VLAN frame format

Abstract

In a network device such as a network switch having a port coupled to a communications medium dedicated to a single virtual local area network and another port coupled to a communications medium shared among multiple virtual local area networks for transmitting data frames between the dedicated communications medium and the shared communications medium, a method of identifying the virtual network associated with each data frame received by the network switch when transmitting the data frames over the shared communications medium. The method comprises receiving data frames from the dedicated communications medium coupled to one port, and, with respect to each data frame so received, inserting a new type field and a virtual network identifier field. The contents of the new type field indicate the data frame comprises a virtual network identifier field. The method further includes placing a value in the virtual network identifier field identifying the virtual network associated with the data frame and transmitting the data frame over the shared communications medium. Upon receipt of the data frames from over the shared communications medium, another network device can discern from the virtual network identifier field in each data frame the virtual network from which the data frames were received and determine whether to forward the data frames accordingly.

We claim: 
     
       1. A method of identifying a virtual network associated with a data frame when transmitting said data frame between a communications medium and a shared communications medium, comprising the steps of:
 a) receiving said data frame from said communications medium, said data frame comprising a first type field and a data field;   b) inserting a second type field at a location within said data frame preceding said first type field, said second type field indicating said data frame comprises a virtual network identifier field;   c) inserting said virtual network identifier field at a location between said second typo field and said first type field;   d) assigning a first value to said virtual network identifier field, said first value corresponding to said virtual network; and   e) transmitting said data frame over said shared communications medium.   
     
     
       2. The method of  claim 1 , further comprising the steps of:
 1) inserting between said second type field and said virtual network identifier field a virtual network identifier type field; and   2) assigning a second value to said virtual network identifier type field indicating a type of said first value in said virtual network identifier field.   
     
     
       3. The method of  claim 1 , further comprising the steps of:
 1) inserting between said second type field and said virtual network identifier field a virtual network identifier length field; and   2) assigning a second value to said virtual network identifier length field indicating a length of said first value in said virtual network identifier field.   
     
     
       4. The method of  claim 1  wherein said virtual network identifier field is 4 bytes. 
     
     
       5. The method of  claim 1  wherein said virtual network identifier field is a multiple of 4 bytes. 
     
     
       6. The method of  claim 1  wherein said first type field indicates a protocol type. 
     
     
       7. A method of identifying a virtual network associated with a data frame when transmitting said data frame between a communications medium and a shared communications medium, comprising the steps of:
 a) receiving said data frame from said communications medium, said data frame comprising a length field and a data field;   b) inserting a type field at a location within said data frame preceding said length field, said type field indicating said data frame comprises a virtual network identifier field;   c) inserting said virtual network identifier field at a location between said type field and said length field;   d) assigning a first value to said virtual network identifier field, said first value corresponding to said virtual network; and   e) transmitting said data frame over said shared communications medium.   
     
     
       8. The method of  claim 7 , further comprising the steps of:
 1) inserting between said type field and said virtual network identifier field a virtual network identifier type field; and   2) assigning a second value to said virtual network identifier type field indicating a type of said first value in said virtual network identifier field.   
     
     
       9. The method of  claim 7 , further comprising the steps of:
 1) inserting between said type field and said virtual network identifier field a virtual network identifier length field; and   2) assigning a second value to said virtual network identifier length field indicating a length of said first value in said virtual network identifier field.   
     
     
       10. The method of  claim 8  wherein said virtual network identifier field is a multiple of 4 bytes. 
     
     
       11. In a network device, a method of transmitting a virtual network identifier in a data frame transmitted on a shared communications medium coupled to said network device, comprising:
 a) transmitting a preamble field;   b) transmitting a destination and source media access control address field;   c) transmitting a first type field whose contents indicate said virtual network identifier is present in said data frame;   d) transmitting a virtual network identifier field containing said virtual network identifier;   e) transmitting a second type field whose contents indicate a protocol type associated with said data frame; and,   f) transmitting a data field.   
     
     
       12. The method of  claim 11  wherein said virtual network identifier field is 4 bytes. 
     
     
       13. In a network device having a first port coupled to a local area network (LAN) segment and a second port coupled to a shared communications medium, a method of associating a virtual network with a data frame received from said LAN segment and transmitted to said shared communications medium, comprising:
 a) receiving said data frame at said first port, said data frame comprising a type field and a data field;   b) replacing a first value in said type field representing a protocol type with a second value indicating said data frame comprises a virtual network identifier field;   c) inserting said virtual network identifier field in said data frame between said type field containing said second value and said data field;   d) assigning a value representing said virtual network to said virtual network identifier field; and   e) transmitting said data frame from said second port.   
     
     
       14. The method of  claim 13  further comprising:
 a) inserting a new type field between said virtual network identifier field and said data field; and 
 b) assigning said first value representing said protocol type to said new type field to preserve said protocol type. 
 
