Re: Open issues list? [Re: New (-02) version of IPv6 CPE Router draft is available for review]

[james woodyatt <jhw@apple.com>]

On Jul 30, 2008, at 17:28, Iljitsch van Beijnum wrote:
> But look at Apple, they've been doing this for some years now wih  
> their airport base stations, although they of course use a special  
> configuration utility, not a web interface.

Apple uses IPv6 link-local transport for a wide variety of user  
application protocols, e.g. AirTunes, iTunes library sharing, iPhoto  
sharing, Time Machine w/ Time Capsule, etc.  The big win for us is  
that we don't have any address realm conflicts with IPv6 link-local  
when hosts are attached as a bastion between their ethernet and Wi-fi  
interfaces.

If it weren't for the utility of IPv6 link-local in preventing address  
realm conflicts, I don't think very many Mac OS X users would today be  
seeing any real-world benefit *at* *all* to having their IPv6 stacks  
enabled.  Indeed, many users are now turning *off* their IPv6 stacks  
altogether to workaround the usual problems caused by it and they're  
finding that the address realm conflict avoidance feature is not  
something they miss all that much.

Still, we remain committed to using IPv6 link-local in this fashion  
for the foreseeable future.  To that extent, we have begun explaining  
to our network interface chipset vendors that hardware support for  
IPv6 checksum calculation/verification and TCP segment offloading is  
one of our considerations when evaluating their products for use in  
our supply chain.

I mention all this to surface the importance of us all getting over  
this bizarre aversion to the idea that link-local scope IPv6 addresses  
are not required for use once there is a global scope prefix  
advertised on the link.  Some of the unique local address arguments we  
are seeing here are red herrings.  Unique local address prefixes are  
only really useful when the CPE LAN is segmented into more than one  
link without any bridges between them, but they still within the same  
administrative domain and routing policy must be used to separate  
them.  These topologies are... rare... in residential networks.  (I  
don't know how rare, but I'd be surprised if they account for more  
than a tenth of a percent of all deployments.)


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