Troubleshooting: no free leases

[timeless]

Hi,
fwiw, I just upgraded isc-dhcp-server, I'm now running: 4.3.1-6+deb8u2
(things were working fine before that point, I'm not sure offhand what
version I was running previously,  unfortunately). And I got the problem
below. I've since upgraded to 4.3.5-3 (Debian stretch) without any
improvement.

And I hit "no free leases".
I'm hoping someone could help me figure out what's going wrong / how to fix
it.

This is most of my dhcpd.conf [1] file.

The client I'm trying to get a lease for is a modern.ie Windows10 VM [2]
running in VirtualBox 5.1.24 on macOS Sierra w/ guest additions Bridging an
Thunderbolt Ethernet Adapter [MAC address: 08:00:27:d0:ad:b7]
WireShark shows the windows 10 system sends:
  MSEDGEWIN10<.MSFT 5.07
WireShark reports it as:
  Client FQDN: MSEDGEWIN10
  vendor-class-data: MSFT 5.0
... which should match my "win" class.

None of my pool ranges appear "full" [3].

The class match is not logged.

For comparison, here's background logging [4], and what I get when I
troubleshoot the Windows 10 network [5].

pool 10.4.6.1 .. 10.4.6.254 has allow unknown-clients, which is where it
would go if it wasn't matched.

One basic question I have is: How do i tell if a pool is "full"?

It would be very helpful to me for debugging if I could get isc-dhcp-server
to "explain" how it decided that it had no more space.

>From my naive perspective none of my pools are full, but I'd rather be able
to ask isc-dhcp-server its opinion.

I also tried stopping isc-dhcp-server


There's no configuration for a failover pair, and the word "failover" isn't
present in my config file.

I read: release notes [6] -- which shows that the logging was introduced in
3.0rc12

I skimmed through: KB looking for "no free leases" [7] and the kb articles
all seem to be about performance or failover.

Thanks

[1] https://www.irccloud.com/pastebin/OU5bsfhX/%2Fetc%2Fdhcp%2Fdhcpd.conf
[2] https://developer.microsoft.com/en-us/microsoft-edge/tools/vms/
[3] https://www.irccloud.com/pastebin/jibZxPPp/dhcpd.leases.trimmed
[4] https://www.irccloud.com/pastebin/YJ6Nt04h/
[5] https://www.irccloud.com/pastebin/HWE9aEvs/
[6] https://kb.isc.org/article/AA-01357/0/DHCP-4.3.4b1-Release-Notes.html
[7]
https://kb.isc.org/index.php?/searchResults/0/10/fU_NCoMwDH4V6RPYOeYWbxMEz-4uVSMK1Y42jg3x3ZeqA0-75fuSfD8KpITZgQxBOFS27h74JpEwcwYxmqC1iIFG5dB59vo7y0cPIxBKaz9deJqoM9YDFtu5WlHe8KcCtukhZPYEIpIiWdgi5qfmVeyCxVSlavXmE7Pq-1iNIsx6TWj3AOxYUj-gh7dtX7bWDAfneKfJHEjJsvXkyAxZj3pLFcLMQbgq_a3tc5gnjvdPaho2rrjJ8gU~
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