Thanks for your comments about 240/4 at the int-area.
After the int-area meeting I had a chance to sit down with Dave Thaler.
Dave's basic concern is that if we say now that we don't want to decide
a use for 240/4 6to4 and other code cannot actually be modified because
it behaves differently based on whether address space is public or private.
Another concern Dave raised was the difference between "controlled" and
"uncontrolled" environments. In an uncontrolled environment one can
never be sure as to whether or not all devices have been modified to
allow for the new range.
Finally, a platform has a choice. It can do one of the following:
* Nothing
* Make the space a compile time option
* Make the space a configuration option
* Just turn it on
Dave is of the opinion that doing the latter (or having default enabled
for the middle two) is akin to inviting the sorts of security concerns
that have been raised about v6 deployment.
Dave can correct me if I've gotten this wrong.
I am less concerned about security considerations in this particular
case, since devices could send packets with 240/4 sources or
destinations NOW. Also, if we are to make this address space usable at
all, ever, we need to get beyond these concerns.
Also, MANY devices and stacks do not use mechanisms like 6to4 that
distinguish between RFC 1918 space and public space. I believe those
devices should make their changes today.
Alain Durand raised concerns that devoting resources to making 240/4
available, while others at the same time said they needed the space now
for private purposes in a controlled environment. I would like to
re-iterate what I said in the meeting, speaking for myself: there is no
Plan B. We need to go to IPv6. The only question for me is how do we
transition in an orderly and responsible fashion?
For the time being I would like to continue the discussions on how to
proceed and would invite interested parties to help.
Eliot
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