I have seen a few devices that consistently ignore DHCPOFFER messages. After
some tinkering with standards compliant permutations of offers that they
might not handle properly (e.g. lease times and RFC6842 client-id options),
I got frustrated enough to try some standards non-compliant possibilities.
It seems that despite requesting a broadcast response, they actually only
receive and/or accept the DHCP message if it is unicast.


I tested this by creating a "-dhcp-unicast" configuration option that is
identical to the "-dhcp-broadcast" option but with the exact opposite
meaning, namely regardless of what the client asks for, use L2 unicast
responses. With that change the devices (some Honewell thermostats and Sony
TVs) started working.


Has anyone else seen problems like this? When I search on Honeywell Lyric
thermostat Wifi connection issues, it does seem like a lot of people have
undiagnosed problems with them, so this may be the cause.


Has anyone else seen devices that don't seem to respond to DHCPOFFER
messages? If so, do the corresponding DHCPDISCOVER messages have the
broadcast bit set?

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