What is DNS Caching

DNS caching is a temporary storage system that keeps records of recent domain name lookups like google.com - 172.217.0.46 to speed up future requests. Instead of querying a DNS server every time you visit a website, your computer or network checks the cache first, reducing load times and improving efficiency.

Now, to learn about DNS caching, check out the article "What is DNS caching" for information on its function, importance, and more.

When the DNS query is made for the first time, the DNS resolver must go through several steps to retrieve its corresponding IP address from the authoritative DNS server. Once this information is obtained, it will stored in the cache memory, so that the subsequent requests for the same domain name can serve more quickly without the need to repeat the entire lookup process.

How DNS Caching Works

1. First Request: When you visit a new website (e.g., example.com), your system asks a DNS server for its IP address.
2. Cache Storage: The IP address is saved locally (on your device, router, or ISP’s servers) for a set time (TTL, or Time to Live).
3. Subsequent Requests: Future visits to example.com skip the DNS lookup and use the cached IP, making the connection faster.

DNS Cache Hierarchy

DNS caching occurs at multiple levels, forming a hierarchical structure that optimizes performance.

• Browser Cache: The first layer of DNS caching occurs in a web browser. When we visit the website the browser stores DNS record domain-to-IP mapping in its cache memory.
• Operating System (OS) Cache: The function of the operating system, if the browser cache does not contain necessary DNS information, the request will be moved to the operating system DNS cache. The OS maintains the local cache of the DNS records retrieved by the applications, including the browsers.
• DNS Resolver Cache: The function of the layer is if the OS cache does not have the required DNS information, the DNS resolver cache comes into play. This cache is maintained by a DNS resolver and typically provided by our ISP or the third-party DNS service.
• Authoritative DNS Server: If the DNS server does not contain the requested DNS record, the resolver queries the authoritative DNS server for the domain. This server holds definite DNS records for the domain.

TTL (Time to Live) and DNS Caching

Time to Live (TTL) dictates how long DNS record should be stored in the cache memory before it is considered outdated and must be discarded or refreshed. TTL is measured in seconds.

Functions of TTL in DNS Caching:

1. Setting the TTL : TTL is set by the authoritative DNS server for each record.
2. Caching and TTL : When a DNS query is resolved, the TTL countdown begins. Once it expires, the cached record is discarded, and a new query is made

Importance of TTL in DNS Caching:

1. It reduces the time taken for DNS lookups.
2. It ensures timely updates to DNS records.
3. It prevents outdated data issues while maintaining speed.

Benefits of DNS Caching

The benefits of DNS caching are:

• Faster Website Loading Times: It eliminates repetitive DNS lookups and allows web pages to load quickly on subsequent visits.
• Reduced Network Traffic: Caching minimizes DNS queries. This decreases the load on the both local networks and the external DNS servers.
• Improved Reliability: If DNS resolver or the external DNS server is become the temporarily unavailable and cached DNS records are allow users to the continue accessing the frequently visited websites without the interruption.
• Lower Load on DNS Servers: With some queries reaching the authoritative DNS servers, the risk of the server overload or slow response times is minimized.

Types of DNS Caching

There are eight types of DNS caching. They are:

• Browser-Level DNS Caching: This cache is allow browser to the quickly resolve the domain names without the needing to query operating systems or external DNS servers again and it will reduce the latency.
• Operating System (OS)- Level DNS Caching: This cache is serve as the next line of the resolution if browser cache does not have required DNS record and further reducing need for the external DNS lookups.
• Router-Level DNS Caching: This is allow router to the server DNS queries locally for all the connected devices and improving the network efficiency and reducing the number of external DNS queries.
• DNS Resolver (ISP/Third-Party DNS Server) Caching: This caching is serve the boarder user base and reduce need to query authoritative DNS servers repeatedly and improving the resolution times for the multiple users.
• Recursive Resolver Caching: This cache in the recursive resolvers are help reduce load on DNS infrastructure by the storing results of the queries that will be used to answer the future requests from the any client.
• Authoritative DNS Server Caching: This caching is help authoritative servers provide the faster responses of the certain types of the queries, especially in the complex DNS setups.
• Content Delivery Network (CDN) Caching: This type of the caching is help CDNs quickly resolve the domain names and direct users to the nearest server with the cached content and improving the load times and reducing the latency.
• Host File Caching: This is acts as the manual override for the DNS resolution and where the system will be first check the hosts file before making the any DNS query.

How to Flush DNS Cache

Browser-level DNS Cache Flush:

• Open chrome and go to the chrome://net-internals/#dns.
• Click the clear host cache button.

Operating System-Level DNS Cache Flush

• Open Command Prompt as an administrator.
• After that type ipconfig /flushdns and press Enter.
• You should see the confirmation message "Successfully flushed the DNS Resolver Cache." .

Read in detail about When and How to Flush DNS Cache.

Best Practices for DNS Caching Management

• Set Appropriate TTL Values: Choose the TTL values that strike the balance between the performance and the data freshness. Shorter TTLs ensure that the updates to the DNS records propagate quickly, while the TTLs reduce the number of the DNS queries and it improve the caching the efficiency.
• Regular Cache Flushing: Implement the regular schedule for the flushing DNS caches, especially in the environments where the DNS records change frequently. It will help to avoid the stale or outdated DNS records from the causing issues.
• Use Reliable DNS Servers: Configure the multiple DNS servers to ensure the redundancy and avoid the single points of the failure.

DNS Caching Security: How to Prevent Cyber Threats

• Protect Against DNS Cache Poisoning: As mentioned, DNSSEC is the crucial in the preventing DNS cache poisoning by the ensuring the integrity and the authenticity of the DNS responses.
• Mitigate DNS Amplification Attacks: Implement the rate limiting on the DNS queries to the prevent attackers from the using your DNS servers in the amplification attacks.
• Prevent Unauthorized DNS Changes: Make sure that the DNS records can be only modified by the authorized personnel using the secure methods like multi-factors authentication and the encrypted communication channels.