     
     
       15. The method of  claim 13  wherein said virtual network identifier field is 4 bytes. 
     
     
       16. The method of  claim 13  wherein said virtual network identifier field is a multiple of 4 bytes. 
     
     
       17. A system for transmitting a data frame associated with a virtual network, the data frame being transmitted between a communications medium and a shared communications medium, the system comprising:
 a first network device coupled to the shared communications medium and configured:   to receive the data frame from the communications medium, the data frame comprising a destination media access control (MAC) address, a source MAC address and a data field;   to insert a type field at a location within the data frame between the MAC addresses and the data field, a value of the type field indicating that the data frame comprises a virtual network identifier field;   to insert the virtual network identifier field at a location between the type field and the data field;   to assign a value to the virtual network identifier field, the value corresponding to the virtual network; and   to transmit the data frame over the shared communications medium and   a second network device comprising a port coupled to the shared communications medium and configured:   to receive the data frame by:   receiving the destination and source MAC addresses;   receiving the type field having the value indicating that the data frame comprises a virtual network identifier field; and   receiving the virtual network identifier field including reading the virtual network identifier field in accordance with the value of the type field to determine the value of the virtual network identifier field; and   to transmit the data frame at least toward the virtual network corresponding to the value of the virtual network identifier field.    
     
     
       18. The system of claim 17, wherein the second network device is configured to transmit the data frame at least toward the virtual network corresponding to the value of the virtual network identifier field by forwarding at least part of the received data frame on a port selected based at least in part on the value of the virtual network identifier field.  
     
     
       19. The system of claim 18, wherein, when the port selected based at least in part on the value of the virtual network identifier field is connected to a dedicated communications medium, the second network device is configured to forward at least part of the received data frame by:
 removing the type field and the virtual network identifier field from the data frame; and   forwarding the data frame without the type field and without the virtual network identifier field on the selected port of the second network device.    
     
     
       20. The system of claim 19, wherein the second network device is configured to forward the data frame without the type field and without the virtual network identifier field by:
 calculating a frame check sequence for the data frame with the type field and the virtual network identifier field removed; and   forwarding the data frame with the calculated frame check sequence.    
     
     
       21. A system for transmitting a data frame associated with a virtual network between a communications medium and a shared communications medium, the system comprising:
 a first network device coupled to the shared communications medium and configured;   to receive the data frame from the communications medium, the data frame comprising a destination media access control (MAC) address, a source MAC address and a data field;   to insert a type field at a location within the data frame between the MAC addresses and the data field, a value of the type field indicating that the data frame comprises a virtual network identifier field;   to insert the virtual network identifier field at a location between the type field and the data field;   to assign a value to the virtual network identifier field, the value corresponding to the virtual network and   to transmit the data frame over the shared communications medium; and   a second network device comprising a port coupled to the shared communications medium and configured:   to receive the data frame, by:   receiving the destination and source MAC addresses;   receiving the type field having the value indicating that the data frame comprises the virtual network identifier field; and   receiving the virtual network identifier field having the value associated with the virtual network including reading the virtual network identifier field in accordance with the value of the type field to determine the value associated with the virtual network; and   to transmit the data frame at least toward the virtual network corresponding to the value of the virtual network identifier field.    
     
     
       22. The system of claim 21, wherein the second network device is configured to transmit the data frame at least toward the virtual network corresponding to the value of the virtual network identifier field by forwarding at least part of the received data frame on a port selected based at least in part on the value of the virtual network identifier field.  
     
     
       23. The system of claim 22, wherein, when the port selected based at least in part on the value of the virtual network identifier field is connected to a dedicated communications medium, the second network device is configured to forward at least part of the received data frame by:
 removing the type field and the virtual network identifier field from the data frame; and   forwarding the data frame without the type field and without the virtual network identifier field on the selected port of the second network device.    
     
     
       24. The system of claim 23, wherein the second network device is configured to forward the data frame without the type field and without the virtual network identifier field by:
 calculating a frame check sequence for the data frame with the type field and the virtual network identifier field removed; and   forwarding the data frame with the calculated frame check sequence.    
     
     
       25. A system for transmitting a data frame associated with a virtual network between a communications medium and a shared communications medium, the system comprising:
 a first network device coupled to the shared communications medium and configured:   to receive the data frame from the communications medium, the data frame comprising a destination media access control (MAC) address, a source MAC address, an original type or length field and a data field;   to insert a type field at a location within the data frame between the MAC addresses and the original type or length field, a value of the type field indicating that the data frame is associated with a virtual network and that the data frame comprises a virtual network header including a virtual network identifier field and at least one other field, the virtual network identifier field having a value corresponding to the virtual network;   to insert the virtual network header at a location between the type field and the data field;   to assign a value to the virtual network identifier field, the value corresponding to the virtual network; and   to transmit the data frame over the shared communications medium; and   a second network device coupled to the shared communications medium and configured:   to receive the data frame, the data frame comprising the type field, and the virtual network header;   to read the type field to determine if the data frame is associated with a virtual network;   in response to determining that the data frame is associated with a virtual network, to read the value of the virtual network identifier field to determine the virtual network with which the data frame is associated; and   to transmit the data frame at least toward the virtual network corresponding to the value of the virtual network identifier field.    
     
     
       26. The system of claim 25, wherein the second network device is configured to transmit the data frame at least toward the virtual network corresponding to the value of the virtual network identifier field by forwarding at least part of the received data frame on a port selected based at least in part on the value of the virtual network identifier field.  
     
     
       27. The system of claim 26, wherein, when the port selected based at least in part on the value of the virtual network identifier field is connected to a dedicated communications medium, the second network device is configured to forward at least part of the received data frame by:
 removing the type field and the virtual network header from the data frame; and   forwarding the data frame without the type field and without the virtual network header on the selected port of the second network device.    
     
     
       28. The system of claim 27, wherein the second network device is configured to forward the data frame without the type field and without the virtual network header by:
 calculating a frame check sequence for the data frame with the type field and the virtual network header removed; and   forwarding the data frame with the calculated frame check sequence.