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3Com Switch 8800 Configuration Guide Chapter 38 MSTP Region-configuration
38-16
If the primary root is down or powered off, the secondary root will take its place, unless
you configure a new primary root. Of two or more configured secondary root bridges,
MSTP selects the one with the smallest MAC address to take the place of the failed
primary root.
When configuring the primary and secondary switches, you can also configure the
network diameter and hello time of the specified switching network. For detailed
information, refer to the configuration tasks “Configure switching network diameter” and
“Configure the Hello Time of the switch”.
Note:
You can configure the current switch as the root of several STIs. However, it is not
necessary to specify two or more roots for an STI. In other words, do not specify the
root for an STI on two or more switches.
You can configure more than one secondary root for a spanning tree through specifying
the secondary STI root on two or more switches.
Generally, you are recommended to designate one primary root and more than one
secondary root for a spanning tree.
By default, a switch is neither the primary root nor the secondary root of the spanning
tree.
38.2.3 Configuring the MSTP Running Mode
MSTP and RSTP are compatible and they can recognize the packets of each other.
However, STP cannot recognize MSTP packets. To implement the compatibility, MSTP
provides two operation modes, STP-compatible mode and MSTP mode. In
STP-compatible mode, the switch sends STP packets via every port. In MSTP mode,
the switch ports send MSTP or STP packets (when connected to the STP switch) and
the switch provides multiple spanning tree function.
You can use the following command to configure MSTP running mode. MSTP can
intercommunicate with STP. If there is a STP switch in the switching network, you may
use the command to configure the current MSTP to run in STP-compatible mode.
Otherwise, configure it to run in MSTP mode.
Perform the following configuration in system view.
Table 38-5 Configure the MSTP running mode
Operation Command
Configure MSTP to run in STP-compatible mode
stp mode stp
Configure MSTP to run in MSTP mode
stp mode mstp