45Make this configuration on the root bridge only. All the routers other than the root bridge in the MSTregion use the maximum hop value set for 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 maximum hopsof the MST region. stp max-hops hops The default setting is 20.Configuring the network diameter of a switched networkAny two terminal devices in a switched network are interconnected through a specific path composed ofa series of devices. The network diameter is the number of devices on the path composed of the mostdevices. The network diameter is a parameter that indicates the network size. A bigger network diameterindicates a larger network size.To configure the network diameter of a switched network:Step Command Remarks1. Enter system view. system-view N/A2. Configure the network diameter ofthe switched network. stp bridge-diameter diameter The default setting is 7.NOTE:• Based on the network diameter you configured, the system automatically sets an optimal hello time,forward delay, and max age for the router.• Each MST region is considered as a router and the configured network diameter is effective only for theCIST (or the common root bridge), but not for MSTIs.Configuring spanning tree timersThe following timers are used for spanning tree calculation:• Forward delayIt is the delay time for port state transition. To prevent temporary loops on a network, the spanningtree sets an intermediate port state, the learning state, before it transitions from the discarding stateto the forwarding state, and requires that the port transitions its state after a forward delay timer tomake sure that the state transition of the local port keeps synchronized with the peer.• Hello timeThe router detects whether a link failure has occurred with the hello time interval. The spanning treesends out a configuration BPDU every hello time interval. If the router receives no configurationBPDUs within the hello time interval, it recalculates the spanning tree.• Max ageIn the CIST of an MSTP network, the router determines whether a configuration BPDU received bya port has expires based on the max age timer. If yes, a new spanning tree calculation processstarts. The max age timer is ineffective for MSTIs.To prevent network instability, make sure that the timer settings meet the following formulas:
