Answer:
A Subnet Mask
Step-by-step explanation:
A Subnet mask is used by the TCP/IP protocol to determine whether a host is on the local Subnet or on a remote network.
In TCP/IP, the parts of the IP address that are used as the network and host addresses are not fixed, so the destination host address 192.168.10.100 cannot be determined by the network host (192.168.10.200) unless it has more information. This information is supplied in another 32-bit number called a Subnet mask.