A payment company has a unique set up where they install their own router behind our router that has an ipsec vpn (my assumption is that its also L2TP) to their server, and all the payment systems are then just hooked up to their router.

So the set up is as follows:

their server <-> internet <-> my router <-> their router

I had a very crappy tp-link router and when VPN passthrough is enabled on it, everything worked beautifully. The router started giving me problems so I've replaced it with an RB751U-2HnD but for the life of me, I can't get it to passthrough the VPN properly.

I've tried forwarding UDP/500, UDP/1701, UDP/4500, IPSEC-ESP, IPSEC-AH to the IP of their router, made exceptions in the filter rules, even disabled the filter rules entirely but it doesnt work. I've had to switch back to the crappy tp link which is requiring bi-daily resets...

What am I missing?

Apologies, this is a double post, I'm new to the forums and misread the thread approval.

Please reply to http://forum.mikrotik.com/viewtopic.php?f=2&t=62816