Ubuntu Linux - Suggestions needed

Rémi Denis-Courmont rdenis at simphalempin.com
Tue Apr 3 16:32:51 CEST 2007

Le mardi 3 avril 2007 13:22, Mikael Karlsson a écrit :
> > I think Remi's proposal not quering for AAAA if you just have
> > link-local should work. It also would be rather safe.
> Hmm, that would probably break zeroconf networks. But it would work
> if just the dns resolving part and not mdns is disabled.

Maybe not. (Assuming it works properly which I have not had time to 
check yet) the patch I posted yesterday will only disable AAAA queries 
when the application did NOT specify an address family explicitly, and 

 - the host has no non-link-local IPv6 addresses,
 - the A query timed out (halves delay if the DNS server is down).

If you want to do IPv6 ad-hoc networking with only link-local addresses, 
your application/resolver will need special support for scoping IPv6 
socket addresses properly (if you don't set sin6_scope_id for 
link-local, the kernel will bust you anyway).

The getaddrinfo resolver always clears scope_id when using the DNS 
(whether "normal" or mDNS), so in any case, the application need to 
special case link-local IPv6. If you are willing to handle this, you 
might as well explicitly request AF_INET6 from the resolver, and then, 
it will do AAAA.

I do not pretend this to be anything close to perfect, but I would 
rather break some link-local IPv6 zeroconf usages (with possible 
work-arounds), than *all* IPv6 usages, or than ask clueless users to 
enable/disable IPv6 manually. Anyway, it's up to Ubuntu, not me.

Rémi Denis-Courmont
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