[arin-ppml] ARIN-prop-127: Shared Transition Space for IPv4 Address Extension

Mark Andrews marka at isc.org
Mon Jan 24 19:46:32 EST 2011

In message <4D3DCABC.70408 at brightok.net>, Jack Bates writes:
> On 1/24/2011 12:43 PM, George, Wes E [NTK] wrote:
> > on an individual basis, the same problem exists. So it's not a surprise, bu
> t
> > that's part of why I'm so adamant about using 1918 space for this if at all
> > possible.
> >
> So your thought is that a CPE might have code which won't do 6to4 if 
> there's RFC-1918 assigned to the WAN, but otherwise might use 6to4 and 
> break.

The 6to4 implementations I'm aware of check for rfc 1918 addresses and
refuse to configure themselves one attempts to use such a address.  One
shouldn't enable 6to4 automatically and if you do attempt to do so you
should perform sanity checks before announcing any prefixes.
> > Not to speak for Joel, but I think that the point he's making is that if
> > this block isn't codified as an update/addition to RFC1918 space, it'll be
> > treated incorrectly by applications which care about global uniqueness in
> > addressing, regardless of where they live. Even if it is codified in that
> > manner, it'll take the applications (host stack and otherwise) a while to
> > catch up.
> Using a specific block will allow these applications to catch up. Using 
> RFC-1918 would be best, but there are so many possible conflicts that 
> using it in large deployments would cause even more support issues. If 
> the /10 isn't assigned for this purpose, organizations will use their 
> own allocated space (not RFC-1918) and there will still be breakage, but 
> the applications won't be able to rewrite their code to recognize the 
> addressing.
> Given the high probability that RFC-1918 won't be used for LSN, 
> assigning a new block is more application friendly than using random 
> assignments.

A new well known block will also allow CPE vendors to add additional
sanity checks before enabling 6to4.
So many things are going to break when ISPs turn on double NAT that we
shouldn't be overly worried about 6to4 breakage.

> Jack
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Mark Andrews, ISC
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PHONE: +61 2 9871 4742                 INTERNET: marka at isc.org

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