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DNS record conflict rules

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Certain DNS record types conflict when they share the same host record and resolution line, which can cause service unavailability.

Causes of DNS record conflicts

Consider the following two DNS records for example.com:

Record type

Host record

Line

Value

MX

www

Default

mx1.hichina.com

CNAME

www

Default

demo.xxx.com

Per RFC standards, CNAME has the highest priority — the CNAME record is returned first during DNS queries, preventing MX from resolving and disrupting email service. Alibaba Cloud DNS detects this DNS record conflict and reports an error, as defined in RFC1034 and RFC2181.

Resolve DNS record conflicts

Delete the conflicting record or change its host record.

Exceptions for the @ host record

Alibaba Cloud DNS relaxes certain conflict rules when the host record is @.

CNAME and MX records can coexist with @

Record type

Host record

Line

Value

MX

@

Default

mx1.hichina.com

CNAME

@

Default

example.com
Warning

This configuration may cause emails to be lost or arrive intermittently.

If the mail server's local DNS prioritizes CNAME resolution for @, MX resolution may fail or produce unexpected results.

CNAME and TXT records can coexist with @

Record type

Host record

Line

Value

TXT

@

Default

db642353e95243c12d3

CNAME

@

Default

example.com
Warning

This configuration may cause TXT verification failures. If this occurs, remove the CNAME record.

Complete rules for DNS record conflicts

The host record is @

The following table shows record type compatibility when the host record and resolution line match:

  1. ❌: Conflict. These record types cannot coexist for the same host record and line. For example, if you add an A record for example.com, you cannot add a CNAME record for example.com.

  2. ✅: No conflict. These record types can coexist for the same host record and line. For example, if you add an A record for example.com, you can also add an MX record for example.com.

  3. ↔️: Repeatable. Multiple records of the same type can be added for the same host record and line. For example, if you add an A record for example.com, you can add another A record for example.com.

    NS

    CNAME

    ALIAS

    A

    URL

    MX

    TXT

    AAAA

    SRV

    CAA

    SVCB (alias mode)

    SVCB (service mode)

    HTTPS (alias mode)

    HTTPS (service mode)

    NS

    ↔️

    ✅

    ✅

    ✅

    ✅

    ✅

    ✅

    ✅

    ✅

    ✅

    ✅

    ✅

    ✅

    ✅

    CNAME

    ✅

    ↔️

    ❌

    ❌

    ❌

    ✅

    ✅

    ❌

    ❌

    ❌

    ❌

    ❌

    ❌

    ❌

    ALIAS

    ✅

    ❌

    ✅

    ❌

    ✅

    ✅

    ✅

    ❌

    ✅

    ✅

    ✅

    ✅

    ✅

    ✅

    A

    ✅

    ❌

    ❌

    ↔️

    ❌

    ✅

    ✅

    ✅

    ✅

    ✅

    ✅

    ✅

    ✅

    ✅

    URL

    ✅

    ❌

    ✅

    ❌

    ❌

    ✅

    ✅

    ❌

    ✅

    ✅

    ✅

    ✅

    ✅

    ✅

    MX

    ✅

    ✅

    ✅

    ✅

    ✅

    ↔️

    ✅

    ✅

    ✅

    ✅

    ✅

    ✅

    ✅

    ✅

    TXT

    ✅

    ✅

    ✅

    ✅

    ✅

    ✅

    ↔️

    ✅

    ✅

    ✅

    ✅

    ✅

    ✅

    ✅

    AAAA

    ✅

    ❌

    ❌

    ✅

    ❌

    ✅

    ✅

    ↔️

    ✅

    ✅

    ✅

    ✅

    ✅

    ✅

    SRV

    ✅

    ❌

    ✅

    ✅

    ✅

    ✅

    ✅

    ✅

    ↔️

    ✅

    ✅

    ✅

    ✅

    ✅

    CAA

    ✅

    ❌

    ✅

    ✅

    ✅

    ✅

    ✅

    ✅

    ✅

    ↔️

    ✅

    ✅

    ✅

    ✅

    SVCB (alias mode)

    ✅

    ❌

    ✅

    ✅

    ✅

    ✅

    ✅

    ✅

    ✅

    ✅

    ↔️

    ❌

    ✅

    ✅

    SVCB (service mode)

