Abstract:
A network device includes a plurality of ports configured to transmit and receive packets of data. A memory is configured to store a routing table. A forwarding engine is configured to transfer the packets of data between the plurality of ports based on the routing table. A processor is configured to define a routing interface. The routing interface comprises a group of the plurality of ports. The processor is configured to assign a media access control (MAC) address to the routing interface. The processor is configured to modify the routing table to direct each packet of data having the media access control (MAC) address as a destination address to a port in the routing interface.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 10/958,077, filed Oct. 4, 2004, now U.S. Pat. No. 7,606,230, which claims the benefit of U.S. Provisional Patent Application No. 60/569,728, filed May 10, 2004, the disclosures thereof incorporated by reference herein in their entirety. 
    
    
     BACKGROUND 
     The present invention relates generally to network communications. More particularly, the present invention relates to link aggregation in a network device. 
     The growing popularity of high-speed data communications has led to an increasing demand for high-bandwidth data channels that exceed the bandwidth of existing communication links. A solution that has enjoyed widespread acceptance is link aggregation, often referred to as “layer-2 trunking” or “trunking.” 
     Link aggregation is a method of combining multiple physical data communication links to form a single logical link, thereby increasing the capacity and availability of the communication channels between network devices such as servers, switches, end stations, and other network-enabled devices. For example, two or more Gigabit Ethernet or Fast Ethernet connections between two network devices can be combined to increase bandwidth capability and to create resilient and redundant links. 
     Link aggregation also provides load balancing, which is especially important for networks where it is difficult to predict the volume of data directed to each network device. Link aggregation distributes processing and communications activity evenly across a network so that no single network device is overwhelmed. 
     Link aggregation is documented in the Institute of Electrical and Electronics Engineers (IEEE) standard 802.3ad, which is incorporated by reference herein in its entirety. 
     However, conventional network devices employ silicon mechanisms to provide link aggregation, and so are limited in the number of trunks they can provide. Furthermore, many conventional network devices do not permit link aggregation at all. 
     SUMMARY 
     In general, in one aspect, the invention features a wireless network apparatus and corresponding method and computer program. It comprises a plurality of ports to transmit and receive data flows comprising packets of data; a memory to store a routing table; a forwarding engine to transfer the packets of data between the ports according to the routing table; and a processor to define a routing interface comprising a selected group of the ports, map a selected media access control (MAC) address to the routing interface, disable link aggregation between the ports in the routing interface, disable bridging between the ports in the routing interface, and modify the routing table to direct each of the data flows having the MAC address as a destination address to one of the ports in the routing interface. 
     Particular implementations can include one or more of the following features. The processor modifies the routing table entries for the ports in the routing interface to provide load balancing among the ports in the routing interface. The load balancing is based on Equal Cost Multi-Path Routing Protocol (ECMP). To define a routing interface, the processor allocates a virtual local-area network (ULAN) to the selected group of the ports. A multi-layer switch comprises the network device. 
     The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features will be apparent from the description and drawings, and from the claims. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1  shows a multi-layer switch in communication with a server over network links according to a preferred embodiment. 
         FIG. 2  shows a process for the multi-layer switch of  FIG. 1  to establish a routed trunk with the server of  FIG. 1  according to a preferred embodiment. 
     
    
    
