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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 Outdated Information: If a website changes its IP address and a user’s DNS cache still has the old IP address, it could prevent the user from accessing the site.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:

• Windows: Use the command ipconfig /flushdns in the Command Prompt.
• macOS: Depending on the version, one can use commands like sudo killall -HUP mDNSResponder in the Terminal.
• Linux: Depending 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.

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