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 as identifier field is a multiple of 4 bytes. 
     
     
       17. A method of transmitting a data frame to a virtual network associated with the data frame, the data frame being transmitted between a communications medium and a shared communications medium, the method comprising:
 a) receiving the data frame, the data frame comprising a type field, and a virtual network header including a virtual network identifier field and at least one other field, the type field having a value indicating that the data frame is associated with a virtual network, and the virtual network identifier field having a virtual network identifier field value corresponding to the virtual network;   b) reading the type field and determining that the data frame is associated with a virtual network;   c) in response to determining that the data frame is associated with a virtual network, reading the virtual network identifier field value to determine the virtual network with which the data frame is associated; and   d) transmitting the data frame at least toward the virtual network corresponding to the virtual network identifier field value.   
     
     
       18. The method of claim 17 wherein the virtual network identifier field value is in one of a plurality of formats, and the method further comprises determining which format the virtual network identifier field value is in based upon a value of the type field, and using the determined format to determine the virtual network identifier field value. 
     
     
       19. The method of claim 17 wherein the virtual network header further includes at least one of a virtual network identifier type field having a value indicative of a type of the virtual network identifier field and a virtual network identifier length field having a value indicative of a length of the virtual network identifier field, the method further comprising reading the at least one of the virtual network identifier type field and the virtual network identifier length field. 
     
     
       20. The method of claim 19 wherein the virtual network header includes the virtual network identifier type field, the method further comprising reading the virtual network identifier type field to determine a format of the virtual network identifier field value and using the determined format to determine the virtual network identifier field value. 
     
     
       21. The method of claim 17 wherein the at least one other field includes a plurality of other fields. 
     
     
       22. A method of transmitting a data frame to a virtual network associated with the data frame, the data frame being transmitted between a communications medium and a shared communications medium, the method comprising:
 a) receiving the data frame, the data frame comprising a type field, and a virtual network header having an associated format and including a virtual network identifier field, the type field having a value indicating which of a plurality of formats the associated format is and that the data frame is associated with a virtual network, and the virtual network identifier field having a virtual network identifier field value corresponding to the virtual network;   b) reading the type field and determining that the data frame is associated with a virtual network and determining the format;   c) in response to determining that the data frame is associated with a virtual network and determining the format, reading the virtual network identifier field in accordance with the determined format to determine the virtual network with which the data frame is associated; and   d) transmitting the data frame at least toward the virtual network corresponding to the virtual network identifier field value.   
     
     
       23. The method of claim 22 wherein the associated format is a format of the virtual network identifier field value. 
     
     
       24. The method of claim 17, wherein transmitting the data frame at least toward the virtual network corresponding to the virtual network identifier field value comprises 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. 
     
     
       25. The method of claim 24 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, forwarding at least part of the received data frame comprises:
 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.   
     
     
       26. The method of claim 25, wherein the dedicated communications medium is dedicated to a virtual network associated with the value of the virtual network identifier field. 
     
     
       27. The method of claim 25, wherein forwarding the data frame without the type field and without the virtual network identifier field comprises:
 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.   
     
     
       28. The method of claim 24 wherein, when a port which is eligible to receive the data frame based on a destination media access control address is assigned a virtual network identifier corresponding to the value of the virtual network identifier field of the data frame, forwarding at least part of the received data frame comprises:
 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 port.   
     
     
       29. The method of claim 28, wherein forwarding the data frame without the type field and without the virtual network identifier field comprises:
 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.   
     
     
       30. The method of claim 22, wherein transmitting the data frame at least toward the virtual network corresponding to the virtual network identifier field value comprises 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. 
     
     
       31. The method of claim 30 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, forwarding at least part of the received data frame comprises:
 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.   
     
     
       32. The method of claim 31 wherein the dedicated communications medium is dedicated to a virtual network associated with the value of the virtual network identifier field. 
     
     
       33. The method of claim 31 wherein forwarding the data frame without the type field and without the virtual network identifier field comprises:
 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.   
     
     
       34. The method of claim 30 wherein, when a port which is eligible to receive the data frame based on a destination media access control address is assigned a virtual network identifier corresponding to the value of the virtual network identifier field of the data frame, forwarding at least part of the received data frame comprises:
 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 port of the network device.   
     
     
       35. The method of claim 34, wherein forwarding the data frame without the type field and without the virtual network identifier field comprises:
 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.