pfsense Virtualbox guest openvpn server cannot reach Virtualbox host

[Raymond Mak]

Openvpn client can access all other ip address except the Virtualbox host.
Virtualbox host is ubuntu 16.04
Virtualbox version 5.18
pfsense guest network, both WAN and LAN are bridged adapter.
I know it can be Virtualbox or ubuntu's problem, I still hope someone can suggest possible reason for me to try. Thank you very much.

[viragomann]

@raymond-mak
Yes, I suspect Ubuntu is blocking access from outside of its network.
So you may have to configure its firewall properly or try to disable it for the first step to get sure that this is the reason.

As a workaround you can also masquerade the traffic from the VPN network to the host by an outbound NAT rule on pfSense.

[Raymond Mak]

@viragomann
The Ubuntu previously a NAT gateway + Virtualbox host + file server + others. Now I replaced the gateway role with pfsense VM. Maybe I can't restore the network setting of the Ubuntu. If so it is out of this forum.
Thank you for your reply.