Mastering™ Network Security, Second Edition

3.4. Routers

Routers are used to connect logical networks, which is why they are sometimes referred to in the IP world as gateways. Figure 3.6 shows the effect of adding a router to a network. Notice that protocols on either side of the device must now use a unique logical network address. Information destined for a nonlocal system must be routed to the logical network on which the system resides. The act of traversing a router from one logical network to another is referred to as a hop. When a protocol hops a router, it must use a unique logical network address on both sides.

So how do systems on one logical network segment find out what other logical segments exist on the network? Routers can either be statically programmed with information ...