When you make a change to your DNS records or update your domains nameservers, you need to wait a certain amount of time before these changes are fully reflected across the internet. This is because DNS records are cached by what's known as a DNS resolver. The job of a resolver is to help speed up browsing and reduce overall traffic by reducing the number of DNS lookups that are made to translate domain names to IP addresses. The time it takes for a resolvers cache to expire and a new lookup to be made is defined as DNS propagation.
The maximum amount of time a resolver will cache a lookup for is known as the records "TTL" value. There's two key cases to remember when it comes to propagation and TTL values:
1. Changes to DNS records
If you are not changing your domains nameservers but just updating records on existing nameservers, the time taken for propagation should be relatively quick. This is because the TTL for the records is being controlled by the operator of the nameserver, and it's very rare you will see a provider offering TTLs of more than 4 hours. The TTL given out by our nameservers is 3600 seconds (1 hour) - So if you're making a change to your records on our nameservers it won't take very long to propagate at all.
2. Changes to your Domains Nameservers
Nameserver changes are by far the slowest propagating, and can take up to 48 hours to propagate worldwide. This is because nameservers records are retrieved from the root nameservers, which most commonly give out a large TTL value of 2 days (172800 seconds) or more causing DNS resolvers to cache these lookups for an extended period.
Can I speed this up?
Firstly, it's good to remember that it is very rare the resolvers you are using have just cached the record you are requesting, so in very few cases will you need to wait the full time specified by the records TTL.
The DNS resolvers most likely impacting you are those operated by your ISP (Internet Service Provider). Although rare, some ISPs ignore TTL settings will only update their cached records every one or two days. There's a chance a simple reboot of your Internet Router will get you another set of DNS resolvers that are yet to cache your records upon reconnection. If you are regularly waiting for DNS propagation and believe your ISP is not obeying TTL values from nameservers you may wish to consider switching to Google Public DNS - A free, global DNS resolution service that you can use as an alternative to your current DNS provider.
What about the WHOIS?
Checking the WHOIS record for your domain name is great way of confirming your nameserver change has completed successfully at the registry, however WHOIS records are not directly related to DNS propagation. At most, a change on the WHOIS confirms the root nameservers should now answer with your new nameservers, however the TTL value is still in effect and DNS resolvers around the world may only ask the root nameservers for any updates once the original TTL has expired.