255.255.255.128 is the correct answer. Windows does not allow you to input CIDR for network configurations. 255.255.255.192 is a /26 netmask, 255.255.255.0 is a /24 netmask.
Classless Inter-Domain Routing (CIDR, or ) is a method for allocating IP addresses and IP routing. The Internet Engineering Task Force introduced CIDR in 1993 to replace the previous addressing architecture of classful network design in the Internet. Its goal was to slow the growth of routing tables on routers across the Internet, and to help slow the rapid exhaustion of IPv4 addresses.
IP addresses are described as consisting of two groups of bits in …