We have a existing class-c network with IP address range 11.22.33.44/24 (just for example). My domain controller has been configured within this subnet. So all servers within this subnet have subnet mask configured to 255.255.255.0.

Now we have got a new subnet with IP address 11.22.88.99/24 (note that only last 2 octets have changed). I want all new hosts in this new subnet to join my existing DC. For this we have configured firewall properly so allow this. (so there is no issue with firewall).

But initially I was not able to join hosts in new subnet in existing domain. Later I doubted on subnet mask used in domain controller (255.255.255.0) and for testing purpose I changed it to 255.255.0.0, it worked like charm, i was able to join subnet-2 hosts in subnet-1 domain.

Now i am wondering whether it will be good practice to change subnet mask of a class-c network to 255.255.0.0? Can any issues arise due to this? Experts please provide your opinion.