I’ve been having intermittent problems with my internet access for a while (who hasn’t?) where everything would be really slow for a day or so and then it would mysteriously recover. I’d kick the modem, the squid cache, the local caching DNS server, etc but I was never sure where the problem lay.

Recently it got so bad that I investigated a bit harder. When it’s all gone bad (which is most of the time now, is seems) It looks like my DNS queries are transmitted as expected but the replies are never forthcoming. All the while I have solid connectivity. I can even flood ping the DNS servers that are not responding!

Before I go hassle my ISP, I thought I’d collect some evidence. Hopefully this will help me bypass the stupid “have you tried rebooting?” questions. So I’ve written a Munin plugin which I will configure to poll my ISP’s DNS servers. I expect that this will show that I frequently don’t get a response, in the evenings at least; I wonder if their traffic shaping is broken…

You can find the plugin at http://ccgi.ambrosia.plus.com/debian/dnsresponsetime. See the documentation therein.

Example daily plot from Munin plugin dnsresponsetime

Example daily plot from Munin plugin dnsresponsetime