I have a hub and spoke network setup. The corporate location has a NetVanta 6355 with three 3120s connecting to it VPN. I want to know what data rates should I see to the 3120s.
All of the 3120 and 6355 are running R10.11.0.E. The 3120s are connected to 35/5 cable modem and the 6355 is 20/20 fiber. At best I'm getting 300KBps when I copy a file. This was at night when everyone else was gone and after I tweaked the TCP/IP settings on both locations to maximize MTU etc..
VPN performance in a 3120 would in the best of circumstances be about 1Mbps, more typically in the 700kbps range. 300kbps seems a bit low but honestly it depends on what else the unit is doing at the time (CPU utilization is an issue obviously) and how the unit is programmed for things that would slow it down like ACL's, QoS, etc, etc.
Based on your cable modem connection speeds (35/5), the 3120 is insufficient for that connection anyway. We don't generally recommend the 3120 for connections greater than 10Mbps. For a 35/5 connection, with the expectation to actually be able to fully utilize that bandwidth, we would recommend a 3430 unit, with the Enhanced Firmware for the VPN functionality.