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