Rules for Handling Record Set Conflicts

Causes for Record Set Conflicts

Some record sets of the same name and line but different types cannot coexist. Otherwise, the resolution fails.

The possible causes are as follows:

CNAME record set restrictions: A CNAME record set cannot coexist with record sets of other types. For example, if a subdomain already has a CNAME record set configured, it cannot have other types of record sets, such as A, MX, and TXT. Otherwise, resolution may fail.
Resolution sequence and priority: The DNS server resolves a domain name based on the record set type and priority. Improper configuration may cause resolution failure or conflict.
Multiple resolution paths: If a domain name has multiple record sets of different types, the DNS server resolves the domain name through different paths. This results in inconsistent or conflicting resolution results.

According to the DNS standard RFC protocol, the CNAME record set has the highest priority. If CNAME and other types (such as MX) of record sets coexist, the CNAME record set hijacks MX record set in specific scenarios. As a result, the mailbox cannot send or receive emails.

For example, if the local DNS has requested and cached the CNAME record set, when the client requests the MX record set (using the mailbox to send emails), the local DNS preferentially returns the cached CNAME record set instead of requesting the MX record set from the Internet. In this case, the MX record set of the email server cannot be obtained. As a result, the mailbox fails to send emails.

Record Set Conflict Rules

If message "This record set is in conflict with an existing one" is displayed, the record set you are trying to add conflicts with or is the same as an existing record set.

Table 1 lists the rules.

**Table 1** Conflicts between public zone record sets
Record Set Type	NS	CNAME	A	AAAA	MX	TXT	PTR	SRV	CAA
NS	No limit^a	Conflict	No limit	No limit	No limit	No limit	No limit	No limit	No limit
CNAME	Conflict^b	No limit	Conflict	Conflict	No limit	Conflict	Conflict	Conflict	Conflict
A	No limit	Conflict	No limit	No limit	No limit	No limit	No limit	No limit	No limit
AAAA	No limit	Conflict	No limit	No limit	No limit	No limit	No limit	No limit	No limit
MX	No limit	Conflict	No limit	No limit	No limit	No limit	No limit	No limit	No limit
TXT	No limit	Conflict	No limit	No limit	No limit	No limit	No limit	No limit	No limit
PTR	No limit	Conflict	No limit	No limit	No limit	No limit	No limit	No limit	No limit
SRV	No limit	Conflict	No limit	No limit	No limit	No limit	No limit	No limit	No limit
CAA	No limit	Conflict	No limit	No limit	No limit	No limit	No limit	No limit	No limit
Conflict: The two types of record sets cannot coexist for the same name and line. No limit: The two types of record sets can coexist. a: NS record sets cannot be added for second-level domain names. There is no such restriction on subdomains. b: For second-level domain names, CNAME and NS record sets can coexist. For subdomains, CNAME record sets conflict with NS record sets.

Record Set Conflict Troubleshooting

Conflicts when Adding an NS Record Set

You have hosted domain name example.com on the DNS service. An NS record set and an SOA record set are automatically created for the hosted zone and cannot be deleted.

If the resolution line is the same, no NS record set can be added to the domain name example.com.

In this case, use either of the following methods to add a record set:

Method 1: Add an NS record set for a subdomain of the domain name.
In the following figure, an NS record set is added for 123.example.com, and the value of the record set is ns.example.com.

Figure 1 Adding an NS record set
Method 2: Add an NS record set for example.com, with a resolution line other than the default line.
In the following figure, an NS record set with the line type set to ISP is added for example.com, and the value of the record set is ns.example.com.

Figure 2 Adding an NS record set with an ISP line
Method 3: Change the value of the NS record set added to example.com.
For details, see Modifying a Record Set.

To configure a new authoritative DNS server address for a domain name, modify the value of the NS record set added to the hosted zone. For details, see What Are Huawei Cloud DNS Servers?

Other Conflicts

If message "This record set is in conflict with an existing one" is displayed, perform either of the following operations if you still want to add a record set.

Add a record set of a different name for a subdomain of the domain name.
Add a record set of a different line type. Select a line other than Default.
Delete the record set that conflicts with others and then add another one.

Deleting a record set may cause domain name resolution to fail.