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.
Using a TTL of 10 seconds, like what Trademe has, doesn't guarantee that, if you change the IP address, it will take only 10 seconds for clients. For example, Internet Explorer will cache the DNS entry for 30 minutes, no matter what was in the TTL (previous versions, <3.0 cached it for 24 hours!). You can change this with a registry key but I doubt anyone does that.
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. 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. -- Nathan Ward