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:

Restrictions on CNAME record sets: 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 private zone record sets
Record Set Type	CNAME	A	AAAA	MX	TXT	PTR	SRV
CNAME	Duplicate	Conflict	Conflict	Conflict	Conflict	Conflict	Conflict
A	Conflict	Duplicate	No limit	No limit	No limit	No limit	No limit
AAAA	Conflict	No limit	Duplicate	No limit	No limit	No limit	No limit
MX	Conflict	No limit	No limit	Duplicate	No limit	No limit	No limit
TXT	Conflict	No limit	No limit	No limit	Duplicate	No limit	No limit
PTR	Conflict	No limit	No limit	No limit	No limit	Duplicate	No limit
SRV	Conflict	No limit	No limit	No limit	No limit	No limit	Duplicate
Conflict: Two types of record sets cannot coexist when the names are the same. No limit: The two types of record sets can coexist. Duplicate: The record set cannot be the same as an existing one.

Record Set Conflict Troubleshooting

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.

Set a different name for the record set for a subdomain of the domain name.
Delete the existing record set and then add the record set again.

Deleting a record set may cause domain name resolution failures. Exercise caution when performing this operation.