Re: you have running code ... I-D Action: draft-ietf-6man-ipv6only-flag-03.txt

[Brian E Carpenter <[e-mail]>]

On 2018-10-31 22:24, Nick Hilliard wrote:
> Job Snijders wrote on 30/10/2018 22:27:
>> Can you (or others running FreeBSD EXPERIMENTAL) share reports on how
>> this pans out in practise?
> Looking at the code, it acts by blocking outbound ipv4 frames from being 
> transmitted on ethernet interfaces.  This would mean - for example - 
> that if there were a default route already configured on the receiving 
> device, any userland code attempting to use ipv4 services would block 
> until ARP times out for the default route (default 20 minutes on freebsd).
> 
> The only part of the ipv6only discussion that was uncontroversial was 
> implementation of the kernel processing side of this flag - there's very 
> little to go wrong when toggling a single flag.
> 
> The problem area is how to handle the interpretation of this flag in 
> userland and in the kernel, which is a much more difficult problem.

It's a question, but I don't know why it's a problem. It isn't an interop
problem, because each host is an independent actor in this. And we now have
running code proof that legacy hosts aren't affected. So I'd say that from
a protocol spec point of view, it's actually a non-issue.

> This in turn depends on consensus in 6man about what the flag actually 
> means, and there doesn't seem to be much consensus on that.

There is specific text in the draft. For the purpose of verifying the
draft via running code, that's fine. Of course, we would need WG rough
consensus to proceed, but I haven't seen any proposed text changes since
the current draft came out.

> This also disregards the issue of whether the flag was either necessary 
> or a good idea to start with, and nearly 700 emails into this 
> discussion, the WG seems to be hopelessly divided on these issues.

I'll leave that one to the WG chair who isn't a co-author. But I will
say that in my mind the issue is whether the feature is one that will
be valuable in 5, 10 or 20 years time rather than whether it's valuable
today.

    Brian