What Is the Purpose of "Vpn 0" in the Configuration

What is the purpose of "vpn 0" in the configuration template when onboarding a WAN edge node?

A) It carries control traffic over secure IPsec connections between vSmart controllers and vEdge routers, and between vEdge and vManager.
B) It carries control traffic over secure IPsec connections between vSmart controllers and vEdge routers, and between vSmart and vBond.
C) It carries control traffic over secure DTLS or TLS connections between vSmart controllers and vEdge routers, and between vSmart and vBond.
D) It carries out-of-band network management traffic among the Viptela devices in the overlay network.