What is DNS prop­a­ga­tion?

When changes are made to a website’s Domain Name System, it takes time for the current state to be adopted by all servers worldwide. This tran­si­tion phase is the DNS prop­a­ga­tion. It can last from a few hours to several days.

Before we can un­der­stand what DNS prop­a­ga­tion is all about, let’s first look at the meaning of DNS. DNS stands for domain name system. This system trans­lates the name of your domain – example.com – into the actual IP address. This IP address is a sequence of numbers that would be difficult to remember. So, to make it easier for users to stay online, there is a two-pronged approach. If a user enters the name of your domain, the DNS de­ter­mines the IP address of your target server. The user isn’t aware of this process and therefore only has to remember the URL of your website.

There are different types of DNS. These are the main groups:

• A: This is where an IPv4 address is entered. The A record assigns a web server to a domain. The domain or sub-domain is also stored on the name server as an A record.
• AAAA: This entry is similar to the A-entry, except that an IPv6 address is entered, which ensures that the browser prefers IPv6.
• CNAME: A CNAME record connects a sub-domain to the cor­re­spond­ing primary domain.
• MX: An MX record connects your website to an email service. If a visitor then writes you an email through your site, it is directed to the correct email server.

The best trans­la­tion of the term “prop­a­ga­tion” is “trans­mis­sion”. When you change your DNS record, this change may take a little time. This time is called DNS prop­a­ga­tion. For example, if you adjust your DNS record or change your hosting provider or name servers, this update may take some time. DNS prop­a­ga­tion varies depending on the server and workload. So, initially, during the tran­si­tion period, some providers may still be accessing your old server, while others are already targeting the current IP address.

One reason for DNS prop­a­ga­tion is that changes them­selves can take a little time. At the same time, however, new IP addresses are not con­tin­u­ous­ly queried by DNS servers. This would otherwise lead to an overload. Instead, the in­for­ma­tion is tem­porar­i­ly stored in a cache. Only when this cache has been updated by all servers, will your website be up to date every­where.

Another factor that is relevant for DNS prop­a­ga­tion is the name server. A name server takes care of the name res­o­lu­tion. This is the con­nec­tion of your domain, which consists of a term that is easy to remember and an ending (example.com), with the IP address, which is made up of a com­bi­na­tion of numbers. Name servers are therefore also called DNS servers. As soon as a visitor clicks on your website, the name server es­tab­lish­es a direct con­nec­tion to the IP address. If the DNS server is changed or adjusted, it can take some time until the updates take effect every­where.

The DNS zone refers to the or­ga­ni­za­tion­al area of the DNS. This serves to better bundle in­di­vid­ual domains and helps to find them faster. This zone includes at least one domain and, op­tion­al­ly, ad­di­tion­al sub-domains.

The so-called TTL value is decisive for DNS prop­a­ga­tion. TTL stands for “time to live” and defines how long settings are tem­porar­i­ly stored and when an update takes place. So, if the TTL value is 24 hours, it takes one day for changes to take effect. The TTL value can be adjusted so that changes occur sooner. However, this ad­just­ment must be made before the update, because it also falls under DNS prop­a­ga­tion and so only takes effect after some time.

Another factor that con­tributes to the duration of DNS prop­a­ga­tion is your Internet Service Provider (ISP). On one hand, the ISP caches the DNS data locally to enable faster browsing, and on the other hand, it reduces data traffic. However, this can have a negative impact on DNS prop­a­ga­tion. In addition, there are ISPs that ignore TTL settings and perform the update only after hours or even days.

The location of your server also plays a role in the duration of DNS prop­a­ga­tion. Although the changeover can take effect after a short time in the en­vi­ron­ment or with secondary DNS servers, it often takes much longer on the other side of the world. This is also due to the fact that the different servers inform each other about the change one after the other. Since the updates, as mentioned, are not permanent, but only occur at certain time intervals, the final and wide­spread ef­fec­tive­ness of the change can take a long time.

But how long does the actual DNA prop­a­ga­tion take? This answer depends on the factors mentioned above and can basically vary greatly. Local servers usually adopt changes after just a few hours. However, it can take con­sid­er­ably more time before all name servers worldwide are informed about the changes and these take effect. While anything between 12 and 48 hours is normal, depending on the provider and settings, it can happen that worldwide ef­fec­tive­ness is only achieved after 72 hours. Therefore, it’s important to schedule DNS prop­a­ga­tion in advance when a change or switch is pending.

DNS prop­a­ga­tion can be a nuisance in some cir­cum­stances, but un­for­tu­nate­ly it can’t be com­plete­ly avoided. For­tu­nate­ly, there are ways you can minimize the duration or at least work around problems. This way, your website will quickly be ac­ces­si­ble again anywhere in the world at its current state.

If you haven’t yet changed your name server, you can already ensure in advance that the DNS prop­a­ga­tion remains as compact as possible. To do this, set the TTL value in the A record on the side of your current server to the minimum. This can vary depending on the provider. Then wait 30 minutes and change the name server for your domain. This way, your domain redirects to the new server when the DNS prop­a­ga­tion has been completed. Wherever the con­ver­sion has not yet taken place, it will still link to your old server, but will at least show the latest version of your website.

If you’ve already completed the move to a new name server, Google provides a DNS tool that allows you to view the new version of your website. The exact steps can be found on the platform page. Af­ter­wards, clear your browser’s cache and then your DNS cache. Now you should already see the current version of your website.

Nev­er­the­less, you still can’t say for sure without tools whether your website’s DNS prop­a­ga­tion has been completed. While the status may already be stored in your en­vi­ron­ment, servers abroad may still have an old status cached. For­tu­nate­ly, there are several ways to do a DNS prop­a­ga­tion check of stored DNS records. The pre-installed standard for Windows, macOS, and Linux, for example, is nslookup, which helps you with name res­o­lu­tion problems and displays the status of all servers. The al­ter­na­tives ping and tracer­oute work similarly.

Other external DNS checkers test DNS prop­a­ga­tion by targeting a selection of random servers and querying your DNS in­for­ma­tion there. Because servers are spread all over the world, you don’t have 100% certainty that DNS prop­a­ga­tion has been completed every­where, but at least a good in­di­ca­tion. Popular providers include whatsmydns and Google, which offers the DNS check via the toolbox.

When moving from one server to another or when making changes that are relevant to the Domain Name System, you should always factor in DNS prop­a­ga­tion. This is es­pe­cial­ly important if time is a factor, should for example the old DNS server not respond or if you’ve become a victim of DNS spoofing, DNS hijacking or a DNS leak. Although you have a few options to shorten DNS prop­a­ga­tion, it still always takes some time until every server worldwide is up to date.