Which method can improve the security of a WiFi network?

Using MAC address filtering can enhance the security of a WiFi network by allowing only devices with specific MAC (Media Access Control) addresses to connect to the network. This method helps create a whitelist of authorized devices, effectively blocking any unauthorized devices from accessing the network, even if they know the WiFi password.

While it's important to note that MAC address filtering is not a foolproof security method, it can serve as an additional layer of security. Intruders can sometimes spoof their MAC address to match a permitted device, but this makes it more challenging for casual attackers.

In contrast, increasing transmission power may improve the range of the network but can also increase the risk of unauthorized access from a greater distance. Changing the frequency band can help reduce interference but does not inherently secure the network. Enhancing buffer size is unrelated to securing the network, as it pertains to performance rather than access control. Therefore, the most effective choice for improving the security of a WiFi network in this context is indeed the use of MAC address filtering.