Setting up UTM with CenturyLink DSL / PPPoE

I recently switched over to CenturyLink's 140/20 small business service and learned a few things along the way that might be helpful to others. The service is VDSL2 bonded & vectored and they supplied me a Zyxel C3000z modem / router / wifi combo unit for my rental or purchase.  Looking around it seems that its tough to beat that modem for $100 and it's going to get full support from CL so I think I'll stick with it, but of course I don't want to use the wireless or router functions.  However after running it in DMZ mode while I was getting everything setup I thought it would be nice to retain access to the GUI in case I needed to troubleshoot the DSL connections themselves. 

NOTE: To make things easier further down the path setup a static route in the C3000z for traffic to make it back to your LAN before enabling transparent bridging.  Otherwise you'll have to either set the PPPoE interface back to Ethernet and set a static IP or use the HTTP proxy service on the UTM to access the config GUI on the C3000z.  Advanced Setup -> Routing -> Static Routing. You want to add a route with the destination IP and subnet mask as your LAN network, and the gateway being the IP address you assign in the 'Additional addresses' section down below. 

Screenshot of static route on C3000z:

To properly connect UTM to the WAN side of things I needed to enable transparent bridging on the modem. Here's the step by step from CL: https://www.centurylink.com/home/help/internet/modems-and-routers/zyxel-c3000z/access-advanced-setup/wan-settings.html

Then setup the WAN connection on the UTM to PPPoE:

Type: DSL (PPPOE)

VDSL: Unchecked  - Not sure why this is, but enabling it allows you to set a vlan tag and it refused to work for me even with 201 entered as the tag.

Username: Your PPPoE credentials username - Example: youracct@centurylink.net

Password: Your PPPoE credentials password

MTU: 1492

Screenshot of my entire interface config:

Now I setup an additional address on the same interface the PPPoE connection was configured on:

Name: C3000z Mgmt

On Interface: Same as PPPoE interface

IPv4 address: 192.168.0.5

Netmask: /24

Screenshot of additional address config:

With that all in place I can still access the DSL modem's web interface from the inside LAN while coexisting with the PPPoE connection.  Access to this can easily be controlled as well however I just disable the additional address entry unless I need to access it.

One other thing I learned; UTM doesn't support IPv6 6rd and while I was trying to set it up I got into a position where I needed to reset the C3000z back to defaults as it just stopped responding at all. Whoops, but at least it was quick to get back up and running.

Hope this helps someone out there!