H3C Technologies H3C S5120 Series Switches - Manual (Page 185)

1-20
To do... Use the command... Remarks
Configure the maximum hops
of the MST region
stp max-hops hops
Required
20 by default
Configuring the Network Diameter of a Switched Network
Any two terminal devices in a switched network are interconnected through a specific path composed of
a series of devices. The network diameter is the number of devices on the path composed of the most
devices. The network diameter is a parameter that indicates the network size. A bigger network
diameter indicates a larger network size.
Make this configuration on the root bridge only.
Follow these steps to configure the network diameter of a switched network:
To do... Use the command... Remarks
Enter system view system-view —
Configure the network diameter
of the switched network
stp bridge-diameter diameter
Required
7 by default
z
Based on the network diameter you configured, MSTP automatically sets an optimal hello time,
forward delay, and max age for the device.
z
The configured network diameter is effective for the CIST only, and not for MSTIs. Each MST
region is considered as a device.
z
The network diameter must be configured on the root bridge. Otherwise, it will not take effect.
Configuring Timers of MSTP
MSTP involves three timers: forward delay, hello time and max age. You can configure these three
parameters for MSTP to calculate spanning trees.
z
To prevent temporary loops on a network, MSTP sets an intermediate port state called learning
between the discarding state and the forwarding state, that is, before a port in the discarding state
can transit to the forwarding state, it needs to go through the learning state. Forward delay is the
delay time for port state transition. This is to ensure that the state transition of the local port and that
of the peer occur in a synchronized manner.
z
Hello time is the time interval at which a device sends configuration BPDUs to the surrounding
devices to ensure that the paths are fault-free. If a device fails to receive configuration BPDUs
within a certain period of time, it starts a new spanning tree calculation process.
z
MSTP can detect link failures and automatically restore blocked redundant links to the forwarding
state. A device on the CIST determines whether a configuration BPDU received by a port has
expired according to the max age parameter. If yes, it starts a new spanning tree calculation
process. The max age set for an MSTI does not take effect.