An organization wants to implement a site-to-site VPN solution that must be able to support 350 sites with direct communications between all sites, fully encrypt the packet header and payload, and…

IPsec full mesh requires approximately 61,000 individual IPsec SA pairs for 350 sites, making it operationally unmanageable and failing the scalability requirement.

DMVPN relies on mGRE and NHRP for spoke-to-spoke resolution and introduces hub dependency for initial NHRP mappings, limiting direct-communication scalability compared to FlexVPN at this site count.

GETVPN is a tunnel-less, group-keyed VPN that preserves the original IP header in the clear (only the payload is encrypted), failing the requirement to fully encrypt the packet header.

FlexVPN uses IKEv2 with virtual-access interfaces derived from virtual templates, enabling dynamic spoke-to-spoke tunnels without NHRP hub involvement for each session, which scales well beyond 350 sites. IPsec tunnel mode encapsulates and encrypts the entire original packet including the IP header and payload. Routing protocols (EIGRP, OSPF, BGP) run natively over the virtual-access interfaces, satisfying all three stated requirements simultaneously.