A firewall is the key component of network security, acting as the guard against malicious traffic, data loss, and unauthorized access. Traditionally, a firewall was put at the perimeter to determine which traffic to let into the network and which to keep out. Today, it’s recommended to have a firewall at the core of your network as well, such as an internal segmentation firewall, as threats do slip in and spread. A firewall platform can be hardware, software, or a combination.