Mstp - Motorola WiNG 5.7.1 System Reference Manual

13 - 138 WiNG 5.7.1 Access Point System Reference Guide

13.3.23.11MSTP

Network
The Multiple Spanning Tree Protocol (MSTP) provides an extension to RSTP to optimize the usefulness of VLANs. MSTP allows
for a separate spanning tree for each VLAN group, and blocks all but one of the possible alternate paths within each spanning
tree topology.
If there is just one VLAN in the access point managed network, a single spanning tree works fine. However, if the network
contains more than one VLAN, the network topology defined by single STP would work, but it is possible to make better use of
the alternate paths available by using an alternate spanning tree for different VLANs or groups of VLANs.
MSTP includes all of its spanning tree information in a single Bridge Protocol Data Unit (BPDU) format. BPDUs are used to
exchange information bridge IDs and root path costs. Not only does this reduce the number of BPDUs required to communicate
spanning tree information for each VLAN, but it also ensures backward compatibility with RSTP. MSTP encodes additional
region information after the standard RSTP BPDU as well as a number of MSTI messages. Each MSTI messages conveys
spanning tree information for each instance. Each instance can be assigned a number of configured VLANs. The frames
assigned to these VLANs operate in this spanning tree instance whenever they are inside the MST region. To avoid conveying
their entire VLAN to spanning tree mapping in each BPDU, the access point encodes an MD5 digest of their VLAN to an instance
table in the MSTP BPDU. This digest is used by other MSTP supported devices to determine if the neighboring device is in the
same MST region as itself.
Refer to the MST Config
The MST Bridge
the port enforces MST root bridge placement.
The MST Port Bridge Detail
To view an access point's MSTP statistics:
1. Select the Statistics
2. Select System
connected access points.
3. Expand the Network
4. Select MSTP.
table to assess the MST configuration invoked and its version information.
table defines whether the bridge is a BDPU filter, guard and Cisco interoperable. A guard determines whether
table has port specific MST state information.
menu from the Web UI.
from the navigation pane (on the left-hand side of the screen). Expand a RF Domain and select one of its
menu from the left-hand side of the UI.