Understanding firewall rules

Firewall rules are another crucial component of network architecture, acting as the first line of defense (perimeter) in network security. Essentially, they are a set of guidelines that dictate how data packets are allowed to enter or leave a network. Network architects must be well-versed not only in understanding how firewall rules are applied on security devices but also in how they affect IT infrastructure, its distributed components, and end user’s/application’s capabilities to reach services.

Let’s consider an example.

We want to create two rules: allow HTTP traffic (port 80) from the internal network (192.168.1.0/24) to the internet while denying all other traffic, and block all SSH traffic from external sources to a specific server (for example, 192.168.1.10) within the internal network.

Figure 7.27 shows the configuration, as configured on a Palo Alto firewall appliance:

Figure 7.27 –...