Some devices can't connect to Time Capsule intermittently

My modem is an Arris Surfboard SB6190 DOCSIS 3.0 which is connected to my Model A1470 ME177LL/A AirPort Time Capsule 802.11AC 2TB. The modem is only a modem, no router.

Thanks for the info.

This is a known bad combo. It is not one we can easily explain but there are long threads here about issues between the AC model airports (either the TC or AE makes no difference), and any of the single port surfboard modems.

It seems the WAN port on the TC is not 100% compatible with the LAN port on the Surfboard.. how or why????

Anyway the solution is fairly easy to replace one or the other.. neither is faulty per se it just is a bad combo.

People around here recommend the Zoom modems. I am not local.. and these threads are fairly old but you can search for 6190 as well as the earlier 6121 or 6141. They all have the same issue.

https://discussions.apple.com/thread/5187450

https://discussions.apple.com/thread/5048548

Personally I would replace the TC with another router.. I use Asus which has very good wireless and controls.. far superior to the Airports.. but I still use the airports in the network for wireless to Apple products. It is a good combo.

You could also try using the Gen4 on the SB6190 although I would recommend you go back a few versions in firmware if the latest one still has issues.. and use the Gen5 elsewhere. It is not unheard of for Gen4 TC to also have issues with surfboard modems.. but from my reading over several years of all the threads about the issue, it was only very recent firmware that introduced the problem.

If you hold down the option key while clicking the version, you can select earlier ones.. try 7.6.1 which should not affect the overall network setup much. It is just a test.. and will help to locate if the newer TC is really the problem.

You likely have the TC bridged to another router which is handling DHCP.

I find this becomes a problem with Apple DNS failing miserably in this setup.

But do answer Tesserax questions.. except the first..

Which exact model is your Time Capsule?

Airport Time Capsule 5th gen.. Some days your glasses slip!! 😉

We need to know the full setup.. what make and model is your modem?? And is it a router or pure modem?

Any other network complexity we need to know about.

Which exact model is your Time Capsule? Regardless of the model, how long have you had it in operation? Was this always an issue or just started to happen recently? Is the Time Capsule your only wireless router? Finally, do you live in an environment where there are multiple other Wi-Fis operating nearby or use things like portable phones or baby monitors so that we can rule out Wi-Fi interference as a potential issue?