SYN proxy is a firewalls solution to protect against SYN flooding. It plays well under the low rate of attacks, but stumbles under heavy loads. In this paper, a novel approach based on SYN proxy is introduced, its design explained, and its performance evaluated. In this approach, the hash table is used to save half-connection states under light loads, and SYN cookie used under heavy loads. A bitmap is introduced into buckets of the hash table,which speedups of the lookup under SYN Flooding. Bucket length of the hash table is limited to a predefined value,thereby the performance degradation is prevented. A firewall implementing our proposal is tested, which shows that good performance is achieved.