 Ethernet network segment is a sec- tion of network where devices can communicate using layer-2 MAC addresses. To communicate outside of an Ethernet segment, an additional device, such as a router, is required. Collisions are also limited to collision domains. A collision domain is an area of an Ethernet network where collisions can occur. If one station can prevent another from sending because it has the network in use, these stations are in the same collision domain. A broadcast domain is the area of an Ethernet network where a broadcast will be propagated. Broadcasts stay within a layer-3 network (unless forwarded), which is usually bordered by a layer-3 device such as a router. Broadcasts are sent through switches (layer-2 devices), but stop at routers. Many people mistakenly think that broadcasts are contained within switches or virtual LANs (VLANs). I think this is due to the fact that they are SO contained in a properly designed network. If you connect two switches with a crossover cable-one configured with VLAN 10 on all ports, and the other configured with VLAN 20 on all ports- hosts plugged into each switch will be able to communicate if they are on the same IP network. Broadcasts and IP networks are not limited to VLANs, though it is very tempting to think SO. Chapter 2: Hubs and Switches Figure 2-5 shows a network of hubs connected via a central hub. When a frame enters the hub on the bottom left on port 1, the frame is repeated out every other port on that hub, which includes a connection to the central hub. The central hub in turn repeats the frame out every port, propagating it to the remaining hubs in the net- work. This design replicates the backbone idea, in that every device on the network will receive every frame sent on the network. Port 4 Port 5 Port 6 Port 7 Port 4 Port 5 Port 6 Port 7 Port 0 Port 1 Port 2 Port 3 Port 0 Port 1 Port 2 Port 3 Port 4 Port 5 Port 6 Port 7 Port 0 Port 1 Port 2 Port 3 Port 4 Port 5 Port 6 Port 7 Port 4 Port 5 Port 6 Port 7 Port 0 Port 1 Port 2 Port 3 Port 0 Port 