I am trying to connect a new soho mk3 (6.6.6 build 1068) to a surfboard 5120. The model spins and spins but never makes the connection. I have tried all the possibilities for the connection (DHCP, PPPoE, L2TP) to no avail. I cannot find a previous discussion to answer my question.
I’m probably going to disappoint you with my answer but the first thing I’d do is to make certain you are running the most current firmware in the SOHO.
Also, if you search the forum, you will find many threads which report issues with Motorola and Arris “surfboard” modems. On our end we we’ve had some that never connect but, more commonly, will work for a while then magically become intermittent. Sadly, this has never been explained or resolved, although many suggestions have been received and tried. One would think that ethernet, properly implemented on each end, router’s WAN port and modem, would yield a reliable, trouble-free connection. But, apparently not so. (See? I told you you would be disappointed in my answer … 
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