    ✅

    ❌

    ✅

    ✅

    ✅

    ✅

    ✅

    ✅

    ✅

    ✅

    ❌

    ↔️

    ✅

    ✅

    HTTPS (alias mode)

    ✅

    ❌

    ✅

    ✅

    ✅

    ✅

    ✅

    ✅

    ✅

    ✅

    ✅

    ✅

    ↔️

    ❌

    HTTPS (service mode)

    ✅

    ❌

    ✅

    ✅

    ✅

    ✅

    ✅

    ✅

    ✅

    ✅

    ✅

    ✅

    ❌

    ↔️

The host record is not @

The following table shows record type compatibility when the host record and resolution line match:

  1. ❌: Conflict. The two types of DNS records cannot coexist for the same host record and resolution line. For example, if you have added an A record for www.example.com, you cannot add a CNAME record for www.example.com.

  2. ✅: No conflict. The two types of DNS records can coexist for the same host record and resolution line. For example, if you have added an A record for www.example.com, you can also add an MX record for www.example.com.

  3. ↔️: Repeatable. Multiple DNS records of the same type can be added for the same host record and resolution line. For example, if you have added an A record for www.example.com, you can add another A record for www.example.com.

    NS

    CNAME

    ALIAS

    A

    URL

    MX

    TXT

    AAAA

    SRV

    CAA

    SVCB (alias mode)

    SVCB (service mode)

    HTTPS (alias mode)

    HTTPS (service mode)

    NS

    ↔️

    ❌

    ✅

    ❌

    ❌

    ❌

    ❌

    ❌

    ❌

    ❌

    ❌

    ❌

    ❌

    ❌

    CNAME

    ❌

    ↔️

    ❌

    ❌

    ❌

    ❌

    ❌

    ❌

    ❌

    ❌

    ❌

    ❌

    ❌

    ❌

    ALIAS

    ✅

    ❌

    ✅

    ❌

    ✅

    ✅

    ✅

    ❌

    ✅

    ✅

    ✅

    ✅

    ✅

    ✅

    A

    ❌

    ❌

    ❌

    ↔️

    ❌

    ✅

    ✅

    ✅

    ✅

    ✅

    ✅

    ✅

    ✅

    ✅

    URL

    ❌

    ❌

    ✅

    ❌

    ❌

    ✅

    ✅

    ❌

    ✅

    ✅

    ✅

    ✅

    ✅

    ✅

    MX

    ❌

    ❌

    ✅

    ✅

    ✅

    ↔️

    ✅

    ✅

    ✅

    ✅

    ✅

    ✅

    ✅

    ✅

    TXT

    ❌

    ❌

    ✅

    ✅

    ✅

    ✅

    ↔️

    ✅

    ✅

    ✅

    ✅

    ✅

    ✅

    ✅

    AAAA

    ❌

    ❌

    ❌

    ✅

    ❌

    ✅

    ✅

    ↔️

    ✅

    ✅

    ✅

    ✅

    ✅

    ✅

    SRV

    ❌

    ❌

    ✅

    ✅

    ✅

    ✅

    ✅

    ✅

    ↔️

    ✅

    ✅

    ✅

    ✅

    ✅

    CAA

    ❌

    ❌

    ✅

    ✅

    ✅

    ✅

    ✅

    ✅

    ✅

    ↔️

    ✅

    ✅

    ✅

    ✅

    SVCB (alias mode)

    ❌

    ❌

    ✅

    ✅

    ✅

    ✅

    ✅

    ✅

    ✅

    ✅

    ↔️

    ❌

    ✅

    ✅

    SVCB (service mode)

    ❌

    ❌

    ✅

    ✅

    ✅

    ✅

    ✅

    ✅

    ✅

    ✅

    ❌

    ↔️

    ✅

    ✅

    HTTPS (alias mode)

    ❌

    ❌

    ✅

    ✅

    ✅

    ✅

    ✅

    ✅

    ✅

    ✅

    ✅

    ✅

    ↔️

    ❌

    HTTPS (service mode)

    ❌

    ❌

    ✅

    ✅

    ✅

    ✅

    ✅

    ✅

    ✅

    ✅

    ✅

    ✅

    ❌

    ↔️
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