christoph ender's

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tuesday the 12th of september, 2023

prompt failover with isc-kea-dhcp

After migrating to the new isc kea dhcp server - the successor to the older isc dhcp server – I've struggled a bit to get a server pair to do a proper failover when one of the servers fails. Turned out that there's a max-unacked-clients parameter, which tells the system how many dhcp clients need to have sent out dhcp requests before the failover occurs. By default, this is set to 5, so until you dont have five different clients waiting for an IP address, nothing's going to happen. I ended up simply setting this to 0, so once the timeout set in max-response-delay is met, there's always a guaranteed failover to the surviving server.