Ensuring proper packet ordering in a cut-through and early-forwarding network switch

A network switch comprising:

• a plurality of input ports configured to receive data forming one or more packets;
• a plurality of output ports configured to convey the packets out of the switch, wherein each output port comprises a plurality of output queues;
• a random access memory;
• and
• data transport logic coupled between the input ports, the output ports, and the memory, wherein each input port has a plurality of sequences, wherein the first input port is configured to assign a sequence number to each received packet, wherein the sequence number accompanies the packet through the switch, wherein each output port is configured to store a last maximum sequence number (LMSN) for each input port register, wherein a first input port is configured to request cut-through routing from a first output port in response to receiving data corresponding to a first packet, and wherein the destination output port is configured to compare (a) the sequence number of the first packet with (b) the stored LMSN for the corresponding input port.

A network switch comprising:

• a plurality of ports, wherein a first one of said ports is an input port configured to receive data forming a packet, wherein a second one of said ports is an output port configured to convey the packet out of the switch, wherein the output port comprises an output first-in first-out memory (FIFO);
• a random access memory (RAM);
• and
• a means for routing the data between the input port, the RAM, and the output port, wherein the means for routing is configured to either route the packet directly to the output FIFO by cut-through routing or route the packet to the RAM for either early forwarding or store and forward routing, wherein the means is configured to route the data from the input port to the output port in response to detecting a cut-through grant signal from the output port, wherein the means is configured to store the data to the RAM in response to not receiving the cut-through grant signal from the output port, wherein the input port is configured to store a time value for the output port, wherein the time value corresponds to the last time that the input port added a packet identifier to one of the output port's output queues.