The present invention relates to the field of local area networks in general and specifically to improvements in managing network traffic between local area network segments and the network backbone.
Local area networks are communication networks extending from several hundred to several thousand feet within a geographical region. These networks provide efficient and high-speed communications between host computers and other devices for the purposes of sharing resources and communicating in a distributed processing environment. For example, local area print servers connected to a local area network eliminate the need for dedicating a printer to each computer. Local area file and disk servers permit the shared use of large data bases without the cost of maintaining multiple copies of the data bases.
One type of local area network that has gained widespread acceptance is the Ethernet local area network. Ethernet is a carrier sense/multiple access with collision detection system (CSMA/CD) utilizing coaxial cable. This system is described in an article by P. M. Metcalfe and D. R. Boggs in Communications of the ACM, July, 1976, and is further described in IEEE specification 802. The Ethernet network transmits information between devices connected to the network in data packets or frames that contain a destination address corresponding to one or more of the devices.
A local area network such as Ethernet may connect several hundred or even thousands of devices or nodes. As the number of nodes on the local area network increases, and the traffic on the network also increases, the network may be divided into smaller segments in order to manage the network traffic more efficiently. Specifically, one or more local network segments may be created to isolate local message traffic from the rest of the network. This is particularly useful where, for example, the local traffic consists primarily of data packets transferred between the nodes on the local network segment and a disk server or other type of host computer.
The local segments of a network are connected to a network backbone for transferring data packets between other nodes on the network and other local segments. Networks and network segments are typically connected by using bridges. The function of a bridge is to receive data packets from one network or network segment and to forward those data packets to the other network or network segment if the data packet contains a destination address corresponding to a node on that other network or network segment. Thus, bridges must act as perfect filters between the networks.
A network bridge, however, is an expensive and complex device. In order for the bridge to filter all data packets transferred on the networks connected by the bridge perfectly and thus completely isolate the traffic on one network or network segment from the rest of the network and vice versa, the bridge must store large tables of addresses corresponding to the nodes on the networks. Furthermore, if the number of nodes on the overall network is large, it becomes impractical to filter all data packets from the network backbone to the local network segment perfectly.