Multiple Spanning Tree Protocol (MSTP)

Multiple Spanning Tree Protocol (MSTP) supports mapping multiple VLANs to one multiple spanning tree instance (MSTI) by means of a VLAN-to-MSTI mapping table. It allows data flows of VLANs to be forwarded along separate paths as defined in the mapping table, thus reducing communication overheads and resource usage. Note that one VLAN cannot map to multiple MSTIs.

Network Diagram

Figure 1-1 Network diagram for MSTP configuration

VLAN	Map to MSTI
VLAN 10	MSTI 1
VLAN 20	MSTI 0
VLAN 30	MSTI 3
VLAN 40	MSTI 4

"Permit:" beside each link in the figure is followed by the VLANs that the link carries.

Networking and Configuration Requirements

On the network as shown in Figure 1-1:

l          Configure all the involved Ethernet ports on the switches as trunk ports that carry the traffic of all VLANs.

l          Enable GVRP both globally and on all the ports on each switch.

l          Configure static VLAN 5 for Switch C, static VLAN 8 for Switch D, and static VLAN 5 and static VLAN 7 for Switch E. Switch A and Switch B are not configured with static VLANs.

l          Set the registration mode of GigabitEthernet 1/0/1 on Switch E to fixed, and display dynamic VLAN registration information of Switch A, Switch B, and Switch E.

l          Set the registration mode of GigabitEthernet 1/0/1 on Switch E to forbidden, and display dynamic VLAN registration information of Switch A, Switch B, and Switch E.

Configuration Example

l          Configuration on Switch A

#

 stp instance 1 root primary

(stp enable)

stp region-configuration

 region-name example

 instance 1 vlan 10

 instance 3 vlan 30

 instance 4 vlan 40

 active region-configuration

l          Configuration on Switch B

#

 stp instance 3 root primary

(stp enable)

stp region-configuration

 region-name example

 instance 1 vlan 10

 instance 3 vlan 30

 instance 4 vlan 40

 active region-configuration

l          Configuration on Switch C

#

 stp instance 4 root primary

(stp enable)

stp region-configuration

 region-name example

 instance 1 vlan 10

 instance 3 vlan 30

 instance 4 vlan 40

 active region-configuration

l          Configuration on Switch D

#

(stp enable)

stp region-configuration

 instance 1 vlan 10

 instance 3 vlan 30

 instance 4 vlan 40

 active region-configuration

Configuration Guidelines

Follow these guidelines when configuring MSTP:

l          MSTP is mutually exclusive with any of the following functions on a port: service loopback, RRPP, Smart Link, and STP BPDU tunnel.

l          MSTP-enabled devices are considered in the same MST region only when they have the same format selector (protocol format selector defined in 802.1s, which is 0 by default and unconfigurable), region name, VLAN-to-MSTI mapping table, and MSTP revision level settings.

l          For devices globally enabled with STP by default, the complete configuration does not display the stp enable command.