Abstract:
A switch includes ports including a first port and a second port. A processor approves associations between the ports and addresses of packets. A memory stores entries having respective indicators indicating approval of an association between respective ports and addresses. The first port receives a first packet sent to the switch. The controller: determines whether one of the entries includes an address of the first packet; if none of the entries includes the address of the first packet, sends a first message to the processor requesting approval of the first packet; if one of the entries includes the address of the first packet, determines whether the indicator of the one of the entries indicates approval and based on this, sends the first message to the processor; receives a response from the processor based on the first message; and based on the response, forwards the first packet to the second port.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present disclosure is a continuation of U.S. patent application Ser. No. 12/917,405 (now U.S. Pat. No. 8,472,445), filed Nov. 1, 2010, which is a continuation of U.S. patent application Ser. No. 10/761,879 (now U.S. Pat. No. 7,826,452) filed Jan. 21, 2004, which claims the benefit of U.S. Provisional Patent Application Ser. No. 60/457,262 filed Mar. 24, 2003. The entire disclosures of the applications referenced above are incorporated herein by reference. 
    
    
     BACKGROUND 
     The present invention relates generally to data communication systems. More particularly, the present invention relates to address learning in data communication switches. 
     Self-routed packet data communication switches route packets according to addresses contained in the packets. For example, level-2 switches route each packet according to the destination media access control (MAC) address in the packet. Each switch comprises a forwarding database (FDB) that stores associations between MAC addresses and the ports of the switch. When a packet is received having with a particular destination MAC address, the switch transmits the packet through the port associated with the particular destination MAC address. 
     Some switches “learn” the FDB associations from the incoming packets. That is, when a packet is received with a particular source MAC address, the switch creates an association in the FDB between the particular source MAC address and the port on which the packet was received. That association is then used to route packets subsequently received by the switch with this MAC address as the destination. 
     For example, Ethernet switches that are compliant with the IEEE 802.1D-1998 specification are required to “learn” the FDB associations from the incoming packets. Learning can be automatic or controlled by a central processing unit (CPU). In either case the switch sends a notification message to the CPU each time the association between a MAC address and a port changes, for example when the switch receives a packet having a source MAC address that is not associated with a port, or when a MAC address associated with one port becomes associated with another port. 
     However, in controlled learning, the switch may receive many more packets having the new source MAC address, and therefore send many more notification messages to the CPU, before the CPU can respond to the first notification message. This plethora of unnecessary messages can burden the CPU unnecessarily, and can even provide an opportunity for a denial-of-service attack. 
     SUMMARY 
     A switch is provided and includes ports, a processor, a memory, and a controller. The ports include a first port and a second port. The processor is configured to approve associations between (i) the plurality of ports and (ii) addresses of packets. The memory is configured to store entries. Each of the entries has a respective indicator indicating approval or disapproval of an association between (i) one of the ports and (ii) one of the addresses of the packets. The first port is configured to receive a first packet sent to the switch. The controller is configured to: determine whether one of the entries includes an address of the first packet; if none of the entries includes the address of the first packet, send a first message to the processor requesting approval of the first packet; if one of the entries includes the address of the first packet, (i) determine whether the indicator of the one of the entries indicates approval, and (ii) based on whether the indicator of the one of the entries indicates approval, send the first message to the processor; receive a response from the processor based on the first message; and based on the response from the processor, forward the first packet to the second port. 
     In other features, a method is provided and includes approving, via a processor, associations between (i) ports of a switch and (ii) addresses of packets. The ports include a first port and a second port. Entries are stored in a memory. Each of the entries has a respective indicator indicating approval or disapproval of an association between (i) one of the ports and (ii) one of the addresses of the packets. A first packet sent to the switch is received at the first port. The method further includes determining whether one of the entries includes an address of the first packet. If none of the entries includes the address of the first packet, a first message is sent from a controller to the processor requesting approval of the first packet. The method further includes if one of the entries includes the address of the first packet, (i) determining whether the indicator of the one of the entries indicates approval, and (ii) based on whether the indicator of the one of the entries indicates approval, sending the first message from the controller to the processor. A response is received from the processor based on the first message. Based on the response from the processor, the first packet is forwarded to the second port. 
     In general, in one aspect, the invention features a method, apparatus, and computer-readable media for a switch comprising a plurality of network ports and a central processing unit (CPU) interface. It comprises receiving, on one of the network ports, a packet comprising a source media access control (MAC) address; sending, to the CPU interface, a request to approve an association between the one of the network ports and the source MAC address when no request to approve the association between the one of the network ports and the source MAC address has been sent to the CPU interface; and sending, to the CPU interface, the request to approve the association between the one of the network ports and the source MAC address when an association between the source MAC address and a different one of the network ports has been approved. 
