During recursive resolution, different record types have different priorities. If the host record and resolution line are the same, some record types cannot coexist. This is because such a configuration can pose a threat and result in service unavailability.
Causes of DNS record conflicts
Assume that you have configured 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 |
According to RFC standards, a CNAME record has the highest priority. During a DNS query, the CNAME record is returned first. This configuration prevents the MX record from being resolved and affects the email service. In this scenario, Alibaba Cloud DNS detects a DNS record conflict and reports an error to help you avoid this risk. For more information, see RFC1034 and RFC2181.
Solutions to DNS record conflicts
If the system reports a DNS record conflict, you can delete the conflicting DNS record or change the host record to resolve the conflict.
Special handling when the host record is @
To accommodate various user scenarios, Alibaba Cloud DNS has optimized the conflict rules for some record types when the host record is @.
When the host record is @, CNAME records and MX records no longer conflict
Record type | Host record | Line | Value |
MX | @ | Default | mx1.hichina.com |
CNAME | @ | Default | example.com |
This scenario configuration has the risk of mailbox not receiving emails normally or receiving emails intermittently.
If a mail server's local DNS prioritizes CNAME record resolution for the @ host record, resolution of the corresponding MX record is affected. This can cause the resolution to fail or produce unexpected results.
When the host record is @, CNAME records and TXT records no longer conflict
Record type | Host record | Line | Value |
TXT | @ | Default | db642353e95243c12d3 |
CNAME | @ | Default | example.com |
This configuration may cause issues such as a TXT verification failure. If you encounter such an issue, remove the CNAME record.
Complete rules for DNS record conflicts
The host record is @
When the host record and resolution line are the same, these different types of resolution records cannot coexist:
❌: 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
example.com, you cannot add a CNAME record forexample.com.✅: 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
example.com, you can also add an MX record forexample.com.↔️: 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
example.com, you can add another A record forexample.com.NS
CNAME
ALIAS
A
URL
MX
TXT
AAAA
SRV
CAA
SVCB (alias mode)
SVCB (service mode)
HTTPS (alias mode)
HTTPS (service mode)
NS
↔️
✅
✅
✅
✅
✅
✅
✅
✅
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✅
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CNAME
✅
↔️
❌
❌
❌
✅
✅
❌
❌
❌
❌
❌
❌
❌
ALIAS
✅
❌
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❌
✅
✅
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❌
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A
✅
❌
❌
↔️
❌
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URL
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MX
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TXT
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↔️
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AAAA
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❌
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❌
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↔️
✅
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✅
✅
SRV
✅
❌
✅
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✅
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↔️
✅
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✅
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CAA
✅
❌
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↔️
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SVCB (alias mode)
✅
❌
✅
✅
✅
✅
✅
✅
✅
✅
↔️
❌
✅
✅
SVCB (service mode)
✅
❌
✅
✅
✅
✅
✅
✅
✅
✅
❌
↔️
✅
✅
HTTPS (alias mode)
✅
❌
✅
✅
✅
✅
✅
✅
✅
✅
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✅
↔️
❌
HTTPS (service mode)
✅
❌
✅
✅
✅
✅
✅
✅
✅
✅
✅
✅
❌
↔️
The host record is not @
When the host record and resolution line are the same, these different types of resolution records cannot coexist:
❌: 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 forwww.example.com.✅: 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 forwww.example.com.↔️: 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 forwww.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
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ALIAS
✅
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❌
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A
❌
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↔️
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URL
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MX
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↔️
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TXT
❌
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AAAA
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✅
SRV
❌
❌
✅
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↔️
✅
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CAA
❌
❌
✅
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↔️
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SVCB (alias mode)
❌
❌
✅
✅
✅
✅
✅
✅
✅
✅
↔️
❌
✅
✅
SVCB (service mode)
❌
❌
✅
✅
✅
✅
✅
✅
✅
✅
❌
↔️
✅
✅
HTTPS (alias mode)
❌
❌
✅
✅
✅
✅
✅
✅
✅
✅
✅
✅
↔️
❌
HTTPS (service mode)
❌
❌
✅
✅
✅
✅
✅
✅
✅
✅
✅
✅
❌
↔️