According to RFC 5969 for 6rd:
 
"  Embedding less than the full 32 bits of a CE IPv4 address is possible
   only when an aggregated block of IPv4 addresses is available for a
   given 6rd domain.  This may not be practical with global IPv4
   addresses, but is quite likely in a deployment where private
   addresses are being assigned to CEs. "
 
So the /64 limitation for 6rd applies when an aggregated block of IPv4 addresses is not being used.
 
Regards,
-Ahmed
 

From: Daniel Roesen
Sent: Tuesday, March 01, 2011 1:15 AM
To: address-policy-wg@ripe.net
Subject: [address-policy-wg] Re: IPv6 allocations for 6RD

On Mon, Feb 28, 2011 at 02:44:53PM +0200, Ahmed Abu-Abed wrote:
> Note that the /64 limitation is specific to 6RD protocol as I explained
> in an earlier email.

I fail to find this email, could you provide archive pointers or explain
again?

I'm not aware of any instrinct /64 limitation of 6RD, and existing
implementations prove the contrary.

Best regards,
Daniel

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