Assuming that you are using the router from your ISP, it is possible
that the firmware has been upgraded without your nolage.
One way to prevent this could be (1), that is, use your own
router/server/gateway so you control everything on your LAN.
I use an EMTA modem only from my ISP which is plugged into a perimiter
firewall.
If you can't have an modem from your ISP, look at 'bridgemode'.
If your not comfortable building your server from scratch, you can
simply buy a router that is accepted by your ISP .
In other words, you need to choose one or the other if you go this way:
- Modem connected to router (most flexible of all)
- Combo modem/router in one box (les flexible but is more compact)
If you use DHCP static lease, you should look at what the DHCP server is
providing as hostname and 'TLD', and also in the dhcp client (dhclient'
to see what you get from the DHCP server.
The file '/etc/resolv.conf' should let you know what TLD is sent from
the DHCP server.
Debian shouldn't modify your configuration files '/etc' without your nolage.
Note that the TLD '.lan' is sometime used.
1) https://www.xfinity.com/support/articles/list-of-approved-cable-modems
--
John Doe