dynamic Multipoint VPN) is the best fit because it combines IPSec for strong encryption, GRE for encapsulating multiple protocols, and NHRP (Next Hop Resolution Protocol) for dynamic tunnel creation. This allows branches to establish direct, on-demand tunnels to each other (spoke-to-spoke) without needing to traverse a central hub for all traffic, significantly simplifying deployment and reducing costs for 100+ branches. MPLS is a service provider technology, not an end-user solution for branch connectivity and encryption. IPSec provides encryption but requires static tunnel configuration, which is not scalable for 100+ branches. GRE encapsulates traffic but lacks built-in encryption and dynamic tunnel capabilities.