A quick run through on how to get the Draytek 2860ac setup and running on BT infinity.
First things first plug the cables in and a network cable to your machine, you should get a DHCP address on the default 192.168.1.0 network and you can open the router admin page up at 192.168.1.1. The default username/password is admin/admin. This can also be done by connecting to the wireless using the default keys supplied on the base of the unit.
Before you get going its a good idea to to upgrade the firmware if you have another means of access to the internet. I pre-downloaded the latest version, v2860_3822_vector3.zip and unzipped. You have two file options in the downloaded zip v2860_3822_vector3.all and v2860_3822_vector3.rst. The RST file will reset the router to default settings and the ALL file will retain all current settings. If you have config on the router this would be a good time to take a backup of the settings.
Once logged in navigate to WAN >> General Setup.
Set Enable to Yes
Set DSL Mode to VDSL2 Only
Set VLAN Tag Insertion VDSL2 to Enable and the Tag Value to 101.
Click OK, the router will reboot.
Once rebooted log back in and navigate to WAN >> Internet Access. Select Details Page for WAN1.
On the details page set the Username to email@example.com and the password to bt. I have read that the details here are not important as long as the username is @btbroadband.com. Click OK, the router will reboot again and that it, once rebooted it should connect.
Once connected you can view the status and check the sync speed on the Online Status page.