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chillsauce
Asked: 2021-01-11 15:52:33 +0800 CST

Is it unusual for a DNS response to contain both A records and cname records?

  • 772

Can a single DNS response contain both A records and cname records? If so, would it be considered unusual or is it typical behavior?

domain-name-system

3 Answers

  1. Best Answer

    If the A record(s) that you refer to are for the canonical name (the "target" of the CNAME record) rather than the query name, then this is perfectly normal.

    It would however be in violation of the standards to return CNAME and A (or any other record) for the same name.

    Valid example:

    foo.example.com.        3600   IN      CNAME   bar.example.com.
bar.example.com.        3600   IN      A       192.0.2.1

    Invalid example (not discouraged, invalid):

    foo.example.com.        3600   IN      CNAME   bar.example.com.
foo.example.com.        3600   IN      A       192.0.2.1
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  2. This is atypical, and in fact is contrary to the RFC. When a CNAME exists, there should be no other types of records for that same result.

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  3. I can confirm that it is not a valid DNS response - and how it will be resolved is down to chance. If you are a DNS server admin who is doing this, then please use either A or CNAME (and preferably A).

    Note:You can return any combination of other types or records, or a CNAME, but if you return a CNAME you can't return any other kind of record aside from the RRSIG DNSSEC signature, and any working DNS resolver will throw several fits if you try and refuse to take the answer seriously at all.

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