MT5000 <> BE3600

Router
1

Hello all:

I’m at a loss and need some help.

I have a be3600 Beryl 7 and a MT5000 Brume 3.

T-Mobile 5 G Wi-Fi home router uses CGNAT

I have Tailscale set up between devices.

At the moment, I’m able to get all traffic through without issue. Web traffic, whatever.

in a few hours, I won’t be able to get any traffic through, yet I haven’t changed anything.

I have no idea what causes the devices to stop all traffic and not talk with each other.

This morning I have manually updated the firmware on both devices via upload from web portal.

Everything was hard reset, and setup is fresh. everything is working smoothly at the moment.

Later today it may not. I have no idea what stops it or where to begin the trouble shooting.

I have spent an extensive amount of time troubleshooting derp. but it looks like its working just fine too.

Any idea on a flow of trouble shooting would be good. everything has been in consistant so I’m kinda stuck.

2

The key is to capture the failure before rebooting, then determine whether the WAN, DNS, Tailscale tunnel, or exit-node routing has failed. CGNAT may prevent a direct peer-to-peer path and cause Tailscale to use DERP, but DERP use alone should not stop traffic.

  1. When it fails, test from a connected client:
    • Can you open the local router admin page?
    • Can you ping 1.1.1.1?
    • Can you resolve a domain name?
    • Can you reach the remote router’s Tailscale address?
  2. On both routers via SSH, run:
    tailscale status
tailscale netcheck
tailscale ping <remote-peer-name>
    Note whether tailscale ping reports a direct path, DERP relay, timeout, or peer offline.
  3. In the Tailscale admin console, check whether both routers still appear online at the failure time. Also temporarily disable exit-node/subnet routing: if normal Internet access immediately returns, the problem is likely the routed Tailscale path rather than T-Mobile’s WAN connection.

Please provide the exact model names, complete firmware versions/builds, Tailscale versions, which router is behind T-Mobile, and whether one router is acting as an exit node or advertising subnet routes. You may post the command results after removing peer names and addresses; do not post full logs, configuration backups, account details, or authentication keys publicly.

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New IA bot
4

Hi,

Since the connection is currently working again, you can check the Tailscale configuration on both routers against the guide, the Exit Node settings if all traffic is expected to pass through the remote router.

If the issue occurs again, please avoid rebooting or resetting either router immediately and perform the connectivity checks suggested above while the issue is still present.

In addition, please run the following commands on both routers:

ip route
ip rule
logread | tail -n 200

And also let us know when the issue occurred whether only Internet access through the Exit Node stopped working, or whether the two routers could no longer reach each other through their Tailscale IP addresses either.

Thanks for your support and understand, and we will continue to help investigate based on the results.