Subnet masking is a Ethernet network Host local/remote identifier when presented to the TCP/IP protocol; it establishes the Host's Local and Network address.
A Subnet mask is a 32-bit number that masks an IP address, and divides the IP address into network address and host address. Subnet Mask is made by setting network bits to all "1"s and setting host bits to all "0"s. It is used mainly for restricting the number of Hosts on any given network segment (subnet).
The most commonly used mask is 255.255.255.0 (11111111 11111111 11111111 00000000) which limits the number of Hosts on the respective subnet to 254.
The OP mask, 255,0,0,0 (11111111 00000000 00000000 00000000) expands the Host limit count to 16,777,216.
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