new ccna topics 2020

new ccna topics 2020.First, you need a network. This chapter uses a common logical topology such as the one shown in Figure 9-1. As you can see, multiple wireless clients are within the coverage of an AP that advertises multiple Service Set Identifiers (SSIDs). One of the SSIDs puts users into a network for visiting users, which is called the Guest network. The other SSID, called UserNet, is used by authenticated users of the corporate network. Of course, users on the UserNet are subject to more security measures, such as authentication and encryption, than those on the Guest network. The Guest network places the user on the 172.30 chokepoint 0/24 subnet. UserNet places users on the 10.99.99.0/24 network. Although the two networks are on different subnets and the users are associated with different SSIDs, the APs mentioned earlier can advertise multiple SSIDs, but actually use the same wireless transceiver. In the wireless space, SSIDs and IP subnets are logically separated.Clients have multiple methods of finding and associating APs. A client can passively scan the network and listen for beacons sent by APs on various frequencies, or a client can use an active scanning process, sending a probe request message to find a specific AP. userNet users prefer to actively scan the network, while Guest users more often use passive scanning. The method of client interaction is described in detail in Chapter 16. Returning now to the association process, a client scans the channel, hoping to listen for a beacon from an AP or to actively send a proberequest. If a probe response is received or a beacon is listened to, then that client can attempt to associate the SSID received from the probe response or beacon. client BGuest user110 Chapter 9 Passing Packets from the Wireless Network to the Wired NetworkMAC: 0000.0001.0001 Figure 9-1 A simple wireless networkThe next step is to authenticate and associate with the AP. Once the client has selected an SSID, an authentication request will be sent. The AP will answer with an authentication response. When this is done and the client receives a "Success" message, the client sends an association request message, which contains the data rate and client performance, and then receives an association response from the AP. The association response from the AP includes the data rate the AP can achieve, other performance, and the association identifier.Next, the client must determine the rate. This is done by determining the RSSL Received Signal StrengthIndicator and the SNR (Signal-to-NoiseRatio), and the best sending rate is selected based on these decisions. All management frames are sent at the lowest rate, while the data headers are sent at a rate that is somewhat faster than the management frames, and the real data frames are sent at the fastest rate. Just as the client has to determine its sending rate, the AP has to do the same. Now that the client is associated, it can try to send the data to other devices on the network.2. Sending data to a host on another subnetWhen a client is associated with an AP, the basic idea is to send data to other devices. To illustrate this, first try sending data between Client A and Client B in Figure 9-2, with Client A on the UserNet network and Client B on the Guest network. For security purposes, a typical network would not allow Guest users to send traffic to internal WLAN users, but here is just an example to illustrate how the connection is established.