RSTP provides significantly faster spanning tree convergence after a topology change, introducing new convergence behaviors and bridge port roles to do this. RSTP was designed to be backwards-compatible with standard STP. The spanning sip trunking cisco press pdf that the bridges compute using the Spanning Tree Protocol can be determined using the following rules.
The example network at the right, below, will be used to illustrate the rules. The lettered clouds represent network segments. The smallest bridge ID is 3. Therefore, bridge 3 is the root bridge. Assuming that the cost of traversing any network segment is 1, the least cost path from bridge 4 to the root bridge goes through network segment c. Therefore, the root port for bridge 4 is the one on network segment c. The least cost path to the root from network segment e goes through bridge 92.
Therefore, the designated port for network segment e is the port that connects bridge 92 to network segment e. This diagram illustrates all port states as computed by the spanning tree algorithm. Any active port that is not a root port or a designated port is a blocked port. After link failure the spanning tree algorithm computes and spans new least-cost tree. ID of a bridge with priority 32768 and mac 0200.
The bridge priority default is 32768 and can only be configured in multiples of 4096. When comparing two bridge IDs, the priority portions are compared first and the MAC addresses are compared only if the priorities are equal. MAC address will be the root. 32768 then switch A will be selected as the root bridge. If the network administrators would like switch B to become the root bridge, they must set its priority to be less than 32768. Determine the least cost paths to the root bridge. The computed spanning tree has the property that messages from any connected device to the root bridge traverse a least cost path, i.
The cost of traversing a path is the sum of the costs of the segments on the path. Different technologies have different default costs. An administrator can configure the cost of traversing a particular network segment. The property that messages always traverse least-cost paths to the root is guaranteed by the following two rules. Least cost path from each bridge.