In the process of website operation and maintenance or cloud server management, it is common to encounter scenarios where the server changes its IP address. This change may be triggered by cloud service migration, BGP line optimization, DDoS cleaning switching, or operator policies. On the surface, changing the IP only requires updating the domain name resolution record, but in actual operation, it is often accompanied by problems such as DNS resolution failure, domain name inaccessibility, and site inaccessibility, which affects business continuity and user access experience.

　　Main reasons for DNS resolution failure after changing the IP:

　　Failure to modify the domain name DNS resolution record in time. After changing the IP, if the domain name management backend is not logged in to update the A record, the resolution still points to the old IP, and the access naturally fails.

　　The DNS service provider's resolution cache is not synchronized. Even if the A record is changed, some DNS nodes may still cache the old IP address, causing access pointing errors.

　　The TTL value is set too high. The TTL setting of the DNS record is high, which will cause the cache to be delayed and invalid after the change.

　　The local or operator DNS cache is not refreshed, and some user devices or network operator nodes have not cleared the old DNS records, resulting in delays or incorrect resolution.

　　Incorrect domain name configuration or incorrect record format, improper input format, record type, and host record when updating DNS records can also cause resolution anomalies.

　　Abnormal DNS service or domain name suspension, domain name suspension by the registrar or unstable DNS service can also cause access failure.

　　Standard troubleshooting and processing flow

　　To quickly locate and solve the problem, you can troubleshoot and process it one by one in the following order.

　　Step 1: Confirm whether the DNS resolution record has been updated

　　Log in to the domain name registrar backend, enter [Domain Name Management], and check whether the IP of the current A record has been updated to the new server address. Check whether the record type is A, whether the host record is correct (such as @ represents the primary domain name), and ensure that the DNS status is "enabled" or "valid". If not modified, please immediately replace the original record IP with the new IP and save it.

　　Step 2: Check TTL settings

　　The effective time after DNS modification is controlled by the TTL value. Recommended use of TTL value cache time: 60010 minutes is recommended for frequent changes, 36001 hour is commonly used for ordinary websites, and 8640024 hours is used for long-term stable services. If TTL is set to 3600 or even 86400, even if the record has been changed, some DNS caches may not expire. It is recommended to temporarily lower TTL to 600 seconds one day before changing the IP.

　　Step 3: Use NSLOOKUP to diagnose the domain name

　　In the command line, enter:

  nslookup yourdomain.com

　　The following is an example of the returned result:

  Server:  dns.google
  Address: 8.8.8.8

  Non-authoritative answer:
  Name:    yourdomain.com
  Address: 1.2.3.4

　　Verify that the returned IP address is the actual new IP address of the current server. If it's still the old IP address or no IP address is returned, DNS synchronization has not taken effect.

　　You can further specify the DNS server to query:

  nslookup yourdomain.com 1.1.1.1

　　Test multiple public DNS servers (e.g., 114.114.114.114, 8.8.8.8, and 223.5.5.5) in sequence to ensure resolution consistency.

　　Step 4: Flush the local DNS cache

　　Sometimes, the local computer, server, or browser may have cached old DNS records that need to be cleared.

　　Windows:

  ipconfig /flushdns

　　Linux system (taking systemd-resolved as an example):

  systemd-resolve --flush-caches

　　Clearing the browser cache: It's recommended to clear the DNS cache on browsers like Chrome and Edge, or restart the browser process.

　　Step 5: Check if domain name resolution is restricted by the service provider.

　　If you've completed all the above steps but DNS still doesn't work: Check if the domain is expired or frozen. Log in to your domain management dashboard to confirm if the DNS server is abnormal. If you use a CDN service, check the proxy status and cache flushing.

　　Step 6: Check the global DNS synchronization status.

　　Use sites like DNSChecker.org or WhatsMyDNS.net to query the A record for your domain name and verify that DNS nodes in multiple regions around the world are synchronized. If most nodes show the new IP address and only a few remain, this is normal propagation delay. If all nodes still show the old IP address, it means the DNS record hasn't been updated or the service provider's cache hasn't been flushed.

　　DNS resolution failure after a server IP change is a critical issue in website operations. It not only disrupts user access and affects search engine indexing, but can also damage brand reputation and business stability. Operations and maintenance personnel should always maintain sensitivity to the synchronization of DNS records, caches, and the actual server IP addresses, and use professional tools and experience to ensure the continued stable operation of network services in IP change scenarios.