@Aaron_Wilson wrote:
Robin, why are you mentioning a Z3C, MS and MX. The OP never mentioned any of these.
Settle down Aaron
The Z3C is a Z3 with a LTE modem. At no point do I discuss the LTE functionality. However, the OP does make mention of being asked to have ATT "reset the card/SIM setting", so possibly has a Z3C, rather than a Z3.
The OP reports that the Z3 is connected to an ISP supplied router. I have described how my Z3C is indirectly attached to a third party router/security appliance, as well as how it is configured when attached directly to a modem/ISP device, covering the bases. It might be a bit technical, but network administrators are involved in sorting out the problem.
The MS was mentioned because of completeness and to indicate that there are no particular port requirements on the upstream device, just an uplink port. In a domestic environment, it may well be more convenient to connect the Z3(C) to the ISP router via a switch. In a domestic situation there may well be subscriptions to such services as multicast IP TV, Chromecast capable A/V equipment, Smart TV/Monitors and IoT derived equipment. From a functionality and security viewpoint it is mandatory/preferable to separate out these packets before it gets anywhere near Meraki security appliances.
At this juncture, I have not addressed potential double NAT issues, although they may be germane to developing a complete solution.
Aaron, I might be old, and decrepit, but I'm not stupid.