ccna exam fees 2020

ccna exam fees 2020.The campaign port role occurs when the ports are connected to the same network segment. These 2 switches exchange BPDU frames to determine which switch port is the designated port and which is the non-designated port. the campaigning principles are in the same order of comparison as the root port campaigning principles.In Figure 14-2, on the link between switches S2 and S3, both ports cannot be in the state of forwarding data at the same time, or else a loop will result and a designated port must be elected on that link. Since both S2 and S3 arrive at the root bridge with an overhead value of 19,it is further important to compare the senders who have the smallest bridge ID. S2 has the smaller bridge ID, so FaO/21 on S2 becomes the designated port, while FaO/22 on S3 becomes the non-designated port and is in a blocked state.14.1.4 STP Topology ChangeWhen a switch detects a topology change (such as a port being blocked or a port being manually shut down), it notifies the root bridge of Spanning Tree, which then floods that topology change information to the entire network. In IEEE802.1d STP operation, the switch will always receive configuration BPDU frames from the root bridge through the root port, it will not send BPDUs to the root bridge o In order to notify the root bridge of the topology change information, a special type of BPDU, called Topology Change Notification (TCN) BPDU, is introduced o When the switch detects a topology change, it starts sending TCNs through the root port in the direction to the root bridge direction to the root bridge. o The TCN is a very simple BPDU that contains only the first three fields in Table 14-1, and it is sent at BPDU intervals. After the switch receives the TCN, it immediately sends back a configuration BPDU with the Topology Change Acknowledgement (TCA) position bit to acknowledge receipt of the TCNo This exchange process continues until the root bridge responds. The TCN and TCA are sent as shown in Figure 14-4. In this figure, Switch E detects a topology change and it sends a TCN to Switch B. Switch B receives the TCN and acknowledges it to Switch E using the TCA. Switch B continues to send TCNs to Root Bridge A, which also acknowledges them to Switch B using TCAs, at which point the Root Bridge is informed that a topology change has occurred in the network, as shown in Figure 14-5 for the Root Bridge sending TC information. The configuration BPDU of the topology change (TC) location bit sent by the root bridge will be propagated to every switch in the network, and all switchesare aware to topology changes occurring in the network, all reduce their MAC address table aging time to forwarding delay time.14.1.5 STP ProtectionThe STP protocol does not have measures to authenticate the identity of a switch. In a stable network, access to an illegal switch would potentially cause catastrophic damage to STP operation in the network, so specific techniques are required to protect STP. the most commonly used are BPDU Guard and RootGuard techniques.Figure 14-4 TCN and TCA Sending Figure 14-5 Root Bridge Sending TC Information.222.Cisco Networking Lab CCNA Lab Guide (Release 2)1. portFast and BPDU Guard.