What is Propagation and How Long Does it Take?
Name server changes usually take 24 to 48 hours to fully start working. This period, called propagation, is the projected length of time it takes for root name servers and cache records across the entire web to be updated with your website’s DNS information. Because of propagation, not all visitors will be directed to your new name servers on your new hosting account; some visitors will continue to be directed to your old name servers on your old hosting account until propagation is complete.
How quickly visitors are directed to the new name servers depends on their physical location, internet service provider and some luck; it is not something Casbay has control over. Once propagation is complete, your site will appear on our server and your email will be fully functional.
There is no definitive way to tell when propagation is complete. During the first 48 hours, even if you are able to see your site on the new server, your next door neighbor might still be seeing the site on the old server.
How DNS Keeps You Connected
The routing of all communication between computers on the internet is handled by IP address rather than domain names. The following example should help you to visualize the process.
Similar to our telephone system, every active phone line has a phone number that is used to facilitate the connection of one line to another. In order to make a call, the phone that initiates the connection must have the number of the line to which it wants to connect.
In much the same way, your computer must find the correct IP address (of the website you want to visit) on the server before it can send the request to that server for a webpage. The same process applies for all other services (such as email, chat or games) on the internet. DNS records function similar to a phone book, relating domain names with IP addresses so that these services can be reached.
Functions of DNS Servers
DNS servers can handle one or both of two primary functions: DNS host and resolver. DNS hosts hold the zones for their domains and answer requests with the records from the zones for those domains. When you make changes to your zone, you are making changes on the host.
A resolver is a DNS server that will send requests to other DNS servers for the records from their zones in an attempt to answer the requests that it receives. These sort of requests are called recursive requests.
When you connect to the internet through your Internet Service Provider (ISP), your ISP will provide you with two or more resolvers that will be responsible for handling the recursive DNS requests sent by your computer as you use the internet.
Time To Live & Remote Caching
Since most DNS records don’t change very often, most resolvers are configured to cache the results of previous look-ups and respond to subsequent requests from the cached results for a period of time until the resolver decides that the cached copy is too old to be trusted. Propagation is the period it takes for the record cached on all resolvers everywhere to expire. In each record in the zone, there is a Time To Live (TTL) value that specifies (in seconds) how long a resolver should cache the record.
One technique to reduce the time it takes for changes to propagate is to reduce the TTL value in the current zone prior to making changes, however the change in the TTL on the record itself will take the length of time specified in original TTL value to propagate before propagation period is lowered for further changes. Also some ISPs configure their resolvers to ignore the TTL value specified in the record altogether and cache the record for a length of time that they specify instead. Some resolvers are configured to cache records for up to 72 hours, although most are configured for less. Ultimately, time resolves propagation issues.
DNS & Browser Caching
Additionally, most computers cache DNS which can cause the computer to “remember” the old IP address for up to 48 hours until the next time it updates. If your computer is caching the DNS, it may be possible to flush the DNS on your computer so that it looks up the IP address for the domain again.
Browser caching has absolutely nothing to do with DNS; however, this can still cause you to see your old page content even after changing your DNS. Browsers will cache a copy of the page content previously viewed by the browser. You can clear your cache to get a fresh copy from the server.