Using a Backbone to Connect the Enterprise
Up to this point, I have discussed how to connect individual workstations in an Ethernet LAN. The hub-based LAN is a broadcast domain in which all connected stations must be capable of receiving a data transmission from all other workstations in the LAN when using hubs. Switches allow for a huge reduction in the collisions on a network, provided either that LAN communications are mostly local or that the switch has a faster uplink to the rest of the LAN.
If other technologies were not available to connect these diverse broadcast domains called LANs, it would not be possible to have the Internet, which is nothing more than an interconnection of hundreds of thousands of smaller networks.
Chapter 10, "Routers," explains how routers work and how they can be used to create larger networks composed of multiple LANs. To put it succinctly, these devices can create a larger network because each network joined by a router is a separate network segment in itself, subject only to the limitations of individual cabling and protocol requirements. Broadcast domains are Layer 2 LAN segments that operate on the Network Layer (Layer 3) of the OSI model. Routers operate at the Network Layer and allow for a hierarchical organization of all networks connected to the Internet as well as all the separate LANs we've just discussed. Routers make decisions about sending packets to other networks and can use many types of high-speed protocols on the LAN-to-LAN or LAN-to-WAN connections.
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