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When you type a website address into your browser, your device needs to translate that domain name (like example.com) into an IP address, a process handled by the Domain Name System (DNS). To speed up this lookup process, Internet Service Providers (ISPs) often cache DNS records, temporarily storing them on their servers. This practice is known as ISP DNS caching.

ISP DNS caching benefits users by reducing the time it takes to access frequently visited sites. Instead of querying DNS servers globally each time a user visits a website, the ISP can quickly retrieve the cached IP address from its local servers, resulting in faster load times. However, this caching process can also lead to complications, especially if a website’s IP address changes.

For instance, if a website owner changes their web hosting provider or updates their server’s IP, the DNS records are updated across the internet. However, cached records at the ISP level may still point to the old IP for a period of time. This is because DNS records have a Time-to-Live (TTL) value, which tells servers how long to cache the information before fetching fresh data. Some ISPs, however, may hold onto outdated DNS entries longer than specified, leading users to outdated or non-functioning versions of a site.

This issue can be particularly frustrating for users and site owners during site migrations or DNS updates. Users can try clearing their own DNS cache or switching to a public DNS service like Google (8.8.8.8) or Cloudflare (1.1.1.1) to bypass the ISP’s cache. In extreme cases, using a VPN can help since it routes traffic through a different DNS server.

Understanding ISP DNS caching helps users navigate potential delays in DNS updates, ensuring faster and more reliable access to updated websites.