Thinking about this some more ... perhaps I can set the WAN address to just a fixed one on the regular LAN and then create a new LAN on the other side of this device for VPN access....

The TP-Link can use dynamic IP for its WAN connection, but it doesn't allow this to be the same network as the LAN. Doesn't it need both connections to operate properly?

@Virgo The actiontech C3000A has several WAN settings including this passthrough mode. There is also an additional tagged-201 option that was suggested by CenturyLink. When this modem is set to...

Trying to connect a tp-link TL-R605 router to a century link ActionTech C3000. Followed Century Link suggestions: physical connection between WAN port on TL-R605 to a non-wan port on the ActionTech....