Many network security problems can be solved in a centralized TCP (CTCP) architecture, in which an organization's edge router transparently proxies every TCP connection between an internal host and an external host on the Internet. This paper describes the design, implementation, and evaluation of a CTCP router prototype that is built on the Linux kernel. By redirecting all packets targeting at non-existent or non-open-to-public ports to a CTCP socket which pretends to be the original receivers, CTCP could confirm the real identification of the packet sources, collect suspicious traffic from them, and make an illusion that the scanned target ports are all open, thus renders port scanning an useless effort. Under CTCP architecture, external hosts only interacts with a secure CTCP router; therefore, any OS fingerprinting attempt and DoS/DDoS attack targeting at TCP/IP implementation bugs could be thwarted. Moreover, By further checking traffic originating from confirmed scanners, the CTCP router can actually identify buffer overflow attack traffic. Finally, the CTCP router solves the TCP connection hijacking problem by introducing an additional check on the sequence number filed of incoming packets. Despite providing a rich variety of protection, the CTCP architecture does not incur much overhead. On a 1.1GHz Pentium-3 machine with gigabit Ethernet interfaces, the throughput of the CTCP router is 420.3 Mbits/sec, whereas the throughput of a generic Linux router on the same hardware is only 409.1 Mbits/sec.