Network interface cards, fabric cards, and line cards for loop avoidance in a chassis switch

A network interface card, installed in a chassis switch, comprising:

• a switch device, comprising a plurality of ports coupled to other network interface cards in the chassis switch, and each of the other network interface cards is a fabric card or a line card;
• and
• a controller, configured to, when the network interface card is a fabric card, perform acts comprising:
• configuring the ports to be in a forwarding state and sending a first control packet through each of the ports;
• receiving a plurality of second control packets from a plurality of line cards through the ports in response to the network interface card being a root fabric card;
• determining one of the line cards to be a designated line card according to a plurality of second identities in the second control packets;
• and
• configuring the ports other than the one coupled to the designated line card to be in a listening state in response to the network interface card being a backup fabric card;
• wherein the controller is further configured to, when the network interface card is a line card, perform acts comprising:
• configuring the ports to be in the listening state and receiving the first control packet from each of a plurality of fabric cards through the ports;
• determining one of the fabric cards to be the root fabric card according to a plurality of first identities in the first control packet;
• and
• configuring the ports to be in the forwarding state in response to the network interface card being the designated line card.