R0106-HP MSR Router Series Layer 2 - LAN Switching Configuration Guide(V7)

• PVST mode—All ports of the device send PVST BPDUs. Each VLAN maintains a spanning tree. In a

network, the amount of spanning trees maintained by all devices equals the number of

PVST-enabled VLANs multiplied by the number of PVST-enabled ports. If the amount of spanning

trees exceeds the capacity of the network, device CPUs will be overloaded. Packet forwarding is

interrupted, and the network becomes unstable.

• MSTP mode—All ports of the device send MSTP BPDUs. A port in this mode automatically transits

to the STP mode when receiving STP BPDUs from the peer device. A port in this mode does not

transit to the RSTP mode when receiving RSTP BPDUs from the peer device.

The MSTP mode is compatible with the RSTP mode, and the RSTP mode is compatible with the STP mode.

Compatibility of the PVST mode depends on the link type of a port:

• On an access port, the PVST mode is compatible with other spanning tree modes in all VLANs.

• On a trunk port or hybrid port, the PVST mode is compatible with other spanning tree modes only

in VLAN 1.

Configuration restrictions and guidelines

When you make configurations in different spanning tree modes, follow these guidelines:

• In STP or RSTP mode, do not specify an MSTI or VLAN. Otherwise, the spanning tree configuration

does not take effect.

• In PVST mode, if you specify a VLAN, the spanning tree configuration takes effect on the specified

VLAN. Otherwise, the spanning tree configuration does not take effect.

• In MSTP mode, if you specify an MSTI, the spanning tree configuration takes effect on the specified

MSTI. If you specify a VLAN, the spanning tree configuration does not take effect. If you do not

specify any MSTI or VLAN, the spanning tree configuration takes effect on the CIST.

Configuration procedure

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 the

MSTP mode.

Configuring an MST region

Spanning tree devices belong to the same MST region if they are both connected through a physical link

and configured with the following details:

• Format selector (0 by default, not configurable).

• MST region name.

• MST region revision level.

• VLAN-to-instance mapping entries in the MST region.

The configuration of MST region-related parameters (especially the VLAN-to-instance mapping table)

might cause MSTP to begin a new spanning tree calculation. To reduce the possibility of topology