Why might two devices fail to communicate even if NIC and IP are correct?

• A. The gateway is misconfigured
• B. The DNS is not configured
• C. The subnet mask is not correct for this network
• D. The IP address is reserved

Answer: (C)

Subnet mask defines which part of an IP address identifies the local network and which part identifies the host. It tells devices whether a destination on the wire is on the same LAN or must be sent through a router. If that mask is wrong for the actual network design, the two devices won’t agree on whether the other device is on the local segment or remote. One side might try ARP to reach the other directly, while the other believes the destination is off-network and forwards it to a gateway that may not know how to reach it. In short, a mismatched or incorrect subnet mask disrupts the local delivery decision, so traffic never reaches the other device despite having a valid NIC and IP. Fixing the subnet mask so it matches the intended network allows direct communication on the local link.