If a domain name changes its DNS server, will the original DNS records be retained? Many people assume that as long as the domain name remains the same, the DNS records will be automatically inherited. However, the actual result is often unexpected: either all DNS records become invalid, the website becomes temporarily inaccessible, or conflicts between the old and new DNS servers cause random redirects. Understanding the relationship between DNS servers and DNS records is a prerequisite for successfully migrating DNS records.

　　First, it's important to understand that DNS records are not stored within the domain name itself, but rather on the authoritative DNS servers provided by your DNS provider. When a user adds an A record, CNAME record, or MX record in a domain management panel, what is actually written is the database of the corresponding DNS server, not "written into the domain name." Therefore, when a domain name changes its DNS server, the DNS records from the old DNS provider will not automatically synchronize to the new DNS server unless you manually copy them over or the provider provides a migration tool.

　　In other words, after a domain name changes its DNS, the old DNS records will not be automatically retained because the authoritative DNS has switched to the new DNS system. If the new system does not have configured DNS records, the domain name will enter a "no-resolver state," and the browser will directly return an NXDOMAIN error. This is the fundamental reason why many website owners find their sites suddenly inaccessible after changing their DNS, not because "the DNS hasn't taken effect yet."

　　The second easily misunderstood point is that while there is a propagation time between DNS switching and the resolution taking effect, the existence of the DNS records is completely unrelated to this delay. After changing DNS, the global root servers need to update the domain's NS records, and then the recursive DNS servers need to re-acquire the new authoritative DNS records. This process typically takes 0-48 hours. Therefore, if the DNS records are not configured correctly, they will not automatically recover even after a long wait. Therefore, confirming that the DNS records have been completely migrated is the most important step before changing DNS.

　　Many DNS service providers offer an "import old records" function. Some support automatic scanning, some offer Zone file import, and some require manual addition. Some advanced DNS platforms even support "smooth switching": adding new DNS records first, but not modifying the NS servers immediately, and then performing the switch after all verifications are successful, thus avoiding business interruption. However, if users change their DNS first and then try to fix the DNS records, it can easily cause prolonged access problems.

　　So what if you've switched DNS but forgot to import the records beforehand? As long as the old DNS service is still accessible, you can find the original records and add them again. Many people believe that the old records will be cleared after the switch, but in fact, the old records still exist, just no longer referenced by the root servers. As long as you can still see A, MX, TXT records when logging into the old DNS platform, you can manually migrate them. If you can't find the old platform, you need to query the public DNS cache or use historical DNS lookup tools, such as dig, nslookup, or online DNS history databases. However, this can only retrieve some records; for example, TXT/SPF records may have been cached and overwritten, requiring you to retrieve the configuration from the mail server.

　　This also involves another important aspect of TTL: even if the DNS server has been switched, as long as the cache hasn't expired, some users will still access the old IP address. Therefore, there is a "resolution split period" during the migration. For example, if the TTL is 24 hours, after switching DNS, some users may still access the old server within the last 24 hours, while some users have already accessed the new server. For cross-datacenter and database write operations, a synchronization mechanism needs to be planned in advance; otherwise, serious problems such as data loss and order splitting may occur.

　　To ensure a smooth switchover, the migration process is generally recommended as follows:

　　Step 1: Reduce the TTL (Time To Live) of all records in the old DNS to 300 seconds 24-48 hours in advance.

　　Step 2: Copy all DNS records completely to the new DNS platform and confirm correct configuration.

　　Step 3: Test if the new DNS resolves correctly.

　　Step 4: Officially change the domain's NS server to the new DNS provider.

　　Step 5: Monitor the ratio of old to new access during the global activation process. Once the switchover is confirmed to be successful, restore the TTL to the normal value.

　　This ensures the shortest possible service interruption time and minimizes the difference in access time between the old and new records to no more than 5 minutes.

　　It's important to note that not all DNS records will "affect access after failure." For example, NS, MX, CAA, and TXT/SPF records are crucial for email services and SSL certificate issuance. Many website owners only migrate A/CNAME records but forget about email resolution, ultimately leading to a complete disconnection of email accounts. This is one of the most common hidden failures in DNS migration.

　　Another common misconception is that "the same domain can use multiple DNS servers simultaneously." In reality, root servers only allow one effective set of DNS servers. Even if you keep multiple DNS addresses in your domain control panel, it's not a matter of multiple platforms resolving the same domain; rather, the authority is being redirected. It's especially important to avoid having different DNS platforms resolve the same domain, otherwise, IP inconsistencies will occur in different regions. What appears to be intelligent route-based resolution is actually a resolution conflict.

　　Furthermore, if a user has enabled CDN, improper DNS resolution migration can lead to lost CDN node pointers or caching policies becoming ineffective. This is because CDN service providers typically require users to point their CNAME records to a dedicated CDN domain. If the CNAME record is forgotten when changing DNS, access will result in origin pulls or 404 errors. Before migration, ensure all resolution types remain consistent, including TTL, weight, priority, etc., not just IP addresses.

　　After a DNS switch, access results for different network users may be asynchronous. This is normal and not a resolution error. To determine if the migration was successful, you can use three methods to verify:

　　Use `dig+trace` to query multiple recursive servers globally to see if the results are consistent;

　　Use an online global DNS propagation testing tool to observe the coverage status of the old and new IP addresses;

　　Use `nslookupdomain.com` to query different DNS servers to see if resolution is normal. If all responses return the same IP address, it means the cache has been refreshed successfully.

　　Many people ask: If I only change the DNS provider but keep the IP address the same, can I directly modify the DNS? The answer is yes, but you must copy the DNS records beforehand. Otherwise, access will still fail because the cache hasn't been updated when the DNS is switched, and the authoritative DNS has lost its records, causing the recursive server query to fail and return NXDOMAIN. Unless both DNS providers support DNS synchronization, manual migration is still necessary.

　　Changing DNS isn't just about "switching to a faster, more stable platform." More importantly, it's about completely migrating the original records, controlling the TTL update cycle, and avoiding cache fragmentation. Organizing the DNS record table, performing switchover simulations, and reducing the TTL in advance—these seemingly redundant operations are actually the core guarantee that your website, email, and API services will not be affected.