North American Network Operators Group

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Re: 240/4

  • From: Daniel Senie
  • Date: Tue Oct 16 16:27:15 2007

At 02:29 PM 10/16/2007, Pekka Savola wrote:

On Tue, 16 Oct 2007, Alain Durand wrote:
Classifying it as private use should come with the health warning "use this
at your own risk, this stuff can blow up your network". In other words, this
is for experimental use only.

Do we need to classify anything (yet)?


I say the proof is in the pudding. Once some major user decides they'll need 240/4 for something, they'll end up knocking their vendors' (probably dozens) and their own ops folks' doors. Once they get those vendors fixed up to support 240/4 in all the releases that they're interested in, and ops to change configs, they can deploy something in 240/4 for whatever (most likely private use, or private use with a NAT to the outside).

It would behoove us to allocate SOME of 240/4 as private address space, and mark the rest as "future, allocatable if it's deemed possible." If all of 240/4 is given over without guidance to private address use, a huge mess will follow, should we later decide it safe to use on the public network.

If the users decide that maybe doing the legwork is too difficult.. well, maybe that's a sign that deploying 240/4 isn't worth the trouble (yet) and reclassifying would also be premature.

It's not like the IETF or any other body is holding 240/4 hostage or something.

Yes, actually, it's specifically reserved, and it's in a block above multicast. I'm sure I was not the only one who saw that and said "this probably won't be 'normal' address space." If it's going to be used as unicast space, then it'd be helpful for an RFC to say so. However, I doubt that would happen, as it will likely be shouted down by those who see it as a threat to IPv6 deployment.

It's what the vendors' code and what ops folks have configured that matters. If the code and configs can be changed and widely deployed, we have some proof that doing this might make sense at least in some context. Prior to that, there is no need to do anything.

Make a few /8's out of it available for experimental, private use. See what happens. But don't just throw the entire /4 out there for private use. We may later find it actually usable (or we may not) and want to visit that possibility later.