Access Lists
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 by utilizing high-speed memory hardware such as ternary content-addressable memory (TCAM). They do not need to see the application layer information. Instead, they just examine the layer 3 and layer 4 headers and decide whether the packets can be forwarded. Therefore, we generally utilize network device access lists as a 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 clients beyond our network boundary. The access list is, therefore, usually placed in the inbound direction on the external facing network interface(s). In our lab scenario, this means we will place an inbound access list at Ethernet2/2 on nyc-cor-r1, which is directly...
