Re: implications of 6to4 for v6coex

[james woodyatt <jhw@apple.com>]

On Sep 19, 2008, at 08:25, Truman Boyes wrote:
> The implications of the "MUST also provide an equivalent IPv4  
> unicast address" are the issue.
Yes.  One of those implications is that relays forwarding IPv6 packets  
encapsulated in IPv4 toward the public Internet are required to use  
their IPv4 interface address as the source address.  This discloses  
the global IPv4 unicast address of the relay to the public, and forces  
providers into managing a special addressing plan for their relays  
that facilitates filtering at their borders.  It's the extra  
addressing management that, I think, is the blocking factor.
Removing the requirement for using a global IPv4 unicast address on  
the relay interface only goes so far, though.  Whatever addresses  
providers choose to use must be legitimate as IPv4 source addresses on  
the public Internet, and RFC 1918 addresses are not.  So, what do they  
use?  Assuming they are willing to go with an addressing plan that  
puts all their 6to4 relays into a single prefix, which I note above is  
a problem by itself, they could use part of the allocation from the  
RIRs and just not advertise it.  The reason this is an issue is that  
it seems like a waste of IPv4 space for something that isn't supposed  
to be reachable, and the waste is replicated for each and every  
provider that deploys relays.  A special-use block would address that  
problem as well.

--
james woodyatt <jhw@apple.com>
member of technical staff, communications engineering