Colo-Connect deployments below the highest available bandwidth tier - specifically deployments in the 1 Gbps to 20 Gbps range, which is the typical range for a Partner Interconnect connection rather than a 50 Gbps- and-above Dedicated Interconnect link - require the CPE device to establish a GRE tunnel as the overlay carrying customer traffic across the underlying GCP interconnect, in addition to the eBGP session used for route exchange between the Colo router and the cloud router. This makes GRE the protocol the CPE must support for this class of Colo-Connect deployment, and it is documented as a hard prerequisite alongside BGP capability before onboarding can begin. IPSec (option B), while it is the overlay protocol used for traditional, internet-based Prisma Access service connections, is not the mechanism used for Colo-Connect, whose entire value proposition is bypassing IPSec overhead and the public internet in favor of a private, high-throughput cloud interconnect; requiring IPSec would defeat the low-latency, high-bandwidth design goal of Colo- Connect. Geneve (option A) is an encapsulation protocol used in other cloud networking and NSX-style overlay contexts, not a protocol required on the customer ' s CPE for Colo-Connect. DTLS (option D) is associated with encrypted UDP-based tunnel protocols such as those used by some VPN clients, not with the Colo-Connect Partner Interconnect overlay, and is not part of this architecture at all.
Reference:Prisma Access Colo-Connect - Requirements and Prerequisites (GRE and eBGP for Sub-20 Gbps Deployments).