I'm not sure what the problem is here:
- UDP checksums are optional
- optional checksums probably aren't applicable to TCP
- IPv4 has IP header checksums
- IPv6 could define an option for IP header checksum
(could be applicable to IPv4 also, if you want a stronger checksum
for the header)
- whether L2 drops packets whose checksum fails is an L2 matter;
the ability to turn this on or off is an L2 feature
- if the app needs a different integrity check than all-or-nothing,
this is something that belongs in the app protocol
so it seems like what we need is a bit in the IP header to indicate that
L2 integrity checks are optional, and to specify for various kinds of
IP-over-FOO how to implement that bit in FOO. and maybe that bit could
go in the IP option to provide a stronger checksum than normally exists
in the IP header (so that the header, at least, is protected)
Keith