3Com Switch 7750 Configuration Guide Guide

Root Bridge Configuration 233
■ MSTP mode: In this mode, the protocol packets sent out of the ports of the
switch are MSTP packets, or STP packets if the ports have STP-enabled switches
connected. But multiple spanning tree function is only enabled for MSTP
packets.
Configuration procedure
Configuration example
# Configure the current switch to operate in the STP-compatible mode.
<SW7750> system-view
[SW7750] stp mode stp
MST Region Maximum
Hops Configuration
The maximum hops values configured on the region roots in an MST region limit
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 a MST region, the value of the remaining hops field in the
configuration BPDU is decreased by 1 every time the configuration BPDU passes a
switch. Such a mechanism disables the switches that are beyond the maximum
hops from participating in spanning tree generation, and thus limits the size of an
MST region.
With such a mechanism, the maximum hops configured on the switch operating
as the root bridge of the IST or an MSTI in a 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 hops settings of their root bridges.
Configuration procedure
Note that only the maximum hops settings on the switches operating as region
roots can limit the size of the MST region.
Table 159 Configure MSTP operation mode
Operation Command Description
Enter system view system-view -
Configure the MSTP
operation mode for the switch
stp mode { stp | rstp | mstp }
Required
A MSTP-enabled switch
operates in the MSTP mode
by default.
Table 160 Configure the maximum hops for an MST region
Operation Command Description
Enter system view system-view -
Configure the maximum hops
for the MST region
stp max-hops hops
Required
By default, the maximum
hops of an MST region are 20.