Brocade Mobility Access Point System Reference Guide (Supporting software release 5.5.0.0 and later) - Manual (Page 269)

Brocade Mobility Access Point System Reference Guide 259
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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.
Select the Enable as Edge Port option 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.
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.
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.
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.
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.
Select the Enable Port Fast option 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. PortFast can be left unconfigured on an
access point.
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.
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.