DNS caching and flushing

Yesterday I moved this domain from one server to another on my Dreamhost account (actually, I moved the whole domain from one Dreamhost account to another, but that's the same).

The DNS saved at the registrar where the same (ns1.dreamhost.com, ns2.dreamhost.com and ns3.dreamhost.com). The transfer went seamlessly and I was able to access my website on the new server in an invisible way.

But, strangely, some hours laters I started to experience slow down when accessing the website and finaly all my requests timed out, be it either from Firefox or a direct ping.

I tried with my windows xp and my Ubuntu 8.04. I even change the DNS on xp to use opendns, run an ipconfig /flushdns, rebooted. On Ubuntu I've done a /etc/init.d/dns-clean start. I even rebooted my adsl box, thinking there was something wrong with the DNS cache on my side.

I even contacted both Dreamhost and Gandi with a complete traceroute to know if they could help me, as I thought having done everything that I could think of to resolve the issue. They assure me that their configuration was fine and the problem wasn't on their side.

When asking friends, or testing with http://downforeveryoneorjustme.com/ it occured that the problem really was on my side.

Everyone were true. The problem lied somewhere in between, in the DNS cache hold by my ISP that wasn't correctly up to date. I don't really understand how that could happen, I thought rebooting my Freebox would clear its cache, and specifying dns addresses of opendns would bypass the dns resolve of my ISP but it seems not to be the case.

Anyway, after waiting for some more hours, my website was again reachable through sshand ftp.

So, if you're sure your dns configuration is correct both on your register and on your hosting service, make sure to clear every DNS cache you can have on your own side. That include windows inner dns cache, those of your browser, those of your router, and those of your specified preferred DNS resolving server.

If all that failed, it should be caching issue with your ISP, and there is nothing you can do about that, except waiting.


Tags : #dreamhost #gandi #cache #dns

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