CCNA 第一章 网际互联(改).pptVIP

* Purpose: This page defines enterprise services. Emphasize: Enterprise services are services common to all users. Examples of enterprise services would be e-mail, Internet access, or video conferencing. Enterprise servers and services exist within a separate subnet placed close to the backbone of the network. Placing the enterprise servers close to the backbone ensures the same administrative distance from each user; however, this also means that all traffic going to an enterprise server crosses the backbone. Because enterprise services exist outside of the broadcast domain of the end user, these services are surrounding by Layer 3 functionality. The Layer 3 switch allows servers to be centralized with no performance penalty, eliminating the cost of numerous server repositories. Layer 3 devices also provide a level of security which protects the information stored on the servers. Transition: The following describes the multilayer model. * Purpose: This page discusses the characteristics of the core layer. Emphasize: The sole purpose of the core layer of the network is to switch packets as fast as possible. Routing, access lists, and packet filtering should not take place in the core as these functions will slow the data packet transfer rate. Transition: The following discusses how Cisco products fit with the multilayer design. * Purpose: This figure illustrates a TCP connection being established. Emphasize: The exchange is sometimes referred to as the “three-way-handshake.” The initiating host requests a synchronization. The receiver acknowledges the synchronization and specify synchronization parameters in the opposite direction. The receiver acknowledges the synchronization and a connection is established. * Purpose: This figure illustrates a TCP connection being established. Emphasize: The exchange is sometimes referred to as the “three-way-handshake.” The initiating host requests a synchronization. The receiver acknowledges the synchronization an