Most computers in organisations connect to a network using a LAN. These networks normally consist of a backbone, which is the common link to all the networks within the organization. This backbone allows users on different network segments to communicate and allows data into and out of the local network. Figure 25.1 shows a local area network which contains various segments: LAN A, LAN B, LAN C, LAN D, LAN E and LAN F. These are connected to the local network via the BACKBONE 1. Thus, if LAN A talks to LAN E then the data must travel out of LAN A, onto BACKBONE 1, then into LAN C and through onto LAN E.