Which of the following is a common use of a firewall?

Filtering incoming and outgoing network traffic is a core function of a firewall. Firewalls serve as a barrier between a trusted internal network and untrusted external networks, such as the internet. By analyzing and controlling the data packets that enter or exit a network, firewalls help protect systems from unauthorized access and various types of cyber threats. This includes blocking harmful traffic while allowing legitimate communications to occur, thereby maintaining the integrity and security of the network.

The other options describe functions that are not specifically related to the firewall's role. Establishing a network connection typically involves networking hardware such as routers or switches, while connecting to the internet relies on Internet Service Providers (ISPs) and network connectivity protocols. Additionally, firewalls do not inherently enhance network speed; their primary purpose is security rather than performance optimization.