Problem with nethserver backups

I’m far from sure this is a problem with Nethserver, but I’m hoping someone may have suggestions as to how to work out where it is…

I look after a current Nethserver, which does daily backups via NTFS to an Ubuntu 20.04 server. The server itself was migrated to a newer box a few month ago, but has been working fine.

Night before last, the backup failed. Looking at the email message, the reason was given as a timeout waiting for the nfs connection. I didn’t have much time on site, but when I checked from my own laptop, using showmount displayed the nfs shares, and I was able to mount the share used for the backup without any errors. Today, I found the backup had failed for a second time, and had a bit more time to investigate. Only trouble is, I don’t understand the results of my investigation.

From the Nethserver machine, showmount hangs, eventually times out and returns to the prompt. In addition, I’m unable to ping the Ubuntu server from the Nethserver console, or ssh from the same console. Yet I can ping or ssh to the Ubuntu server from my own laptop, and I can ping the server from other machines on the local network.

From the Ubuntu server console, I can’t ping the Nethserver machine. I’m also finding that the Ubuntu machine seems to have no DNS for the local network, though I can ping other machines on the network by IP.

The Nethserver machine was not quite fully up-to-date. I had not applied the Roundcube update, or the firewall updates. I applied all the updates, and restarted the Nethserver (it had been running for around 3 months without any restart). No change - still not able to see the Ubuntu server.

There were some Ubuntu updates a few days ago, so I suspect some change on it is most likely the cause of the problem, but I have no idea about deeper diagnosis and I’m hoping someone may be able to suggest way in which I might be able to narrow the cause of the problem?

You may check firewall logs, /var/log/firewall.log on the Nethserver and /var/log/ufw.log on the Ubuntu server.

You could disable firewalls for testing.
Just execute shorewall clear on Neth and ufw disable on Ubuntu.

Do you use fail2ban or IPS on the Nethserver (or Ubuntu server) ? Maybe one server is banned or blocked?

Thank you. I hadn’t considered fail2ban, which I do have running on the Nethserver. That was the cause. Looking through the logs, it appears that postfix got 3 failed attempts to connect in quick succession, causing the ban. I’ve cleared the ban and whitelisted the Ubuntu server. Now all I need to do is work out what triggered the problem on the Ubuntu machine.s

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