Re: Resolver not always resolving hostnames

On 2006.10.27 02:56:00 +0900, Hiroki Sato wrote:
"Jiawei Ye" <leafy7382@xxxxxxxxx> wrote
in <c21e92e20610240824n7e94e4c1jf454697cab4120a9@xxxxxxxxxxxxxx>:

le> On 10/24/06, Hajimu UMEMOTO <ume@xxxxxxxxxxx> wrote:
le> > leafy7382> This is much better. It would be great if this is commited.
le> >
le> > I've committed it into 7-CURRENT, and I'll MFC it into RELENG_6 after
le> > 3 days.
le> >
le> > The fix should help in certain case. However, it seems doesn't help
le> > for nork-san's case. He could reproduce it, and sent me his ktrace
le> > output. As far as I can see his output, his local name server (BIND
le> > 9.3.2-P1) returned the response with no answer record. As a result,
le> > his csup ended up with following error:
le> >
le> > Name lookup failure for "cvsup.jp.freebsd.org": hostname nor
le> > servname provided, or not known
le> >
le> > I suspect that the BIND9's named have some problem.
le> >
le> > "Name lookup failure for "cvsup.jp.freebsd.org": hostname nor servname \
le> > provided, or not known
le> > "
le> You are correct, I just ran into that a few times in the last hour.
le> But it is a lot less frequent than before. I also run a local BIND9
le> for our company. I think some commits happening after between Sept 30
le> and Oct 15th caused it, because I did not see such symptom before late
le> Sept and I rebuilt my system around mid Oct.

According to log files on my public cvsup server which is suffering
from this problem, this happened on 22 September at least. I have
not looked into the source files closely yet, but is it possible that
the 9.3.2-P1 patch has a bug that can return 0/0/0 with NOERROR
answer packet? I confirmed that behaviors of 4.x's resolver and
6.x's against such a malformed packet are the same, so I think it is
not likely a bug in the resolver.

After I upgraded my development server to include the fix I started a
tcpdump of all my DNS traffic in case the resolving issue happened
again, and it did :-/. So, the above fix does not fix the issue and
as hrs@ notes it actually seems to be a a bug in the nameserver and
not resolver.

When my latest cvsup failed this is the DNS packets captured:

15:06:45.036710 IP eddie.54684 > ns.nitro.dk.domain: 51917+ A? cvsup3.dk.freebsd.org. (39)
15:06:45.224002 IP ns.nitro.dk.domain > eddie.54684: 51917 0/0/0 (39)
15:06:45.224796 IP eddie.50804 > ns.nitro.dk.domain: 51918+ A? cvsup3.dk.freebsd.org.nitro.dk. (48)
15:06:45.226255 IP ns.nitro.dk.domain > eddie.50804: 51918 NXDomain* 0/1/0 (98)

I still have the pcap file around if it's needed.

The nameserver in question is running BIND 9.3.2 from 6.1-SECURITY
base.

--
Simon L. Nielsen
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