Router Board High CPU (Watchdog timer Reboots) with FTP

So I have been working on a problem with FTP traffic (which I originally thought was a IPSEC issue). When I changed the FTP traffic to transfer from remote to a server behind the router board via NAT. I was seeing about 1.5MBs from a 100Mbs connection.

Also I was seeing 100% CPU and when looking at the profile shows very high encryption load. It has been getting so high the watchdog timer has been rebooting the RB!

After much playing around I discovered the issue to be passive FTP. If I change the transfer to active FTP i’m seeing about 9MBs (around 70Mbs) with only 40% CPU load.

Has anyone else seen this?

If so what was the work around?

Alan Scott
http://www.logicalsolutions.co.nz