I've recently removed my TalkTalk hub3 router and connected my Vigor 2860n directly to the Openreach VDSL modem setting up PPOE on WAN2 port of the Vigor to establish VDSL connection. At the same time I upgraded the 2860n to the latest firmware 3.8.4.1BT.

Since then I have mysteriously lost any remote connection functions which requires the Vigor's own responses on the WAN side. In particular, the following functions don't work:
I can't ping the Vigor from WAN even if I enable the PING from WAN option in the Management section.
I can't establish a Remote Dial user VPN connection to the Vigor from WAN. The VPN request just fails without any responses from the Vigor.
The Remote Management function of the Vigor does not respond to http://wan-ip or https://wan-ip from the WAN side even though these options are switched on in the Remote Management section.

I can ping the Vigor from the LAN side and login to its HTTP management panel from LAN. Furthermore, if I do a http://wan-ip from the LAN side of the Vigor then its management panel responds.
The Vigor makes good PPOE internet connection through the VDSL modem. The devices on the LAN side of the Vigor get internet connection and port forwarding from WAN through the Vigor to my server and PCs work fine too. So port forwarding of the Vigor is functioning correctly.

In the Vigor I have changed HTTP remote management port to 8080 and HTTPS remote management port to 444. However with no difference in being able to connect to it from the WAN side. Needless to say that I have made sure the PPTP is ticked in the General setup screen of the Remote Management section for the remote dial-in VPN user.

Has anyone got any ideas that might help please?

If you revert to 3.8.2.3 does it work again?

I (and others here) have had issues with 3.8.4 versions and I've had to revert to 3.8.2.3

Thanks Piste Basher. I was beginning to suspect that myself. I am currenty away from the router and must wait until I get back to downgrade the firmware. Would you know if applying 3.8.2.3 will be compatible with the 3.8.4.1 settings or will I need to reset the router and start again?

I am just reporting that I downgraded the firmware of my Vigor 2860n to version 3.8.2.3.v1. The issues described in my original post still remain. I am now suspecting that the Openreach VDSL modem may be having a part to play in filtering handshaking communications to the Vigor from the WAN side. The BT Openreach VDSL modem has no management panel or user definable controls as far as I am aware so I am not quite sure what route to take at present to resolve the issues.

Sorry for late reply. As far as I know the 3.8 settings are compatible (not sure what happens if you enable features in 3.8.4 that aren't in 3.8.2.3 though ) but I guess you've found that out for yourself.

I used an Openreach modem (Huawei version) on my 2860 for some time and didn't have the problem you are experiencing. That was several firmwares ago though.

I have now gone back to firmware version 3.7.4.5 dated 29/12/2014, version by version, and all the problems persist. I think there is no point in going back in firmware versions furthermore and the assumption must now be that there is something wrong with the way the Openreach VDSL modem is working with the Vigor 2860n in this configuration.

Before this, I did try to connect the copper wire directly to the VDSL port of the Vigor to make either an MPOA or PPOE connection, however it did not work for me and no matter what settings I tried I could not get internet connection successfully. The Vigor modem synced correctly with the TalkTalk server but connection status remained at 'SHOWTIME' with WAN1 VDSL remained 'DISCONNECTED'.

Since then I have discovered that there are Vectoring variants of firmware version 3.8.4.1 available too which I did not try for connecting the Vigor's modem directly to the VDSL copper wire. I think I'll be exploring that path soon in an attempt to remove the Openreach VDSL modem from the setup.