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getaddrinfo address ordering [Re: IPv6 transition architecturediscussion]
On Mon, 25 Nov 2002, Keith Moore wrote:
[...]
> at least not right now. attempts to talk to v6 sites typically
> time out (which is annoying because the v6 addresses are tried first -
> another thing which needs to be fixed)
Do I sense this as a voice for support to modify or at least explore the
current de-facto standard ordering?
> > We were considering turning on 6to4 by
> > default when there are no routing advertisements. This working group
> > has dissuaded us from doing so. If we did turn on 6to4, we would want
> > to add some extra smarts to getaddrinfo to list IPv4 addresses first
> > when 6to4 is in use to reduce the load on the relays.
>
> it turns out that you need the address ordering to be sensitive to both
> network configuration and to the particular application. some apps will
> be v4 by default, others will be v6 default, others will be exclusively
> one or the other.
There are already some variables that affect this, namely:
1) whether the DNS lookup produces A, AAAA, or both; ie "remote
site configuration"
2) what ordering for DNS records is used when both are used
(default is AAAA first everywhere I know, no possibility to change that)
3) whether the application uses AF_INET, AF_INET6 or AF_UNSPEC
(with server apps, this is even a bit muddier.)
These help quite a bit, but I guess adding some getaddrinfo hint like
AI_PREFERV4 or AI_PREFERV6 could be added in the case that DNS lookup
returns both addresses, you use AF_UNSPEC and you want to influence the
default DNS record ordering.
--
Pekka Savola "Tell me of difficulties surmounted,
Netcore Oy not those you stumble over and fall"
Systems. Networks. Security. -- Robert Jordan: A Crown of Swords