Hi, On 6/3/2012 12:12 PM, Masataka Ohta wrote: > 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. This is already noted throughout this document, however there is little impact to such non-compliance if datagrams don't persist that long. > Worse, without hard value of MSL, it is a meaningless > requirement. Note that MSL=2min derived from RFC793 breaks > 150Mbps TCP. It breaks at 6.4 Mbps for 1500 byte packets, as is already noted in the doc. > 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. That doesn't help ID uniqueness; it helps avoid fragmentation overload. FWIW, such issues were discussed at length in the INTAREA WG when this doc was developed. > A source host, then, is only required to remember the > previous ID used for each destination. They don't do anywhere near that right now, but even if they did it would still be prohibitive in speed (as per above). Joe