     Particular implementations can include one or more of the following features. Implementations comprise determining whether an association exists between any of the network ports and the source MAC address. Determining whether an association exists between any of the network ports and the source MAC address comprises searching a forwarding database for the source MAC address. Implementations comprise determining whether no request to approve the association between the one of the network ports and the source MAC address has been sent to the CPU interface. Determining whether no request to approve the association between the one of the network ports and the source MAC address has been sent to the CPU interface comprises determining whether an unapproved association between the one of the network ports and the source MAC address exists. Determining whether the unapproved association between the one of the network ports and the source MAC address exists comprises determining whether the association between the one of the network ports and the source MAC address exists; and when the association between the one of the network ports and the source MAC address exists, determining whether the association between the one of the network ports and the source MAC address is approved. Determining whether the association between the one of the network ports and the source MAC address exists comprises searching a forwarding database for an entry comprising the source MAC address. Determining whether the association between the one of the network ports and the source MAC address is approved comprises determining whether an approval flag is set for the entry comprising the source MAC address. Implementations comprise creating an unapproved association between the one of the network ports and the source MAC address. Creating the unapproved association between the one of the network ports and the source MAC address comprises creating the association between the one of the network ports and the source MAC address; and marking the association between the one of the network ports and the source MAC address as unapproved. Creating the association between the one of the network ports and the source MAC address comprises creating an entry in a forwarding database, the entry identifying the one of the network ports and the source MAC address. Marking the association between the one of the network ports and the source MAC address as unapproved comprises setting an approval flag for the entry. Implementations comprise receiving, from the CPU interface, in response to the request to approve the association between the one of the network ports and the source MAC address, an approval of the association between the one of the network ports and the source MAC address; and clearing the approval flag for the entry. Implementations comprise receiving, from the CPU interface, in response to the request to approve the association between the one of the network ports and the source MAC address, a disapproval of the association between the one of the network orts and the source MAC address; and deleting the entry. Implementations comprise receiving, from the CPU interface, in response to the request to approve the association between the one of the network ports and the source MAC address, an approval of the association between the one of the network ports and the source MAC address; and approving the unapproved association between the one of the network ports and the source MAC address. Implementations comprise receiving, from the CPU interface, in response to the request to approve the association between the one of the network ports and the source MAC address, a disapproval of the association between the one of the network ports and the source MAC address; and deleting the unapproved association between the one of the network ports and the source MAC address. The packet further comprises a destination MAC address, and implementations comprise processing the packet according to the destination MAC address when an association between the destination MAC address and a further one of the network ports exists and the association between the destination MAC address and the further one of the network ports has been approved; and processing the packet without regard to the destination MAC address when no association between the destination MAC address and any of the network ports exists; and processing the packet without regard to the destination MAC address when the association between the destination MAC address and the further one of the network ports exists but the association between the destination MAC address and the further one of the network ports has not been approved. Processing the packet according to the destination MAC address comprises transmitting the packet from the further one of the network ports. Processing the packet without regard to the destination MAC address comprises transmitting the packet from all of the network ports but the one of the network ports. 
     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 network switch according to a preferred embodiment of the present invention. 
         FIG. 2  shows a learning process for the controller of the switch of  FIG. 1  according to a preferred embodiment of the present invention. 
         FIG. 3  shows another learning process for the controller of the switch of  FIG. 1  according to a preferred embodiment of the present invention. 
         FIG. 4  shows a forwarding process for the controller of the switch of  FIG. 1  according to a preferred embodiment of the present invention. 
     
    
    
     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 techniques to ensure that, for each new source media access control (MAC) address encountered by a switch, only one notification message is sent to the central processing unit (CPU), thereby reducing traffic between the CPU and the switch, reducing the workload of the switch and CPU, and reducing the opportunities for denial-of-service attacks on the switch. In particular, embodiments of the present invention send a notification message for a new source MAC address to the CPU only when no such notification message has been sent. Embodiments of the present invention keep track of whether a notification message has been sent to the CPU by creating an association between the source MAC address and the port on which the packet was received. The association is marked unapproved until a message is received from the CPU in response to the notification message. No notification message is sent for an unapproved association, thereby ensuring that only one notification message is sent to the CPU for each new source MAC address. 
     Embodiments of the present invention create an association between a source MAC address and a port by storing an entry in the forwarding database (FDB) of the switch. The entry includes the source MAC address and the port identifier for the port. Embodiments of the present invention record whether such an association is approved using a flag for each such entry, referred to herein as the approval flag. When the approval flag for an entry is set, the entry is referred to as an unapproved entry. When the approval flag for an entry is clear, the entry is referred to as an approved entry. Only approved entries are used for bridging packets. 
