Chaper 05-Working with Proxy Servers and Application-Level Firewalls.ppt

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2016-12-24 发布于河南
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Chaper 05-Working with Proxy Servers and Application-Level Firewalls.ppt

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Working with Proxy Servers and Application-Level Firewalls Chapter 5 Learning Objectives Understand proxy servers and how they work Understand the goals that you can set for a proxy server Make decisions regarding proxy server configurations Choose a proxy server and work with the SOCKS protocol Learning Objectives Know the benefits of the most popular proxy-based firewall products Know the uses of the reverse proxy Understand when a proxy server isn’t the correct choice Overview of Proxy Servers Scan and act on the data portion of an IP packet Act primarily on behalf of internal hosts—receiving, rebuilding, and forwarding outbound requests Go by many names Proxy services Application-level gateways Application proxies How Proxy Servers Work Function as a software go-between, forwarding data between internal and external hosts Focus on the port each service uses Screen all traffic into and out of each port Decide whether to block or allow traffic based on rules Add time to communications, but in return, they: Conceal clients Translate network addresses Filter content Steps Involved in a Proxy Transaction Internal host makes request to access a Web site Request goes to proxy server, which examines header and data of the packet against rule base Proxy server recreates packet in its entirety with a different source IP address Steps Involved in a Proxy Transaction Proxy server sends packet to destination; packet appears to come from proxy server Returned packet is sent to proxy server, which inspects it again and compares it against its rule base Proxy server rebuilds returned packet and sends it to originating computer; packet appears to come from external host Steps Involved in a Proxy Transaction Proxy Servers and Packet Filters Are used together in a firewall to provide multiple layers of security Both work at the Application layer, but they inspect different parts of IP packets and act on them in different ways How Proxy Servers Differ from Packet Filters Scan entir