Got vlan DNS failures, but AP can still run

[DeathOctopus]

I got some DNS failures with my APs, and the dashboard alert me the AP got a 802.1X failure.

Then I use the test tools make a test, nothing shows wrong.

And the weird is all my devices can still access internet through those APs.

Anyone can explain why?

[GreenMan]

An intermittent performance problem or capacity issue with your WAN, maybe?    Assuming both your DNS and RADIUS servers are in some centralised datacentre...

[DeathOctopus]

An upgrade: the external DNS server are offline, that's maybe cause the DNS failures. But how the APs still working?

[BlakeRichardson]

@DeathOctopus Are the AP's set to use that DNS or are they using a public DNS server like Google? 

I'm not 100% but I suspect Meraki have some fail safe settings so that if internal DNS is offline the devices can still talk to the dashboard. 

[DeathOctopus]

Yes, they are public DNS  server. Maybe the Meraki has some kind of backup server by themself.

But anyway the APs and Switchs are all good now, and I will keep an eye on them.