G VIA SPANNING DEVICES 11.7.1 Repeaters A repeater is nothing more than a regenerative repeater (see Section 6.6). It extends a LAN. It does not provide any kind of segmentation of a LAN, except the physical regen- eration of the signal. Multiple LANs with common protocols can be interconnected with repeaters, in effect making just one large segment. A network using repeaters must avoid multiple paths, as any kind of loop would cause data to circulate indefinitely and could ultimately make the network crash. The multiple path concept is shown in Figure 11.14. The following example shows how a loop can be formed. Suppose two repeaters connect CSMA/CD LAN segments as shown in Figure 11.14. Station #1 initiates an interchange with station #3, both on the same segment (upper in the figure). As data packets or frames are transmitted on the upper segment, each repeater will transmit them unnecessarily to the lower segment. Each repeater will receive the repeated packet on the lower segment and retransmit it once again on the upper segment. As one can see, any LAN segment #1 (repeater repeater LAN segment #2 Figure 11.14 Repeaters in multiple paths. (Courtesy of Hewlett-Packard Co., Ref. 9.) 6The adding of dummy octets (bytes) to meet minimum frame length requirements. 11.7 LAN INTERWORKING VIA SPANNING DEVICES traffic introduced into this network will circulate indefinitely around the loop created by the two repeaters. On larger networks the effects can be devastating, although perhaps less apparent (Ref. 9). 11.7.2 LAN Bridges Whereas repeaters have no intelligence, bridges do. Bridges can connect two LANs, at the data-link or MAC protocol level. There are several varieties of bridges, depending on the intelligence incorporated. There is the transparent bridge that builds a list of nodes the bridge sees transmitting on either side. It isolates traffic and will not forward traffic that it knows is destined to another station on the same side of the bridge as the sending station. The bridge is able to isolate traffic ac