Site A and Site B will have open VPN client configured on pfsense. Windows machines on the Site A and Site B are able to ping the Open VPN Access Server Internal Ip (10.0.0.4), But Windows machines on Site A LAN is not able to reach the Site B LAN desktop and vice versa.

Site-to-Site IPSEC VPN Between Cisco ASA and pfSense IPSEC is a standardized protocol (IETF standard) which means that it is supported by many different vendors. Therefore if you want to create a VPN between different vendor devices, then IPSEC VPN is the way to go. Implement Azure v2 Site to Site VPN with Pfsense – Gareth Jul 12, 2016 Site to Site IPSec VPN using PfSense - YouTube Jun 21, 2020

Step 1: Install pfsense and set local IP’s on both firewalls. Step 2: Logon to the web interface for pfsense on each box and assign the WAN addresses. Step 3: Enable IPSEC (VPN->IPSEC->Enable IPSec). Do this on both firewalls. Step 4: Add a tunnel on Site 1’s firewall to Site 2 by adding a tunnel and changing only the following items:

Oct 08, 2017 Site-to-Site IPSEC VPN Between Pfsense - Cisco Community

Hướng dẫn cấu hình VPN Site to Site trên Pfsense - YouTube

OpenVPN based Site-to-Site VPN between Azure and pfSense Feb 10, 2017