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196 CHAPTER 8: STP OPERATION
that is too short, the switch frequently sends configuration BPDU, which adds
burden and wastes the network resources.
A max age that is too short, can cause the network device to calculate the
spanning tree frequently and mistake the congestion as a link fault. If the max age
is too long, the network device may not be able to discover the link fault and
recalculate the spanning tree in time, which weakens the auto-adaptation capacity
of the network. The default value is recommended.
To avoid frequent network flapping, the values of hello time, forward delay and
maximum age should guarantee the following formulas equal.
2 * (forward-delay - 1seconds) >= maximum-age
maximum-age >= 2 * (hello + 1.0 seconds)
You should use the stp root primary command to specify the network diameter
and hello time of the switching network so MSTP will calculate automatically and
give better values.
By default, forward delay is 15 seconds, hello time is 2 seconds, and max age is 20
seconds.
Configuring the Max
Transmission Speed on
a Port
The max transmission speed on a port specifies how many MSTP packets will be
transmitted, every hello time, through the port.
The max transmission speed on a port is limited by the physical state of the port
and the network structure. You can configure it according to the network
conditions.
You can configure the max transmission speed on a port in the following ways.
Configuring in system view
Perform the following configuration in system view.
Configuring in Ethernet port view
Perform the following configuration in Ethernet port view.
For more about the commands, see the Switch 7750 Command Reference Guide.
Table 198 Configure the Max Transmission Speed on a Port
Operation Command
Configure the max transmission speed on a
port.
stp interface interface-list
transit-limit packetnum
Restore the max transmission speed on a port. undo stp interface interface-list
transit-limit
Table 199 Configure the Max Transmission Speed on a Port
Operation Command
Configure the max transmission speed on a
port.
stp transit-limit packetnum
Restore the max transmission speed on a port. undo stp transit-limit