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172 CHAPTER 13: MSTP CONFIGURATION
Configuration example
Configure the bridge priority of the current switch to be 4,096 in spanning tree
instance 1.
<S5500> system-view
System View: return to User View with Ctrl+Z.
[S5500] stp instance 1 priority 4096
Configuring MSTP
Operation Mode
A switch running MSTP can operate in one of these three modes:
■ STP mode: In this mode, ports of the switch send STP packets. If the switched
network contains STP-enabled switches, you can configure the current
MSTP-enabled switch to operate in this mode by using the stp mode stp
command.
■ RSTP mode: In this mode, ports of the switch send RSTP packets. If the switched
network contains RSTP-enabled switches, you can configure the current
MSTP-enabled switch to operate in this mode by using the stp mode rstp
command.
■ MSTP mode: In this mode, ports of the switch send MSTP packets or STP packets
(if the ports have STP-enabled switches connected). In this case, the multiple
spanning tree function is enabled as well.
Configuration procedure
Configuration example
Configure the current switch to operate in STP mode.
<S5500> system-view
System View: return to User View with Ctrl+Z.
[S5500] stp mode stp
Configuring the
Maximum Hop Count of
an MST Region
The maximum hop count of an MST region is used to limit the size of the MST region.
Normally, it is configured on the region roots.
A BPDU contains a hop counter field. In a MST region, after a BPDU leaves the root
bridge, its hop counter decreases by 1 whenever it is forwarded by a switch; once its
hop counter reaches 0, it is dropped. Such a mechanism disables the switches that are
beyond the maximum hop count from participating in spanning tree calculation, and
thus limits the size of an MST region.
With such a mechanism, once a switch becomes the root bridge of a CIST or MSTI,
the maximum hop count configured on it determines the network diameter of the
spanning tree and limits the size of the spanning tree. The switches that are not the
root bridge in an MST region adopts the maximum hop count configured on the root
bridge.
Table 146 Configure MSTP operation mode
Operation Command Description
Enter system view system-view -
Configure the MSTP
operation mode of the
switch
stp mode { stp | rstp | mstp } Required
An MSTP-enabled switch operates
in MSTP mode by default.