Thank a lot viragomann
To get this to work - I ended up providing domain name (factory.local) to my remote office DHCP clients so those client PCs can resolve short (NetBIOS) names as well as FQDN for our local domain. I typed Main-Office DNS server IP (10.0.1.20) on the top of the list in General->Setup for Remote-Office pfSence machine (as you suggested)
So now Remote Office client PCs can join the Main Office domain and listed in AD-DNS with 10.0.5.x addresses :)
I did not use DNS-Forwarder… do I really have to use DNS-Forwarder ? I think AD-Client PCs are better left with their "natural" AD-DNS server for name resolution...
Question: We have an extra subnet in Main Office (10.0.3.0/24) used for IP-Phones… Is it possible to connect that subnet through our VPN connection ? We need to install a few IP-Phones in the Remote-Office location ?
I tried adding extra gateways and static routes at pfSence - nothing works... Please advise :)