Here is one things that I need to known about DNS.
If you want to known, how long an addresse will be cache with a dns server, you can execute this command :
# dig 192.168.1.1 www.belgacom.be
where the IP address correspond to the ip address of the dns server that you want to get the answer from. It can also be from a [root server] as well or your local dns server.
For more information :
# man dig