Re: Running code (Was: I-D Action: draft-ietf-6man-ipv6only-flag-03.txt)

[Simon Hobson <[e-mail]>]

Manfredi (US), Albert E <[e-mail]> wrote:

>> The problem you have is that you are only considering the sort of network you seem to be familiar with. There are lots and lots of network topologies - some of which are isolated networks with no routers.
> 
> And these pose no problem at all. They would exist even if they were connected, and even if all of the IPv6 routers had that IPv6-only flag set. It will always be possible to create such IPv4 networks that have no DNS and no routing.
> 
> If I were to design a heuristic, at a time when IPv4 is actually being sunset, I would have the host always try IPv6 first. If it works, don’t even try IPv4. You try IPv4 only if IPv6 doesn’t work, or doesn’t work for a particular destination.

Bzzzt, fail. You've just designed hosts which break their networking. So you try IPv4 if you can't reach a destination by IPv6 - but how do you even know about an IPv4 destination if you are relying on (for example) mDNS to find them ? If you configure IPv4 so as to be able to find them, then you've defeated one of the main points of doing this in the first place which is to avoid expending battery power on doing IPv4 when it's not required.

So, here's the challenge which you seem to be holding back from, write down the actual rules. No hand waving that "that's a good clue", but actual rules that "if you see <some observable state> then <do some specific action>".

Desired result - on a network that is, by the subjective criteria decided on by the network operator/admin, IPv6 only; you disable IPv4 and don't try sending IPv4 packets.
You must not break anything that does not meet this criteria - which is a subjective decision made by humans.

Put another way, you can connect to network A and be expected to disable IPv4; but connecting to network B which may look exceedingly similar, you do not disable IPv4. The decision whether you should or not is down to a subjective choice made by a human - now write your heuristics to do that.

So, challenge laid down, you're the one saying it's not difficult ;-)