[Pdns-users] Possible bug observed in PowerDNS Recursor 3.2.1

Imre Gergely gimre at narancs.net
Wed Aug 4 11:05:40 UTC 2010

On 08/04/2010 01:36 PM, Nuno Nunes wrote:
> Hello all,
> I've gone through the last few months of the ML, up until the
> announcement of the release of 3.2.1, and didn't find any reference to
> this bug I'm apparently seeing, so I'm reporting this to you all for
> help.
> I work at an ISP where we have a number of servers running PowerDNS
> Resolver 3.2.1 as our customer-facing resolvers.
> We have had this setup for a few months now and sometimes a weird thing
> happens (and no, I can't reproduce it in any deterministic way and it
> only happens sometimes): when the TTL for a record of a given zone
> expires and a new request comes in for it, some of the caches on the
> farm go out and get the new information, but some others just seem to
> ignore the TTL and stick with the old data forever.
> This is most notable when a zone changes name servers and the owner of
> the zone comes complaining to us that we still have the old data, even
> after the appropriate amount of time has elapsed for it to have been
> refreshed (and on these cases we typically observe this behaviour on NS
> records, but we have observed it on A records also, for example).
> Now we have had this happen at least three times over the last months
> and we've tried to narrow it down to a specific set of circumstances,
> but we haven't been able to really find a pattern.
> What we do know is that every time this happens, some of the servers
> behave correctly (TTL expires => get new data) and others don't. And
> when that happens not even `rec_control wipe-cache` will work.
> The servers are all identical (same HW, same OS and same SW).
> Has anyone else observed something like this before? Is it a known bug
> and I just failed to find it being discussed? More importantly: is there
> a fix for this behaviour?

Indeed. I saw the exact same thing, like 3 or 4 times in the last couple
of months, with the exact same simptoms. Also at an ISP, customers
complaining about old records after changing nameservers for a domain.
Couldn't find the cause either, although I did not investigate in
detail. Good to know I'm not crazy ;)

I have to look into it next time this pops up with a domain. I have no
further details unfortunately.

I don't think it came up until now on the list, it's pretty rare and
vague to get good details on the problem.

Imre Gergely
Yahoo!: gergelyimre | ICQ#: 101510959
MSN: gergely_imre | GoogleTalk: gergelyimre
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