Lubuntu 18.04 RTS x64 networking problem

[mikeymikec]

I've been using it for a year and a half now and this weird little problem just came out of the woodwork and I have no idea what might have caused it.

I have my own server (web/mail/other stuff) on my LAN. I have TB set up to check mail with it and I also pick up my calendars off it. Recently TB has started reporting 'connection refused' for it, and will do this for approximately a minute before inexplicably deciding that it can actually communicate with the server.

During this minute-or-so, telnetting to the server's hostname or IP on mail ports results in a timeout. Internet access works fine.

telnet says:

Trying 192.168.0.7...
telnet: Unable to connect to remote host: No route to host

I think the issue isn't intermittent, I'm not 100% sure though. Booting from cold or a reboot doesn't seem to make any difference. One time I booted into Lubuntu, left it on the login screen for about half an hour, then the problem occurred after sign-in. However, signing out and back in again doesn't seem to trigger the issue.

Nothing interesting in dmesg that I can see. I've tried dropping/resetting the firewall (ufw), no difference.

Ethernet connection coupled with mains networking.

 

[serpretetsky]

During this minute-or-so, telnetting to the server's hostname or IP on mail ports results in a timeout. Internet access works fine.

Can you ssh to the server during this time? Or telnet on other ports?

 

[mikeymikec]

Can you ssh to the server during this time? Or telnet on other ports?

It's a Windows server so no ssh, but I did try to telnet to port 80 and nothing (independent service running on port 80 compared to mail ports).

The problem is intermittent, it was fine this morning. Argh...

 

[appybix]

What is the difference between ubuntu & lubuntu?

 

[mikeymikec]

What is the difference between ubuntu & lubuntu?

Lubuntu is meant to be a lighter footprint version, using LXDE as the desktop environment.

 

[mikeymikec]

Hum, this is not a software problem! Just booted with a live CD and into Win10, same problem. My phone also had the same issue over wifi. Power cycling the router (with the power physically disconnected for a minute) didn't help.

 

[serpretetsky]

While you are having the problem you can double check make sure your arp table is correct on the clients. Try connect to the server, once it fails goto 'cmd' and type 'arp -a' ( I forget what the command is for linux)

Make sure the ip and MAC of the server match what they should be.