If a domain name is inaccessible or has abnormal resolution, a common cause is a misconfigured DNS server. This topic describes how to use the Alibaba Cloud DNS console to quickly check your DNS server status, identify the root cause of an issue, and restore normal domain name resolution.
Terms
DNS servers for a domain name: The public addresses of the authoritative servers responsible for a domain name. After you register a domain name, the domain name registrar sets default DNS servers and synchronizes their addresses with the Top-Level Domain (TLD) name servers. During DNS resolution, a local server queries a TLD name server to retrieve the addresses of the domain name's DNS servers. The TLD name server returns these addresses. The local server then queries the DNS servers at these addresses to obtain the DNS records for the domain name.
Check the DNS Server IP Address for a domain name
Using the console
Go to the Alibaba Cloud DNS - Authoritative Zone page.
Find the target domain name. In the DNS Server IP Address column, you can view the DNS server status. Hover over the status in the DNS Server IP Address column to view the Current NS and System-assigned NS.
Using commands
nslookup -type=ns example.com
# or
dig NS example.comThe output is similar to the following:
example.com. 3547 IN NS dns30.hichina.com.
example.com. 3547 IN NS dns29.hichina.com.Go to the domain name registrar
Go to your domain name registrar to query the DNS server addresses that are currently configured for your domain name. The following steps use a domain name that is registered with Alibaba Cloud as an example:
Go to the Domain Names console. In the domain name list, find the target domain name and click it to view the details.
In the navigation pane on the left, select the Change DNS Server menu to view the DNS server addresses.
Diagnose and resolve status exceptions
The system periodically runs a health check to verify that your domain name correctly points to its assigned DNS servers. The system simulates a standard DNS query flow. It queries the upstream Top-Level Domain (TLD) server for the Name Server (NS) records configured for your domain name at the registrar. It then compares these records with the authoritative DNS server addresses assigned by the system. The possible statuses are as follows:
Exception 1: Query NS failed
This status indicates that Alibaba Cloud DNS cannot find the DNS configuration information for the domain name.
Possible cause | Impact | Solution |
DNS servers are not configured. | The domain name cannot be resolved. | Change the DNS Server IP Address to the DNS servers assigned by the Alibaba Cloud DNS system. For more information, see Modify DNS Servers. |
If the current domain name is a subdomain, this issue may be caused by missing NS records for the primary domain name. | The domain name cannot be resolved. | You must add two NS records on the DNS server for your primary domain name to point the subdomain's DNS Server IP Address to the DNS servers assigned by Alibaba Cloud DNS. For more information, see Subdomain Management. Important If you receive the Query NS failed message after you configure the NS records for the primary domain name, a synchronization delay may occur. This is because the system checks the DNS server status on a schedule and sends notifications asynchronously. Wait 5 minutes and then refresh the page. |
Exception 2: Assigned NS not used
The domain name is not using the DNS Server IP Address assigned by the Alibaba Cloud DNS system.
Possible cause | Impact | Solution |
The DNS Server IP Address values for the domain name are not Alibaba Cloud DNS addresses. |
| To use Alibaba Cloud DNS, modify the DNS servers for your domain name. Important If you have modified the DNS servers but the DNS Server IP Address column still displays the message Assigned NS not used, this is because the DNS server status is checked periodically and notifications are sent asynchronously. This can cause a synchronization delay. Wait 5 minutes and then refresh the page to check the status again. |
The domain name is configured with Free Edition DNS servers, but the system-assigned instance is a paid edition. | The domain name can be resolved over free lines but not over paid lines. For more information about lines, see Line Enumeration. | Change the DNS servers to the System-assigned NS. |
The domain name is configured with paid edition DNS servers, but the system-assigned instance is the Free Edition. | The domain name cannot be resolved. | Change the DNS servers to the System-assigned NS. |
The domain name has expired. The system automatically changes the DNS servers to | The domain name cannot be resolved. | Renew the domain name with your domain name registrar promptly. |
Exception 3: Detection Timed Out
This status indicates that the query for the domain name's DNS server information timed out.
Possible cause | Solution |
The query for the domain name's DNS server information timed out due to network issues or other intermittent reasons. | This does not affect normal domain name resolution. The status will recover after a few minutes if you refresh the page. You can also use the network probe tool to verify if the domain name can be resolved normally. |
Appendix
System-assigned NS
If you use Alibaba Cloud DNS for domain name resolution, Alibaba Cloud assigns different DNS Server IP Address values to your domain name based on whether you use a paid edition or the Free Edition. The DNS Server IP Address ranges are as follows:
Public Zone | DNS Server IP Address |
Paid Edition | vip(1-8).alidns.com |
Free Edition | dns(1-32).hichina.com, ns(1-8).alidns.com |
References
For more information about the classification of DNS servers and the role of authoritative DNS servers, see DNS Server Levels.
For more information about the domain name resolution process, see DNS resolution process.
Modifying the DNS servers for a domain name can cause abnormal resolution and service disruptions. To reduce the risks associated with configuration migration, see How to smoothly migrate domain name resolution to Alibaba Cloud DNS.