have two routers cisco 2811 with vpn hardware and 871 which I am not sure has hardware vpn. Have a high speed cable connection at both ends. I set up a nat from site A to site B to test ftp directly and got 1.7M speed. I have adjusted tcp mss and ran the same test through dmvpn which uses ipsec and gre and got around 400K. Is that to be expected from the overhead?