On 3/13/07, Nathan Ward
On 13/03/2007, at 12:22 PM, Bojan Zdrnja wrote:
I've seen a lot of ISPs that cache all DNS entries, no matter what the TTL value says.
Can you back that up? We've seen numerous claims like that over the years, with little/no backing evidence.
I worked with some broken DNS resolves at my old University that did the same thing. My current ISP(s) do the things properly. There was a discussion about this somewhere else recently, I'll see what I can dig out.
http://support.microsoft.com/kb/263558 confirms that. Do you have any details on IE 7? This document was written 27/01/07, but doesn't mention IE7.
Yeah, I'm not sure what IE7 does but I would expect a similar thing. One other thing - I haven't tested this, but I saw on various places where people claimed that Internet Explorer doesn't cache A records (at all), but only CNAME records. This can be tested easily if someone has a bit of free time.
Though, using a lower TTL here helps a bit, because the client's ISP's recursive resolver won't cache it for too long, meaning switchover is 30 minutes + 10s max, not 30 minutes + $higher_ttl.
Definitely. Cheers, Bojan