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.

1. A method of identifying a virtual network associated with a data frame when transmitter 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, a value of 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 type 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  a ) inserting between said second type field and said virtual network identifier field a virtual network identifier type field; and  
         2  b ) 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  a ) inserting between said second type field and said virtual network identifier field a virtual network identifier length field; and  
         2  b ) 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 a value of 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, a value of 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  a ) inserting between said type field and said virtual network identifier field a virtual network identifier type field; and  
         2  b ) 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  a ) inserting between said type field and said virtual network identifier field a virtual network identifier length field; and  
         2  b ) 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. The method of  claim 1  wherein said virtual network identifier field is an integer number of bytes long. 
     
     
       18. The method of  claim 17  wherein said virtual network identifier field is  4  bytes. 
     
     
       19. The method of  claim 8  wherein said virtual network identifier field is an integer number of bytes in length. 
     
     
       20. The method of  claim 19  wherein said virtual network identifier field is a multiple of  4  bytes. 
     
     
       21. The method of  claim 13  wherein said virtual network identifier field is an integer number of bytes long. 
     
     
       22. The method of  claim 21  wherein said virtual network identifier field is  4  bytes. 
     
     
       23. A method of identifying a virtual network associated with a data frame transmitted between a communications medium and a shared communications medium, the method comprising:
   a )  obtaining a first data frame from the communications medium, the first data frame comprising a data field and either an e - type or a data length field having a corresponding value indicating a protocol type or a length of the data field, respectively; and        b )  producing a second data frame using the first data frame, the second data frame comprising a vtype field, a virtual network identifier field, a virtual network identifier type field, the data field, and whichever of the e - type field or data length field that the first data frame contains, a value of the vtype field indicating that the second data frame comprises the virtual network identifier field, and the virtual network identifier field having a virtual network identifier field value corresponding to the virtual network;        wherein the second data frame is configured such that the vtype field will be transmitted before the virtual network identifier type field, the virtual network identifier type field before the virtual network identifier field, and the virtual network identifier field before whichever of the e - type field or the data length field that the second data frame contains.     
     
     
       24. The method of  claim 23  further comprising transmitting the second frame via the shared communications medium. 
     
     
       25. The method of  claim 23  wherein the virtual network identifier field value is an integer number of bytes in length. 
     
     
       26. The method of  claim 25  wherein the virtual network identifier field value is a multiple of four bytes in length. 
     
     
       27. The method of  claim 26  wherein the virtual network identifier field value is four bytes in length. 
     
     
       28. The method of  claim 23  wherein a value of the virtual network identifier type field indicates a type of the virtual network identifier field value. 
     
     
       29. The method of  claim 28  wherein the second data frame further comprises a virtual network identifier length field having a corresponding value indicating a length of the virtual network identifier field value, wherein the second frame is configured such that the virtual network identifier length field will be transmitted after the virtual network identifier type field and before the virtual network identifier field. 
     
     
       30. The method of  claim 23  wherein producing the second data frame includes determining the virtual network identifier field value in accordance with at least one rule. 
     
     
       31. The method of  claim 30  wherein determining the virtual network identifier field value in accordance with the at least one rule uses at least one of a number of a port through which the first data frame is obtained, a protocol type of the first data frame, a MAC address of the first data frame, a network-layer source address of the first data frame, and a time of day when the first data frame is received. 
     
     
       32. The method of  claim 23  wherein the second data frame is produced with the e- type field if the first data frame is an Ethernet frame and is produced with the data length field if the first data frame is an LLC frame.   
     
     
       33. A method of identifying a virtual network associated with a data frame transmitted between a communications medium and a shared communications medium, the method comprising:
   a )  obtaining a first data frame from the communications medium, the first data frame comprising a data field and either an e - type field or a data length field having a corresponding value indicating a protocol type or a length of the data field, respectively; and        b )  producing a second data frame using the first data frame, the second data frame comprising a vtype field, a virtual network identifier field, a virtual network identifier length field, the data field, and whichever of the e - type field or the data length field that the first data frame contains, a value of the vtype field indicating that the second data frame comprises the virtual network identifier field, and the virtual network identifier field having a virtual network identifier field value corresponding to the virtual network;        wherein the second data frame is configured such that the vtype field will be transmitted before virtual network identifier length field, the virtual network identifier length field before the virtual identifier field, and the virtual network identifier field before whichever of the e - type field or the data length field that the second data frame contains.     
     
