Redundant link management switch for use in a stack of switches and method thereof

#This application is a continuation-in-part of copending application Ser. No. 10/041,505, filed Jan. 10, 2002.

#1. Field of the Invention

#The invention relates to computer networks, and more particularly to a stackable switch offering resilient stacking and backup management.

#The present invention will be described by way of exemplary embodiments, but not limitations, illustrated in the accompanying drawings in which like references denote similar elements, and in which:

#FIG. 1 illustrates stacking of switches;

#FIG. 2A is a stack of switches forming a closed-loop link topology in accordance with the invention;

#As illustrated in FIG. 2A, switches 210a˜d are stacked together to form a switch stack 200. Each switch—to wit, 210a, 210b, 210c and 210d—is equipped with a stacking module, 212a, 212b, 212c and 212d, respectively. Each stacking module includes an uplink port and a downlink port. On the switch 210b of the stack 200 for example, uplink port 214b connects a next-higher switch, i.e. the switch 210a, and downlink port 216b connects a next-lower switch, i.e. the switch 210c. According to the invention, every two switches are connected to form a closed-loop link topology. That is, a link 220a is connected between a downlink port 216a of the stacking module 212a and an uplink port 214b of the stacking module 212b. A link 220b is connected between a downlink port 216b of the stacking module 212b and an uplink port 214c of the stacking module 212c. As well, a link 220c is connected between a downlink port 216c of the stacking module 212c and an uplink port 214d of the stacking module 212d. Specifically, there is a link 220d connected between a downlink port 216d of the stacking module 212d and an uplink port 214a of the stacking module 212a. The switches 210a˜d are connected together in the above-described manner to form the closed-loop link topology instead of a simple chain.

#At least one switch in the switch stack 200 can be equipped with an agent module, e.g. management module 222. In one embodiment, the management module 222 is installed in the switch 210b. The management module 222 allows administrators to configure or monitor the switch stack using the network management applications. In addition, the management module 222 performs a redundant link management function. When the management module 222 is installed, the switch 210b becomes a redundant link management switch in the switch stack 200. It should be understood to those skilled in the art that additional switches equipped with the management modules to provide fault tolerance are contemplated by the principles of the invention. As shown in FIG. 2D, for instance, a second management module 222′ is installed in the switch 210c to serve as a backup.

#Returning again to FIG. 2A, every unit IDs 218a˜d in the respective switches continues changing at power-on if the switches 210a˜d are connected with the closed-loop link topology in accordance with the invention. During power-on initialization, the management module 222 informs the stacking module 212b to block the signals of downlink port 216b so that the link 220b (marked ‘T’ in FIG. 2A) is terminated or isolated. As a result, the switches 210a˜d in the stack 200 transmit/receive control signals over a path including the links 220a, 220c, 220d like the simple chain, in which the link 220b is a redundant link for the stack 200. After initialization, digit ‘1’ is assigned to the unit ID 218b of the switch 210b, digit ‘2’ is assigned to the unit ID 218a of the switch 210a, and digits ‘3’ and ‘4’ are respectively assigned to the unit IDs 218d, 218c of the switch 210d, 210c.