On Sat, 22 May 2010 17:04:49 -0600, Alex Rousskov <rouss...@measurement-factory.com> wrote: > On 05/14/2010 01:38 PM, Henrik Nordström wrote: >> As you may have noticed I have been looking at the IPv6 support in the >> last days, and now I am looking at how we perform DNS queries. >> >> Today we first do an AAAA query, followed by an A query. As we anyway do >> both queries it would be better if we ran both in parallell. The
Except when configured with dns_v4_fallback == off. In which case the A look starting requires a NXDOMAIN result from the AAAA query. >> benefits of this is twofold: >> >> a) Lower latency. >> >> b) Easier policy on re-transmission >> >> But needs a bit of reshuffling to get done unfortunately, separating the >> actual queries a bit from the lookup. > > Is there an RFC or somesuch that recommends parallel lookups over > sequential ones or vice versa? > > Thank you, > > Alex. No RFCs that I'm aware of (though I have not been following the newest ones). Just whitepapers about methods of encouraging and helping the world-wide v6 transition. For comparison the OS resolver does them sequentially with A first unless the options "inet6" entry is set. That default encourages non-v6 traffic which we want to reverse. Doing them in parallel I think is a good idea from the speed viewpoint. We will need to be careful over which lookup uses, such as forwarding, can go ahead with just ONE set and want the fastest path; versus lookups like config and ACL which require BOTH to be completed before it is reliably answered. Amos
