A DNAME record or Delegation Name record is defined by RFC 2672. A DNAME record creates an alias for one or more subdomains of a domain. In contrast, the CNAME record creates an alias only of a single name (and not its subdomains). Like the CNAME record, the DNS lookup will continue by retrying the lookup with the new name. If a DNS resolver sends a query without EDNS, or with EDNS version 0, then a name server synthesizes a CNAME record to simulate the semantics of the DNAME record.
For example, if there is a DNS zone as follows:
foo.example.com. DNAME bar.example.com. bar.example.com. A 192.0.2.23 xyzzy.bar.example.com. A 192.0.2.24 *.bar.example.com. A 192.0.2.25An A record lookup for foo.example.com will fail because a DNAME is not a CNAME.
However, a look up for xyzzy.foo.example.com will be DNAME mapped and return the A record for xyzzy.bar.example.com which is 192.0.2.24; if the DNAME record had been a CNAME record, this request would have failed.
Lastly, a request for bar.foo.example.com would be DNAME mapped and return 192.0.2.25.
Read more about this topic: CNAME Record
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