What is DNS propagation?
When you make a change to your DNS records or update the nameservers of your domain(s), you have to wait a certain amount of time before these changes are fully reflected on the Internet.
This is because DNS records are stored in the cache of what is 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 performed to translate domain names to IP addresses. The time it takes for a resolver’s cache to expire and perform a new lookup is called DNS propagation.
The maximum time a resolver caches a lookup is known as the “time-to-live” (TTL) value of the record. There are two key cases to remember when dealing with propagation and TTL values:
DNS record changes
If you are not going to change the nameservers of your domain(s), but only update the records of the existing nameservers, the propagation time should be relatively fast. This is because the TTL of the logs is controlled by the log operator, and it is very rare that you will see a vendor offer TTLs longer than 4 hours. The TTL offered by our nameservers is 3600 seconds (1 hour). So if you make a change to your records in our nameservers, it won’t take long for it to propagate.
Changes in the nameservers of your domain(s)
Changes to nameservers take the longest to propagate, and can take up to 48 hours to propagate worldwide. This is because the nameservers records are retrieved from the root nameservers, which typically give a large TTL value of 2 days (172800 seconds) – or more – causing DNS resolvers to cache these lookups for a long time.
Can I speed this up?
First of all, it is good to remember that it is very rare that the resolvers you use finish caching the record you are requesting, so in very few cases you will have to wait the whole time specified by the TTL of the records.
The DNS resolvers most likely to affect you are those operated by your Internet Service Provider (ISP). Although rare, some ISPs ignore the TTL setting and only update their cached logs every day or two. There is a chance that a simple reboot of your Internet router will get another set of DNS resolvers that have not yet cached their records when reconnecting. If you regularly expect DNS propagation and believe that your ISP is not obeying the TTL values of the nameservers, you may consider switching to Google Public DNS. It is a free global DNS resolution service that you can use as an alternative to your current DNS provider.
What about WHOIS?
Checking your domain’s WHOIS record is a good way to confirm that your nameservers change has been successfully completed at the registry. However, WHOIS records are not directly related to DNS propagation. At most, a change in the WHOIS record confirms that the root nameservers should now respond with your new nameservers. The TTL value is still in effect and DNS resolvers around the world can only ask the root name servers for any updates once the original TTL has expired.