2008 Oct 18
Ethernet LANs use Hubs and Switches as building blocks. They have physical interfaces for connecting Ethernet cables. Each computer system in a LAN is connected to one of these physical interfaces via an Ethernet cable. Internally, the Hub or Switch has backplane where data is transmitted between the physical inetrfaces.
A Hub is relatively simple, it broadcasts information received on any physical interface to all other physical interfaces. When on system transmits via Hub all other systems on the LAN connected to that Hub see the data.
data +----------+
//===========>| System 2 |
|| +----------+
+--------+ ||
+----------+ data | |<==// data +----------+
| System 1 |<======>| Hub |<===============>| System 3 |
+----------+ | |<==\\ +----------+
+--------+ ||
|| data +----------+
\\===========>| System 4 |
+----------+
A Switch has added intelligence, enabling it to listen to the MAC addresses of traffic moving through it. The switch associates MAC addresses with each of its physical interfaces, and will only pass on packets to the single physical interface asscoiated with the destination MAC address. A Switch can either auto discover these associations or a network administratot can configure the MAC address and physical interface associations.
+----------+
/----------->| System 2 |
| +----------+
+--------+ |
+----------+ data | |<---/ +----------+
| System 1 |<======>| Switch |<--------------->| System 3 |
+----------+ | |<==\\ +----------+
+--------+ ||
|| data +----------+
\\===========>| System 4 |
+----------+
2005-2008