H3C Technologies H3C S12500 Series Switches - Manual (Page 89)

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Step Command Remarks
1. Enter system view. system-view N/A
2. Configure the network diameter of
the switched network.
• In STP/RSTP/MSTP mode:
stp bridge-diameter diameter
• In PVST mode:
stp vlan vlan-list bridge-diameter
diameter
Use either command.
The default setting is 7.
NOTE:
•
In STP/RSTP/MSTP mode, each MST region is considered as a device and the configured network
diameter takes effect only on the CIST (or MSTI 0), but the diameter does not take effect on other MSTIs.
• In PVST mode, the network diameter configuration takes effect only on the root bridge.
Configuring spanning tree timers
The following timers are used for spanning tree calculation:
• Forward delay
It is the delay time for port state transition. To prevent temporary loops on a network, the spanning
tree sets an intermediate port state, the learning state, before it transits from the discarding state to
the forwarding state, and requires that the port transits its state after a forward delay timer to make
sure the state transition of the local port keeps synchronized with the peer.
• Hello time
The switch detects whether a link failure has occurred with the hello time interval. The spanning
tree sends out a configuration BPDU every hello time interval. If the switch receives no
configuration BPDUs within the hello time interval, it recalculates the spanning tree.
• Max age
In the CIST of an MSTP network or each VLAN of a PVST network, the switch determines whether
a configuration BPDU received by a port has expires based on the max age timer. If yes, a new
spanning tree calculation process starts. The max age timer does not take effect on other MSTIs
except the CIST (or MSTI 0).
To prevent network instability, make sure the timer settings meet the following formulas:
• 2 × (forward delay – 1 second) ƒ max age
• Max age ƒ 2 × (hello time + 1 second)
H3C recommends not manually setting the spanning tree timers. Instead, you can specify the network
diameter and let spanning tree protocols automatically calculate the timers based on the network
diameter. If the network diameter uses the default value, the timers also use their default values.
Configure the timers on the root bridge only, and the timer settings on the root bridge apply to all the
devices on the entire switched network.
Configuration restrictions and guidelines
• The length of the forward delay timer is related to the network diameter of the switched network. The
larger the network diameter is, the longer the forward delay time should be. If the forward delay
timer is too short, temporary redundant paths might be introduced. If the forward delay timer is too