Can I bridge the same subnet across a VPN?

[Geoff Roberts]

Hi,

Is it possible to join two sites with the same subnet across a VPN?

I have two sites that have the same subnet/mask.

I need these two separated networks to behave as one across a VPN.

All configuration examples I've come across so far assume that each site will 
have a different subnet. Eg, one site with 192.168.1.0/24 the other with 
192.168.2.0/24

I control the firewalls at each end. One will be a pfsense firewall, the other 
an existing FreeBSD 7.4 system.

For example I would want to be able to do the following:

Site A                           Site B
------                           ------
Firewall A 10.1.1.3  --------- Firewall B 10.1.1.4
      |                                       |
Subnet: 192.168.20.0/24       Subnet: 192.168.20.0/24

Happy to use either IPSec or OpenVPN to actually encrypt the traffic.

Kind regards,

Geoff