Unknown client alerts and clients not getting IP addresses

[Fleming, Tony]

Good afternoon folks!
We ran into a problem today and it has me completely dumfounded
Background:
                We create a host record for each device that connects to our network
                Over the years our dhcpd.conf file has grown due to little purging (yeah - I know we should be purging the data)
Symptom:
                Suddenly today, we began getting reports users are unable to get an IP address.
                The clients vary from iphones, to OS X and PC laptops
                                The issue doesn't seem to be OS or hardware dependent
                My logs are alerting:
                                dhcpd: DHCPDISCOVER FROM xx:xx:xx:xx:xx:xx via x.x.x.x: uknown client
In my dhcpd file there is a "host" record for each device - so I am scratching my head to why the device isn't getting an IP address.
                Not all devices are having trouble getting IP leases
Workaround:
                We have removed the directive in dhcpd.conf to "deny unknown clients"
                Now all of our devices are getting IP addresses.

Questions:
                Has anyone experienced a problem like this?
                                If so, what did you find to be the root cause?
                Is it possible my 300k line dhcpd.conf file is causing this behavior?
                                Could there be a programmatic time-out searching through host records in memory that is causing the host lookup to fail?

Thank you.

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.isc.org/pipermail/dhcp-users/attachments/20160822/75e4e5a4/attachment.html>