How does DNS propagation work?

Internet is a hard game. Managing a website or a network demands constant changes to your strategy. Expansion, to be more visible, efficient, competitive, etc., are common triggers of change. That directly pushes DNS modifications and daily challenges for administrators.

What’s DNS propagation?

DNS propagation is the time period that it takes to update DNS modifications all across the Internet.

Let’s think about extensive networks. They work by including a large number of servers. Servers with different functions, internationally located, etc. Therefore, even the smallest modification has to be updated not on a machine but on many. 

And there are extra factors to consider, like the cache of those machines. Cache has a lot of advantages, but in this case, it can delay the update. For instance, recursive DNS servers’ cache, based on the time-to-live (TTL) they have configured, can keep previous DNS records’ versions for a while. 

The reason for them not to update immediately is simple. Recursive servers are originally programmed to look for updates only when the DNS records they have in their cache memory get expired.

If you add the milliseconds, minutes, hours… that it can take to copy the new data in the whole network, this can mean from minutes to hours or days of waiting.

How does DNS propagation work?

Different situations demand a DNS change. The migration to a new hosting provider, the renovation of an old website into a new one, the redirecting from the main domain to subdomains, adding of new services (FTP, e-mail, etc.), etc. All of these actions require creating, deleting, or editing different DNS records.

You or your administrator will execute these changes directly on the authoritative server. Once you save the modifications there, the updating process must happen. Meaning, every DNS server on the network, no matter its place in the world, has to get a copy with the updated DNS records. 

In the meantime, it shouldn’t surprise you that, for instance, in some countries, users can get the new version of your website after two hours, while others in a different country or region still are getting the previous one. The DNS propagation process is working, but it doesn’t happen totally in the blink of an eye or at the same time for all servers.

Factors that affect DNS propagation speed.

The following are the basic ones:

  • Time-to-live (TTL) value. TTL is a very useful tool to program the time-lapse for DNS information to live on a machine. When the time you set up expires, the machine will look for updated versions of that DNS information. Usually, administrators set up longer TTL values for data that don’t suffer frequent changes. There’s not a fixed rule. It really depends on the website’s or network’s needs. Just consider that the higher TTL values are, the longer DNS propagation will take. 
  • Internet service providers’ (ISPs) servers. ISPs use their own recursive servers, and they are configured to make traffic agile. They could use longer TTLs to stress less their servers and to provide a quicker response to users through their cache. While obeying their TTLs, and not yours, those servers can delay your DNS propagation. 
  • Domain name registrar. If you get a new domain name with a registrar or if you change your website’s authoritative name server, that must be registered on the highest level of the DNS hierarchy. For efficiency and security reasons, root servers use longer TTLs. 

Conclusion. 

Since DNS is a complex infrastructure, changes, especially deep ones, take some time to be updated. Internet’s game also requires a lot of patience. This is one of the first lessons every administrator gets.

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