In website maintenance and server management, to migrate your website to a new server or connect to a new cloud service, you carefully modify the DNS records in your domain control panel, pointing the domain to a new IP address. After saving, the system may indicate "Modification successful." However, when you verify this, or bind the domain to certain platforms, the system will tell you "Domain DNS not modified yet," and the detection results still show the old IP address. This can be confusing—why is it showing as ineffective even though the changes have been made?

The main reason behind this isn't that your changes haven't taken effect, but rather that an efficient but somewhat "slow" caching system in the internet world is at work. The core design goal of this system is to allow global internet users to access websites faster, but this also means that any changes need time to "spread" to every corner of the globe. Understanding this process helps explain why patience is needed and how to deal with it more intelligently.

When you modify a domain's DNS records, this new information is first updated in real-time at your domain registrar (i.e., the authoritative DNS server). However, on the "road" between the end user and your website, there are many "intermediary stations," each remembering the old address. These "intermediate stations" include:

1. Your local computer and browser: They cache recently visited domain names to speed up subsequent visits.

2. Your router or company network: Network devices may also have their own caches.

3. Your Internet Service Provider's (ISP) DNS server: This is the most critical and impactful layer of caching. To reduce the load on their own servers and improve user access speed, ISPs retain the resolution results of popular domain names for a period of time.

When the system prompts "DNS has not been modified," it's usually because the DNS server it uses for checking (which may be an ISP's server) still retains old records for your domain name in its cache.

So, how long do these caches retain these records? This is determined by a parameter called TTL. TTL stands for "Time to Live," measured in seconds. It explicitly tells all intermediate caches: "This record can be kept for XX seconds; please get a new one after it expires."

For example, if you previously set the TTL to 86,400 seconds (24 hours), then for up to 24 hours after you modify the DNS record, ISP servers around the world may still be using the old cache. Only when their respective cache timers reach zero will they re-query the authoritative server to obtain the new IP address. Some conservative ISPs, for absolute stability, sometimes even retain the cache for a longer period after the TTL expires, which can make the global effective time 24 to 48 hours.

This explains why people in different regions and network environments see different speeds of effectiveness. A cache node whose TTL is about to expire can update quickly; while a node that has just cached the old record needs to wait for the full TTL cycle.

While it's impossible to forcibly clear all global caches, you can use some methods to verify and achieve limited acceleration.

First, you need to confirm that the modification operation itself is correct. You can use online global DNS lookup tools (such as `dnschecker.org`), which query DNS servers in multiple locations worldwide. This allows you to visually see which regions the new records are effective in and which are still outdated, effectively proving that your changes have been successfully submitted and are beginning to propagate.

You can also use the `dig` or `nslookup` commands in the command line to specify a particular, more up-to-date public DNS server (such as `8.8.8.8` or `1.1.1.1`) to check if the records are correct.

nslookup yourdomain 8.8.8.8

You can manually clear your computer's DNS cache, which will immediately show you the latest resolution results, although this only applies to yourself.

Windows: Open Command Prompt as administrator, type

ipconfig /flushdns

and press Enter.

macOS: In Terminal, type

sudo killall -HUP mDNSResponder

and press Enter.

Linux systems: Depending on the distribution, the command may be:

sudo systemd-resolve --flush-caches

or

sudo service nscd restart

If you can anticipate future DNS changes (such as server migration), the best practice is to plan the TTL in advance. For example, 24-48 hours before the planned migration, change the domain's TTL value to a very short time, such as 300 seconds (5 minutes). This shortens the "validity period" of the global cache. When you change the IP address again during the migration, the new record can become effective in most parts of the world within 5 minutes, instead of waiting the originally set 24 hours. After the change stabilizes, you can adjust the TTL back to a longer value to reduce query load.

There is a special operation called "changing the domain's DNS server," such as switching the domain's DNS service from provider A to provider B. This change usually takes longer to take effect because its effectiveness depends not on the TTL of your domain's record, but on the TTL recorded by the top-level domain (such as .com) registry, which is usually fixed at 24-48 hours, during which resolution may be unstable. Therefore, such operations require greater caution and allow sufficient waiting time.

What you can do is: First, ensure the changes themselves are correct; second, use tools to verify that the changes are propagating; third, refresh your local cache and that of your team members; and finally, and most importantly, allow sufficient time (usually 24-48 hours) for the changes to spread globally. Understanding and respecting this mechanism will make your website migration and server switchover process smoother and more successful.