Motorola WiNG 5.4.2, Справочное руководство системы

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Multiple Spanning Tree Protocol (MSTP) provides an extension to RSTP to optimize the usefulness of VLANs. MSTOP 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.
A MSTP supported deployment uses multiple MST regions with multiple MST instances (MSTI). Multiple regions and other
STP bridges are interconnected using one single
common spanning tree (CST).
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.
22. Select the Enable as Edge Port check box to enable or disable the port as an edge port. An edge port is a port that is
known to connect to a LAN which has no other bridges connected or is directly connected to a user device.
23. Select either the Point-to-Point or Shared radio button for the Link Type field. When Point-to-Point is selected, it
indicates that the port should be treated as connected to a point-to-point link. Selecting Shared indicates that the port is
shared between multiple devices. An example for Shared connection would be when the port is connected to a hub.
Similarly, an example for a Point-to-Point connection would be when the port is connected to an access point.
24. Select either the Enable or Disable radio button for the CISCO MSTP Interoperability field. This enables or disables
inter operability with CISCO’s implementation of the Multiple Spanning Tree Protocol (MSTP) which is incompatible with
the standard MSTP implementation.
25. Select one of the available choices for Force Protocol Version field. Select STP to use the standard Spanning Tree
Protocol. Select RSTP to use Rapid Spanning Tree Protocol. Select MSTP to use Multiple Spanning Tree Protocol.
Select Not Supported to disable spanning tree protocol for this interface.
26. Select either the None or Root radio button for the Guard field . Root guard is a mechanism to prevent election of roots
other than those designated as roots in a network. When this port receives a better (superior) BPDU, the port state becomes
Blocked. It retains this state till the port no longer receives the better (superior) BPDU and then the state is changed to
Forwarding. Select
Root to enable this feature. Select None to disable.
27. Select the Enable Port Fast check box to enable or disable PortFast. PortFast enables reducing the time taken for a port
to complete the MSTP state changes from Blocked to Forward. PortFast must only be enabled on ports on the wireless
controller which are directly connected to a Server/Workstation and not to another hub or controller.
28. Set the Enable PortFast BPDU Filter value from the drop-down list. MSTP BPDUs are messages that are exchanged when
controllers gather information about the network topology. When enabled, PortFast enabled ports do not transmit BPDU
messages. When set to 'Default' sets the PortFast BPDU Filter value to the bridge's BPDU filter value.
29. Set the Enable PortFast BPDU Guard value from the drop-down list. MSTP BPDUs are messages that are exchanged
when controllers gather information about the network topology. When enabled, PortFast enabled ports are forced to shut
down when they receive BPDU messages. When set to 'Default' sets the PortFast BPDU Guard value to the bridge's BPDU
guard value.
30. Configure the Spanning Tree Port Cost value. Select the + Add Row button to add a row to the table. Configure an
Instance Index value and its corresponding cost in the Cost column. This is the cost for a packet to traverse the current