What Is DNS Propagation?
Posted by Shaker B. on 03 August 2016 01:25 PM
Before a domain can begin to resolve, it would first need to be registered with a registrar and be pointing to at least two nameservers. These nameservers will host the domain's DNS records and will also be the authoratative servers for this domain. When someone tries to ask/query your domain's DNS information, the request will first go to the root name servers for all top level domains (COM,NET,ORG etc.). From there the root servers will in turn respond back with the authoritative nameservers that have all the DNS information for the domain.
For example, the domain yourdomain.com is currently being web hosted at the IP address 188.8.131.52.5. If we use the example of someone trying to get to your website it would look like the following:
Users should also note that their Internet Service Provider (ISP) retains a DNS cache on their own servers. If we continue to use the example from above, your ISP's servers will cache the IP 184.108.40.206.5 which prevents repeat querying of the authoritative nameservers when they receive a request for yourdomain.com. So when you type a domain name in a browser, the request goes to the ISP's nameservers where the information gets stored. This helps them save on network traffic and this is why sometimes you will see old DNS information for your domain even though you've cleared your browser cache.
Furthermore, the stored record remains in the local nameserver memory according to the Start of Authority (SOA) settings that is specified under the domain's DNS settings. You can find this under the DNS SETTINGS page for your domain name. These settings govern the length of time other nameservers will cache a domain's current DNS data.
Each function is as follows:
Minimim Time to Live
So when your ISP caches the DNS information for a domain, it keeps the record in its memory as long as its been specified under the TTL settings. When you make another request for the same record (i.e. 220.127.116.11.5) before the TTL passes, your ISP's servers will respond with the stored record as opposed to querying the authoritative nameservers again. This process will continue until the TTL time has elapsed and once it has, the ISP servers will query the authoritative servers again.
This is why you'd sometimes need to wait up to 24 hours once you've made a change to your zone records.