Trouble with Meraki DHCP AutoMagic

[TBisel]

We have a site that guest wifi isnt working but internal is. Wireless health is saying that it is a DNS failure, but we can reach 8.8.8.8, since we can get out to an address and not a name I have to agree with it. But thing is I have no idea how to see any of the information for the Meraki DHCP that it is actually handing out. This is connected up to a Comcast gateway but cant confirm any of its settings. Any tips?

Also, How does this actually work? Does it use a make believe VLAN or is it encapsulating the traffic on that VLAN somehow? 

[NolanHerring]

The access points acts as the gateway, dns etc. So the client will only see 10.128.128.128

Check the access point itself, what DNS does the AP get? That is the DNS that the AP will use via proxy for your guest.

Unless you have the SSID access control overridden via Content Filtering which allows you to specific custom DNS.

Try the TOOLS page on the AP in question and see if he can resolve DNS out to the internet etc.

[BrechtSchamp]

Also, a quick ipconfig /all on a windows client can show you the DNS settings it's using.

[TBisel]

Meraki DHCP returns 10.128.128.128. Which isnt a DNS server thats where one of my issues where.

[BrechtSchamp]

10.128.128.128 is the IP address of the AP. The AP can handle DNS resolving for the guests. Previous posts should help troubleshooting if you're experiencing issues with that if it's not working.

However, if you want you can still configure a custom DNS server too:

https://documentation.meraki.com/MR/Client_Addressing_and_Bridging/Configuring_Custom_DNS_for_an_SSI...

Edit: My reply was meant for your previous post.

[TBisel]

So funny thing, AP was working fine. Tools section could ping both my DNS servers, resolve addresses and ping websites. All we did was took Primary 1.1.1.1 and secondary 8.8.8.8 DNS servers for AP, and swapped them. Now its working fine. If anyone can tell me why, that would be awesome.

[NolanHerring]

When you swapped from 1.1.1.1 and 8.8.8.8, I have experience with AT&T Internet service where 1.1.1.1 won't resolve, so I had to use 1.0.0.1 instead. For some reason they blocked in and/or their hardware was improperly using 1.1.1.1, so I would ping it and get 1ms response time (which is basically saying its pinging the provided AT&T router) so I knew that wasn't right. Once I changed to 1.0.0.1 I started getting realistic pings of like 20 or 30ms and everything started working.

Not sure if your using AT&T, but it might be something worth checking out as well.

[TBisel]

Comcast. But strange thing is, the Normal non-NAT Mode network worked fine. Just the Nat Mode/Meraki DHCP stuff decided not to resolve DNS. I mean its working now, just dont understand why it didnt.

[Bruce]

The Meraki DHCP doesn't operate as a full DHCP server per se. It creates the client IP address using a hash of the client's MAC address, and responds with that and a gateway and DNS server of 10.128.128.128 - which is an IP address that the access point responds to. The access point then proxies the DNS requests from the clients to the DNS servers it has configured (i.e. the ones you can see on the main access point summary/dashboard page), so you need to ensure that the access point can reach these DNS servers. By using this approach if the client roams to another access point it will most likely receive the same IP address, and maintain the same gateway and DNS server, so it will be as seamless as is possible without using any of the various roaming technologies/protocols out there.