This topic provides simple troubleshooting steps to help you quickly resolve domain name resolution failures.
Before you start
To confirm whether the DNS resolution has taken effect, see DNS resolution test methods.
DNS updates take time to propagate. After you modify or delete a DNS record, wait for a period equal to the TTL value plus 10 minutes before you start troubleshooting. For more information, see How long does it take for a modified or deleted DNS record to take effect?.
Quick issue identification
Symptom | Possible cause | Details |
Cannot access from any region |
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Access is abnormal in some regions |
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A modified or deleted DNS record does not take effect |
| How long does it take for a modified or deleted DNS record to take effect? |
DNS resolution does not take effect after DNS servers are changed |
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Cannot send or receive emails |
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DNS resolution has taken effect, but the website is inaccessible |
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1. Abnormal domain status or incorrect DNS configuration
DNS server status check
Check: Go to Alibaba Cloud DNS - Authoritative DNS and view the DNS Server Address column.
Symptom: System-Assigned DNS Servers Not Used, Domain Name DNS Information Not Found, or Detection Timed Out.
Solution: For more information, see View DNS server status and handle exceptions.
DNS record configuration issues
Check: Go to Alibaba Cloud DNS - Authoritative DNS, select the domain name, and then view the list of DNS records.
Symptom: No relevant DNS records are found, the DNS record is paused, the host record is incorrectly set, or the record value is incorrectly set.
Solution:
Scenario | Description | Solution |
No relevant DNS records are found | The list of DNS records does not contain the required type of DNS record for the domain name. | Add the required DNS records. |
The DNS record is paused | The DNS resolution fails because the required DNS record for the domain name is in the Paused status. | Enable the DNS record. Make sure that its status is Enabled. |
The host record is incorrectly set |
| Change the host record to the correct value. |
The record value is incorrectly set |
| Change the record value to the correct value. |
2. Access is abnormal in some regions
Unconfigured resolution request source: Default line
Check: Go to Alibaba Cloud DNS - Authoritative DNS, select the domain name, and then view the list of DNS records.
Symptom: The DNS Request Source is configured within Smart DNS for a specific region or carrier, but a request does not hit the corresponding smart DNS line.
Solution:
Method 1: Set the DNS Request Source to Default.
This method is suitable for common DNS resolution requirements that do not require line-specific configurations.
Method 2: Add a Default DNS record while retaining the line-specific configurations.
If you want to retain the line-specific configurations, you can add a DNS record whose DNS request source is Default. Keep the other parameters the same.
Caused by the local DNS server cache
Check: After you modify a DNS record, the time it takes for the change to take effect depends on the cache refresh time of the local DNS server. In regions where the DNS cache is refreshed quickly, the change takes effect faster. In regions where the DNS cache is refreshed slowly, the cache still stores the original DNS record. This can cause DNS resolution or access failures in these regions.
Solution: Wait for the DNS resolution to take effect. Alibaba Cloud DNS cannot resolve this issue. You can contact your local Internet Service Provider (ISP) for assistance.
3. Email resolution does not take effect
Incorrect DNS record settings
Check: Go to Alibaba Cloud DNS - Authoritative DNS, select the target domain name, and then view the list of DNS records.
Symptom: The host record is incorrectly set, DNS records are missing, or DNS records are duplicated.
Solution:
Scenario | Description | Solution |
The host record is incorrectly set | The configured host record, such as | Modify the DNS record based on the configuration checklist from your email service provider. |
DNS records are missing | Required DNS records, such as MX, CNAME, and TXT records, are missing from the configuration checklist provided by your email service provider. This causes the email service to become unavailable. | Add the required DNS records based on the configuration checklist from your email service provider. |
DNS records are duplicated | DNS configurations with the same host record and record type exist. This can cause the email service to become unavailable. For example, a new MX record is added before an existing one is deleted. | Delete or pause the duplicate DNS record. |
The cache of the newly configured email DNS record has not taken effect
After you add a DNS record for a domain name, it can take up to 2 hours for the record to take effect. You can try sending and receiving emails later.
4. Troubleshoot website access failures
Make sure that the protocol in the access URL is http, not https
If you enter a URL for which you have just configured DNS resolution, such as demo.example.com, in a browser, the browser might add the https protocol header by default and attempt to access https://demo.example.com. However, your website may only support access over http.
Check: Copy the link from the browser and check whether it contains the https protocol header.
Solution:
Method 1: Change https to http and paste the new URL into the address bar of the browser to access the website.
Method 2: Configure an HTTPS certificate for the website, enable the service to listen on port 443, and then access the website over https.
Abnormal website service
Website access may fail due to various exceptions in the website service, such as a network disconnection, a disabled firewall, or a service that is not listening on the correct port. For more troubleshooting ideas, see Quickly troubleshoot failures to access websites that are deployed on ECS instances.
FAQ
How long does it take for a modified or deleted DNS record to take effect?
After you modify or delete a DNS record, the maximum time required for the change to take effect is the Time to Live (TTL) value that was set for the record before the change. For example, if the TTL value is 10 minutes, the change theoretically takes 10 minutes to propagate globally.
However, if the local DNS servers of some carriers enforce a longer cache time, the propagation of the change is delayed. The change may take up to 48 hours to take full effect. Therefore, when you modify a record, make sure that the IP addresses before and after the modification can provide services as normal to avoid affecting the user experience.
How long does it take for DNS server changes to take effect? Why is a 48-hour propagation period required?
The time required for DNS server changes to take effect depends on the TTL value of the DNS server name that is cached on the local DNS server. In general, the TTL value can range from a few minutes to 48 hours, depending on the settings of the top-level domain (TLD).
For example, the DNS servers for the .com TLD may cache the DNS server information of a domain name for up to 48 hours. The DNS servers for the .cn TLD typically cache the information for 24 hours. Because the DNS servers for different TLDs may have different TTL values, a change to the DNS servers of a domain name theoretically takes up to 48 hours to propagate globally.