DNS propagation – what is it, and how long should it take?

When we make a change online, we expect it to be instantaneous. After all, if we can communicate with people halfway across the world with almost zero delay, why can’t everything work like that? Unfortunately, the infrastructure of the internet is such that some tasks do take time – and domain name system (DNS) propagation is one of those.

While you may have the knowledge and tools to make changes to your DNS settings, if you don’t have a keen understanding of the domain name system itself, you may not understand exactly why DNS propagation can take so long.  But do not fear – in this blog we’ll help you learn more about the DNS architecture, what DNS propagation is, how long it  takes, plus some helpful tips on how you can speed it up.

For the past few decades, we’ve largely thought about the internet in terms of web addresses. You go into a browser, type in an address – let’s say google.com – and the browser takes you there. Apps have made this connection somewhat ambiguous, but for many people, browsing the internet is still synonymous with visiting a website using a web address, also known as a uniform resource locator (​​URL). Even when we use a search engine, we end up being forwarded to a site we can type in and visit later.

Look under the hood, however, and this isn’t exactly how the internet works. Like many aspects of computing, the bit we see up front is a user-friendly interface for something that’s actually quite complex. This is the role that DNS serves. When we type an address in, our browser uses the DNS to look up the internet protocol (IP) address (a long string of numbers separated by periods) that corresponds to that URL. It’s this number that your browser actually uses to communicate with and visit the website.

This process involves multiple points of contact. First, a server called a recursive resolver interprets your browser’s requests, and forwards them to a root nameserver. This provides the correct top-level domain (TLD) server address for the site you want to access (e.g. .com or .net). The TLD server then provides you with the address of the authoritative nameserver which holds up-to-date records about that site; and finally, the nameserver gives you the exact IP address of the web server you want to access. This entire process may only take a second or two to resolve – not bad for the number of virtual hoops it needs to jump through.

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As you can see, the DNS is a chain with many different links, each of which serves a singular purpose. When you think about all of the different TLD servers for different domain suffixes, and all of the nameservers for individual websites, this is a huge amount of digital infrastructure. On top of this, records for most websites are stored in multiple servers, both for redundancy and to speed up requests in different parts of the world.

DNS propagation is the process of updating DNS records. When you update your DNS records – such as to change the IP of your web server or nameservers – this change has to propagate out across the entire internet. This involves updating relevant links in the chain, as well as servers operated by internet service providers (ISPs), which store copies of each step in the DNS process in caches around the world.

DNS caches allow ISPs to skip most of the steps in the DNS lookup process, using their existing records to jump straight to the resources users are looking for. This not only reduces strain on the ISPs’ networks, but also makes sites load more quickly for users.

The DNS records in these caches have a time to live (TTL) value that dictates how often they’ll  be updated, before which any changes will not be reflected. It is this value that ultimately decides how long it will take for your DNS records to be propagated fully. All clear so far? Good. Let’s explore how long DNS propagation takes – and how you can speed it up.

The length of DNS propagation is often overstated, but it’s worth noting that it   varies. In most cases, DNS propagation will only take a few hours, with local records being updated very quickly. But DNS propagation can take as long as 48 hours. This is because the TTL value of DNS caches differs from ISP to ISP, something that is entirely out of your control. Sometimes ISPs even ignore the TTL value and store the records for longer!

The good news is that there are a few steps you can take to speed this up. While TTL values won’t necessarily limit the speed of your DNS propagation, they can help to disseminate the change more quickly in certain circumstances – particularly when ISPs may otherwise ignore your own TTL values. Here’s a quick guide on how to speed up DNS propagation.

As mentioned above, DNS propagation isn’t something you can ‘push out’ faster, as it’s based on how often remote servers choose to update their copies of your website. However, if you’re  planning a DNS propagation, there are steps you can take to hopefully speed up the process, and reduce the amount of downtime for your site in different regions. These are:

1. Make sure you’ve defined or modified an existing DNS A record (address record) that points your hostname to the new IP address.
2. Change the minimum TTL for your records to 300 seconds (5 minutes). Doing this at least 24 hours before the records change should ensure that most ISPs and DNS servers will update the records more frequently. Setting a value below this may cause some to ignore it in favour of a much longer TTL.
3. Flush your NS (nameserver) and A records on Google Public DNS, OpenDNS, 1.1.1.1 and other major DNS providers.

DNS propagation can be a frustrating process, but something that all developers have to deal with when updating their DNS records. Good planning should help you to reduce how long DNS propagation takes, although some aspects of this will always depend on ISPs and DNS servers. It’s a good idea to undertake DNS propagation in quiet periods to reduce the impact of downtime, and to avoid changing records for active websites where possible.