Short posts on topics that come up in operation: addressing, backups, access. All from hands-on experience — and without details that are nobody else's business. https://alexanderjanzen.de/en/blog 2026-09-22T09:00:00+02:00 Alexander Janzenhttps://alexanderjanzen.de/ © 2026 Alexander Janzen https://alexanderjanzen.de/en/blog#adressplan 2026-09-22T09:00:00+02:00 2026-09-22T09:00:00+02:00 Alexander Janzen

A device without a fixed address once took a server's address. The service was unreachable for a few minutes, and the cause was unspectacular: the range used for automatic addressing contained addresses I had assigned by hand.

<p>A device without a fixed address once took a server's address. The service was unreachable for a few minutes, and the cause was unspectacular: the range used for automatic addressing contained addresses I had assigned by hand.</p><p>The solution was not new technology but an order — every fixed place first, the automatic range behind it. Since then a device from the automatic range cannot take an address that is already in use. In addition, every address change is followed by checking each device individually.</p> https://alexanderjanzen.de/en/blog#sicherung 2026-09-08T09:00:00+02:00 2026-09-08T09:00:00+02:00 Alexander Janzen

A backup run that finishes without an error message says nothing about whether the data really comes back when it matters. That experience is why the goal here is not the backup but the successful restore.

<p>A backup run that finishes without an error message says nothing about whether the data really comes back when it matters. That experience is why the goal here is not the backup but the successful restore.</p><p>So there is a second storage target, and at fixed intervals a restore is genuinely rehearsed: fetch a file back, restore a machine, tick off the result. What has never been tested does not count as a backup.</p> https://alexanderjanzen.de/en/blog#fernzugang 2026-08-25T09:00:00+02:00 2026-08-25T09:00:00+02:00 Alexander Janzen

Nothing on the router is reachable from outside. The path runs through a tunnel with an identity check and a second factor in front — no interface appears at all until the sign-in is complete.

<p>Nothing on the router is reachable from outside. The path runs through a tunnel with an identity check and a second factor in front — no interface appears at all until the sign-in is complete.</p><p>The actual proof was a hardening test: after rebuilding access I requested every published address without signing in. All of them answered "access denied" and not a single interface was visible. Also verified: after several failed attempts the lock kicks in and raises an alert — "should be protected" is not proof.</p>