Yeah, some sites use some bad ju-ju in bypassing DNS's safeguards. They hold onto the numbers and only release on scheduled reboots, etc., meaning that their customers (as I assume this is largely ISP behavior) get worse service. My favorite problem with DNS involves poorly aged ARP caches on my local network! OOps...restart the Ethernet switch...ah...
I was wondering about that. It's driving me crazy as I try to move services from machine to machine ... In order to provide a "seamless" experience I think I will have to set up the new machine to answer to the old machine's IP address for a while.
Some ISPs here in India refresh their DNS caches only every 24 hours to once a week. When I made a nameserver switch for one of my domains, I had to wait 4 days before my ISP's DNS server recognised the change :(
Of course, none of this helps when crapware or deliberately misconfigured servers refuse to behave. One .nz ISP, for example, forcibly caches DNS records (and, no doubt many other things) for days, overriding the TTLs supplied for the record.
When moving from an old servers to new, set up a web server answering on the old IP address which redirects to the new one. I don't know about IIS, but it's a one-liner in Apache:
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