The network access lists are usually the first line of defense against outside intrusions and attacks. Generally speaking, routers and switches process packets at a much faster rate than servers, because they utilize hardware such as Ternary Content-Addressable Memory (TCAM). They do not need to see the application layer information, rather they just examine the layer 3 and layer 4 information, and decide whether the packets can be forwarded on or not. Therefore, we generally utilize network device access lists as the first step in safeguarding our network resources.
As a rule of thumb, we want to place access lists as close to the source (client) as possible. Inherently, we also trust the inside host and distrust the clients outside of our network boundary. The access list is therefore usually placed on the inbound direction on the external facing network interface...