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I am trying to figure out the following and want to know "why" this is or is not possible.

  1. May an MX record “point to” a CNAME record?

  2. May a CNAME record “point to” a CNAME record?

  3. May an A record “point to” a CNAME record?

  4. May a PTR record “point to” a CNAME record?

  5. May an NS record “point to” a CNAME record?

Are there official rules for pointing records to CNAME records?

masegaloeh
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I-1
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2 Answers2

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Short answers:

  1. No
  2. Yes
  3. No
  4. No
  5. No

Long answers: (edit in progress)

  1. No as per the standard. Ths was clarified in RFC-2181 sectin 10.3.
  2. Standard says that it is possible, but not a good practice and should be avoided whenever possible. There's a risk of creating loops, slowing down name resolution and failure by broken resolver libraries.
  3. I may not understand the question properly - the data of an A record is an IPv4 address - i don't see how it could point to a cname.
  4. This is not legal, as clarified in RFC-2181 section 10.2
  5. This has been properly answered in In DNS can an IN NS point to a CNAME?
Community
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Urgoll
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Correct me if i'm wrong but i think this is your answer.

May an MX record “point to” a CNAME record?

No it is stated in the RFC that an MX, record should not point to a CNAME record.

May a CNAME record “point to” a CNAME record?

Yes, it is allowed. But it is not considered good practise, this could cause a DNS loop.

May an A record “point to” a CNAME record?

No, that is not possible. An A record should point to an IPv4 address.

May a PTR record “point to” a CNAME record?

Yes, this is allowed. Note, however, that the name server will not continue resolving the CNAME record, as the PTR record always only returns its value.

May an NS record “point to” a CNAME record?

No, current BIND implementations, ignore these records. BIND ignores these records to prevent spoofing.

TheCleaner
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Pietertje
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