H3C Technologies H3C S12500 Series Switches - Manual (Page 85)

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Setting the spanning tree mode
The spanning tree modes include:
• STP mode—All ports of the device send STP BPDUs. Select this mode when the peer device of a port
supports only STP.
• RSTP mode—All ports of the device send RSTP BPDUs. When a RSTP port receives STP BPDUs from
a peer device, it automatically transit to the STP mode. When a RSTP port receives MSTP BPDUs
from a peer device, it stays in RSTP mode.
• MSTP mode—All ports of the device send MSTP BPDUs. When an MSTP port receives STP BPDUs
from a peer device, it automatically transit to the STP mode. When an MSTP port receives RSTP
BPDUs from a peer device, it stays in MSTP mode.
• PVST mode—All ports of the device send PVST BPDUs and maintain a spanning tree for each
VLAN.
MSTP mode is compatible with RSTP mode, RSTP mode is compatible with STP mode, and PVST mode is
incompatible with any other mode.
To set the spanning tree mode:
Step Command Remarks
1. Enter system view. system-view N/A
2. Set the spanning tree mode. stp mode { mstp | pvst | rstp | stp }
The default setting is MSTP
mode.
Configuring an MST region
Configuration restrictions and guidelines
• Two or more spanning tree devices belong to the same MST region only if they are configured to
have the same format selector (0 by default, not configurable), MST region name, MST region
revision level, and the same VLAN-to-instance mapping entries in the MST region, and they are
interconnected by using a physical link.
• The configuration of MST region–related parameters, especially the VLAN-to-instance mapping
table, will result in a new spanning tree calculation. To reduce the possibility of topology instability,
the MST region configuration takes effect only after you activate it by using the active
region-configuration command, or enable a spanning tree protocol by using the stp enable
command in the case that the spanning tree protocol is disabled.
• The switch in PVST mode supports more MSTIs than in MSTP mode. When you change the spanning
tree mode from PVST to MSTP, exceeding MSTIs (arranged in ascending order of their IDs) and their
configurations are silently deleted and cannot be recovered even if you change the spanning tree
mode back. To prevent loss of MSTIs, map all VLANs in the MST regions to the CIST in PVST mode.
Configuration procedure
To configure an MST region: