Question

Is a wildcard CNAME DNS record valid?

Hello,

I have four subdomains. First two subdomains are set with wildcard *.static.MYSITE.com and .*v2.MYSITE.COM Another two subdomains are set without wildcard test.z3lab.info, cms.z3lab.info

Which subdomains are more correct, and why do we use wildcard?

This is my zone file

$ORIGIN z3lab.info.
$TTL 1800
z3lab.info. IN SOA ns1.digitalocean.com. hostmaster.z3lab.info. 1472229537 10800 3600 604800 1800
z3lab.info. 1800 IN NS ns1.digitalocean.com.
z3lab.info. 1800 IN NS ns2.digitalocean.com.
z3lab.info. 1800 IN NS ns3.digitalocean.com.
z3lab.info. 1800 IN A 46.101.197.231
*.static.z3lab.info. 1800 IN CNAME z3lab.info.
*.v2.z3lab.info. 1800 IN CNAME z3lab.info.
test.z3lab.info. 1800 IN CNAME z3lab.info.
cms.z3lab.info. 1800 IN CNAME z3lab.info.

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A wildcard means you can replace that with any name and it will resolve to the same record, whether you type example.static.z3lab.info or example1.static.z3lab.info.

Neither of them are “more correct”.

Which subdomains are more correct, and why do we use wildcard?

Both are just as correct as they are both valid types of CNAME records. Both CNAME and A records will generally support a wildcard (*) like what is shown in your records. For example if you have the record:

*.static.z3lab.info. 1800 IN CNAME z3lab.info.

Any request for www.static.z3lab.info or someothername.static.z3lab.info will be directed to z3lab.info

RFCs are the great information for this.

https://www.ietf.org/rfc/rfc1912.txt