200 301 ccna exam topics

200 301 ccna exam topics.When STP is enabled, all interfaces of the switch that are working are adjusted to STP forwarding or blocking state, and access ports are no exception. For a switch connected to a host or router, the switch forwards Hello messages through these interfaces even if STP is not enabled. Since it is the only device that sends Hello messages on that LAN segment, the switch can send Hello messages with minimal overhead on the LAN segment, and naturally the switch becomes the designated port for that LAN segment. In this way, as a result of processing the designated port during STP, STP sets the working access interface to the forwarding state.1.2 Basic Content 17Reactions that affect STP topology state changesOnce the administrator has completed all STP configurations, the STP topology is also determined, unless the network topology changes. This subsection first explains the real-time operations performed by STP when the network topology is stable, and the following section analyzes how STP converges to the new topology when the network topology changes.By default, the root switch sends a new Hello BPDU every 2 secondsOvery non-root switch forwards this Hello message to all specified ports, but first changes the items listed in Hello. The switch calculates the root overhead of the local switch and sets it. The switch also sets the "Sender's BID" field to its own BID (the root switch's BID does not change).By forwarding all received (and changed) Hello's to all DP's, all switches continue to receive one Hello every 2 seconds. o The following describes the steady state operation when the current STP topology has not changed.Step 1 The root switch creates a Hello BPDU and forwards it to all of its working interfaces (in the forwarding state), at which point the root overhead is 0. Step 2 The non-root switch receives a Hello message on its root port and modifies the Hello message by changing the sender's BID to its own BID, and then lists the switch's overhead to the root. The switch then forwards the revised Hello message to all designated ports. Step 3 Repeat steps 1 and 2 until the network topology changes. Each switch periodically receives a Hello message from the root switch, and based on this Hello message, the switch is confident that the path to the root is still working. When the switch receives a broken Hello message, or when the received Hello lists different information indicating a failure, the switch reacts by initiating the process of changing the spanning tree topology. How the switch reacts through STP changes For various reasons, the entire convergence process requires the use of three types of timers. Note that the timers used by all switches are dictated by the root switch, which includes them in the HelloBPDU messages that are sent periodically. Table 1-7 lists these timers and the corresponding descriptions. Table 1-7 STP Timers(1Timer Description Default ValueHello Time period for the root switch to create Hello messages 2 seconds