Intranet Example

Configuring the static route to null0 on an internal company router would prevent connectivity to the defined network because all traffic to that destination would be forwarded to a nonexistent interface. In Figure 2-8, Workstation A would not be capable of connecting to Server C, the development server used by the Research and Development department. The result is that the Research and Development department would be capable of seeing the rest of the organization. Indeed, the rest of the world can see the Research and Development department in a routing table. Any attempt to direct traffic to the network will be unsuccessful, however. The first router that sees the traffic will statically route it to the null interface, which metaphorically is a black hole. No error messages will be sent to the transmitting node because the traffic was successfully routed—although, unfortunately, to a black hole. This is considered beneficial for several reasons, one of which is additional security.

WARNING Because the static route is entered into the routing table, it is important to remember that all the rules of static routing apply. If the router hears of the destination route via another source, it is ignored in favor of the static route that has a lower administrative distance (which gives it a higher priority).

Figure 2-8 The Use of the Null Interface Within an Organization

Figure 2-8 The Use of the Null Interface Within an Organization

autonomous, and silicon switching. These functions are now supported, particularly if NetFlow features are turned on. In this context, switching refers to traffic forwarding, a Cisco solution that was implemented in the earliest of Cisco's products and that has been consistently enhanced.

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