Propagation refers to the process by which nameservers throughout the Internet update their records for a specific domain name. For example, when a domain name is moved from one host/network to another, it takes some time for the new numeric IP address associated with the domain’s new location to be recorded and recognized by nameservers throughout the world wide web.
Across the Internet, the DNS resolution process is aided by caching DNS requests records for an interval of time following a request. This process involves locally recording responses and then referring to those cached responses rather than initiating subsequent new requests during the caching interval. The caching period is set by a value referred to as the TTL, or time to live that corresponds to each cached record. The administrator of any given server handing out authoritative responses sets the TTL for that server, and the length of the TTL can vary widely, from mere seconds up to weeks of time.
Propagation delay is one of the chief consequences of the distributed caching architecture that underpins the Internet, as changes to DNS records do not spread through the network instantaneously, instead requiring all caches to expire and refresh after the TTL.