That is only a forward zone and as @bodgit answered that is perfectly valid for all use cases.
The main potential disadvantage of the above is an administrative one. For a single zone not too much of an issue but with many host names in many different domains much more so: in case of a change of ip-address every
A record with that ip-address will need to be updated, where
CNAME records will automatically follow the ip-address change of their target FQDN and would not need to be updated.
For a reverse zone, doing something almost similar is AFAIK also technically valid:
10.1.168.192.in-addr.arpa. IN PTR subdomain1.example.com.
10.1.168.192.in-addr.arpa. IN PTR subdomain2.example.com.
10.1.168.192.in-addr.arpa. IN PTR subdomain3.example.com.
but that won't have the effect people usually seem to expect.
subdomain1.example.com. will always point to 192.168.1.10 but the reverse lookup will most of the time NOT point back to subdomain1.example.com.
The above will become a round-robin DNS record where:
- 1/3 of the responses will return an "incorrect" response of subdomain2.example.com.
- 1/3 of the responses will return an also "incorrect" response of subdomain3.example.com.
- only a 33% chance exists that the "correct" response of subdomain1.example.com. will be seen.