> From: Joe Touch <to...@isi.edu>
> The source can fragment, though, and THEN set DF on the fragments.
> ...
> it can be changed from 0 to 1 by a router.
FWIW, I don't believe either of these cases was considered when we were
finalizing the IPv4 spec. If you read RFC-791, it's clear from the
discussion there of DF that it was intended to prevent fragmentation of
complete datagrams (e.g. for interacting with a host which could not do
reassembly, perhaps because it was a ROM bootloader with limited code
space), not further fragmentation of fragments. Before this discussion, I
would have considered a packet with DF=1 and Offset!=0 to be in error.
Which doesn't mean we _shouldn't_ allow them, but I'm pretty sure it was
never contemplated that it could/would be done.
Noel
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