"Custom DNS Server" issue

[Swood]

We have a satellite classroom that uses as "home" internet service as it is far away from our school/LAN. We want to put a Meraki access point in this location and set it up with some of the SSIDs found on our main network so that users will automatically connect when at the satellite location. I have created a separate Meraki network for this location and I have created a couple of SSIDs on this network set up to use Meraki NAT mode. This configuration works fine, but when I add in the "Custom DNS server" settings to use a content filtering DNS service, we lose access to the internet. I have tested this in two locations with "home" internet with two different ISPs, and the result is the same. We use the same DNS filtering service on several SSIDs on our main network with no problem. Any thoughts as to why we lose internet connectivity when using "Custom DNS server"?

[BlakeRichardson · Accepted solution]

Is the custom DNS server accessible externally. I am guessing the problem is the DNS server you are trying to use isn't available externally. 

[Malwina]

When Custom DNS service is set to some other DNS, for example, 8.8.8.8, do you still encounter this issue? As Blake said, this is likely due to your DNS server's availability. 
Also, please note that when connected to an SSID with NAT mode the wireless clients will still be assigned the AP's internal IP 10.128.128.128 as their DNS server IP (this customizes the destination server of the AP's DNS proxy).

[Swood]

Turns out it was an issue with the DNS filtering service. Thanks for your assistance!