ccna 7 answers

ccna 7 answers.generation. All switches participating in STP exchange BPDU frames to determine which switch on the network has the smallest bridge ID (BID) O The switch with theThe switch with the smallest BID automatically becomes the root bridge used in the spanning tree algorithm to calculate the root bridge.Note: For simplicity, it is assumed that all ports on all switches are assigned to VLAN1, unless otherwise noted. Each switch has a unique MAC address associated with VLAN1.A BPDU is a frame of information that a switch exchanges in response to STP. Each BPDU contains a BID, which identifies the switch that sent the BPDU. The BID contains a priority value, the MAC address of the sending switch, and an optional extended system ID. o The combination of these three fields together determines the size of the BID value.After the root bridge is determined, the spanning tree algorithm calculates the shortest path to that bridge. Each switch uses the spanning tree algorithm to determine which port to block. Traffic cannot be forwarded through the network while the spanning tree algorithm determines the best path to the root bridge for all switch ports in the broadcast domain. The spanning tree algorithm needs to consider both path and port overhead when determining which port to block. Each switch port speed on a given path has a port overhead value associated with it, and the path overhead is calculated using the port overhead value. The sum of the port overhead values determines the overall path overhead to the root bridge. If there are multiple paths to choose from, the spanning tree algorithm will select the path with the lowest path overhead.Once the spanning tree algorithm has determined the most desirable path for each switch, it assigns port roles to the participating switch ports. The port role describes the relationship of the port to the root bridge in the network, and whether the port is allowed to forward traffic.Root port (root port): The switch port closest to the root bridge. Root ports are selected on a per-switch basis.Designated port: All non-root ports that are still allowed to forward traffic in the network. Designated ports are selected on a per-trunk basis. If one end of a trunk is the root port, the other end is the designated port. All ports on the root bridge are designated ports.Alternate and backup ports: Alternate and backup ports are configured to be blocked to prevent loops. The alternative port is selected only if neither end of the trunk link is the root port.Disabled port (disabled port): a disabled port is a switch port that is shut down. 6.2.4.3 Spanning Tree Algorithm: Root Bridge