|  | 9.5 | Microsegmentation of a Network
| 9.5.3 | A flat network
In many LANs, hubs and switches are interconnected as a series. What this means is that the switches must maintain MAC address not only for hosts that are directly connected to one of its switch ports, but also MAC addresses of hosts connected to other switches and hubs. In Figure , Switch 1 and Switch 2 are interconnected. If Hosts A, B, C, and D send information to Server H, Switch 2 will “learn” that these Hosts (their MAC addresses) can all be reached via Switch 2’s port 1. Figure , shows what Switch 2 SAT table would like. Remember, that if the switch does not have the destination MAC address in its SAT table, then it must flood the frame out all ports. A completely switched network with all switches (and hubs) is known as a “flat network.” A flat network is a LAN made up entirely of hubs and switches, no routers. All hosts on this LAN are on the same network or subnetwork. These networks are easy to maintain, as there are no routers, so adding a new host or other device is a relatively simple operation. However, a flat network has several disadvantages, including a single Layer 3 broadcast domain. As we will see later, a Layer 2 broadcast like an ARP Request will travel to every host and device on the LAN. These and other layer 2 broadcasts can use up a great deal of a LANs available bandwidth. There are other disadvantages as well, including less manageability of network traffic and security. In a flat network, once the switches have learned about what MAC addresses are on which ports, the network traffic will flow accordingly. Except for the placement of the switches, the network administrator has little or no control over the path of the frames.