TAILIEUCHUNG - CCNA Wireless Official Exam Certification Guide part 16

CCNA Wireless Official Exam Certification Guide part 16 is a best of breed Cisco® exam study guide that focuses specifically on the objectives for the CCNA® Wireless IUWNE exam. Senior instructor Brandon Carroll shares preparation hints and test-taking tips, helping you identify areas of weakness and improve both your conceptual knowledge and hands-on skills. Material is presented in a concise manner, focusing on increasing your understanding and retention of exam topics. | 122 CCNA Wireless Official Exam Certification Guide Key Topic Figure 7-6 Beacon Frame Details process of how a client searches channels and displays connection capability information. For now just understand that the beacon frame allows a client to passively scan a network. Sometimes however you do not want to passively scan a network. Perhaps you know exactly what cell you want to connect to. In this situation you can actively scan a network to determine if the cell you are looking for is accessible. When a client actively scans a network it uses probe request and probe response messages. Figure 7-7 shows a client actively scanning. Client Probe request Is SSID CARROLL out there SSID CARROLL 000000 To Distribution Probe response Here I am Figure 7-7 Active Scanning As you can tell in the figure the client is looking for a wireless cell with the SSID of Carroll. This client sends a probe request and the AP upon receiving the probe request issues a probe response. The probe response is similar to the beacon frame including capability information authentication information and so on. The difference is that a beacon frame is sent frequently and a probe response is sent only in response to a probe request. Connecting After a Probe or Beacon After a client has located an AP and understands the capabilities it tries to connect using an authentication frame. This frame has information about the algorithm used to authenticate a number for the authentication transaction and information on whether authentication has succeeded or failed. Chapter 7 Wireless Traffic Flow and AP Discovery 123 One thing to note is that authentication can be Open meaning that no authentication algorithm such as WEP is being used. The only reason an authentication message is used is to indicate that the client has the capability to connect. In Figure 7-8 the client is sending an authentication request and the AP is sending an authentication response. Upon authentication the client sends an .

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