I originally had this same issue about a year ago and was able to resolve the issue here, but after upgrading to this firmware (see below) I am no longer able to connect to the internet. I have chatted with centuryLinks support and they say that I am connected to the internet and it should be working. I basically did this without touching any other configuration besides following the steps in the previous thread. Any ideas or advice would be appreciated. Thank you.
Start with some basic checks: on the main status page see if anything is shown for IPv4 Upstream or IPv6 Upstream. Read the logs to see the ppp exchange, if any. "Timeout Waiting for PADO Packets" is common and indicates a complete lack of connectivity to the modem or ISP.
I haven't tested the wan.N syntax on a new release I assume that it still works.