Stackable network units including registers for identifying trunk connection status of stacked units.

摘要

A stack of network units each includes a multiplicity of ports for receiving and forwarding addressed data packets and a forwarding engine which in response to address data selects at least one port for the forwarding of a data packet. A cascade connects the units and allows the transmission of a packet placed on said cascade by a unit to all the other units. Each unit is responsive to a packet received from the cascade to forward or discard the received packet according to predetermined forwarding rules. A trunk A includes a respective port of each of some but not necessarily all the units. Each unit 0-7 includes a 'trunk box member' register 100-107 indicating which of the units has at least one port connected in the trunk. When a first unit in the stack receives, at a port connected neither to the trunk nor the cascade, a packet destined for the trunk, the first unit directs that packet to a port connected to the trunk if the first unit has such a port and otherwise sends that packet to the cascade. When a second unit in the stack, having a port connected to the trunk, receives by way of the cascade from the first unit a packet destined for the trunk, the second unit determines with recourse to the forwarding rules, data identifying the first unit and the respective register whether to forward said packet to the trunk. The invention is particularly intended for use in stack-wide trunks operating according to 'local forwarding' and 'next-in-line' rules and allows units in the stack to be omitted from direction connection to the trunk.