     
       34. The method of  claim 33  further comprising transmitting the second frame via the shared communications medium. 
     
     
       35. The method of  claim 33  wherein the virtual network identifier field value consists of an integer number of bytes. 
     
     
       36. The method of  claim 35  wherein the virtual network identifier field value is a multiple of four bytes in length. 
     
     
       37. The method of  claim 36  wherein the virtual network identifier field value is four bytes in length. 
     
     
       38. The method of  claim 33  wherein a value of the virtual network identifier length field indicates a length of the virtual network identifier field value. 
     
     
       39. The method of  claim 38  wherein the second data frame further comprises a virtual network identifier type field having a corresponding value indicating a type of the virtual network identifier field value, wherein the second frame is configured such that the virtual network identifier type field will be transmitted after the type field and before the virtual network identifier length field. 
     
     
       40. The method of  claim 33  wherein producing the second data frame includes determining the virtual network identifier field value in accordance with at least one rule. 
     
     
       41. The method of  claim 40  wherein determining the virtual network identifier field value in accordance with the at least one rule uses at least one of a number of a port through which the first data frame is obtained, a protocol type of the first data frame, a MAC address of the first data frame, a network- layer source address of the first data frame, and a time of day when the first data frame is received.   
     
     
       42. The method of  claim 33  wherein the second data frame is produced with the e- type field if the first data frame is an Ethernet frame and is produced with the data length field if the first data frame is an LLC frame.   
     
     
       43. In a network device comprising a first port coupled to a local area network ( LAN )  and a second port coupled to a shared communications medium, a method of transmitting a data frame associated with the LAN via the second port, the method comprising:      transmitting destination and source media access control addresses,        transmitting a virtual network type field having a value indicating that a virtual network identifier field will be transmitted;        transmitting at least one of a virtual network identifier type field and a virtual network identifier length field, a value of the virtual network identifier type field indicating a type of the virtual network identifier field, and a value of the virtual network identifier length field indicating a length of the virtual network identifier field; and        transmitting the virtual network identifier field having a value associated with the LAN.     
     
     
       44. The method of  claim 43  wherein transmitting at least one of a virtual network identifier type field and a virtual network identifier length field includes transmitting both the virtual network identifier type field and the virtual network identifier length field. 
     
     
       45. The method of  claim 44  wherein the transmitting occurs in an order of: destination media access control address, source media access control address, virtual network type field, virtual network identifier type field, virtual network identifier length field, and virtual network identifier field. 
     
     
       46. The method of  claim 45  further comprising transmitting a data field. 
     
     
       47. The method of  claim 46  wherein transmitting the data field occurs after transmitting the virtual network identifier field. 
     
     
       48. The method of  claim 47  further comprising transmitting either an e- type field or a data length field having a corresponding value indicative of a protocol type or a length of the data field, respectively.   
     
     
       49. The method of  claim 48  wherein transmitting whichever of the e- type field or the data length field occurs after transmitting the virtual network identifier field and before transmitting the data field.   
     
     
       50. A network device comprising:
   a first port configured to be coupled to a local area network  ( LAN ) ;        a second port configured to be coupled to a shared communications medium;        a processing unit configured to receive a first data frame via the first port, the first data frame including a destination address field, a source address field, either an e - type field or a data length field having a corresponding value indicating a protocol type or a length of a data field, respectively, and the data field, the processing unit being further configured to produce a second data frame and transmit the second data frame via the second port, the second data frame including the destination address field, the source address field, a virtual network type field having a value indicating that the second data frame includes a virtual network identifier field, at least one of a virtual network identifier type field and a virtual network identifier length field, the virtual network identifier field, whichever of the e - type field or the data length field was received, and the data field, the virtual network identifier field having a value indicative of the LAN, the virtual network identifier type field having a value indicating a type of the virtual network identifier field and the virtual network identifier length field having a value indicating a length of the virtual network identifier field.     
     
