A circuit used in a network device, which includes a memory and an analyzer. The memory stores an ACL look-up table, wherein the ACL look-up table includes multiple ACL rules, and each ACL rule contains at least a comparison field, a control field, and a logical operation field. The comparison field includes comparison information of a communication protocol, the control field indicates whether said each ACL rule needs to be combined with a next ACL rule, and the logic operation field indicates a logical operation used when said each ACL rule needs to be combined with the next ACL rule. The analyzer is configured to sequentially compare the packet according to multiple ACL rules recorded in the ACL look-up table, so as to generate at least one comparison result for determining the processing method of the packet.