The Time-to-Live Value
The TTL value for a RR is the amount of time (in seconds) that a resolver or name server will keep a cached DNS request before requesting it again from the original name server. This value helps to keep the information in the DNS database relevant. Setting TTL levels is essentially a balancing act between the need for updated information and the need to reduce DNS query traffic across the network.
In the example from the “Performing Iterative Queries” section, if Client1 already requested the IP address of www.microsoft.com, and the information was returned to the DNS server that showed the IP address, it would make sense that that IP address would not change often and could, therefore, be cached for future queries. The ...
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