Based On Link Layer Firewall Spam Transparent Gateway Design And Implementation

As a killer application of the internet, e-mail has become the most commonly used tool for people's daily life and work. No matter in electronic business or electronic government affair or communication between normal people, e-mail has become the key role. Beside the development of e-mail, spam's overflow has become the key problem that effecting the Internet's security and development, it not only consume the users'time, raise the running cost of the enterprise, and also the spam is the main channel to spread the information of retroaction, terror, eroticism and the computer virus.Though there are a lot of solutions to filtrate the spam, but the existing solution mainly attached to the software of mail server or client, the universal property and the performance are both not good enough, and to build a unified and high efficient architecture of anti-spam filter system has become one of the most important researche directions. This thesis first analyzes the existing anti-spam filter techniques, explains the disadvantage of them, and brings forward the new thought that filtrate the spasm when they are being transferred. And brings out the new solution which associate with the newest Linux Data Link Layer firewall filter technique, then designs and implement carry out the anti-spam filter system based on the transparent network bridge according the this solution.The mainly contributions of this thesis are using the Linux Data Link Layer firewall filter technique to be the architecture of this system; carrying out the IP packets transmission between kernel space and user space; carrying out the interception of the key packet in the SMTP session, designing the management and the scheduling of buffering mail queues; fix the protocol stack of IP defragment, TCP session reassembly, SMTP session reassembly, and the restore the mail content; integrating the different spam filter techniques, designing the open interface of the filter module. And finally, this thesis completes a transparent anti-spam filter system. This system is highly security (invisible on the IP layer), easy to management and will not effect the setting of the existing network; it use the way of protocol analysis on the data link layer, quickly restore the e-mail, this kind of solution only focus on the protocol so it can realize the one-to-many service. The system's technique and design is very advanced all over the country and it already been accepted by the Huawei Beijing Research Center.