Fast convergence with topology switching

An intermediate network device having a plurality of ports for forwarding messages in a computer network in which a plurality of logical virtual local area networks (VLANs) are defined each having one or more members, the intermediate network device comprising:

• a topology switch engine configured to associate each logical VLAN with a set of physical VLANs each having its own identifier, and to designate one physical VLAN from the respective set for each logical VLAN;
• means for establishing a loop-free topology within the computer network for each physical VLAN;
• a port configuration entity in communicating relationship with the topology switch engine, the port configuration entity configured to associate each port directly coupled to members of a first logical VLAN with the identifier of the designated physical VLAN for the first logical VLAN;
• and
• a link state detection engine coupled to the ports and in communicating relationship with the topology switch engine, the link state detection engine configured to detect failures at the ports,
• whereby, in response to the detection of a failure at a port affecting the forwarding of messages for the first logical VLAN, the topology switch engine selects a back-up physical VLAN for the first logical VLAN and directs the port configuration entity to switch the association of each port directly coupled to members of the first logical VLAN to the back-up physical VLAN.

In an intermediate network device configured to forward messages in a computer network in which a plurality of logical virtual local area networks (VLANs) are defined, a set of physical VLANs are defined for each logical VLAN, each physical VLAN having an identifier, and a loop-free topology is established within the network for each physical VLAN, a computer readable medium containing executable program instructions for switching the logical VLANs from between different loop-free topologies, the executable program instructions comprising program instructions for:

• for a given logical VLAN, designating a first physical VLAN and its respective loop-free topology for tagging and forwarding messages associated with the given logical VLAN;
• detecting a failure in the loop-free topology of the first physical VLAN;
• and
• in response to the step of detecting, switching the given logical VLAN from the first physical VLAN to a second physical VLAN.

In an intermediate network device configured to forward messages in a computer network in which a plurality of logical virtual local area networks (VLANs) are defined, a method for switching the logical VLANs between different loop-free topologies, the method comprising the steps of:

• defining a set of physical VLANs for each logical VLAN, each physical VLAN having an identifier;
• for each physical VLAN, establishing a corresponding loop-free topology within the computer network;
• and
• for a given logical VLAN, designating a first physical VLAN and its respective loop-free topology from the respective set for use in tagging and forwarding messages associated with the given logical VLAN.