Site-to-Site OpenVPN behind Router

[ccmks]

Hello All pfSense Guru…

I am newbie to VPN, but at least I have little bit knowledge in networking.

I am having problem creating site-to-site OpenVPN behind router. I have searched on the forums and Google and I haven't found anything related to this topic. I apologize before if the similar thread was exist and I would be happy if someone can refer to it. I will describe my problem in detail below:

Situation
There are two office I am working on. First one is in LA and the other office in Irvine. They need a way to have connection between these two office. Normally, I would suggest to have the router with site-to-site VPN capability like sonicwall, cisco, even pfSense itself. However, the internet was provided by the office building on each location which we don't have any control over it. I only can submit request to have port forwarded to the IT of office building on each site, so hardware based site-to-site VPN is out of options.

They have a server on each location for file sharing. I am thinking about using server itself to have pfSense hosted on virtualbox and create site-to-site VPN tunnel by utilizing the OpenVPN. So far what I know, only OpenVPN is application based VPN which can work behind router/NAT.

Problem
I have followed tutorial about creating site-to-site OpenVPN in pfSense. The result, I got link up between these two location. Please see the network topology on the attachment before continue reading the problem.

The problem, I see no route between two office. For instance, one PC in LA office can't ping to PC in Irvine office and vice versa.

Conclusion
I am basically stuck and don't know what to do. I have researched it and only found pfSense site-to-site Openvpn work if the pfSense itself is the primary router. Again, in my scenario, the pfSense is behind router and only for site-to-site VPN only.

I would be really happy if someone who can shed even a little knowledge to help me solve this problem.

Thank you very much