Cisco Cisco SG500-52PP 52-port Gigabit Max PoE+ Stackable Managed Switch 维护手册

Multiple Spanning Tree

Cisco 500 Series Managed Switch Administration Guide

304

 

Multiple Spanning Tree Protocol (MSTP) is used to separate the STP port state 
between various domains (on different VLANs). For example, while port A is 
blocked in one STP instance due to a loop on VLAN A, the same port can be 
placed in the Forwarding State in another STP instance. The MSTP Properties 
page enables you to define the global MSTP settings.

To configure MSTP:

1. Set the STP Operation Mode to MSTP as described in the 

 page.

2. Define MSTP instances. Each MSTP instance calculates and builds a loop free 

topology to bridge packets from the VLANs that map to the instance. Refer to 
the 

 section. 

3. Decide which MSTP instance be active in what VLAN, and associate these 

MSTP instances to VLAN(s) accordingly.

4. Configure the MSTP attributes by:

•

•

•

The global MSTP configures a separate Spanning Tree for each VLAN group and 
blocks all but one of the possible alternate paths within each spanning tree 
instance. MSTP enables formation of MST regions that can run multiple MST 
instances (MSTI). Multiple regions and other STP bridges are interconnected using 
one single common spanning tree (CST).

MSTP is fully compatible with RSTP bridges, in that an MSTP BPDU can be 
interpreted by an RSTP bridge as an RSTP BPDU. This not only enables 
compatibility with RSTP bridges without configuration changes, but also causes 
any RSTP bridges outside of an MSTP region to see the region as a single RSTP 
bridge, regardless of the number of MSTP bridges inside the region itself.

For two or more switches to be in the same MST region, they must have the same 
VLANs to MST instance mapping, the same configuration revision number, and the 
same region name.