Determining Whether To Use a Routed or Bridged VPN
Refer to this community wiki article for an overview of routing versus bridging: What is the difference between bridging and routing?. You can also refer to Ethernet Bridging for more notes and details on bridging.
Overall, routing is probably a better choice for most people, as it is more efficient and easier to set up (as far as the OpenVPN configuration itself) than bridging. Routing also provides a greater ability to selectively control access rights on a client-specific basis.
We recommend using routing unless you need a specific feature which requires bridging, such as:
The VPN needs to be able to handle non-IP protocols such as IPX.
You're running applications over the VPN which rely on network broadcasts (such as LAN games).
You would like to allow browsing of Windows file shares across the VPN without setting up a Samba or WINS server.