DNS cache

Understanding DNS cache.

Since its creation, due to its utility and efficacy, the Domain Name System (DNS) became very demanded. No network can fully function without it. And considering the number of networks that currently exist, be sure that the DNS it’s permanently busy!

Considering all the important processes that rely on this system, different mechanisms have been created to reduce its stress by helping it with the execution of some tasks. Here comes the DNS cache that makes DNS work better and faster!

What is the DNS cache?

The DNS cache is the temporary cache memory for saving DNS records of already queried domain names. This memory mechanism is available in different machines, DNS recursive servers, computers, mobiles, tablets…

The mechanism’s purpose is clear, not to repeat a DNS lookup every time that a specific domain name is requested. Think about that news site you request every morning. When you requested it for the first time, a DNS lookup took place to search for its corresponding IP address. Once a DNS recursive server got its IP address, it was possible to load the domain for you, and the DNS record (IP address) was saved in the DNS cache. The following day, you typed the news domain name for revisiting it, and loading it for you was easier and faster since its IP address was available in the DNS cache. A new DNS lookup was not needed this time.

These and all the DNS records related to the different domain names will only be available on the DNS cache temporarily, not permanently. If you wonder how long? The exact time is the one that you or your administrator establish in their TTL (time-to-live). 

It allows to respond to DNS users’ queries faster and to optimize the resources efficiently. DNS recursive only do the really necessary lookups. 

How does the DNS cache work?

Whenever a user requests a domain name, a DNS lookup will be triggered. As a first step, the user’s device will search in the DNS cache included in its operating system (OS). It’s a database where different DNS records get saved and their corresponding TTL values. As mentioned before, that TTL is set by the DNS administrator of the domain. If the TTL hasn’t expired, the requested DNS records can be found directly there. The request will be responded to, and the domain loaded really fast. But if the TTL already expired, a new lookup will be needed, and this means extra time for the complete process to occur again.

This means a DNS recursive server will take the user’s request and ask other servers for the necessary DNS records. It will ask the root server, this will point to the exact TLD server that should be queried, and this last will send the recursive to the authoritative name server that can finally provide the DNS data (records).

The data will be sent to the user’s browser for loading the domain. And on the way, those data will be stored on the DNS cache of the recursive server, and the user’s device (computer, tablet, or mobile) to be available for a while, the time that their TTLs allow.

Conclusion.

The DNS cache is an efficient mechanism for making quicker and more efficient the DNS resolution process. It saves time, effort, and resources for the network (its different servers involved) and the user’s device.

Its utility is very appreciated by everybody, including the dark side of the web. DNS cache can be used for criminal purposes, so don’t forget to protect its security!