The list of held IP addresses in the user group.
The IP addresses in this table are not available
for use.
When an IP address is released from use and if
the re-use delay feature is enabled, the IP address is added
into this table for a configured time period before it can
be used again. An IP address that was discovered to be used
by an external device is also added into this table
for configured time period also. When the timer
expires, the IP address is removed from this table.