I already made one Last Call comment, but I neglected to state unambiguously
whether I supported the proposal.
I do support this proposal.
I think that this question needs to be viewed as a choice between two risks:
1) the risks associated with this proposal
2) the risks associated with reuse of RFC 1918 address space by ISPs, and/or
reuse of public IPv4 address space by ISPs
To me it seems clear that the risks associated with this proposal are less than
the other risks. Software that assumes that IPv4 space other than RFC 1918
space is unambiguous will break in either case. But at least with this
proposal, there's a well-defined and easily-understood path to fix such
software to minimize the breakage.
It needs to be understood that at this point, there is no path that will avoid
widespread breakage of much existing IPv4-based software, including some
software that is widely used. Upgrades to that software will be needed in
order to continue using such software on a widespread basis.
Furthermore, even with such upgrades, the reliability of IPv4-based
applications can generally be expected to decrease over time. There is no
path to permit IPv4-based applications to continue to be used reliably, at
Internet scale, over the existing Internet infrastructure.
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