     The leading digit(s) of each reference numeral used in this specification indicates the number of the drawing in which the reference numeral first appears. 
     DETAILED DESCRIPTION 
     Embodiments of the present invention employ routing techniques, for example in a multi-layer switch, to implement link aggregation without using conventional layer-2 link aggregation techniques, thereby creating what are referred to herein as “routed trunks.” A significant advantage of these routed trunks is that the number of routed trunks a switch can employ is not restricted by any link aggregation limit of the switch. Large numbers of routed trunks are especially useful when communicating with a large number of servers, which often requires a number of trunks that exceeds the link aggregation limit of conventional switches. 
     Network devices employing the routed trunks of the present invention are compatible with existing networks such as the Internet. The techniques disclosed herein are internal to the device employing them, and are transparent to other devices which can, but need not, employ those techniques. Thus embodiments of the present invention have broad applicability. 
       FIG. 1  shows a multi-layer switch  100  in communication with a network device  112  such as a server over network links  102  according to a preferred embodiment. A multi-layer switch is a switch that combines aspects of data link layer switches and network-layer switches, as is well-known in the relevant arts. But although embodiments of the present invention are described with respect to a multilayer switch, these embodiments are applicable to other sorts of network devices such as routers and the like. In addition, although embodiments of the present invention are described as establishing routed trunks with a server, these embodiments are equally applicable in establishing routed trunks with other sorts of network devices such as network switches and the like. 
     Multi-layer switch  100  comprises a plurality of ports  104 , a forwarding engine  106 , a processor  108 , and a memory  110 . Ports  104  transmit and receive data flows comprising packets of data. A data flow is an ordered set of packets transmitted from one network device to another, as is well-known in the relevant arts. Forwarding engine  106  transfers the packets between ports  104  according to entries in routing tables stored in memory  110  according to techniques well-known in the relevant arts. Processor  108  creates and modifies the routing tables according to other well-known techniques such as learning. 
       FIG. 2  shows a process  200  for multi-layer switch  100  to establish a routed trunk with server  112  according to a preferred embodiment. First a group  114  of the ports  104  that are in communication with server  112  is selected for routed link aggregation (step  202 ). The group  114  of ports  104  can be selected by the user manually or with the help of some automated process such as the link aggregation control protocol (LACP) documented in the Institute of Electrical and Electronics Engineers (IEEE) standard 802.3ad, which is incorporated by reference herein in its entirety. 
     Processor  108  then defines a routing interface comprising the selected group  114  of ports  104  according to techniques well-known in the relevant arts (step  204 ). In some embodiments, the routing interface is defined by allocating a virtual local area network (VLAN) to the selected group  114  of ports  104 . VLANs are documented in the Institute of Electrical and Electronics Engineers (IEEE) standard 802.3q, which is incorporated by reference herein in its entirety. 
     Processor  108  assigns one of the media access control (MAC) addresses belonging to multi-layer switch  100  to the routing interface (step  206 ). 
     As mentioned above, the routed trunks of the present invention provide the benefits and appearance of conventional link aggregation without employing conventional trunking, thereby permitting more trunks that conventional switches allow. Therefore, to prevent multi-layer switch  100  from employing conventional layer-2 trunking, processor  108  disables layer-2 link aggregation between the ports  104  in the routing interface (step  208 ). 
     If bridging were enabled between the ports  104  in the selected group  114 , traffic received from server  112  by one port  104  in the group  114  could be sent back to server  112  by one or more of the other ports  104  in the group  114 . To prevent this problem, processor  108  disables bridging between the ports  104  in the routing interface (step  210 ). 
     As mentioned above, a data flow is an ordered set of packets transmitted from one network device to another. As long as the order of the packets in each data flow is preserved, a network switch can employ any mechanism for trunking. To ensure that the packet order is preserved, processor  108  modifies the routing table to direct each of the data flows having the routing interface&#39;s MAC address as a destination address to one of the ports  104  in the routing interface (step  212 ). 
     Processor  108  optionally modifies the routing table entries in memory  110  for the ports  104  in the routing interface to provide load balancing among the ports  104  in the routing interface. One well-known routing protocol that can be used for load balancing is the Equal Cost Multi-Path Routing Protocol (ECMP), which provides multiple routed paths to an end destination. Again, as long as packet order is preserved within each data flow, any load-balancing technique can be used, while still maintaining compliance with applicable standards such as IEEE standards. 
     The routed trunk comprising the links between the selected group  114  of ports  104  and server  112  now performs in the same manner as a conventional trunk. Server  112  need not perform routed trunking, and indeed needs no knowledge of the routed trunking. To server  112 , the routed trunk appears the same as a conventional layer-2 trunk. The techniques described above can be used to establish additional routed trunks to server  112  or to other servers. Because these techniques are implemented using layer-3 mechanisms, the maximum number of trunks that multi-layer switch  100  can provide is limited only by the size of the routing table, which can be very large, rather than by the silicon area of switch  100 , as is the case in conventional layer-2 trunking. 
     The invention can be implemented in digital electronic circuitry, or in computer hardware, firmware, software, or in combinations of them. Apparatus of the invention can be implemented in a computer program product tangibly embodied in a machine-readable storage device for execution by a programmable processor; and method steps of the invention can be performed by a programmable processor executing a program of instructions to perform functions of the invention by operating on input data and generating output. The invention can be implemented advantageously in one or more computer programs that are executable on a programmable system including at least one programmable processor coupled to receive data and instructions from, and to transmit data and instructions to, a data storage system, at least one input device, and at least one output device. Each computer program can be implemented in a high-level procedural or object-oriented programming language, or in assembly or machine language if desired; and in any case, the language can be a compiled or interpreted language. Suitable processors include, by way of example, both general and special purpose microprocessors. Generally, a processor will receive instructions and data from a read-only memory and/or a random access memory. Generally, a computer will include one or more mass storage devices for storing data files; such devices include magnetic disks, such as internal hard disks and removable disks; magneto-optical disks; and optical disks. 
     Storage devices suitable for tangibly embodying computer program instructions and data include all forms of non-volatile memory, including by way of example semiconductor memory devices, such as EPROM, EEPROM, and flash memory devices; magnetic disks such as internal hard disks and removable disks; magneto-optical disks; and CD-ROM disks. Any of the foregoing can be supplemented by, or incorporated in, ASICs (application-specific integrated circuits). 
     A number of implementations of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, other implementations are within the scope of the following claims.