The value of tmnxNatPlPortResvType specifies
how the whole ephemeral port range is split up in blocks.
Each of those blocks can be associated with a host.
The type of port reservation specifies the meaning of the value of
the object tmnxNatPlPortResvVal.
The value of the object tmnxNatPlPortResvType must be changed together
with the value of the object tmnxNatPlPortResvVal.