     
       51. The network device of  claim 50  wherein the second data frame includes both the virtual network identifier type field and the virtual network identifier length field. 
     
     
       52. The network device of  claim 51  wherein the processing unit is configured to transmit components of the second data frame in an order of: virtual network type field, virtual network identifier type field, virtual network identifier length field, and virtual network identifier field. 
     
     
       53. The network device of  claim 51  wherein the control unit is configured to transmit components of the second data frame in an order of: destination address, source address, virtual network type field, virtual network identifier type field, virtual network identifier length field, virtual network identifier field, whichever of the e- type field or the length field that the second data frame contains, and data field.   
     
     
       54. The network device of  claim 50  wherein the processing unit is configured to produce the second data frame by determining the virtual network identifier field in accordance with at least one rule. 
     
     
       55. The network device of  claim 54  wherein determining the virtual network identifier field in accordance with the at least one rule uses at least one of a number of the first port, a protocol type of the first data frame, a MAC address of the first data frame, a network-layer source address of the first data frame, and a time of day when the first data frame is received. 
     
     
       56. The network device of  claim 50  wherein the processing unit is configured to produce the second data frame with the e- type field if the first data frame is a type - encoded frame and to produce the second data frame with the data length field if the first data frame is a length - encoded frame.   
     
     
       57. A method of identifying a virtual network associated with a data frame transmitted between a communications medium and a shared communications medium, the method comprising:
   a )  obtaining a first data frame from the communications medium, the first data frame comprising a data field and either an e - type field or a data length field having a corresponding value indicating a protocol or a length of the data field, respectively; and        b )  producing a second data frame using the first data frame, the second 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 second data frame is associated with the virtual network, and the virtual network identifier field having a virtual network identifier field value corresponding to the virtual network.     
     
     
       58. The method of  claim 57  further comprising obtaining the virtual network identifier field value dynamically. 
     
     
       59. The method of  claim 58  wherein the virtual network identifier field value is obtained from a network- wide authority.   
     
     
       60. The method of  claim 59  wherein the network- wide authority is a network administrator.   
     
     
       61. The method of  claim 57  wherein the virtual network identifier field has one of a plurality of formats, and wherein the type field value further indicates which of the plurality of formats the virtual network identifier field has. 
     
     
       62. The method of  claim 57  wherein the at least one other field includes a plurality of other fields. 
     
     
       63. The method of  claim 57  wherein producing the second data frame includes determining the virtual network identifier field value in accordance with at least one rule. 
     
     
       64. The method of  claim 63  wherein determining the virtual network identifier field value in accordance with the at least one rule uses at least one of a number of a port through which the first data frame is obtained, a protocol type of the first data frame, a MAC address of the first data frame, a network- layer source address of the first data frame, and a time of day when the first data frame is received.   
     
     
       65. A method of identifying a virtual network associated with a data frame transmitted between a communications medium and a shared communications medium, the method comprising:
   a )  obtaining a first data frame from the communications medium, the first data frame comprising a data field and either an e - type field or a data length field having a corresponding value indicating a protocol or a length of the data field, respectively; and        b )  producing a second data frame using the first data frame, the second data frame comprising a type field, and a virtual network header including a virtual network identifier field, the type field having a value indicating that the second data frame is associated with the virtual network, and the virtual network identifier field having a virtual network identifier field value corresponding to the virtual network;        wherein the virtual network header has an associated format and the type field value further indicates which of a plurality of formats the associated format is.     
     
     
       66. The method of  claim 65  wherein the associated format is a format of the virtual network identifier field value. 
     
     
       67. The method of  claim 65  wherein producing the second data frame includes determining the virtual network identifier field value in accordance with at least one rule. 
     
     
       68. The method of  claim 67  wherein determining the virtual network identifier field value in accordance with the at least one rule uses at least one of a number of a port through which the first data frame is obtained, a protocol type of the first data frame, a MAC address of the first data frame, a network- layer source address of the first data frame, and a time of day when the first data frame is received.