3Com 4200G 24-Port - Configuring the MSTP Operation Mode; Configuring the Maximum Hop Count of an MST Region

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[Sysname-GigabitEthernet1/0/1] undo stp compliance
Configuring the MSTP Operation Mode
To make an MSTP-enabled switch compatible with STP/RSTP, MSTP provides the following three
operation modes:
z STP-compatible mode, where the ports of a switch send STP BPDUs to neighboring devices. If
STP-enabled switches exist in a switched network, you can use the stp mode stp command to
configure an MSTP-enabled switch to operate in STP-compatible mode.
z RSTP-compatible mode, where the ports of a switch send RSTP BPDUs to neighboring devices. If
RSTP-enabled switches exist in a switched network, you can use the stp mode rstp command to
configure an MSTP-enabled switch to operate in RSTP-compatible mode.
z MSTP mode, where the ports of a switch send MSTP BPDUs or STP BPDUs (if the switch is
connected to STP-enabled switches) to neighboring devices. In this case, the switch is
MSTP-capable.
Configuration procedure
Follow these steps to configure the MSTP operation mode:
To do... Use the command... Remarks
Enter system view
system-view
—
Configure the MSTP operation
mode
stp mode { stp | rstp | mstp }
Required
An MSTP-enabled switch
operates in the MSTP mode by
default.
Configuration example
# Specify the MSTP operation mode as STP-compatible.
<Sysname> system-view
[Sysname] stp mode stp
Configuring the Maximum Hop Count of an MST Region
The maximum hop count configured on the region root is also the maximum hops of the MST region.
The value of the maximum hop count limits the size of the MST region.
A configuration BPDU contains a field that maintains the remaining hops of the configuration BPDU.
And a switch discards the configuration BPDUs whose remaining hops are 0. After a configuration
BPDU reaches a root bridge of a spanning tree in an MST region, the value of the remaining hops field
in the configuration BPDU is decreased by 1 every time the configuration BPDU passes one switch.
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, the maximum hop count configured on the switch operating as the root bridge
of the CIST or an MSTI in an MST region becomes the network diameter of the spanning tree, which
limits the size of the spanning tree in the current MST region. The switches that are not root bridges in
the MST region adopt the maximum hop settings of their root bridges.