Cool, that makes a lot of sense. I'm actually reengineering the DNS infrastructure here, so it will be easy to account for and trace that at this stage. I'll let you know when I find the rogue queries, many thanks, Alberto Cuesta-Canada GaaS Team Lead Excelian Ltd. +44 (0) 7942633361
________________________________ From: Simon Kelley [mailto:si...@thekelleys.org.uk] Sent: Wed 17/02/2010 10:30 To: Alberto Cuesta-Canada Cc: dnsmasq-discuss@lists.thekelleys.org.uk; Grid Support Subject: Re: [Dnsmasq-discuss] server forwarding all traffic to parents after a successful PTR query of itself Alberto Cuesta-Canada wrote: > Hi Simon, > > the parents of 250 (my dnsmasq server) have forwarding rules for the > dselgrid.local domain, that I run. So I assumed that the queries pushed > upstream would be routed down again, and timeout in a loop. Ahh, that could easily be the problem. If you generate a loop between two DNS servers, each forwarding to the other, then the queries can easily bounce back-and-forth forever. Dnsmasq will manage this situation reasonably well, and manage to server other traffic, but the circulating queries will eat bandwidth and CPU. The logs would seem to show a "strange" query of some sort (dnsmasq can't parse a domain-name from the query, hence "forwarded query" rather than "forwarded <domain-name>) If such queries can circulate forever then you have a problem. > > That said, in the logs I could still see successful PTR and A queries, > outnumbered 10 to 1 by forwards. I'm not sure about the behaviour of > local queries, I don't remember from yesterday, but I think they worked. > > 94 is a Platform Grid Master, that is a W2K3 machine which runs only one > application. It keeps a cache of machines but it doesn't give DNS > services, or anything similar. The interesting thing is that the PTR > request doesn't always produce this effect. I have enterprise support > for that software, so I will ask them. > > dnsmasq is running in a quite complicated setup. We have a XenServer > host running a Ubuntu 9.04 VM. I have just 1GB free on that machine and > out of disk space scenarios are fatal, so I can't tcpdump. There is a > rebuild of it coming in the next two weeks that will give me another 50GB. > > Any idea on what to look for, or any hypothesis of what could be > happening should be enough, I can keep investigating and contain it with > workarounds for a while. See above. a loop, possibly only of "odd" queries. Cheers, Simon. > > Many thanks, > > *Alberto Cuesta-Canada* > GaaS Team Lead > Excelian Ltd. > +44 (0) 7942633361 > > ------------------------------------------------------------------------ > *From:* Simon Kelley [mailto:si...@thekelleys.org.uk] > *Sent:* Wed 17/02/2010 10:04 > *To:* Alberto Cuesta-Canada > *Cc:* dnsmasq-discuss@lists.thekelleys.org.uk; Grid Support > *Subject:* Re: [Dnsmasq-discuss] server forwarding all traffic to > parents after a successful PTR query of itself > > It's not clear to me what is going on here. How does the pattern > continue? Do you just see "forwarded query to 172.30.48.192" from now > on until the server is restarted, or do you still see "query[A]...." and > "query[PTR}...." lines? > > Do queries which get pushed upstream continue to work? How about queries > which should be answered locally? > > What is 172.30.158.94? Is it running anything that may generate "odd" > DNS queries? The holy grail would be to able prod that machine to > reproduce this at will. > > What sort of machine are you running dnsmasq on? Does it have a > reasonable amount of spare storage so that you could tcpdump all traffic > to/from port 53,UDP for offline analysis? > > > Simon. > > > The information contained in this email and any attached files are > confidential and intended solely for the addressee(s). The email may be > legally privileged or prohibited from disclosure and unauthorised use. > If you are not the named addressee you may not use, copy, or disclose > this information to any other person. 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