We have a Digital Video Recorder behind a customer-provided BEFSR41 (v2.0) router with a static IP (216.41....). Ports 21, 23, 8234-8235 & 80 are forwarded to this DVR (192.168.2.200).
The DVR is programmed to periodically transfer an image file to the customers off-site FTP server (maintained by 3rd party). Because the DVR must see a successful ping response prior to sending the image file, the FTP server is setup to accept pings only from the static IP. So here's the problem...
The FTP server is seeing the Ping requests, but instead of the origin being the static IP (216.41...), the origin is showing as the internal DVR address of 192.168.2.200, and is therefore being rejected.
BTW, I can telnet into the DVR and then successfully create a FTP connection from the dos prompt.