System – Kea IPv4 DHCP server (ver 2.2.0) running on Debian 12, serving addresses on second network interface (PCIe card).
On reboot the server starts, but warns that it could not open the socket on the prescribed interface, and so is not serving any addresses. Running
systemctl status kea-dhcp4-server.service
The error is
kea-dhcp4[582]: WARN DHCPSRV_OPEN_SOCKET_FAIL failed to open socket: the interface enp3s0 is not running
kea-dhcp4[582]: INFO DHCP4_OPEN_SOCKETS_FAILED maximum number of open service sockets attempts: 0, has been exhausted without success
Restarting the service afterwards works normally. This is a known problem. There are various suggestions to fix the ordering, but the simplest (albeit slightly inelegant) way to get it to work is to tell it to retry a bunch of times with the service-sockets-max-retries and service-sockets-retry-wait-time options. So the start of the configuration looks like this:
"Dhcp4": {
"interfaces-config": {
"interfaces": [ "enp3s0" ],
"dhcp-socket-type": "raw",
"service-sockets-max-retries": 100,
"service-sockets-retry-wait-time": 5000
},
This retries every 5 seconds up to 100 times, which should be enough to get things in order. Note that, annoyingly, there is no message logged when a retry succeeds.