Device, network, and system for forwarding frames between geographically dispersed user networks

A frame forwarding device for use as a node in a frame forwarding system which has a plurality of nodes and links to transport frames between external networks that belong to the same group, comprising:

• system state sharing means for sharing system state information with other nodes in the frame forwarding system, whereby the nodes and links behave as a single virtual device for forwarding frames between the external networks;
• and
• frame forwarding means for forwarding received frames according to the system state information shared among all the nodes in the frame forwarding system.

An edge network device on an intermediary network that interconnects a plurality of LAN segments to form a network system, comprising:

• frame forwarding means for forwarding an incoming frame to other network devices on the intermediary network, when the incoming frame contains information for detecting a physical loop on the network system and avoiding loop traffic on the physical loop;
• and
• loop preventing means for preventing a logical loop from being formed on the physical loop, while maintaining logical paths on the intermediary network, based on the information contained in the incoming frame and parameters that characterize the intermediary network as a single virtual bridge device.