Planning to place RB450G as server in HK, one RB750 in mainland China and one RB750 aboard.
Since I haven't any experience in VPN, detailed help required and highly appreciated:
1. OpenVPN or IPsec?
2. Three site should be within the same VLAN.
3. Site-to-site from aboard/mainland to HK.
Though the code is not open and it is more of a commercial offering, RouterOS from MikroTik is Linux-based.
It installs onto and turns regular PCs into a enterprise-level router.
It gives you all the necessary features, including routing, firewall, bandwidth management, wireless access point, backhaul link, hotspot gateway, VPN server, and more.
You can download and use all the features for free, for the first 24 hours.
After the free trial you can use limited features or purchase a license starting at US$45
In the past, I used DD-WRT's pptp servers to connect VPN tunnels each other. However sometimes they failed to connect each other, I needed to reboot the machines in order to get connnection. As a result, I used Draytek routers for vpn connection. Draytek 2200E Plus is not reliable, sometimes it needs reboot in order to resume connection. The HK one is Draytek 2930n. It is pretty stable and without any problems encountered so far.