--On Friday, November 22, 2013 11:37 +1300 Brian E Carpenter
<brian.e.carpenter@xxxxxxxxx> wrote:
>...
> Actually there has been a clear market choice among many ISPs
> for years: straightforward dual stack. It works very well. We
> also have a plethora of tunnelled solutions, some better than
> others, which apply to various different scenarios where the
> provider's view is that OPEX for dual stack is higher than
> OPEX for tunnels. The service to the application software is
> still dual stack (in most cases).
Brian,
Keeping in mind that, with respect to this question, I'm just an
apps guy, but my impression is quite different, mainly:
(1) Unless the service levels between the endpoint machines are
always equivalent when IPv4 and IPv6 are both present and there
are no circumstances in which a choice between IPv4 and IPv6
would make a service difference, there is no such thing as
"straightforward dual stack".
(2) The non-straightforward version requires that applications,
at least TCP-based applications, be able to make rather complex
route optimization decisions about which protocol and addresses
to use and make those decisions in a way that completely
violates clean layering models. We have, in general, never
figured out how applications are supposed to do that, nor how to
make the needed information available to them.
(3) If one is going to have dual stack on the applications
(generally "client") machines, they need either wired-in
simplistic preference models (e.g., "always prefer IPv6") or
protocols for getting information from and controlling border
routers to which they have default routes. The former has not
served us well and we haven't done the protocol work for the
latter. Another alternative would be to actually do routing
from the applications machines with either packets source-routed
through the border routers or the latter being completely
transparent. As far as I know, the Internet has not worked that
way in a very long time and no one has seriously proposed
changing the way it does work.
Now I'm obviously missing, or misunderstanding, something that
allows you to assert that straightforward dual stack is the
clear market choice and works well despite the above. Could
you explain what it is?
>> And the market is not going to make a choice because the
>> market stakeholders find NAT works well enough for its needs.
>
> And when it doesn't, they will switch to IPv6.
Or they will build bigger NATs or invent a latter-day version of
X.75 gateways at peering points or national boundaries. It
isn't clear to me that IPv6 is the only remaining choice when
the easiest-to-deploy NAT technologies turn out to be
insufficient or too hard to operate. If it is not, then we have
no guarantees that IPv6 will be chosen over options and most of
us would consider worse.
>> What I would do as a government entity is to get a group of
>> techies to describe a minimum set of technical capabilities
>> for Internet access points.
>
> Please don't. The history of government mandates for IPv6 is,
> to say the least, chequered.
Indeed. Just like the history of government mandates for other
networking technologies.
john