Digital Equipment Corporation

Jeffrey A Lomicka

Willem A Engelse

Gary V Vacon

Stephen D Metzger

Pat Gili

An arrangement for selective filtering, e.g. one-way filtering, of messages received by a 2-port bridge from stations connected to two LANs of an extended LAN is provided. The bridge includes a message filtering database containing the addresses of all stations connected to one of the LANs. The database also contains a list of higher-level protocols employed by the stations. Associated with each protocol-type is information used by the bridge to dispose of the message. The message filtering database comprises a single table memory capable of supporting both ports of the bridge. The selective filtering process involves a two-step analysis by the bridge to determine whether to discard the message or forward it to another port. The analysis is based on a destination address and a protocol-type of the received message.

Disposition filtering of messages using a single address and protocol

Automatic tracking of the topology of an extended local area network by augmenting a station address list kept by a bridge with a list of repeater numbers and repeater port numbers. The bridge periodically iterates through its list of stations to select a station address. The selected address table is forwarded to all of the repeaters connected to the bridge. The repeaters watch for the selected address appearing as a source address in a message on one of their ports. If the address is seen, they report the repeater port number back to the bridge. Because the repeaters are interconnected such that a predetermined port number is always used as the common port between repeaters, any possible ambiguities are eliminated.

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Maynard, MA, United States of America

Jeffrey A Lomicka