Tag: DNS query

What is Time To Live (TTL)?

Time To Live TTL

What is TTL?

Time To Live (TTL) sounds like a horror movie, but luckily it is not related to people. It is the value that shows how long the information should be kept in a particular device. There are many pieces of data that have their own TTL value. Here we will see DNS TTL and CDN TTL. 

When we are talking about DNS TTL, it is related to the time that the DNS resolvers must keep the DNS records in their cache. Each of the DNS records will have its TTL value. There are some with longer TTL because there is less chance that the value will change and others with shorter TTL value, where there are often changes. 

You can use these values as an orientation for your DNS records:

  • A and AAAA records – 2 hours (7200 seconds) is ok.
  • CNAME records – up to 12 hours (43200 seconds)
  • MX records – keep it as low. 1 hour (3600 seconds) is ok. 
  • TXT records – up to 12 hours (43200 seconds).

And about the CDN TTL, there we are talking about caching the whole content and how long should the cache servers keep the photos, videos, or whatever needs to be cached. 

When the TTL expires, the servers need to discard the current data that they have and make a new query to get the updated information from the primary servers. 

How does TTL work with DNS queries?

Talking about DNS requests, they are packets of data that also have TTL value. Imagine if they didn’t have such a parameter! The first-ever DNS query could still be around, going from server to server. 

So the TTL value of a DNS request is there to stop the perpetual search or answer and reduce pointless stress on the system. 

The value starts with a bigger number and gets dropped when it comes to zero by the routers. 

How to check the TTL value on Windows?

If you are a Windows user, you can use the Nslookup command and check a particular DNS record like – SOA, A, MX, AAAA, and more. Change the type with the one you want to see.

Start the Command Prompt as an administrator, and use this:

nslookup –types=soa yourdomainhere.com

How to check TTL value on Linux or macOS?

You have more options on Linux and macOS. You can use different commands through the Terminal application. 

The Dig command can show you different DNS records, and you can see their TTL value. This example will be with A DNS record.

dig a yourdomainname.com

You can also use the Host command in a very similar way:

host –a yourdomainname.com

This command will show you all of the visible DNS records with their TTL values.

Conclusion

The TTL value is a necessary part that limits the time a data is valid. It will show if the data is current or if it needs to be updated soon. It makes data updates easier.

 

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