To speed up resolution, the client will often store the results of resolution locally (in the browser quite often) so that it does not have to query again if the same resolution needs to be done. This is known as DNS caching, and this is also done by caching nameservers (also known as recursive nameservers). Since it is possible that values change (a different IP address issued to a host than it previously had), caches typically come with TTL (time to live) values and time out after a while.