What's the difference between Policy base and Route base VPN?
Route based VPN is the vpn connection is act as a virtual interface, and to determine if the VPN is used is based on the route table. (基于路由表)
Policy based VPN is the vpn connection is included in the policy to determine if the VPN is used. If the rule is hit, then the VPN is used.（基于vpn rule）
Route base VPN有一个好处：多个subnet可以共享一个VPN rule，方便管理。
Policy base：一个IP或一个Subnet或一个Range。
