3Com Switch 8800 Advanced Software V5 Configuration Guide

114 CHAPTER 11: MSTP CONFIGURATION
Configuration example
# Set the maximum hops of the MST region to 30.
<Sysname> system-view
[Sysname] stp max-hops 30
Configuring the
Network Diameter of a
Switched Network
Any two stations in a switched network are interconnected through specific paths,
which are composed of a series of devices. Represented by the number of devices
on a path, the network diameter is the path that comprises more devices than any
other among these paths.
Configuration procedure
Follow these steps to configure the network diameter of the switched network:
n
■ Network diameter is a parameter that indicates network size. A bigger network
diameter represents a larger network size.
■ Based on the network diameter you configured, MSTP automatically sets an
optimal hello time, forward delay, and max age for the device.
■ The configured network diameter is effective for the CIST only, and not for
MSTIs.
Configuration example
# Set the network diameter of the switched network to 6.
<Sysname> system-view
[Sysname] stp bridge-diameter 6
Configuring Timers of
MSTP
MSTP involves three timers: forward delay, hello time and max age.
■ Forward delay: the time a device will wait before changing states. A link failure
can trigger a spanning tree computing process, and the spanning tree structure
will change accordingly. However, as a new configuration BPDU cannot be
propagated throughout the network immediately, if the new root port and
designated port begin to forward data as soon as they are elected, a temporary
loop may occur. For this reason, the protocol uses a state transition mechanism.
Namely, a newly elected root port or designated port must wait twice the
forward delay time before transitioning to the forwarding state, when the new
configuration BPDU has been propagated throughout the network.
■ Hello time is sued to detect whether a link is faulty. A device sends a hello
packet to the devices around it at a regular interval of hello time to check
whether any link is faulty.
■ Max time is used for determining whether a configuration BPDU has "expired".
A BPDU that has expired will be discarded by the device.
To do... Use the command... Remarks
Enter system view system-view -
Configure the network
diameter of the switched
network
stp bridge-diameter
bridgenum
Optional
7 by default