It depends on si you want to delegate hosting le subdomain off to a différent DNS server (or to le même server, mais in a différent zone file). You delegate a zone quand you want certains autre entity to control it, such as a différent IT department ou organization.
If you do, alors you need NS records. If not, A ou CNAME records will suffice.
Let's say you have le domain example.com. Vous avez an A record for www.example.com et you want to create le subdomain info.example.com avec www.info.example.com as a host in it.
Delegation
In le this situation, let's further say you have two DNS servers that will be hosting that subdomain. (They could be le même servers that are currently hosting example.com.) In this case, you will create two NS entries in le example.com zone file:
info IN NS 192.168.2.2
info IN NS 192.168.2.3
On those two servers, you will create le info.example.com zone et populate it as you would tout autre domain.
www IN A 192.168.2.6
No delegation
Here, juste ajoutez unn A record in le example.com zone file, using a dot to indicate that you want to create le www.info host in le example.com domain:
www.info IN A 192.168.2.6
Using CNAME
The decision of si to use a CNAME is independent of le delegation choice. I generally like to use a CNAME for le "generic" names qui point to spécifique machine names. Par exemple, I might name mon machines using an organizational naming convention such as cartoon characters (daffy, elmer, mickey, etc.) ou something bureaucratic (sc01p6-serv) et point le generic names to them. If le IP address of le machine ever changes, J'ai besoin de look in seulement one place to modify it.
www IN CNAME sc01p6-serv
mail IN CNAME sc01p6-serv
sc01p6-serv IN A 192.168.2.6
