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How would you resolve this issue: Your server's internet randomly becomes inaccessible until reboot. (Ubuntu 22.04, Netplan)

I've been having this issue very sporadically (sometimes a couple times a week, sometimes once a month). I'm curious as to how the more veteran folk here would try and narrow down the cause of this issue.

I can provide more info if needed!

Edit: More Info:

  • Using a static IP (no DHCP) through Netplan.
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33 comments

  • Check if there's some weirdness in IP allocation. A reboot can cause DHCP to give it a new one that works as long as it does, then fail on some weird collision.

    • I forgot to mention that I'm not using DHCP, statically allocating a local IP

      • There might still be another device on the network that is using DHCP and is getting an IP that conflicts. Do you have any visibility on the rest of the network, IP addressing, DHCP leases etc? I would check there first for a potential easy fix.

        • Hey thanks for the suggestion. It's the only client on this modem/router. I have a dedicated internet for it. So there shouldn't be any DHCP conflicts. I will double check to see if anything else is on that network and double-check the range of assignable IPs

      • Is there a DHCP server at play? Is the static IP outside of the DHCP range? This does sound like a typical IP collision.

        • DHCP is enabled on the router, but I believe the IP address is outside the designated DHCP range.

          I'll double check when I'm home!

          Edit: I will also say that this modem/router is dedicated only for the server, so there shouldnt be any other clients on it at all.

          • This might not be applicable to your use case, but maybe it helps.

            Couple of years ago I had a problem where ONE windows laptop was unable to access the internet. Sometimes it would work right away, sometimes it took 1 or 2 reboots, sometimes the damn thing wouldn't budge.

            lo and behold, it turns out the windows laptop was assigned a DHCP address that one linksys router had as a static ip. Why that resulted in a sporadic error and not a constant one I'll never know.

            So next time you have this issue, rip out the network cable from the server and try to ping the ip the server is supposed to have.

            Other than that, check the journal if something start to pop up around the time you experience the problem.

            • Thanks for the suggestion. So I have the static IP assigned with DHCP disabled both through Netplan, not through the router.

              I'll remember to check the Netplann (?) journal/logs around that time, or are you referring to dmesg?

              • Since you're not really sure what the issue is, check all the logfiles around the time the problem starts. maybe you'll see a service stopping or starting.

                • Thank you I'll do that! It's hard to catch exactly when it happens. I think I need to get some monitoring and alert services up and running

                  • Changedetection.io it can send you an email or message when your server fails to ping it.you will then have the times. Its a 5 minute job to set it up. Make an account and your email or number or whatever and make a curl request to the specific endpoint in a cronjob

                  • Easiest route you could go is setup a systemd timer which runs every 5 mins, pings an ip and write the result into a logfile. that way you have a timestamp for the problem start without going all out with monitoring.

                    Good luck!

                  • You don't need to catch that moment live, it was already recorded.

                    Take a look at journalctl -b -1 (previous boot).

33 comments