Spanning tree loop guard

A method for preventing the formation of loops by an intermediate network device having a plurality of ports for receiving and forwarding network messages to one or more other devices, the method comprising the steps of:

• executing a Rapid Spanning Tree Protocol (RSTP) at the intermediate network device to transition at least one of the intermediate network device's ports among a plurality of port states, including a discarding port state, a listening port state, and a forwarding port state;
• detecting a stoppage of a periodic receipt of bridge protocol data units (BPDUs) on a given port of the intermediate network device's ports;
• and
• in response to the stoppage, preventing the given port from transitioning to the forwarding port state, if the given port is in a port state other than the forwarding port state.

An intermediate network device configured to receive and forward network messages, the intermediate network device having a plurality of ports to connect the intermediate network device to one or more other devices, the intermediate network device comprising:

• means for executing a Rapid Spanning Tree Protocol (RSTP) at the intermediate network device to transition at least one of the intermediate network device's ports among a plurality of port states, including a discarding port state, a listening port state, and a forwarding port state;
• means for detecting a stoppage of a periodic receipt of bridge protocol data units (BPDUs) on a given port of the intermediate network device's ports;
• and
• means for preventing the given port from transitioning to the forwarding port state, in response to the stoppage, if the given port is in a port state other than the forwarding port state.

An intermediate network device configured to receive and forward network messages, the intermediate network device having a plurality of ports to connect the intermediate network device to one or more other devices, the intermediate network device comprising:

• a given port, of the plurality of ports, associated with one or more virtual local area networks (VLANs);
• a spanning tree protocol engine configured to implement a Spanning Tree Protocol (STP) to transition the given port among a plurality of port states for each VLAN of the given port, such that the given port has a separate port state for each VLAN, the port states including a discarding port state, a listening port state, and a forwarding port state;
• and
• a loop guard engine configured to, in response to a stoppage of a periodic receipt of bridge protocol data units (BPDUs) associated with a particular VLAN of the given port, prevent the given port from transitioning to the forwarding port state for the particular VLAN, if the given port is in a port state other than the forwarding port state for the particular VLAN.

An intermediate network device configured to receive and forward network messages, the intermediate network device having a plurality of ports to connect the intermediate network device to one or more other devices, the intermediate network device comprising:

• a virtual port including two or more ports aggregated to function as a single port;
• a spanning tree protocol engine configured to implement a Spanning Tree Protocol (STP) to transition the virtual port among a plurality of port states, including a discarding port state, a listening port state, and a forwarding port state;
• and
• a loop guard engine configured to cooperate with the spanning tree protocol engine, the loop guard engine configured to, in response to a stoppage of a periodic receipt of bridge protocol data units (BPDUs) on the virtual port, prevent the virtual port from transitioning to the forwarding port state, if the virtual port is in a port state other than the forwarding port state.