DNS Caching: Why Old Website Addresses Get Stuck

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Summary
Learn how DNS caching works, what TTL means, and why your computer might still see an old version of a website in Bangladesh.

DNS Caching: Why Old Website Addresses Get Stuck

Summary

DNS Caching is a process where your computer, router, or ISP saves the IP address of a website you’ve visited so that it doesn’t have to “ask” for it again. While this makes browsing faster, it can cause problems if a website moves to a new server and your cache is still pointing to the old, broken address.

Overview

Think of DNS caching like a contacts list on your phone. If your friend changes their phone number but you don’t update your contacts, you will keep calling the old, wrong number. Similarly, if a website’s IP address changes, your device may continue to use the “stale” cached IP until the timer (TTL) expires or you manually clear the cache.

Technical Deep-Dive

  • TTL (Time to Live): Every DNS record comes with a TTL value (measured in seconds). This is the “expiration date” of the cache. Once the TTL hits zero, the device must perform a fresh lookup.
  • Caching Layers: DNS is cached at multiple levels:
    1. Browser Cache: Chrome or Firefox remembers sites for a few minutes.
    2. OS Cache: Windows or macOS keeps a system-wide list.
    3. Router Cache: Your home router often caches queries for all devices.
    4. ISP Cache: Your broadband provider maintains a massive cache for all its users.

Bangladesh Context

In Bangladesh, DNS caching issues are particularly common due to local network management:

  1. Transparent DNS Proxies: Some ISPs in BD use “Transparent Proxies” to intercept and cache DNS queries to save international bandwidth. This can sometimes cause you to see an old version of a site even after you’ve cleared your local computer’s cache.
  2. BDIX Sites: Local BDIX-connected FTP or TV servers often change IPs during maintenance. If your ISP’s cache doesn’t update quickly, you may lose access to these local services while other users on different ISPs can still see them.

Troubleshooting

  • Flush DNS: Use ipconfig /flushdns in Windows to clear your system cache.
  • Change DNS: If your ISP’s cache is “stuck,” manually setting your DNS to 1.1.1.1 (Cloudflare) or 8.8.8.8 (Google) can bypass the ISP’s stale records.

FAQ

How long does a DNS cache last?

It depends on the website owner. Some sites have a TTL of 300 seconds (5 minutes), while others may be set to 86,400 seconds (24 hours).

Related Content

References