Double Nat Error and No DNS Server

Bad combo.. SB6141 and TC have known issues.. Just do a search here.. sb6121 or sb6141 and apple AC routers have some incompatibility .. wan on the TC somehow comes up wrong settings.

Nor do I have a simple fix.. the TC or the modem should be replaced.

Line of least resistance says just buy a cheap wireless router.. eg TP-Link WR1043ND.. cheap and quite a powerful unit. Can also be flashed to a very good firmware.. gargoyle.

Another one rather out of date is Netgear WNDR3800.. you might need to buy it second hand.. ebay for instance.. $40 or so. but the new TP-Link is about the same. Again flash over to gargoyle.

The TC can then work in bridge plugged into the router.. it will provide wireless and hard disk access etc for backups ..

You can replace the modem.. Zoom or ubee I have heard work ok.. but you will need to check COX for which is supported.

I have suggested to people in the past to try using a small switch 10/100, between the SB modem and the TC.. or a crossover cable.. but it is not terribly successful of late. The problem seems to be getting worse rather than better.

You can also take the TC back to apple for replacement and get another one.. but the issue affects.. 4 out of 5 and perhaps doesn't show up immediately either.

I was considering replacing the modem with the new Motorola SURFboard SB6183, do you think this would solve the problem?

Please stay away from a Motorola / Apple combo. The Motorola modems are fine products and the Apple AirPorts are as well. But, they just don't work well together.

As with Bob.. we are seeing too many issues with the whole range of SB and ARRIS modems..

There is some real issue between them such that one or the should be replaced. But finding modems that work is harder than finding routers that work.. all routers work fine.. except the apple. That pretty much shows where the issue is.. but it is strange because the apple does work ok with some brands.

Also what exact ally does running the TC in bridge mode do? Will the TC still act as a router broadcasting internet wirelessly or will it just act as a switch?

As far as your network is concerned it is not that different.. TC would be the wireless AP and switch and Hard Disk for TM.. routing is handled by the replacement.. after all, pure modems are now actually rather rare as almost all ISP hand out gateways and most people run their apple routers in bridge.

It does have a couple of network implications..

BTMM to the TC itself may not work.

Guest wireless will not work.

Both of these have easy work arounds.. the fact you replaced the TC with another router means it is now able to handle guest wireless.. and remote access as well.. just you cannot do it the way apple says.