Its time limit is 20 sec or unlimited. An interface always enters the blocking state when you enable STP. The listening state is the first state. It is an interface that is entered after the blocking state. The interface helps you to determine that the interface that should participate in frame forwarding. Learning state helps to prepare for participating in frame forwarding. The interface allows us to enter the learning state from the listening slate. An interface in the forwarding state form the forward frames.
This interface enters the forwarding state from the learning state which performs the following functions:.
This state does not participate in the Spanning Tree loop because the port is administratively disabled, and its timing is also unlimited. It is the bridge that offers an interconnection point for all segments. All the bridges in a LAN have a path to the root. STP allows you to select the root bridge automatically. The port ID helps you to decide the root port.
It consists of a configurable 1-byte priority value and a unique port number of each bridge. Path Cost, which is also known called PC, helps to decide the best topology with regard to forwarding speed. STP uses the concept of Path Cost. A designated port is a disabled port, and it is blocked by a network admin. A non-Designated port is a switch port that is blocked. With multiple uplinks, STP is a must in our switched environment to provide multiple redundancies in case one goes down, another link is there to takes it place within a matter of seconds.
Spanning Tree Protocol Explained! Share this blog. Special Offer. Valid first name is required. Valid last name is required. Here we have altered the diagram slightly to introduce the RPC values.
We now know the root ports for the switches and need to determine the designating and blocking ports. SW1 will have all ports set to designated as no ports will enter blocking mode. One will be designated, but the other will have to go blocking; this is because there can only be one designated port on a collision domain, and the root port has already been selected on both switches. With this information, we can quickly work out which will become the designated port, and which will go blocking.
First, which has the lowest RPC? Second, which has the lowest BID? This basically ends the function of STP, however there is one last concept to cover which is helpful to understand why it takes a long time for STP to converge reach its final state.
When something changes to a port, e. It will first place the port that changed into blocking mode, which quickly moves into listening mode. The minimum time to reach forwarding state is 30 seconds, with the maximum being 50 seconds. PortFast should only be placed on access ports pointing at clients, as this mode will skip the states, so from blocking it would actually go straight to forwarding.
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