Frequently asked questions about smart DNS resolution in Alibaba Cloud DNS.
Q: Why is smart DNS resolution scheduling inaccurate?
A: This applies only to domain names using Alibaba Cloud DNS. If your domain is hosted on another provider's DNS server, contact that provider. For domain names on Alibaba Cloud DNS, if the resolution line shows inaccurate scheduling, see Troubleshooting inaccurate intelligent parsing scheduling.
Q: How is smart DNS resolution billed?
A: Smart DNS resolution is not billed separately. The cost is included in the Cloud DNS edition fee. Different editions support different resolution line ranges. Pricing. Version comparison.
Q: How does smart DNS resolution determine a visitor's location?
A: Cloud DNS identifies the visitor's location by the egress IP of the LocalDNS that the visitor uses.
Q: Can resolution lines be set by Chinese region?
A: Yes. Supported regions include East China, North China, Central China, South China, Southwest China, Northwest China, and Northeast China. Chinese regional lines require the Enterprise Edition of Cloud DNS. Parsing line enumeration.
Q: How do I automatically switch traffic to healthy servers when a server fails?
A: Smart DNS resolution does not support automatic failover or faulty IP removal. Use What is Global Traffic Manager 3.0 instead.
Q: Does smart DNS resolution support nearest-server access for China Mobile and China Unicom?
A: Yes. The DNS resolution policy works as follows:
|
Parsing source |
Returned IP address |
|
China Mobile |
Server IP address on China Mobile line |
|
China Unicom |
Server IP address on China Unicom line |
|
Default |
Server IP address on China Mobile line |
The system matches the Carrier of each request and returns the corresponding server IP. Requests from other carriers fall back to the China Mobile line IP.
Q: Can resolution lines have overlapping geographic locations?
A: Yes. For resolution sources based on Region, the following priorities apply.
|
Parsing source |
Parsing priority |
|
Singapore |
High |
|
Asia |
Medium |
|
Outside China |
Low |
For example, if you set resolution lines to Outside China, Asia, and Singapore: a request from Singapore returns the Singapore line address; a request from elsewhere in Asia returns the Asia line address; a request from another continent returns the Outside China line address.
Q: Can I serve only users in mainland China?
A: Yes. Configure the DNS resolution policy as follows:
|
Parsing source |
Returned IP address |
|
Regions in the Chinese mainland |
Server IP address |
|
Outside China |
127.0.0.1 |
For mainland China request sources, the system returns your actual server IP. For the Outside Mainland China group (including Hong Kong (China), Macao (China), Taiwan (China), and other regions), return an invalid IP such as 127.0.0.1 or 0.0.0.0 to block resolution.
A record resolution failures when the default line is a CNAME record
Problem description
A host record has two DNS records: a CNAME record on the default line and an A record on the Mainland China line. When a client in mainland China requests an A record, the default line's CNAME record is returned instead.
Cause
When an end user on a non-default line requests a non-A record type, the authoritative DNS server returns the CNAME record. The local DNS server caches it. Because CNAME records take the highest priority, a subsequent A record request hits the cached CNAME instead of querying the authoritative server again. This is standard DNS protocol behavior.
Solution
Do not set the default line to a CNAME record when other specific resolution lines are configured. Remove the CNAME record from the default line. DNS records resolve correctly after the carrier's local DNS cache TTL expires.