Broadcast and multicast traffic reduction in stacking systems

#I. Stackable Devices and Stacking Systems

#As known in the art, a “stackable device” is a network device (typically an L2/L3 switch) that can operate independently as a standalone device or in concert with one or more other stackable devices in a “stack” or “stacking system.” FIG. 1A illustrates the front face of an exemplary stackable device 100 according to an embodiment. As shown, stackable device 100 includes a set of data ports 102, a set of stacking ports 104, and a console port 106. Data ports 102 are operable for connecting stackable device 100 to one or more hosts and/or data networks. Stacking ports 104 are operable for linking stackable device 100 (via “stacking links”) to other devices in the same stacking system/topology. Unlike data ports 102, stacking ports 104 are considered internal ports (like a switching fabric in a chassis-based switch) and thus only forward packets within the stacking system. Stacking ports 104 can be dedicated ports (i.e., ports designed specifically for stacking) or high bandwidth data uplink ports that operate in a stacking mode. Console port 106 is operable for accessing the management console of stackable device 100 in order to perform various device management functions.

#FIG. 1B illustrates an exemplary stacking system 120 according to an embodiment. As shown, stacking system 120 comprises a number of stackable devices 122, 124, and 126 (each similar to stackable device 100 of FIG. 1A) that have been linked together via their respective stacking ports. In the example of FIG. 1B, stackable devices 122, 124, and 126 form a ring topology. In addition, stackable device 124 is designated as the “master” device of stacking system 120, which means that stackable device 124 serves as the point of user contact for all management functions of system 120. For instance, stackable device 124 can accept and process user commands directed to the overall configuration of stacking system 120. Stackable device 124 can also communicate with non-master devices 122 and 126 as needed in order to propagate various types of management commands and data to those devices.

#FIG. 1A depicts a stackable device according to an embodiment.

#FIG. 1B depicts a stacking system according to an embodiment.

#FIG. 1C depicts an advanced stacking system according to an embodiment.

#In the following description, for purposes of explanation, numerous examples and details are set forth in order to provide an understanding of various embodiments. It will be evident, however, to one skilled in the art that certain embodiments can be practiced without some of these details, or can be practiced with modifications or equivalents thereof.

#The present disclosure describes techniques for reducing broadcast and multicast traffic within a stacking system. At a high level, a master device of the stacking system can automatically determine a minimal set of VLAN associations for the stacking links in the system, where the minimal set of VLAN associations minimize or eliminate “unnecessary” transmission of broadcast/multicast packets through the system's topology (i.e., the transmission of broadcast/multicast packets to stackable devices that do not have any data ports in the packets' VLANs). In one embodiment, the determination of the minimal set of VLAN associations can be based on a complete set of single-source spanning trees that are calculated in view of the topology. The master device can then cause VLANs to be assigned to stacking ports in the stacking system in accordance with the minimal set of VLAN associations.

#With these techniques, the amount of broadcast and multicast traffic flowing through the system can be substantially reduced in comparison to existing practices/implementations (which typically involve associating all VLANs to all stacking ports). This, in turn, can avoid link saturation in large stacking systems, or advanced stacking systems that mix high bandwidth and low bandwidth stacking ports/links. Further, the algorithm for determining the minimal set of VLAN associations is not limited to certain types of topologies, and instead can apply to any general, mesh-like topology. The details of this algorithm are described in the sections that follow.