This object is a wildcard bitmap to specify a group of source IP addresses. The bit value 1 indicates the corresponding bit will be ignored. The bit value 0 indicates the corresponding bit will be checked. In other words, when the value of all 'ff'Hs indicates any IP source address is specified. When the value of all '00'Hs indicates host IP source address is specified.
Sources for this description
D-Link official switch MIBsD-Link MIB copies (LibreNMS/Observium Community)