allan2545 wrote:Just received my CM500 today.
Day and night!
Using the Arris modem, I was getting 10-12Mbps downstream over the VPN from site A(100Mbps upstream) to Site B (125Mbps downstream). Ideally, I should be able to get 100Mbps downstream at Site B, but as I understand it, latency plays a role in IPSEC bandwidth, so I am willing to accept something less.
With CM500, I can get consistently over 14Mbps using the defaults in the Bandwidth tool on the EdgeRouter. I increased the window size to 1024KB and the parallel flows to 20. Then I was able to consistently get 50Mbps, sometimes peaking to over 60Mbps. When I did this with the Arris modem, I still only got 10-12Mbps.
At least for me, the mystery is closed. It's the darn modem!!! Let me know how your experiments go.
BTW, I played with the MSS-Clamping just for a few minutes. Didn't make any difference for me. So I have removed all MSS-Clamping settings and put everything back to default.
Wow, that's very interesting to hear, thank you so much for reporting back with your results. I have an Arris DG2470A with RCN cable in New York City. I have nothing but good things to say about their Internet service. I'd really love to find out what's going on, but I don't have a device to sniff the packets on a coax wire 
Thanks again, many Kudos to you!