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

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

-----Original Message-----
From: ipv6 <[e-mail]> On Behalf Of Simon Hobson

>> That should occur when you set up the printer, when you load the printer driver. In my own experience, I have had to enter the actual IP address, EVEN OF enterprise printers, when the DNS for some reason or other didn't contain its name. So that's one way the host can determine to use IPv4, for that printer.
>
> You are still looking at this in a "this is my known network" manner.
>
> You go onto a network you've not been on before, how does your device know whether it should be using IPv4 to look for a printer via mDNS ?

Does the device see IPv4 mDNS, listing A records? That's a hint, in a network you've never been on previously. If no IPv4 DNS, no IPv4 default router configured (or reachable, if an old static default router still set in your device), no DHCPv4, stop attempting IPv4, assuming you have ever attempted IPv4.

What you seem to be missing, all this IPv6 flag means is "no IPv4 packets transit THIS router." That's the extent of it. You seem to be attributing a lot more to the flag than it actually intends.

Here's another example. In a network where all routers have the flag set, can you bring your own IPv4 router, and then use a ROUTE command in your host, to send IPv4 packets to a particular device across that router? Could be a tinynet of peripheral devices, for example. Yes, you can. This would be a case of BYOR, as opposed to BYOS, which should also be perfectly okay.

> If you turn on IPv4 to look for what could be a non-existent printer then you've missed the opportunity to save power, if you don't then you may not know about a printer that should be available to 

You have just violated one of the new heuristics I mentioned. Look at it this way: no matter what, these new hosts will need updated heuristics. Flag or no flag, makes no difference. With the heuristics I have already described, if you are not bringing along IPv4 peripherals with you, and IPv6 seems to be available (DNS, RAs, etc.), then your device will have *no reason* to attempt IPv4. Same goal is achieved. The flag may perhaps help, as an extra input to the new heuristics, but you are giving it much too much importance!

Bert