Modification of tag fields in Ethernet data packets

A method of modifying an Ethernet data packet, comprising:

• (i) determining whether the packet includes a VLAN tag header and a VLAN identification field;
• (ii) inserting, when the packet does not include a VLAN tag header and a VLAN identification field, a first field, including a first indication of the absence of the said VLAN tag header and said VLAN identification field, and a second field constituting a dummy field;
• and
• (iii) inserting in place of the VLAN tag header if said header and said VLAN identification field are present, a field including a second indication, denoting the presence of said VLAN identification field, and selected information.

A method of transmitting an Ethernet packet through a stack of network devices, said packet including a VLAN tag comprising a standard tag header and a VLAN identification field, the method comprising:

• (a) receiving the packet at a first device in said stack of devices;
• (b) performing determination whether said packet is to be dispatched externally of said stack from said first device or is to be dispatched from a second device in said stack;
• (c) in the event that said determination is that said packet is to be dispatched externally of said stack from said first device, forwarding said packet without modification of said standard tag header;
• and
• (d) in the event that said determination is that said packet is to be dispatched from said second device:
• (i) modifying said standard tag header to include selected information such that the tag header ceases to be a standard tag header, while retaining said VLAN identification field;
• (ii) transmitting said packet through said stack to said second device in said stack;
• and
• (iii) before said packet leaves said second device, replacing said selected information with said standard tag header.

A network device having ports for receiving and forwarding data packets conforming to an Ethernet standard, said network device being organized:

• (a) to receive at one of said ports an Ethernet packet having a standard VLAN tag header and a VLAN identification field;
• (b) to insert in place of said standard VLAN tag header a field of the same size including a first field indicating the presence of said VLAN identification field and a second field of proprietary information so that said standard VLAN tag header ceases to be a standard VLAN tag header;
• and
• (c) to retain in said Ethernet packet said VLAN identification field.

A stack of network devices for the reception and forwarding of an Ethernet packet including a VLAN tag comprising a standard tag header and a VLAN identification field, wherein

• (a) a first device in said stack of devices receives said Ethernet packet;
• (b) said first device makes a determination whether said packet shall be forwarded to an external network directly from said first device or shall be forwarded to a second device in said stack;
• (c) in the event that said determination is that said packet shall be forwarded to an external network directly from said first device, said first device forwards said packet to said external network without modification of said VLAN tag header;
• (d) in the event that said determination is that said packet shall be forwarded to said second device, said first device modifies said standard tag header to include selected information while retaining said VLAN identification field;
• (e) said second device in said stack receives said Ethernet data packet from said first device;
• and
• (f) said second device replaces said selected information with said standard tag header before said Ethernet data packet leaves said second device.

A network device for the forwarding and reception of Ethernet data packets, said network device including packet processing means organized:

• (i) to determine whether a received packet includes a VLAN tag header and a VLAN identification field;
• (ii) to insert in said received packet, when said received packet does not include a VLAN tag header and a VLAN identification field, a first field, including a first indication of the absence of said VLAN tag header and said VLAN identification field, and a second field constituting a dummy field;
• and
• (iii) to insert in place of said VLAN tag header if said VLAN header and said VLAN identification field are present in said received packet, a field including a second indication, denoting the presence of said VLAN identification field, and selected information.

A method of transmitting an Ethernet data packet within a stack of units acting as a single logical entity, comprising:

• receiving at one of said units said Ethernet data packet, which includes a standard VLAN tag header and a VLAN identification field;
• inserting in place of the standard VLAN tag header a field of the same size including selected stack information such that the VLAN tag header ceases to be a standard VLAN tag header, while retaining said VLAN identification field;
• and
• elsewhere in said stack, decoding the selected information.

A stack of units acting as a single logical entity, wherein:

• a first unit is organized to receive an Ethernet data packet which includes a standard VLAN tag header and a VLAN identification field;
• said first unit inserts in place of said standard VLAN tag header a field of the same size including selected stack information such that the VLAN tag header ceases to be a standard VLAN tag header, while retaining said VLAN identification field;
• and
• a second unit is organized to receive said Ethernet data packet from said first unit and to decode the selected stack information.