That's unclear to me. One of the arguments for dropping the layer 3
checksum in IPv6 is that modern layer 2 solutions come with error
detection. Making the layer 4 checksum compulsory strengthened
that argument, of course. But I don't remember discussion of
why the pseudo-header checksum is essential. In fact, when the IPNG WG
was chartered in 11/94, the charter said:
TCP/UDP: The IPng Working Group will specify the procedures for
hosts to
compute and verify TCP/UDP pseudo-headers. Any other changes to TCP
beyond making TCP work with IPng are out of scope of the working
group
and should be dealt with by a TCPng Working Group.
So it was taken for granted that we needed it.
I recall the IPng directorate wanted to make the fewest changes to the
transport layers. The only changes that were required was to lengthen
the address and that is what turned out.
The same reason why the low-order 64-bits were not used as a socket-id
for TCP for tcb lookups.
Dino
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