This value indicates the format version of the ARP rate-limit trap message being sent, letting the receiving management station know how to correctly parse the accompanying trap fields, particularly the cell-encoded trap message object. It exists so future firmware updates could change the trap's cell format without breaking older management tools that check this version first. For example, a management station seeing trap version 1 would parse the accompanying trap message cells according to the 17-octet-per-cell layout defined for that version.