omatically disable selected routes Because both repeaters and gateways are network specific, within the extended network to create a 'loop-free' network. This in bridges and routers emerged as the most popular solutions to inter- effect changes a looped or 'mesh' network into a tree structure for networking problems. which there is one and only one active path from one station to any Nevertheless, considerable confusion remains as to when it is best and every other station. However, the Spanning Tree algorithm to bridge and when it is best to route. This confusion has been carries the disadvantage that alternate paths, and in many cases, compounded by several factors. Firstly, conventional bridge func- expensive wide area network bandwidth, remain unused and tionality has expanded into the territory originally monopolised by become active only when other paths fail. routers. Secondly, routers are now performing at speeds tradition- The latest bridges are now capable of automatically configuring ally associated with bridges, and thirdly the developments in both themselves upon insertion into a network, and have become true bridge and router technology have been accompanied by a host of 'plug and play' devices. totally new hybrid internetworking products. 56.5.6 Developments in router technology 56.5.5 Developments in bridging technology While developments in bridge technology were occurring, router The first major development in bridging was the addition of 'learn- technology was also advancing. ing'. Learning enabled bridges to automatically track the source Conventional routers only supported the interconnection of local addresses of data packets received by the bridge in order to build up area networks that had identical characteristics (e.g. Ethernet net- a learned address table of locally attached devices. This capability works). Similarly, these routers only operated for a single routing enabled the bridge to automatically and dynamically filter local protocol over the extended network, such as TCP/IP or DEC