Knowledgebase: DNS
Why do I get an error about a CNAME already existing?
Posted by Lance Vita on 12 June 2008 09:17 PM

By defiition of an RFC, CNAME records are required to be unique values which means there can be no other record of any type defined in a domain with the same name as a CNAME record. This is reguardless of record type. You will see a message that indicates there is an existing record with that name already configured in the domain if an attempt to made to create a record which violates this requirement.

From RFC1034:
"The domain system provides such a feature using the canonical name (CNAME) RR. A CNAME RR identifies its owner name as an alias, and specifies the corresponding canonical name in the RDATA section of the RR. If a CNAME RR is present at a node, no other data should be present; this ensures that the data for a canonical name and its aliases cannot be different. This rule also insures that a cached CNAME can be used without checking with an authoritative server for other RR types."

How do I create a CNAME record?

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