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If a cached DNS record expired it would not be a problem. If a bad or old record was cached before TTL, clearing your cache works to update it. Maybe ITs ego

If a cached DNS record expired it would not be a problem. If a bad or old record was cached before TTL, clearing your cache works to update it. Maybe ITs ego didn't like your terminology of DNS cache being expired, and telling them theirs is- by definition expired records get looked up again because they no longer exist locally. As former IT it was mildly irritating to get unsolicited advice, But still it sounds like a redicilous over reaction on ITs part. I'm assuming you didn't actually clear a local IT managed server's local DNS cache.

Declanomous 10y ago
Right, the DNS records weren't expired, they were no longer accurate. I'm not sure what the word for that is. The Windows DNS Cache on the local machines was inaccurate. Basically, I couldn't access any websites I had accessed before, but if I tried accessing a new site it worked fine. If I forced a DNS request for a site I had already visited, that site would start working but all the other sites would still be broken. I knew what the problem was because I had run in to that issue a few years back with my own computers. After I updated my DNS, all the Windows computers were having issues, but none of the Linux ones were. That's when I learned that Linux doesn't typically cache DNS records on local machines.
- xorcist 10y ago
  It's called the resolver cache, and Linux does it too. Most commonly with nscd (use "nscd -i hosts" to clear it, keep in mind this is not specific to DNS requests). In the specific situation of a web browser it's more complicated and you'll find that the web browser caches these things too. If you run Chrome check out chrome://net-internals to get a glimpse of what's going on there.
  - Declanomous 10y ago
    Thanks for the tip on net-internals. I think I used a similar feature in Firefox a long time ago, but I've never used this tool in Chrome before. I know Chrome in Linux definitely doesn't cache DNS requests. I believe Linux only keeps the DNS info around until the socket closes, but I don't know the actual implementation. I looked in to the ncsd man page, and it looks like DNS info isn't cached, only open sockets. I know Chrome uses the system DNS cache in Windows, and my understanding was that all browsers in Windows used the system DNS cache. I don't know a lot about how sockets are handled. I thought they were discarded as soon as they were closed, but they could function similarly to a DNS cache. I though a DNS cache stuck around for a lot longer though.
    - ChoGGi 10y ago
      I have the DNS cache service on Windows 7 disabled, and Chrome still caches DNS requests.

Declanomous 10y ago

Right, the DNS records weren't expired, they were no longer accurate. I'm not sure what the word for that is. The Windows DNS Cache on the local machines was inaccurate. Basically, I couldn't access any websites I had accessed before, but if I tried accessing a new site it worked fine. If I forced a DNS request for a site I had already visited, that site would start working but all the other sites would still be broken. I knew what the problem was because I had run in to that issue a few years back with my own computers. After I updated my DNS, all the Windows computers were having issues, but none of the Linux ones were. That's when I learned that Linux doesn't typically cache DNS records on local machines.

xorcist 10y ago
It's called the resolver cache, and Linux does it too. Most commonly with nscd (use "nscd -i hosts" to clear it, keep in mind this is not specific to DNS requests). In the specific situation of a web browser it's more complicated and you'll find that the web browser caches these things too. If you run Chrome check out chrome://net-internals to get a glimpse of what's going on there.
- Declanomous 10y ago
  Thanks for the tip on net-internals. I think I used a similar feature in Firefox a long time ago, but I've never used this tool in Chrome before. I know Chrome in Linux definitely doesn't cache DNS requests. I believe Linux only keeps the DNS info around until the socket closes, but I don't know the actual implementation. I looked in to the ncsd man page, and it looks like DNS info isn't cached, only open sockets. I know Chrome uses the system DNS cache in Windows, and my understanding was that all browsers in Windows used the system DNS cache. I don't know a lot about how sockets are handled. I thought they were discarded as soon as they were closed, but they could function similarly to a DNS cache. I though a DNS cache stuck around for a lot longer though.
  - ChoGGi 10y ago
    I have the DNS cache service on Windows 7 disabled, and Chrome still caches DNS requests.