Thursday, July 19, 2012

Just Call Me DNS of the Morning, Angel

I use a Windows desktop on a daily basis and attach to a Windows 2003 domain, but these days I've had little need to mess with Windows on an administrative level. A few antivirus updates here, adding an AD account there – simple stuff. Well, last night I moved some of our sub-domains over into the Amazon cloud and edited the DNS entries (hosted by our ISP) to reflect their new home. This was after hours and done at home, and I verified connectivity and functionality of the sites.

This morning upon arriving at work I was told that none of the sub-domains in question were accessible. I got that pIT of the stomach feeling that comes when it looks like your day is going to be hosed. I quickly logged on to my machine and found that indeed I was getting a 500 error, indicating an issue at the server level. On a hunch though I checked the DNS resolution (pinging the sub-domain) and saw that it was resolving to the old IP. No problem; ipconfig /flushdns should do the trick.

Except it didn't.

Now I had been messing around with my hosts file so I verified that it had been returned to normal, and it had. I happened to have brought my Mac in today so I tested the domains on it and sure enough, most was well. There was a slight problem that I had to log in to the server to fix, but that was something else altogether. The resolution problem was just that. So, it worked on my Mac, it worked on a couple of other non-domain machines. What's the deal?

I tried ipconfig /displaydns to see what was cached. I saw the entry to the domain in question. Cleared the cache again, ran the displaydns command, and it was empty. Should be good, except when I pinged I was still getting the old IP and displaying DNS showed that same entry in the cache. To be on the safe side I deleted temp files, emptied the Recycle Bin, turned the dns client on and off (net stop dnscache). Same results. Okay, so the issue is at the DNS server level. I logged in to the Windows AD machine and launched dnsmgmt.msc. I cleared the cache from the console. I also cleared it from the command line. Windows still showed the results there when I cleared the cache though. I went back a few minutes later (after starting this post) and the entry was gone. Hmmm...maybe it took a bit? At any rate, the problem was solved.

And now I can go and eat my cold Pop Tart.

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