NAT để thay thế các tiêu đề của các gói tin đến với các tiêu đề riêng của mình trước khi gửi các gói tin. Điều này có thể không được có thể bởi vì IPsec thông tin được mã hóa Một loạt địa chỉ để lưu ý khi thiết kế không gian địa chỉ IP là IP tự động tư nhân biểu (APIPA). | 102 Chapter 3 Infrastructure Basics security logging and caching. When the proxy server receives a request for an Internet service it passes through filtering requirements and checks its local cache for previously downloaded web pages. Because web pages are stored locally response times for web pages are faster and traffic to the Internet is substantially reduced. The web cache can also be used to block content from websites that you don t want employees to access such as pornography social or peer-to peer networks. This type of server can be used to rearrange web content to work for mobile devices. It also provides better utilization of bandwidth because it stores all your results from requests for a period of time. TIP An exposed server that provides public access to a critical service such as a web or email server may be configured to isolate it from an organization s network and to report attack attempts to the network administrator. Such an isolated server is referred to as a bastion host named for the isolated towers that were used to provide castles advanced notice of pending assault. Internet Content Filters Internet content filters use a collection of terms words and phrases that are compared to content from browsers and applications. This type of software can filter content from various types of Internet activity and applications such as instant messaging email and office documents. Content filtering will report only on violations identified in the specified applications listed for the filtering application. In other words if the application will filter only Microsoft Office documents and a user chooses to use open Office the content will not be filtered. Internet content filtering works by analyzing data against a database contained in the software. If a match occurs the data can be addressed in one of several ways including filtering capturing or blocking the content and closing the application. An example of such software is Vista s Parental Controls.
