I have had several scenarios recently where I have needed to terminate an ADSL circuit onto a Cisco router that doesn't have the capability of an ADSL modem. In my specific scenarios this covers the Cisco 829 Industrial Router as seen below.
There are several reasons we choose to use the Draytek series which is summarised in the below statement taken from the Draytek website.
The DrayTek Vigor 130 is an ADSL and VDSL modem with an Ethernet connection; it is not a router but a true ADSL/VDSL Ethernet Modem (bridge). The Vigor 130 provides compatibility with all current UK VDSL/ADSL technologies; it has been extensively tested and tuned to provide a robust and reliable DSL connection.
By providing a PPPoE bridge, the connected device (firewall, router or PC) can log into the Internet (your ISP) directly and have full control over the Internet connection - that makes the Vigor 130 a unique product. You can connect any device to the Vigor 130 which has a PPPoE client facility, which includes PCs, most Ethernet-WAN routers and the Apple Airport/Time Capsule™ products.
By default the Draytek modem is configured as a PPPoE client, we need to enable bridge mode so that our router can particiate as the PPPoE client.
First power up the modem and connect a PC into the LAN port of the modem, you should get allocated an IP address in the 192.168.2.x/24 range by the Draytek's DHCP server. Open a web browser and navigate to http://192.168.2.1, login with the default credentials of admin/admin.
Once logged in navigate via the menus to Internet Access -> MPoA / Static or dynamic IP. As per the below screenshot ensure that MPoA is enabled and that the checkbox for Enable Bridge Mode is ticked.
You can now apply changes and disconnect your PC from the modem. The LAN port of the modem should now be connected to the WAN port of your router. Your router will need to be correctly configured as a PPPoE client, with appropiate authentication (if required) and either a static IP or dynamic IP configuration.