C. M. Heard wrote: >> Existing routers, which was relying on ID uniqueness of atomic >> packets, are now broken when they fragment the atomic packets. > > Such routers were always broken. An atomic packet has DF=0 and any > router fragmenting such a packet was and is non-compliant with > the relevant specifications (RFCs 791, 1122, 1812). Thank you. I have overlooked that atomic implied DF=1. But, then, >> Sources emitting non-atomic datagrams MUST NOT repeat IPv4 ID values within one MSL for a given source address/destination address/protocol triple. makes most, if not all, IPv4 hosts non compliant if MSL=2min. Worse, without hard value of MSL, it is a meaningless requirement. Note that MSL=2min derived from RFC793 breaks 150Mbps TCP. The proper solution, IMHO, to the ID uniqueness is to request a destination host drop fragments from a source host after it receives tens (or hundreds) of packets with different IDs from the same source host. A source host, then, is only required to remember the previous ID used for each destination. Masataka Ohta