       FIG. 1  shows a network switch  100  according to a preferred embodiment of the present invention. Network switch  100  comprises a switch  102 , which can be fabricated as a single integrated circuit, and a central processing unit (CPU)  104 . Switch  102  comprises a controller  112  and a CPU interface  106  to permit controller  112  to communicate with CPU  104 . Switch  102  also comprises a plurality of network ports  114 A through  114 N for exchanging packets of data with a network  116  such as the Internet under the control of controller  112  and according to the contents of a forwarding database (FDB)  110  stored in a memory  108 . 
       FIG. 2  shows a learning process  200  for the controller  112  of the switch  102  of  FIG. 1  according to a preferred embodiment of the present invention. Learning process  200  begins when switch  102  receives a packet on one of network ports  114  (step  202 ). Controller  112  determines whether an association exists between the source MAC address of the packet and any of the network ports  114  (step  204 ), preferably by searching FDB  110  for an entry comprising the source MAC address. 
     If there is no entry in the FDB for the source MAC address of the packet, controller  112  determines whether learning is enabled for switch  102  (step  206 ). If learning is disabled, process  200  is complete (step  208 ). However, if learning is enabled, controller  112  creates an unapproved association, preferably by storing an entry in FDB  110  that comprises the source MAC address of the packet and the port identifier (PID) of the network port  114  on which the packet was received, and by setting an approval flag for the entry (step  210 ). Controller  112  also sends a notification message to CPU  104  that requests approval for the association (step  212 ). Then process  200  is complete (step  208 ). 
     However, if an association exists for the source MAC address (step  204 ), controller  112  determines whether FDB  110  is static (Step  214 ). If FDB  110  is static, process  200  is complete (step  208 ). But if FDB  110  is not static, controller  112  determines whether the association is approved, preferably by determining whether the approval flag is set for the association&#39;s FDB entry (step  216 ). If the approval flag is set, indicating that a notification message was sent to CPU  104  but no reply has been received, then process  200  is complete (step  208 ). 
     However, if the approval flag is clear (that is, not set), indicating that the entry has been approved by CPU  104  (step  216 ), then controller  112  determines whether the packet was received from the network port indicated in the association, preferably by comparing the port identifier (PID) in the FDB entry to the PID of the network port on which the packet was received (step  218 ). If the PIDs are the same, then process  200  is complete (step  208 ). 
     But if the PIDs differ (step  218 ), switch  102  must learn the new association. Therefore, controller  112  creates an unapproved association, preferably by storing an entry in FDB  110  that comprises the source MAC address of the packet and the port identifier (PID) of the network port  114  on which the packet was received, and by setting the approval flag for the entry (step  210 ). Controller  112  also sends a notification message to CPU  104  that requests approval for the association (step  212 ). Then process  200  is complete (step  208 ). 
       FIG. 3  shows another learning process  300  for the controller  112  of the switch  102  of  FIG. 1  according to a preferred embodiment of the present invention. Learning process  300  begins when switch  102  receives a reply from CPU  104  to a notification message (step  302 ). Controller  112  determines whether the reply message approves the association for which approval was requested in the notification message (step  304 ). If the reply message comprises a disapproval of the association, then controller  112  deletes the association, preferably by deleting the FDB entry for the association (step  306 ). 
     But if the reply message comprises an approval of the association (step  304 ), then controller  112  approves the association, preferably by clearing the approval flag for the FDB entry for the association (step  308 ). Controller  112  may also respond to other instructions in the reply message, for example by changing one or more attributes of the association. Controller  112  can delete associations in other ways as well. For example, controller  112  can delete an association when it reaches a certain age. In some embodiments, controller  112  routinely scrubs FDB  110  to delete associations older than a predetermined age. In such embodiments, CPU  104  need not send a reply message to disapprove an association, instead relying on the scrub process to delete the association. 
       FIG. 4  shows a forwarding process  400  for the controller  112  of the switch  102  of  FIG. 1  according to a preferred embodiment of the present invention. Process  400  begins when switch  102  receives a packet (step  402 ) comprising a destination MAC address. Controller  112  searches FDB  110  for an association for the destination MAC address (step  404 ). If no association exists for the destination MAC address, then controller  112  proceeds as though the destination MAC address is unknown (step  406 ). For example, controller  112  can transmit the packet from all of the network ports of the switch except the network port on which the packet was received. 
     However, if controller  112  finds an association for the destination MAC address in FDB  110  (step  404 ), controller  112  determines whether the association is approved, preferably by testing the approval flag for the association&#39;s FDB entry (step  408 ). If the approval flag is set, meaning the association is unapproved, then controller  112  proceeds as though the destination MAC address is unknown (step  406 ). 
     However, if the approval flag is clear (step  408 ), then controller  112  proceeds according to the destination MAC address (step  410 ). For example, controller  112  transmits the packet from the network port  114  that is associated with the destination MAC address in the FDB entry. 
     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.