Defining Spanning Tree - Alcatel OmniStack LS 6248 User Manual

3
Configuring the Switch
network topology.
RSTP is designed as a general replacement for the slower, legacy STP. RSTP is
also incorporated into MSTP. RSTP achieves must faster reconfiguration (i.e.,
around one tenth of the time required by STP) by reducing the number of state
changes before active ports start learning, predefining an alternate route that can be
used when a node or port fails, and retaining the forwarding database for ports
insensitive to changes in the tree structure when reconfiguration occurs.
When using STP or RSTP, it may be difficult to maintain a stable path between all
VLAN members. Frequent changes in the tree structure can easily isolate some of
the group members. MSTP (an extension of RSTP) is designed to support
independent spanning trees based on VLAN groups. Once you specify the VLANs to
include in a Multiple Spanning Tree Instance (MSTI), the protocol will automatically
build an MSTI tree to maintain connectivity among each of the VLANs. MSTP
maintains contact with the global network because each instance is treated as an
RSTP node in the Common Spanning Tree (CST).

Defining Spanning Tree

You can display a summary of the current bridge STP information that applies to the
entire switch using the STP Information screen.
Command Attributes
• Spanning Tree State — Indicates whether STP is enabled on the device. The
possible field values are:
• Enable — Enables STP on the device.
• Disable — Disables STP on the device.
• STP Operation Mode — Specifies the STP mode that is enabled on the device.
The possible field values are:
• Classic STP — Enables Classic STP on the device. This is the default value.
• Rapid STP — Enables Rapid STP on the device.
• Multiple STP — Enables Multiple STP on the device.
• BPDU Handling — Determines how BPDU packets are managed when STP is
disabled on the port or device. BPDUs are used to transmit spanning tree
information. The possible field values are:
• Filtering — Filters BPDU packets when spanning tree is disabled on an
interface.
• Flooding — Floods BPDU packets when spanning tree is disabled on an
interface. This is the default value.
• Bridging — Indicates that if the spanning tree protocol is globally disabled,
untagged and tagged BPDU packets are flooded, and are subject to ingress and
egress VLAN rules. Bridging BPDU can only be enabled if the spanning tree
protocol is enabled on port groups.
• Path Cost Default Values — Specifies the method used to assign default path
cost to STP ports. The possible field values are:
192