VPN passthrough problem with BEFSR41 V4.3

[Link2221]

I have two BEFSR41 V4 routers cascaded. Second router's WAN port connects to the first router's LAN port. First router connects to the Internet via a PPoE connection. VPN Passthrough enabled on both. PC running the VPN client software is connected to a LAN port on the second router. Internet surfing works and VPN works.

When I replace the second router with a BEFSR41 V4.3 router, Internet surfing still works but VPN stops working. The V4 and V4.3 routers have virtually the same config. VPN passthrough is enabled and I changed the subnet to 192.168.3.0 so that it wouldn't conflict with the first router. The V4.3 router has the latest firmware.  

VPN also works if I remove the first router and connect the V4.3 router directly to my PPoE Internet connection; but I need the cascaded setup to work. In our enduser environments, the first router is usually provided by the enduser so it is not always a Linksys BEFSR41; so I need these new BEFSR41 V4.3 routers to always be the second router. The idea being that we can add-on our security environment without affecting the enduser's environment.

What is different about the V4.3 router that is causing my setup to stop working?

[Mort]

Make sure that you connect the BEFSR41 v4.3 router from the WAN Port to the LAN Port on the First Router...

Do not Disable the DHCP Server on the BEFSR41 v4.3 Router...

I could not understand why you are replacing the second BEFSR41 router with BEFSR41 v4.3 Router...

Did you try a factory reset on the BEFSR41 v4.3 Router ?

[Link2221]

1. v4.3 router's WAN port is connected to the LAN port on the first router. That was stated in the original post

2. DHCP wasn't disabled.

3. It isn't replacing. When we bought our last batch of routers, they were V4.3. New users who received V4.3 routers complained that they were not working. It was our trouble-shooting that identified that the V4.3 routers were the source of the problem. The replacement mentioned in the post was to illustrate the point that the older routers worked and the V4.3 do not work. 

4. A factory reset was one of the first things we did.