iOS App Not Working When Using T-Mobile LTE

I’m not sure when this started happening, but I’ve recently noticed that I can’t connect to any of my remote devices when either my IPad or iPhone is on a T-Mobile LTE network. I have no problem when using WiFi. This used to work, but I probably haven’t checked this in a couple of months. Any suggestions?

That’s a pain.
Is t-mobile giving your a ipv6 or a 4 ip address? http://ifconfig.co/ to check. And then do you remote devices have access to the same ipv4/6?
I don’t think the iphone gives you any access to any settings that can help, but I don’t have t-mobile.

Is your app up to date, 1.8.1?

Both my iPhone and iPad are using an IPv6 address from T-Mobile. Could this be a v4 vs. v6 issue? I have had other situations where the use of a v6 address was causing issues. The thing is the iOS devices have been getting v6 addresses for quite a while, and I wasn’t previously having any ZT problems.

Yes… both devices are running version 1.8.1.

Unfortunately, right now my visibility of the situation is temporarily gone since the router that remote devices are behind is down.

if one device has v4 only and the other v6 only, the connection will be relayed. This should still “work” but be slower. More likely zerotier is just having trouble with whatever the provider is doing.
Sorry about your router!

Opening up the other routers more may help the LTE devices connect.

If it helps, I am running into the same symptoms - recently checked and it stopped working on LTE on iOS

Running 1.8.1 but iOS is 14.8.1

My LTE provider is Mint Mobile, which is a T-Mobile MVNO

Thanks for confirming that the issue isn’t just with me. My devices are running iOS 15.1 and ZeroTier One v 1.8.1. Hopefully there’s some resolution to this in the near future. Not having access via my iOS devices over LTE significantly reduces the utility of ZeroTier for my use case.

Makes me wonder if T-Mobile is rolling out some sort of change over their network, but it isn’t everywhere yet. I have T-Mobile and an iPhone, yet things work absolutely fine 100% of the time on LTE

Is your iPhone getting an IPv6 address from T-Mobile?

Yes, it does indeed have an IPv6 address.

Does the ios app ever get to the “connected” state? Do you get the vpn status bar icon and does the network details screen say status: ok?
Does it say “online” in Central?

Yes, when I toggle the network enable switch within the app I get a status window. The status window populates and indicates Status OK. On the ZeroTier account webpage, the network shows both my iPad and iPhone as being ONLINE.

Interesting. Thanks. Will the phone respond to pings?

If I understand your question correctly, I don’t believe it will unless it’s pinged from another device running on the T-Mobile network (in which case ZeroTier is out of the picture).

That definitely shouldn’t be the case, and I’ve never seen such behavior

Go figure. It seems to be working again today. I don’t know what changed.

I wonder if PercyJax is seeing the same thing.

Well…. Not completely working. I noticed it works for HTTP, but not for ICMP, SSH or TELNET. Is this a possible clue to the issue?

Not really. The ZeroTier app doesn’t do anything to allow or disallow different software protocols. If it’s TCP or UDP, ICMP, ARP or NDP it just goes. Nothing outside ZeroTier can inspect the contents of the packets to do any sort of filtering either as the traffic is all encrypted.

So if HTTP is working, then so should anything else, unless there’s a firewall elsewhere blocking the traffic

Keep in mind, this behavior is only when using the T-Mobile LTE connection. When using a WiFi connection everything works fine.

This exact thing is happening to me on Telstra (Australia) when the phone has an IPv^ public IP. My iPad on Telstra gets an IPv4 address and it works fine. iOS ZeroTier 1.8.1

For the last month or so, ZeroTier on my T-Mobile LTE works for HTTP but not for ICMP, TELNET or SSH when getting an IP v6 connection. This is better than nothing, but I am still hobbled to some degree.