Configuring The Work Mode Of Mstp Device - H3C S5500-EI series Operation Manual

Operation Manual – MSTP
H3C S5500-EI Series Ethernet Switches
There is one and only one root bridge in effect in a spanning tree instance. If two or
more devices have been designated to be root bridges of the same spanning tree
instance, MSTP will select the device with the lowest MAC address as the root
bridge.
You can specify multiple secondary root bridges for the same instance. Namely,
you can specify secondary root bridges for the same instance on two or more than
two devices.
When the root bridge of an instance fails or is shut down, the secondary root
bridge (if you have specified one) can take over the role of the instance. However,
if you specify a new root bridge for the instance at this time, the secondary root
bridge will not become the root bridge. If you have specified multiple secondary
root bridges for an instance, when the root bridge fails, MSTP will select the
secondary root bridge with the lowest MAC address as the new root bridge.
When specifying the root bridge or a secondary root bridge, you can specify the
network diameter and hello time. However, these two options are effective only for
MST instance 0, namely the CIST. If you include these two options in your
command for any other instance, the configuration can succeed, but they will not
actually work. For the description of network diameter and hello time, refer to
Configuring the Network Diameter of a Switched Network
of MSTP.
Alternatively, you can also specify the current device as the root bridge by setting
the priority of the device to 0. For the device priority configuration, refer to
Configuring the Priority of the Current
III. Configuration example
# Specify the current device as the root bridge of MST instance 1 and a secondary root
bridge of MST instance 2.
<Sysname> system-view
[Sysname] stp instance 1 root primary
[Sysname] stp instance 2 root secondary

1.3.3 Configuring the Work Mode of MSTP Device

MSTP and RSTP can recognize each other's protocol packets, so they are mutually
compatible. However, STP is unable to recognize MSTP packets. For hybrid
networking with legacy STP devices and full interoperability with RSTP-compliant
devices, MSTP supports three work modes: STP-compatible mode, RSTP mode, and
MSTP mode.
In STP-compatible mode, all ports of the device send out STP BPDUs,
In RSTP mode, all ports of the device send out RSTP BPDUs. If the device detects
that it is connected with a legacy STP device, the port connecting with the legacy
STP device will automatically migrate to STP-compatible mode.
Device.
1-23
Chapter 1 MSTP Configuration
and Configuring Timers