Network-connection redundant system for devices with cascade networking capability and method applied on the system

A network-connection redundant method for devices with cascade networking capability, comprising:

• initializing a network with one or more network nodes and one or more networking devices, wherein the each network node at least has two network ports and one or more device ports, and the each network node connects to the one or more networking devices via the device ports, and the each networking device at least has two network ports connecting the same one or different network nodes, and the networking device connects an external network via the network node;
• defining roles of ports for each device port of each network node according to network packets generated by each network node and each networking device, wherein the roles of ports are a plurality of forward ports and one or more blocked ports;
• each network node periodically broadcasting or receiving a connection-confirmation packet;
• determining whether any connection changes according to a relative response packet;
• if the connection does not change, continuously broadcasting connection-confirmation packet;
• if the connection changes, including failure of connection, failure of device, and modification of connection, redefining the roles of ports for each device port;
• and
• accomplishing a redundant connection.