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

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

-----Original Message-----
From: Mark Smith <[e-mail]> 

> I think the current convention for hosts to acquire addresses upon
boot or more recently upon attachment to a (new) link is probably more
of a tradition from back when minicomputers were the norm and network
interface configuration was always static. Hosts now widely support
dynamic address acquisition or generation, and release.
>
> Hosts acquiring or generating addresses at boot or upon link
attachment could be seen as an optimisation, with the optimisation
being to avoid address acquisition latency at the time of the first
application network API call.
>
> With IPv4 being the legacy protocol in this scenario, IPv4 addresses
could be acquired and released on demand by hosts when IPv4
applications need them.

Or more precisely, when IPv4-only applications need them. If an app needs access to a printer, scanner, the OS should be able to oblige, with IPv6 or IPv4. If an IPv6-only flag is set at every router, the presumption usually would be, IPv6 printers, and other such basic services, have been provided on the network, by the net admin. Normally. The question is, without that flag, are there other clues? (Yes, there are.)

> I think on-demand IPv4 would be a compliment to an IPv6 Only flag
signalled by an IPv6 only router. There are still optional things that
Dual Stack hosts do that aren't really networked application driven,
such as responding to ICMP Echo Requests or registering host presence
via a HINFO record using Multicast DNS.
>
> An IPv6 Only flag would be an explicit signal to a Dual Stack host
that these optional IPv4 things should be switched off. If they're the
only thing remaining that uses IPv4, then the host would cease to use
DHCPv4 to acquire an IPv4 address.

Except, they aren’t necessarily the only thing that uses IPv4. They are the only thing the network admin might have had control over, that used IPv4. But a robust host should not be programmed to preclude functionality that users have come to expect. Go to Best Buy, buy whatever printer, and make it work, on that network. Seamlessly, 

> When a host stops running any applications the use IPv4, and these
other optional IPv4 hosts do are switched off, then the host would
cease sending or receiving an IPv4 or IPv4 related ARP packets
entirely.

Yes. And so in your post, you have listed several heuristics. I agree with these improved heuristics. I'd be hard pressed to make the case that a flag is the only way, or even the most robust way, to achieve any of this.

But, why is this not a relief, for 6man? You can achieve increased efficiencies in hosts, you can shut off IPv4 services in the network, and you don’t even need to add complexity to an already complex-enough IPv6.

Bert