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Help Center/ Domain Name Service/ FAQs/ Public Zones/ How Do I Handle Inaccurate Scheduling Caused by the CNAME Record Set Cache in the Default Lines?

How Do I Handle Inaccurate Scheduling Caused by the CNAME Record Set Cache in the Default Lines?

Updated on 2025-02-10 GMT+08:00

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Original DNS Record Sets

A CNAME record set with a default line
Record sets of other types (excluding CNAME), with a non-default line for each record set

Take the hwtest-example.com domain name as an example. DNS record sets are configured as follows.

**Table 1** Original DNS record sets
Domain Name	Line Type	Record Set Type	Record Set Value
hwtest-example.com	Default line for China Telecom	AAAA	ff03:x:x:x:x:x:x:x
hwtest-example.com	Default line for China Telecom	A	1.x.x.x
hwtest-example.com	Default	CNAME	www.huaweicloud.com

Figure 1 DNS record sets

Cause Analysis for Inaccurate Scheduling

**Table 2** Responses of different types of record sets with a non-default line
Requested Record Set Type	Record Set Type for the Line	Responses
A	Not found: A Found: AAAA	The CNAME record set with the default line is returned and cached on the local DNS server. CNAME record sets have the highest priority. Within the TTL, the CNAME record set with the default line is used for DNS resolution even if DNS queries to the A or AAAA record set with a non-default line are initiated. As a result, DNS scheduling is inaccurate.
A	Not found: A and AAAA Found: TXT, MX, and other
AAAA	Not found: AAAA Found: A
AAAA	Not found: A and AAAA Found: TXT, MX, and other
MX	Not found: MX
TXT	Not found: TXT

Solutions

Configure A and AAAA record sets for a subdomain of the domain name, with a non-default line.
Configure a CNAME record set for the domain name with a non-default line (which must be the same as the line type specified in 1) to map the domain name to the subdomain specified in the A and AAAA record sets.

Take hwtest-example.com as an example.

Configure A and AAAA record sets for www.hwtest-example.com (a subdomain of hwtest-example.com), with a China Telecom default line for each record set.

Then, configure a CNAME record set for hwtest-example.com to map it to www.hwtest-example.com.

CAUTION:

www.hwtest-example.com is only an example domain name. Select a second-level domain name that has no record sets configured based on your service requirements.
You must add A and AAAA record sets before adding a CNAME record set. If you add a CNAME record set first, DNS resolution may be interrupted.
The CNAME record set configured for the domain name remains unchanged.

Table 3 and Figure 2 show the optimized DNS record sets.

**Table 3** Optimized DNS record sets
Domain Name	Line Type	Record Set Type	Record Set Value
hwtest-example.com	Default line for China Telecom	CNAME	www.hwtest-example.com
www.hwtest-example.com	Default line for China Telecom	AAAA	ff03:x:x:x:x:x:x:x
www.hwtest-example.com	Default line for China Telecom	A	1.x.x.x
hwtest-example.com	Default	CNAME	www.huaweicloud.com

Figure 2 Optimized DNS record sets

NOTE:

A CNAME record set with a default line and a CNAME record set with a non-default line are configured, and the two record sets have the same priority. If you request an MX or TXT record set with a non-default line and no record set of the corresponding type is configured, no response is returned. In this case, cache pollution will not occur and DNS scheduling will be accurate.

Parent topic: Public Zones

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