Setting this field to a 4 octets length value means that ip mapping (using rlSNMPv3IpAddrToIndexTable)
is used for this row. If such a mapping is not used, a 0-length octet string
value should be used for this field (this is also the default).
This field value is determined only once, upon creation of an entry in the
snmpTargetAddrTable. A change in its value while updating an existing entry
is ignored.
Prior to creating a snmpTargetAddrTable entry with a 4 octets length value for
this field, the rlSNMPv3IpAddrToIndexTable must be used in order to retrieve
this value.