[Kea-users] New user, trying to use ip-reservations-unique feature

[Kevin P. Fleming]

Hello there! I've just deployed Kea 2.0.1 (using the ISC packages) on
a pair of machines in my network to provide HA DHCP4/DHCP6 services
(replacing the ISC DHCPd-based service in my layer 3 switches, which
don't provide sufficient functionality for my needs).

I've got the daemons running and HA mode working; most DHCP4
functionality is working fine.

However, one feature of Kea DHCP that I'd like to use is 'multiple
reservations for the same IP address', which was enabled when the
'ip-reservations-unique' configuration option was added. In my case I
have laptops with both WiFi and Ethernet connections, with different
MAC addresses, but I want them to have the same IP addresses
regardless of the connection mode. They will never be connected via
both interfaces at once, in fact the laptop BIOSes have been
configured to 'rfkill' the WiFi interfaces when the Ethernet
interfaces are connected.

I've posted a copy of my configuration here: https://km6g.us/kea-dhcp4.conf

If you take a look at subnet4 id '88', you'll see two reservations for
'balrog22' with the same IP address but different MAC addresses. While
the DHCP4 server accepts this configuration, when the laptop attempts
to obtain an address the server logs a message complaining about the
duplication:

Jan 29 09:39:10 edge21-b kea-dhcp4[725279]: WARN
ALLOC_ENGINE_V4_DISCOVER_ADDRESS_CONFLICT [hwtype=1
a8:64:f1:30:88:0b], cid=[01:a8:64:f1:30:88:0b], tid=0xcf6b412e:
conflicting reservation for address 192.168.88.192 with existing lease
Address:       192.168.88.192
Jan 29 09:39:10 edge21-b kea-dhcp4[725279]: Valid life:    86400
Jan 29 09:39:10 edge21-b kea-dhcp4[725279]: Cltt:          1643462468
Jan 29 09:39:10 edge21-b kea-dhcp4[725279]: Hardware addr: 90:2e:16:d6:a4:1e
Jan 29 09:39:10 edge21-b kea-dhcp4[725279]: Client id:     (none)
Jan 29 09:39:10 edge21-b kea-dhcp4[725279]: Subnet ID:     88
Jan 29 09:39:10 edge21-b kea-dhcp4[725279]: State:         default
Jan 29 09:39:10 edge21-b kea-dhcp4[725279]: INFO  DHCP4_LEASE_ADVERT
[hwtype=1 a8:64:f1:30:88:0b], cid=[01:a8:64:f1:30:88:0b],
tid=0xcf6b412e: lease 192.168.88.128 will be advertised
Jan 29 09:39:10 edge21-b kea-dhcp4[725279]: INFO  DHCP4_LEASE_ALLOC
[hwtype=1 a8:64:f1:30:88:0b], cid=[01:a8:64:f1:30:88:0b],
tid=0xcf6b412e: lease 192.168.88.128 has been allocated for 86400
seconds

Have I overlooked something in the configuration, or am I trying to
use this feature in a way that it is not expected to operate?