Application Level Proxies on Bridges

Filtering data transmitted over the Internet into a company´s network for viruses, Trojans, worms and spam is an important part of a security concept to protect the local network from being taken over by attackers. Those filters are either implemented on the client, on a local network server or on a proxy system, depending on how the respective data is transmitted over the network. Where mail and file server are often locally installed, web servers are usually remote and require a proxy for filtering. A proxy however takes over communication for the client and thus might change important communication parameters such as the remote machine´s identification when using SSL. We have developed several application level content filters running on bridges, i.e. ISO/OSI level 2 devices filtering ISO/OSI level 7 content. This papers gives an overview of our research and discusses advantages of application level filtering on bridges.