When an end-user's PC makes a DNS query, it doesn't contact the Traffic Manager name servers directly. Instead, these queries are sent via "recursive" DNS servers run by enterprises and ISPs. These servers cache the DNS responses, so that other users' queries can be processed more quickly. Since these cached responses don't reach the Traffic Manager name servers, they don't incur a charge.
The caching duration is determined by the "TTL" parameter in the original DNS response. This parameter is configurable in Traffic Manager—the default is 300 seconds, and the minimum is 30 seconds.
By using a larger TTL, you can increase the amount of caching done by recursive DNS servers and thereby reduce your DNS query charges. However, increased caching will also impact how quickly changes in endpoint status are picked up by end users, i.e. your end-user failover times in the event of an endpoint failure will become longer. For this reason, we don't recommend using very large TTL values.
Likewise, a shorter TTL gives more rapid failover times, but since caching is reduced the query counts against the Traffic Manage name servers will be higher.
By allowing you to configure the TTL value, Traffic Manager enables you to make the best choice of TTL based on your application's business needs.