Created attachment 824319 [details]
The complete original dhcpd.conf

See also:
https://forums.opensuse.org/showthread.php/538232-Now-DHCP-has-decided-to-quit?p=2920155#post2920155

For no apparent reason dhcpd (v4) has decided to not work.
The only significant change made to the network is the addition of IPv6
addresses to the hosts, the activation of a IPv6 DHCP in a different host which
included a RA.

----[ manual start ]----
$ systemctl start dhcpd.service 
Job for dhcpd.service failed because the control process exited with error
code.
See "systemctl  status dhcpd.service" and "journalctl  -xe" for details.
----[ end ]----

Journal:
----[ System journal entry ]----
2019-11-16T21:27:57-0700 sma-server3 dhcpd[29103]: Starting ISC DHCPv4 Server
2019-11-16T21:27:57-0700 sma-server3 dhcpd[29103]:   please see
/var/log/rc.dhcpd.log for details ..failed
2019-11-16T21:27:57-0700 sma-server3 systemd[1]: dhcpd.service: Control process
exited, code=exited status=1
2019-11-16T21:27:57-0700 sma-server3 systemd[1]: Failed to start ISC DHCPv4
Server.
2019-11-16T21:27:57-0700 sma-server3 systemd[1]: dhcpd.service: Unit entered
failed state.
2019-11-16T21:27:57-0700 sma-server3 systemd[1]: dhcpd.service: Failed with
result 'exit-code'.
----[ end ]----

----[ rc.dhcpd.log ]----
Config file: /etc/dhcpd.conf
Database file: /db/dhcpd.leases
PID file: /var/run/dhcpd.pid
Wrote 0 deleted host decls to leases file.
Wrote 0 new dynamic host decls to leases file.
Wrote 39 leases to leases file.

No subnet declaration for eth0 (no IPv4 addresses).
** Ignoring requests on eth0.  If this is not what
   you want, please write a subnet declaration
   in your dhcpd.conf file for the network segment
   to which interface eth0 is attached. **
Not configured to listen on any interfaces!
----[ end ]----

dhcp subnet that is supposedly "undeclared". There has been no problem with
this for years.
----[ dhcpd.conf subnet excerpt ]----
subnet 192.168.69.0 netmask 255.255.255.0 {
 option time-servers time.sma.com;
 option domain-name "sma.com";
 authoritative;
 ddns-updates on;
 range dynamic-bootp 192.168.69.200 192.168.69.239;
 default-lease-time 14400;
 max-lease-time 172800;
 zone sma.com. { primary 192.168.69.246; key smacom; }
 zone 69.168.192.rev. { primary 192.168.69.246; key smacom; }
}
----[ end ]----

I have tried running DHCPD on a different opensuse host. It failed in exactly
the same way.
I reduced the conf to a minimum set. It failed in exactly the same way.
----[ dhcpd.conf stripped version, complete ]----
option domain-name "sma.com";
option domain-name-servers 192.168.69.246;
option routers 192.168.69.1;
default-lease-time 14400;
ddns-update-style none;
subnet 192.168.69.0 netmask 255.255.255.0 {
  range 192.168.69.200 192.168.69.240;
  default-lease-time 14400;
  max-lease-time 172800;
}
----[ end ]----