We have 160+ offices around the country, all using the same basic setup - MX with MS switch(es) and MR AP(s). No other hardware anywhere on our network, and every site is built using the same template so only the subnet info is different. We are finding a persistent issue that only seems to be affecting sites using AT&T fiber as the ISP (we use several different ISP's based on whatever is available in the area). Every once in a while, seemingly random, the switch will go into Disabled switch (bad DNS) state. This tends to happen overnight when the office is closed, so it's not due to any kind of traffic or changes on the network. It will stay like this until we reboot the MX - that's the only thing we've found that fixes it but it does fix it every time. We've discussed this with Meraki support and their suggestion was to change our management vlan settings to use Google DNS (we currently use Umbrella). The problem appears randomly so we can't reproduce it, but it did happen today and changing to Google DNS did not fix it. The modem at these sites is the BGW320-505. It does not allow a true bridge mode, but we have disabled packet filtering and enabled IP passthrough mode. Even so, the DNS it gives the MX is 192.168.1.254 and apparently this cannot be changed on this modem. Maybe this is causing an issue? Has anyone seen this issue? Is this a known problem with these AT&T modems, and if so is there a solution? This tends to happen overnight so there's no users generating traffic that could be triggering the error state, and the same configuration at 100+ other offices never results in this problem, it is only the offices with AT&T fiber.
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