The IPv4 Identification (ID) field enables fragmentation and reassembly and@ as currently specified@ is required to be unique within the maximum lifetime for all datagrams with a given source address/destination address/protocol tuple. If enforced@ this uniqueness requirement would limit all connections to 6.4 Mbps for typical datagram sizes. Because individual connections commonly exceed this speed@ it is clear that existing systems violate the current specification. This document updates the specification of the IPv4 ID field in RFCs 791@ 1122@ and 2003 to more closely reflect current practice and to more closely match IPv6 so that the field's value is defined only when a datagram is actually fragmented. It also discusses the impact of these changes on how datagrams are used.