Method and apparatus for learning and switching frames in a distributed network switch

A method for learning and switching frames between line cards that are interconnected by a switch fabric of a distributed network switch, the cards including an ingress card having an incoming port for receiving a frame at the switch, an egress card having an outgoing port for transmitting the frame from the switch and a switch management card (SMC) containing a router, the method comprising the steps of:

• executing a routing decision operation on the frame at the router, the frame comprising a header having a port-of-exit (POE) mask field, a source index field and a destination index field, the POE mask field including a plurality of bits, one for each port interface of the switch fabric;
• modifying the header of a frame during execution of the routing decision operation to ensure that copies of the routed frame are provided to the ingress card and egress cards;
• asserting a first bit in the POE mask field of the header, wherein the first bit denotes the port interface on the switch fabric corresponding to the ingress card as specified by the contents of the source index field;
• rendering a forwarding decision for the routed frame at a forwarding engine on the SMC using a destination media access control (MAC) address of the routed frame;
• asserting a second bit in a POE vector that denotes the port interface on the switch fabric corresponding to the egress card as specified by the contents of the destination index field;
• logically combining the asserted first bit of the POE mask field with the asserted second bit of the POE vector;
• loading the logically combined asserted bits into the POE mask field of the frame;
• and
• forwarding the frame to the switch fabric, whereby the logically combined asserted bits of the POE mask field instruct the switch fabric to switch copies of the routed frame through its port interfaces coupled to the ingress and egress cards.

Apparatus for learning and switching frames between line cards that are interconnected by a switch fabric of a distributed network switch, the cards including an ingress card having an incoming port for receiving a frame at the switch, an egress card having an outgoing port for transmitting the frame from the switch and a switch management card (SMC) containing a router, the apparatus comprising:

• means for executing by a router a routing decision operation on the frame, the frame comprising a header having a port-of-exit (POE) mask field, a source index field and a destination index field, the POE mask field including a plurality of bits, one for each port interface of the switch fabric;
• means for modifying the header of a frame during execution of the routing decision operation to ensure that copies of the routed frame are provided to the ingress card and egress cards;
• means for asserting a first bit in the POE mask field of the header, wherein the first bit denotes the port interface on the switch fabric corresponding to the ingress card as specified by the contents of the source index field;
• a forwarding engine on the SMC to render a forwarding decision for the routed frame using a destination media access control (MAC) address of the routed frame;
• means for asserting a second bit in a POE vector that denotes the port interface on the switch fabric corresponding to the egress card as specified by the contents of the destination index field;
• means for rendering a forwarding decision comprises a forwarding engine on the SMC;
• and
• means for asserting the second bit in the POE vector comprises a local target logic memory.

A method for operating a router comprising:

• receiving a frame at a port of an ingress card, the frame having a source field (SF) and a destination field (DF);
• executing, in response to receiving the frame, a routing decision by a microprocessor to designate a port of exit (POE);
• transferring the frame from the ingress card to an egress card having the POE;
• and
• transferring to the ingress card the designation of the POE, to permit the ingress card to update it's forwarding table so that a next frame can be forwarded by the ingress card without the microprocessor executing a routing decision.

A router comprising:

• an ingress card;
• an egress card;
• a port of the ingress card to receive a frame, the frame having a source field (SF) and a destination field (DF);
• a microprocessor to execute, in response to receiving the frame, a routing decision to designate a port of exit (POE);
• a switch fabric to transfer the frame to the egress card having the POE, and to transfer to the ingress card the designation of the POE, to permit the ingress card to update it's forwarding table so that a next frame can be forwarded by the ingress card without the microprocessor executing a routing decision.

A router, comprising:

• means for receiving a frame at a port of an ingress card, the frame having a source field (SF) and a destination field (DF);
• means for executing, in response to receiving the frame, a routing decision by a microprocessor to designate a port of exit (POE);
• means for transferring the frame from the ingress card to an egress card having the POE;
• and
• means for transferring to the ingress card the designation of the POE, to permit the ingress card to update it's forwarding table so that a next frame can be forwarded by the ingress card without the microprocessor executing a routing decision.