DHCP DUID file not preserved across reboots when "Use RAM Disks" is enabled
The file "/var/db/dhcp6c_duid" contains a DHCP Unique Identifier (DUID) that a host uses to uniquely identify itself to a DHCPv6 server. According to RFC6355 (https://tools.ietf.org/html/rfc6355), "DUIDs are intended to remain constant over time, so that they can be used as permanent identifiers for a device."
This is not working properly in pfSense 2.3.2-RELEASE if the option for "Use RAM Disks" is selected in "System->Advanced->Miscellaneous." In this case, it appears that the duid file is not preserved before a shutdown, and therefore regenerated on each startup. As a result, a DIFFERENT DUID is created, and the system appears to be a different device to a DHCPv6 server.
This file should either NOT be stored in /var, or be preserved across reboots in a manner similar to how RRD and DHCP Leases are preserved.