DNS Cache

DNS Cache, also known as resolver cache, is a temporary database maintained by a computer’s operating system that contains records of all recent visits and attempted visits to websites and other internet domains. Essentially, it’s a store of DNS query results.

How DNS Cache Works:

  1. Initial Request: The first time you visit a new website, your computer sends a DNS query to a DNS server to resolve the website’s domain name into an IP address. This IP address is required to establish a connection to the server hosting the website.
  2. Storing the Response: Once the DNS server responds with the IP address, your computer will store this information in its DNS cache. The next time you visit the same website, your computer will check the DNS cache first to see if it already knows the IP address, reducing the need for an external query.
  3. TTL (Time-To-Live): Each entry in the DNS cache has a TTL value, which dictates how long the entry should be kept in the cache. Once the TTL expires, the entry is deleted. This ensures that changes to domain setups or migrations are eventually reflected on all clients.

Benefits of DNS Caching:

  1. Faster Web Browsing: By referencing the local DNS cache first, there’s no need to wait for a response from an external DNS server for domains that have been recently visited, which can speed up web browsing.
  2. Reduced DNS Server Load: DNS caching reduces the number of queries made to DNS servers, decreasing their overall load and traffic.
  3. Connectivity: If a user tries to access a recently visited website while the DNS server is temporarily unavailable, they might still be able to reach the website using the cached IP address (assuming the website itself is available).

Potential Issues:

  1. Outdated Information: If a website changes its IP address and a user’s DNS cache still has the old IP address, it could prevent the user from accessing the site. This can be resolved by manually clearing the DNS cache.
  2. Cache Poisoning: This is a malicious attack where corrupt DNS data is inserted into the cache. It can redirect users to fraudulent websites without them realizing it.

Clearing DNS Cache:

Sometimes it might be necessary to clear (or “flush”) the DNS cache, especially if a website has recently moved servers or if there are connectivity issues. The method to do this varies by operating system:

  • WindowsUse the command ipconfig /flushdns in the Command Prompt.
  • macOSDepending on the version, one can use commands like sudo killall -HUP mDNSResponder in the Terminal.
  • LinuxDepending on the system’s configuration, one might restart the nscd or dnsmasq services.

By understanding and effectively managing DNS cache, users can ensure more efficient internet browsing and reduce potential connection issues.

Key terms in plain language

Open a term for a concise explanation of language used on this page.

Cloud Computing

Computing resources—such as applications, servers, storage, or databases—delivered from remote infrastructure and scaled as requirements change.

Infrastructure as a Service (IaaS)

Cloud-based servers, storage, and networking that customers configure and manage without owning the underlying data-center hardware.

Software as a Service (SaaS)

Software accessed as an online service instead of being installed and maintained entirely on the customer’s own computers or servers.

Disaster Recovery (DRaaS)

A plan and service for restoring applications, data, and operations after an outage or disruption. DRaaS provides recovery infrastructure through a managed cloud service.

Identity and Access Management (IAM)

The systems and policies that determine who a user is, what resources they may access, and how that access is authenticated and reviewed.

API

An application programming interface is a defined way for software systems to exchange data or request functions from one another.