What is DNS Propagation
DNS propagation is the term commonly used to describe what happens when DNS changes are made to a DNS zone. DNS entries are cached by many applications including browsers and other DNS servers. A cached DNS entry will be saved locally and reused for every request until the cached entry expires. The length of time that a record is cached for is determined by the TTL (Time To Live) of each record. This means that when a website administrator makes a change to a website's DNS entries (for example, changing the IP address of an A record), users of the website will continue using the old IP address from the old record until all of the cached entries between them and the authoritative name servers for the domain expires and are refreshed.
One way for a website administrator to limit this problem is to reduce the TTL (Time To Live) value before the record is changed. The TTL value is specified in seconds, so a value of 60 is one minute, 3,600 is one hour and 86,400 is one day. However, the TTL should be reduced with enough time left before making the DNS change. If a record has a TTL of 86,400 (24 hours) the TTL must be reduced more than 24 hours before the change is made. If the TTL in this example is reduced 10 minutes before making the change, all entries cached more than 10 minutes ago will still be cached for 24 hours!
The DNS Lookup tool on this website is a non-caching lookup (it does not use cached entries). It performs a complete hierarchical lookup, starting from the root servers of the internet. Any changes made to a DNS zone should show straight away using this tool.