Connection drops after 2 second. How to reset every service and configuration that may be causing the issue (18.04)?

de flag

I am on Ubuntu 18.04.

  • I have become unable to access internet (or better: I stop receiving data after 2 seconds from the initial connection) from all access points – both wired and wireless – of a specific network. I don't know why, since it used to work fine until some time ago.

  • It's not a DNS issue since even pinging works only for a few seconds before deteriorating beyond usability. Also, this network does not require special configurations, e.g. custom proxy or gateways: plugging in the Ethernet or entering a password on a normal WPA2 protected wifi usually work

  • On all other networks, my computer works just fine. Just any access point on this one network fails.

  • Trying a live distro on the same computer on the same network, with the same authentication details, works fine too, both wired and wireless. And I know that I've not been blocklisted (via hostname or MAC address or other) by the network admins.

Since "forgetting" the configurations via the Network Manager didn't solve the issue, what are the extra steps (e.g. services to purge and restart) I could take before wiping the whole OS?

Hint: I have used Docker on this computer, and I'm happy to purge it, revert all its changes to routing tables or similar (I don't need Docker right now), if that's a possible cause of the issue! How could I find these changes and revert them to a factory default?

waltinator avatar
it flag
Not an answer, but a diagnostic hint: Look at the logs! `sudo journalctl -b 0 -u NetworkManager`. Read `man journalctl`.
de flag

What finally solved my issue did not require wiping all networking configuration: I finally realized that the docker0 network manager interface was using the same IP range assumed by the network I was trying to connect to.

Since I don't need to use any docker service from that network, I just do

nmcli connection down docker0

when I'm on that network.

If someone finds themselves in a situation that is hard to troubleshoot via GUI or ip tools, then checking for potential offenders in nmcli connection show and trying deactivating them (if it's safe to do so!) may be a step to take.

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