Shared spanning tree protocol

A device for use in a computer network having a plurality of virtual local area network (VLAN) designations, each VLAN designation being classified as either a primary VLAN or a secondary VLAN wherein each secondary VLAN designation is associated with zero, one or more than one primary VLAN designations, the device comprising:

• a plurality of ports for use in connecting the device to one or more neighboring devices;
• one or more frame objects operatively coupled to the plurality of ports for receiving, transmitting and temporarily storing frames;
• spanning tree circuitry coupled to the one or more frame objects and configured and arranged to receive, process and generate bridge protocol data units (BPDUs) tagged with a primary VLAN designation so as to place one or more ports in a forwarding mode for each primary VLAN designation;
• and
• shared spanning tree circuitry configured and arranged to receive, process and forward shared spanning tree protocol data units (SST-PDUs) tagged with a VLAN designation and, where the VLAN tag of the SST-PDU corresponds to a primary VLAN to which one or more secondary VLANs are associated, the SST-PDU configured to contain at least one secondary VLAN designation, the shared spanning tree circuitry further configured and arranged to associate all secondary VLAN designations contained in a received SST-PDU with the primary VLAN designation with which the received SST-PDU is tagged,
• wherein data frames received at the device and tagged with a given secondary VLAN designation are forwarded through the one or more ports placed in a forwarding mode for the primary VLAN designation associated with the given secondary VLAN designation of the data frames, provided that the given secondary VLAN designation is associated with only one primary VLAN designation.

A network system having a plurality of predefined virtual local area network (VLAN) designations comprising:

• at least one shared spanning tree region in which each VLAN designation is classified as either a primary VLAN or a secondary VLAN, the at least one shared spanning tree region including a plurality of shared spanning tree devices configured and arranged to exchange and process bridge protocol data unit (BPDU) frames each tagged with a primary VLAN designation so as to create a shared spanning tree for each primary VLAN designation within the respective shared spanning tree region, and to associate each secondary VLAN with a single primary VLAN;
• and
• at least one single spanning tree region connected to the at least one shared spanning tree region, the at least one single spanning tree region including a plurality of single spanning tree devices configured and arranged to exchange and process untagged BPDUs to create a single spanning tree within the respective region,
• wherein untagged BPDUs entering the at least one shared spanning tree region from the at least one single spanning tree region are mapped to a preselected common spanning tree within the respective shared spanning tree region, and wherein tagged BPDUs entering the at least one single spanning tree region are tunneled through the respective single spanning tree region such that the tagged BPDUs are not processed by the single spanning tree devices.

A network system having a plurality of predefined virtual local area network (VLAN) designations comprising:

• at least one enhanced per-VLAN spanning tree region, the at least one enhanced per-VLAN spanning tree region including a plurality of enhanced per-VLAN spanning tree devices configured and arranged to exchange and process bridge protocol data unit (BPDU) frames each tagged with a VLAN designation so as to create a separate spanning tree for each VLAN designation within the respective enhanced per-VLAN spanning tree region;
• and
• at least one single spanning tree region connected to the at least one enhanced per-VLAN spanning tree region, the at least one single spanning tree region including a plurality of single spanning tree devices configured and arranged to exchange and process untagged BPDUs to create a single spanning tree within the respective single spanning tree region,
• wherein untagged BPDUs entering the at least one enhanced per-VLAN spanning tree region from the at least one single spanning tree region are mapped to a preselected common spanning tree within the respective enhanced per-VLAN spanning tree region, and wherein tagged BPDUs entering the at least one single spanning tree region are tunneled through the respective single spanning tree region such that the tagged BPDUs are not processed by the single spanning tree devices.

A computer readable medium containing executable program instructions for creating a plurality of shared spanning trees each defining a loop-free path among a plurality of devices in a computer network having a plurality of predefined virtual local area network (VLAN) designations, the executable program instructions comprising program instructions for:

• classifying each VLAN designation as either a primary VLAN or a secondary VLAN;
• exchanging among the devices bridge protocol data units (BPDUs) each tagged with a given primary VLAN designation so as to form a shared spanning tree corresponding to each primary VLAN designation;
• and
• associating each secondary VLAN with a single primary VLAN at one or more devices.

A shared spanning tree protocol data unit (SST-PDU) for use in associating one or more secondary virtual local area network (VLAN) designations with a single primary VLAN designation, the primary and secondary VLAN designations being predefined in a computer network having a plurality of devices, the SST-PDU generated and transmitted by a first device and received by and stored in a memory of a second device, the SST-PDU comprising:

• a first field containing a given primary VLAN designation;
• and
• a second field containing at least one secondary VLAN designation associated with the given primary VLAN designation contained in the first field, wherein the second field comprises:
• a first sub-field containing a list of all secondary VLAN designations associated with the primary VLAN designation contained in the first field;
• a second sub-field identifying the first secondary VLAN designation contained in the first sub-field;
• and
• a third sub-field containing a value corresponding to the size of the first sub-field.

A method of creating a plurality of shared spanning trees each defining a loop-free path among a plurality of intermediate network devices in a computer network having a plurality of predefined virtual local area network (VLAN) designations, the method comprising the steps of:

• exchanging protocol data units (PDUs) among the intermediate network devices;
• processing received PDUs so as to form a plurality of shared spanning trees such that there is more than one shared spanning tree but less than the total number of predefined VLAN designations;
• associating each VLAN designation with a single shared spanning tree at a plurality of intermediate network devices;
• and
• forwarding messages tagged with a given VLAN designation along the loop-free path defined by the single shared spanning tree to which the given VLAN designation is associated.

A method of creating a plurality of shared spanning trees each defining a loop-free path among a plurality of devices in a computer network having a plurality of predefined virtual local area network (VLAN) designations, the method comprising the steps of:

• classifying each VLAN designation as either a primary VLAN or a secondary VLAN;
• exchanging among the devices bridge protocol data units (BPDUs) each tagged with a given primary VLAN designation so as to form a shared spanning tree corresponding to each primary VLAN designation;
• and
• associating each secondary VLAN with a single primary VLAN at a plurality of devices,
• whereby messages tagged with a given secondary VLAN designation are forwarded along the loop-free path corresponding to the primary VLAN designation to which the given secondary VLAN is associated.