[dns-operations] To A or to AAAA - was Re: Signaling client

[Mark Andrews]

In message <alpine.LSU.2.00.1101191603010.3329 at hermes-1.csi.cam.ac.uk>, Tony Fi
nch writes:
> On Wed, 19 Jan 2011, Joe Abley wrote:
> > On 2011-01-19, at 09:38, Mark Andrews wrote:
> >
> > > 99.999% of AAAA lookups work fine.
> >
> > Are there public test results that confirm this?
> 
> I just took a sample of 10000 different domain names from my mail server
> logs. 0.8% of the AAAA lookups returned SERVFAIL or timed out. If I don't
> uniquify the domain names I get a failure rate of 0.5%.
> 
> This probably doesn't correspond very well to the query pattern on a
> normal recursive DNS server. Also I did not count other failure modes such
> as returning NXDOMAIN when the domain name has A records but not AAAA.
> 
> Tony.
> -- 
> f.anthony.n.finch  <dot at dotat.at>  http://dotat.at/
> HUMBER THAMES DOVER WIGHT PORTLAND: NORTH BACKING WEST OR NORTHWEST, 5 TO 7,
> DECREASING 4 OR 5, OCCASIONALLY 6 LATER IN HUMBER AND THAMES. MODERATE OR
> ROUGH. RAIN THEN FAIR. GOOD.

Anyone with access to a nameserver can do something similar to this.
Dump the contents of the cache.  Extract all the A/AAAA records and
make a unique list of the names then make lookups for the A/AAAA
records.  Alternatively you can just extract all the owner names
of any record and look those up.  junk turns the multi-line records
into a single line and add ownernames for those records that inherit
from the previous line.

% rndc dumpdb
% awk -f junk < /var/named/named_dump.db |
  awk '$3 == "A" || $3 == "AAAA" {print $1}' |
  sort -u > junk1
% dig AAAA -f junk1 | grep status | grep -v SERVFAIL | wc
    1560   12480   90226
% dig A -f junk1 | grep status | grep -v SERVFAIL | wc
    1565   12520   90523
% 

As you can see the success rate really doesn't vary much by type.
If there is a address record in the cache named will query for it
at some point.  This nameserver has a typical household set of
queries being directed to it.  Facebook, twitter etc.

Mark
-- 
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742                 INTERNET: marka at isc.org