Multi-port network device using lookup cost backpressure

A packet network device comprising:

• multiple packet port buffers, at least one of which is assigned a lookup credit which is a relative cost associated with lookup operations performed by a lookup engine over a fixed period of time on a packet data type;
• an arbiter for selecting packet data from the multiple packet port buffers;
• a packet processor;
• a lookup credit manager to maintain a lookup credit account associated with the at least one packet port buffer which is assigned the lookup credit, the lookup credit account credited with the costs of the lookup operations and storing a current lookup credit value;
• the lookup engine performing the lookup operations for packets received from the arbiter and sending the results of the lookup operations to the packet processor which the packet processor uses to modify at least one of the received packets and to send the cost of the lookup operations to the lookup credit manager;
• and
• a backpressure channel to request the arbiter to reduce the relative rate of packets submitted to the lookup engine from the at least one packet port buffer that is assigned the lookup credit when the lookup credit value in the lookup credit account assigned to the at least one packet port buffer falls below a lower credit threshold.