VLAN frame format

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.

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.

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.

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.

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.