What is the simplest way to filter network traffic?

The simplest way to filter network traffic is by using a firewall, which can be configured to allow or block traffic based on predefined rules such as IP addresses, ports, and protocols. Additionally, implementing access control lists (ACLs) on routers can also help in filtering traffic by specifying which packets are permitted or denied. For more granular control, using intrusion detection systems (IDS) can help identify and filter malicious traffic.