3com Corporation

Neil J Clifford

Daniel M O'Keeffe

Eoin O'Brien

David J Law

Paul J Moran

Peter Furlong

Eoghan Stack

Annette E Sohor

Derry M O'Donoghue

A stackable multi-port communication device for a packet-based data communication system, having a multiplicity of physical ports for the reception and dispatch of data in the form of packets, includes switch logic for selecting for a packet at least one destination selected from a multiplicity of ports which include a logical port common to a specified group of said physical ports. A cascade trunk logic, coupled to the switch logic, is used for determining, for the dispatch of a packet directed to said logical port, a selected port of said group of said physical ports; and a remote monitoring logic is used for forwarding a copy of the packet. The remote monitoring logic stores an indication of all the physical ports on the unit from which the copy may be forwarded by the remote monitoring logic and prevents the forwarding of the copy of the packet to any physical port which corresponds to the port selected by the cascade logic for the dispatch of said packet, whereby a packet which is forwarded from any of the specified group of physical ports is not duplicated by the remote monitoring logic.

Port mirroring across a trunked stack of multi-port communication devices

In a stack of multi-port network communication units each unit has a forwarding database, the units are connected by way of a cascade, and at least some of the units are connected to links constituting a trunk. When a unicast data packet is received at a first of said units and the unicast data packet has a destination address which is not the subject of an entry in the forwarding database of the first unit, the unicast data packet is sent by way of the cascade to the other units in the stack, accompanied by a flag. When a second unit has in its forwarding database an entry, associating the destination address with forwarding data, it sends a management packet indicating said destination address and the identity of said second unit, so that the database of the first unit can be immediately updated.

Method for synchronizing databases in stacked network units

A network unit includes a forwarding database which includes entries relating packet addresses to forwarding data and is operative to form linked chains of entries wherein the entries in a chain represent different packet addresses which are reduced by hashing to the same pointer for the database. A seed for a hashing algorithm is provided by a combination, such as an exclusive-OR combination, of part of an input address word and a selected word. Hashing is preferably performed in at least two cycles, wherein in one cycle a hash function is applied to a portion of the input address not including the part which is combined with the selected word to constitute a hash seed and in another (preceding) cycle a further part of the address and the aforementioned hash seed are subject the hash function. The selected word may be a software programmable mask and it is possible thereby to ensure a high degree of randomness in the hash seed and to reduce the incidence of convergence of different addresses to a common pointer.

Network unit including address hashing

Growing community of inventors

Dublin, Ireland

Neil J Clifford