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DNS propagation overview

DNS propagation overview


The time it takes for DNS records to expire on a server is known as DNS propagation. If you change your nameservers to point to a new hosting provider, for example, the new nameservers must propagate over the Internet. Each ISP sets its own schedule for updating and expiring cached DNS records. Because there is no uniform Internet standard, the complete procedure can take anything from a few hours to up to 72 hours.

Furthermore, the phrase “DNS propagation” is a misnomer when it comes to describing the DNS resolution process. The term “propagation” indicates that DNS changes propagate from one DNS server to the next and that you have no control over how rapidly this occurs. In actuality, DNS servers communicate with your local DNS server as needed, and the TTL values for all DNS entries in your domain are controlled by the administrator of your local DNS server.

DNS Propagation, DNS Caching, TTL, Flushing DNS Cache, and Tools for Checking Propagation Status are all covered on this page.

GreggHost has no influence over how quickly your DNS is propagated throughout the Internet.


How DNS caching works

DNS caching in action
The authors wanted to create a technique to lessen the burden on individual DNS servers because of the enormous volume of queries made by a system like DNS. To this aim, after a successful answer, the DNS resolution process allows for caching (i.e., the local recording and subsequent consultation of the results of a DNS query).

Simply put, DNS caching allows every DNS server in the world to store DNS records for a domain on that server locally. This eliminates the need for a new DNS query and allows the server to use those entries right away. However, the DNS must be updated at some point, and this is where the time to live (TTL) number comes into play.

Time to live (TTL)

A value called the time to live determines how long a resolver caches a DNS answer (i.e., how long a DNS response is valid) (TTL). The TTL is established by the DNS server administrator who sends out the response. The validity period might range from seconds to days or even weeks.

The TTL on GreggHost’s server, for example, is set at 5 minutes by default. The DNS record is cached on the server for this amount of time.

Caching time

Changes to DNS aren’t always immediately and globally effective. The simplest way to demonstrate this is with an example: If an administrator sets a TTL of 6 hours for the host www.dreamhost.com and then changes the IP address to which www.dreamhost.com resolves at 12:01pm, the administrator must take into account that anyone who cached a response with the old IP address at 12:00pm will not consult the DNS server again until 6:00pm. The caching time in this example is between 12:01pm and 6:00pm, and it is best defined as a period of time that begins when you make a DNS record modification and ends when the TTL expires after the maximum length of time specified.

It’s worth noting that because DNS records can take several hours to resolve in all locations, individual machines in various areas will notice the update at different times.

When making a DNS update, many individuals wrongly allude to a mysterious 48- or 72-hour propagation time. When you modify your domain’s nameserver records or the IP addresses for the hostnames of authoritative DNS servers that use your domain (if any), it can take a long time for all DNS servers to use the new information. This is because the zone parent DNS servers (for example, the.com DNS servers if your domain is example.com) handle such records, which are normally cached for 48 hours. Those DNS modifications, on the other hand, are immediately available to any DNS servers that haven’t cached them. And, if you like, any DNS updates on your domain other than nameserver records and authoritative DNS server names can be done almost instantly (by lowering the TTL ahead of time, and waiting until the old TTL expires before making the change).

Adjusting Time To Live (TTL)

A domain’s Time-To-Live (TTL) number indicates how long a website is cached (stored in memory) by a web server. The average length of time is four hours.

If you’re migrating a domain from one hosting provider to another, it’s a good idea to reduce the TTL as much as feasible before proceeding. This permits your current host’s DNS records to expire sooner, so you don’t have to wait the entire 4 hours for the records to update.

You must wait until the current TTL expires once the TTL for a domain is dropped. This could take up to four hours (depending on the TTL of your hosting provider). The new TTL value will affect DNS changes only once the current TTL has expired.

You should update your DNS to point to the new hosting provider once the 4 hours have passed and your new TTL has been operational.

If you need to change the TTL for a name hosted at GreggHost for any reason, follow these steps:

Create a ticket on your panel’s Contact Support page, and GreggHost will make the necessary changes.
Make sure you notify support at least four hours ahead of time if you want to update your DNS, as it will take that long to enable the new TTL.

Flushing the DNS cache

If you’ve recently made changes to a domain or other DNS-related services and aren’t getting results, you may need to flush your DNS cache to see the new changes take effect.

For additional information about cleaning DNS cache on Windows, Mac, and Linux, see the following article:

Viewing your site before the DNS has propagated

The following tools can assist you figure out where your DNS has changed:

What is my domain name system (DNS)?
Checker for DNS Propagation
Using GreggHost’s DNS propagation checker in the panel to view your GreggHost DNS entries.
Visiting your website before the DNS has been updated
Before the DNS changes, you can still access your site. There are two options for accomplishing this:

Before changing DNS, test your site with a dreamhosters.com subdomain.
How to use your hosts file to view your GreggHost site