FRITZ!Box 7590 DNS server forgets hostname after lease time

[tiwoli]

I have a Raspberry Pi 2 running Archlinux ARM. The Raspberry has a wired network connection to my FRITZ!Box 7590, it gets its IPv4 address via DHCP and after establishing the network connection, it is reachable through the set hostname.
After the lease time for the IPv4 address is over, the hostname gets somehow lost in the DNS of the FRITZ!Box, it is not resolvable anymore until I unplug and replug the wired network connection of the Raspberry.
The Raspberry is still listed with its hostname on the web interface fritz.box as Network Device after the DNS entry in the FRITZ!Box is lost. The Raspberry can still be reached through the IPv4 address.

Until now, I only know that it is related to the lease time.
With the default lease time of the FRITZ!Box of 10 days, it happens after exactly 5 days.
If I set the lease time to 24 hours in the FRITZ!Box, it happens after these 24 hours.
In the journal of the Raspberry, I get this when lease time is over:

[code]
systemd-timesyncd[261]: Network configuration changed, trying to establish connection.
systemd-timesyncd[261]: Synchronized to time server 195.201.20.16:123 (de.pool.ntp.org).
[/code]

At a different location I have a set of Raspberry Pi 1 (also running Archlinux ARM) together with a FRITZ!Box 7490. The problem is non-existent in that environment.

I contacted the manufacturer AVM with no luck, they could not help me with this at all.

Does anybody know the problem or could help me with finding out the cause for this?

Thanks in advance.

[tiwoli]

Which developers, the developers of the router? I tried without success, they have just blamed the Raspberry.

How do I get to find out the actual communication during the renewal process between the DNS server of the router and the DNS client of the Raspberry? In the journal, there is nothing from the DNS client. Maybe there is a way to run the DNS client in debug mode in foreground?

[moonman]

there is no DNS client on RPi. The router just picks up hostname and publishes it in the local DNS directory. The issue is on the router side. You can try to work around the issue by setting a static DHCP lease with a name on the router, if it allows for that.