Date: Wed, 07 Feb 2018 15:14:39 +0000
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From: tmark@isc.org
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Subject: delayed-ack default of 0 interferes with lease ACK commits in ISC
 DHCP 4.4.0.
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A change made for 4.4.0, to compile in delayed-ack support by default but to default the number of acks to 0, was intended to include the popular feature but with it turned off.

The default of 0 is causing lease ACKs to not be written to the database.  The work around without recompiling, is to add:

delayed-acks 1;

To the dhcpd configuration file. Alternatively, you may change the default explicitly in the code to be the desired value:

# define DEFAULT_DELAYED_ACK 0  /* default SO_SNDBUF size / 576 bytes */

or disable the feature at compile time by rebuilding with --disable-delayed-acks.