3Com 4210 PWR Configuration Manual page 162

160 C 14: MSTP C
HAPTER
Configuring the
Maximum Hop Count of
an MST Region
ONFIGURATION
Configuration procedure
Table 108 Configure the MSTP operation mode
Operation
Enter system view
Configure the MSTP
operation mode
Configuration example
# Specify the MSTP operation mode as STP-compatible.
<4210> system-view
[4210] stp mode stp
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.
Configuration procedure
Table 109 Configure the maximum hop count for an MST region
Operation
Enter system view
Configure the maximum hop
count of the MST region
The bigger the maximum hop count, the larger the MST region is. Note that only
the maximum hop settings on the switch operating as a region root can limit the
size of the MST region.
Configuration example
# Configure the maximum hop count of the MST region to be 30.
<4210> system-view
[4210] stp max-hops 30
Command
system-view
stp mode { stp | rstp | mstp } Required
Command
system-view
stp max-hops hops
Description
-
An MSTP-enabled switch
operates in the MSTP mode
by default.
Description
-
Required
By default, the maximum hop
count of an MST region is 20.