Firewall packet filtering

Mechanisms are provided for performing an operation on a received data packet. A data packet is received and a hash operation on a header field value of a header of the data packet is performed to generate a hash value. A lookup operation is performed in a hash table associated with a type of the header field value to identify a hash table entry. A bit string associated with the hash table entry is retrieved, where each bit in the bit string corresponds to a class of rules of a rule set of a firewall. A matching operation of the header field value to rules in classes of rules corresponding to bits set in the bit string is performed to select one or more search trees. Operations are performed based on rules in the classes of rules being matched by header field value of the data packet.