Zerotier and Mobile Hotspot Connection Problem

Community Support
1

Hi guys,
I have an issue. When I’m trying to connect to my server via Zerotier using a normal WiFi connection, it works perfectly. However, when I try to connect using a mobile hotspot, I can’t connect to any server. This issue started about two weeks ago, and it used to work without any problems before. I’ve tried different mobile operators, different accounts, different laptops, and operating systems, but it still doesn’t work.
What could have changed, and why is it not working?
I am curious if there have been any recent updates or changes to Zerotier, mobile networks, or other related configurations that might be causing this issue. Has anyone else experienced similar problems, or does anyone have suggestions on what might be causing this connectivity issue?

Thank you in advance for your assistance.

2

I’ve got exactly the same issue. Noticed it about a week ago.

Still have no idea how to fix it.

3

Are you using the same mobile hotspot device? What is it?

Some popular devices like the Inseego are intentionally crippled by carrier firmware, and you might get a better result by installing generic firmware.

ZeroTier tends to work best in this kind of deployment when one or both sides can open a port through UPnP, which is a feature that many hotspot devices lack.

4

After digging further I found the solution. You have to set MTU of the ZeroTier network from default 2800 to 1280. See this comment @ GitHub, and this comment.

First create ZeroTier API key, and then execute this:

TOKEN="your_my.zerotier.one_api_token"
NETWORK_ID="your_network_id"
curl -X POST \
  -H "Authorization: token ${TOKEN}" \
  -d '{"config": {"mtu": 1280}}' \
  "https://my.zerotier.com/api/v1/network/${NETWORK_ID}"
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5

I have always assumed that Zerotier will fragment its packets, since the default MTU of 2800 is definitely larger than the MTU of most physical interfaces (1500). If this is true, then maybe you should set the MTU of the physical interface, i.e. the WiFi interface connected to the hotspot device, instead of setting it on the Zerotier network?

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6

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