78Configuration BPDUs sent by the regional root bridge always have a hop count set to the maximumvalue. When a device receives this configuration BPDU, it decrements the hop count by one, anduses the new hop count in the BPDUs that it propagates. When the hop count of a BPDU reacheszero, it is discarded by the device that received it. Devices beyond the reach of the maximum hopscan no longer participate in spanning tree calculations, so the size of the MST region is limited.Make this configuration only on the root bridge. All other devices in the MST region use the maximumhop value set for the root bridge.You can configure the maximum hops of an MST region based on the STP network size. As a bestpractice, set the maximum hops to a value that is greater than the maximum hops of each edgedevice to the root bridge.To configure the maximum number of hops of an MST region:Step Command Remarks1. Enter system view. system-view N/A2. Configure the maximumhops of the MST region. stp max-hops hops The default setting is 20.Configuring the network diameter of a switchednetworkAny two terminal devices in a switched network can reach each other through a specific path, andthere are a series of devices on the path. The switched network diameter is the maximum number ofdevices on the path for an edge device to reach another one in the switched network through the rootbridge. The network diameter indicates the network size. The bigger the diameter, the larger thenetwork size.Based on the network diameter you configured, the system automatically sets an optimal hello time,forward delay, and max age for the device.In STP, RSTP, or MSTP mode, each MST region is considered a device. The configured networkdiameter takes effect only on the CIST (or the common root bridge) but not on other MSTIs.In PVST mode, the configured network diameter takes effect only on the root bridges of the specifiedVLANs.To configure the network diameter of a switched network:Step Command Remarks1. Enter system view. system-view N/A2. Configure the networkdiameter of the switchednetwork.• In STP/RSTP/MSTP mode:stp bridge-diameter diameter• In PVST mode:stp vlan vlan-id-list bridge-diameterdiameterThe default setting is 7.Setting spanning tree timersThe following timers are used for spanning tree calculation:• Forward delay—Delay time for port state transition. To prevent temporary loops on a network,the spanning tree feature sets an intermediate port state (the learning state) before it transitsfrom the discarding state to the forwarding state. The feature also requires that the port transit
