VPN and bonded ADSL

I have client who has taken it upon themselves to replace their standard ADSL connection with a bonded ADSL connection using two ISP.

I am not sure of the exact setup but basically they have 2 router - one for each of the broadband lines. They are from two different ISPs.

These routers then feed into a Draytek router to which all the clients PCs and the server are linked.

Since moving over to bonded ADSL the remote workers have been unable to establish a VPN conection to the Draytek.

The remote workers are using Windows 8.1 and PPTP.

When I try to telnet from outside the LAN to the internet on port 1723 the connection fails.

I am guessing that the first 2 bonded adsl routers are somehow blocking the VPN traffic.

I am unsure exactly how bonding works but is this likely to be the problem?
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The Draytek router is basically, still a router. The NAT rules still works the same (of course, now you have to be more careful where to send the packets). The 2 modems are required to forward everything to the Draytek too of course (so all 3 devices need to be carefully configured). There are no problems specifically when bonding two ADSL connections together, you just have more work to do.

Step by step:

modem 1, forward VPN to draytek
modem 2, forward VPN to draytek
draytek, forward VPN from WAN1 to VPN server
draytek, forward VPN from WAN2 to VPN server

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roy_battyDirectorAuthor Commented:
Well the Draytek is the VPN server do that simplifies things a little.
Indeed, obviously, the two latter lines are not needed.
roy_battyDirectorAuthor Commented:
Thanks for the help
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