Please, talk me down.

Mark Andrews marka at isc.org
Wed Oct 17 05:21:44 UTC 2012


In message <2801F5F8-B8E2-4A9F-9A89-02D7783CCDA7 at josephholsten.com>, Joseph Ant
hony Pasquale Holsten writes:
> I want to like IPv6. I do. But I'm seriously considering turning off
> IPv6 support from our servers.
> 
> First off, I'm using djbdns internally and it doesn't support AAAA
> records. So we really aren't using it internally.

djbdns doesn't support lots of things.
 
> But today I noticed that we have a lot of traffic to our DNS cache, and
> started to investigate. Turns out that every DNS request would start
> with one for the AAAA record. Ah, no luck. Maybe you forgot the search
> domain? Let's retry that DNS request with that tacked on. Failed again?
> Meanwhile, lets simultaneously try for the AA record then. Repeat.

It looks like your getaddrinfo implementation is a searching for
AAAA records and then searching for A records.  With a A record for
name2 you get a query path like this.

e.g.	name1 AAAA	-> NXDOMAIN
	name2 AAAA	-> NODATA
	name3 AAAA	-> NXDOMAIN
	name1 A		-> NXDOMAIN
	name2 A		-> DATA

You could ask you vendor to implement a alternating search strategy.

e.g.	name1 AAAA	-> NXDOMAIN
	name1 A		-> NXDOMAIN
	name2 AAAA	-> NODATA
	name2 A		-> DATA

Additionally you could get your vendor skip the A lookup on NXDOMAIN
from AAAA.

e.g.	name1 AAAA	-> NXDOMAIN
	name2 AAAA	-> NODATA
	name2 A		-> DATA

> I'm _this_ close to turning IPv6 off entirely. Anyone want to talk me
> off this ledge?
> --
> http://josephholsten.com
> 
-- 
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742                 INTERNET: marka at isc.org



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