How can I speed up file transfers over VPN?

Solution 1:

This is most likely due to the SMB protocol being very "chatty", and requring many requests/acknowledgements before and during transfer. Here a couple of things that may help:

• Adjust TCP windowing to be optimal for your network. A google search will bring up many tutorials
• Upgrade to Server 2008 AND Vista machines (requires both to take advantage), as they use SMB2.0 which specifically targets this issue.
• Install a WAN accelerator on either end, be it a dedicated device like a Riverbed device, or the BranchCache feature in Server 2008 R2.

Solution 2:

We had problems in the past because the VPN system used UDP as its underlying protocol. The problem with that is the routers between the VPN user and the network would depriortize/drop UDP packets.

Switching the underlying connection to TCP seemed to solve this issue for us.