You should not need the subnet mask if you are storing endpoint IP addresses.
Networks are said to be super netted when grouped together. So you would not x out the left (network) side of the address, you would x out the right side, i.e., 10.12.x.x/24. Each x represents 8 bits of address space.
IPv4 endpoints are configured with a subnet mask that specifies how many of its 32 address bits represents network addressing vs host numbering. Each network has a network address (all 0's) and a broadcast address (all 1's).
The network address is synonymous to the subnet, e.g., the 10.1 network (10.1.0.0/16).