This read-only value is a unique index for a row in the ARP table, ranging between 0 and 65535, though the values may not be contiguous. An admin or management application uses this index to enumerate individual ARP table entries when walking the table, without assuming index values are sequential. For example, an SNMP walk of this table might return index values 1, 3, and 7 rather than a contiguous sequence, reflecting entries that have been added and removed over time.