Getting a 'No DNS Server' error on AirPort Time Capsule

Unfortunately, AirPort Utility for iOS is not really the same application as AirPort Utility for the Mac.

Do you have a Mac that you could use for the setup?

You should not have a Double NAT error if the Time Capsule is set up correctly, but AirPort Utility for iOS does not detect the type of signal that it is receiving from an upstream device all that well.....while AirPort Utility for Mac will normally work much better in this regard.

We want to avoid that Double NAT if at all possible, because ignoring a problem does not make it go away.

Post back if you want to try DHCP Only mode and we'll go through the manual setup with you.....but the only reason to do this would be if you want the Time Capsule to be in charge of handing out IP addresses to all of your network devices.

Other than personal preference, there is no need to set up the Time Capsule this way.

PPPoE won't work, so don't bother messing with that.

The next step is to get rid of the Double NAT.

What happens if you start over and select a Router Mode of "Off (Bridge Mode)" instead of DHCP and NAT?

Should I try a Static IP instead of Double NAT?

No, that won't help at this time.

Static IP would help if you were using a Router Mode of "DHCP Only", which is a very rarely used type of setup on the Apple AirPort routers. Apple never officially supported this type of setup.

Since the fibre optic modem is just a modem

The giveaway was your initial statement that you were seeing a Double NAT error when you initially set up the Time Capsule as a router.

The device that you call your "modem" is not really a modem. It is actually a simple router because it is providing DHCP and NAT service.

Since your "modem" was really a router "upstream" from the Time Capsule, the correct setting for the Time Capsule would be Bridge Mode.

But, there might be a question as to how many IP addresses the Fibre Converter can provide to the devices on your local network. If you are running out of IP addresses, there is a way to set up the Time Capsule to provide DHCP service......(but not NAT....which would create another Double NAT situation)......by setting up the Time Capsule to use a Router Mode of DHCP Only.

This can get complicated, because it requires some manual settings, and as I mentioned before Apple does not officially support this type of setup.

If everything is working OK now, I would leave well enough alone.

Is this the Optic Fibre router assigning new IP addresses every day?

Appears to be the case based on your report. Normally a router will assign the same IP address to a device though that has already been assigned. It simply "renews" the same IP address, not changes it.

Should I go for a static IP in bridge mode?

Worth a try, but the trick will be to get into the settings on your Fibre router and have it assign a Static IP Address to the Time Capsule.

Yes, you can configure the Time Capsule using AirPort Utility to "request" a Static IP Address, but that assumes that the Fibre router will honor that request......and if it is automatically changing things at midnight.....it may try to change the "static" address that the Time Capsule is requesting.

This might be a situation where OP wants to actually consider PPPoE - configuring the fiber modem to use PPPoE Passthrough (which is roughly equivalent to a Bridge Mode for a fiber modem), and then configuring the TC to be the router.

The specifics of how to do that can be modem model-dependent and need the assistance of their ISP Tech Support, though.

The OP indicated that they tried PPPoE and kept receiving errors.....no server, no DNS, incorrect password, etc.

I don't think the ISP provided the Fibre Optic Converter. Most ISPs want to provide their own router for their fibre service.

Not sure who their ISP is of course, but I don't know of any fiber modem or converter that can make an ISP connection without a PPPoE username and password. Usually that's provided or provisioned by the ISP when the technician installs the device. I know I had to get those from my ISP to use PPPoE passthrough on my modem.

I did see where the OP indicated they tried it and had errors - but couldn't tell if they actually had the right credentials from their ISP.

Again, ISP dependent, but in my experience most ISP now are providing all-in-one fiber modem/router/wireless AP devices like Hitron Homehub models (and then renting additional wifi extenders as well as cable set-top boxes).

Why PPPoE, try Using DHDP.

https://cleanbrowsing.org/help/docs/change-dns-on-a-apple-time-capsule-airport-utility/

Use these numbers...

8.8.8.8

8.8.4.4

1.1.1.1

9.9.9.9