A network administrator is creating a subnet that needs a maximum of two networks in the DMZ. Which of the following subnet masks should the administrator use?

255.255.255.0 (/16) represents a Class B network boundary and defines a single very large network with 65,534 host addresses rather than creating multiple subnets.

255.255.255.0 (/24) defines a single Class C-sized network block with 254 usable host addresses and does not subdivide the space into two separate subnets.

A subnet mask of 255.255.255.128 (/25) borrows exactly one bit from the host portion of a /24 network, creating 2^1 = 2 equal subnets each with 126 usable host addresses. This precisely satisfies the requirement for a maximum of two networks in the DMZ without over-allocating address space or under-segmenting the network.

255.255.255.254 (/31) is defined in RFC 3021 for point-to-point links with only two addresses and is not appropriate for creating two routable subnets in a DMZ serving multiple hosts.