SMC Networks 8126PL2-F, Management Manual

Page: 195 / 614

Spanning Tree Algorithm Configuration
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3
Configuring Global Settings for STA
Global settings apply to the entire switch.
Command Usage
• Spanning Tree Protocol
9
Uses RSTP for the internal state machine, but sends only 802.1D BPDUs. This
creates one spanning tree instance for the entire network. If multiple VLANs are
implemented on a network, the path between specific VLAN members may be
inadvertently disabled to prevent network loops, thus isolating group members.
When operating multiple VLANs, we recommend selecting the MSTP option.
• Rapid Spanning Tree Protocol 9
RSTP supports connections to either STP or RSTP nodes by monitoring the
incoming protocol messages and dynamically adjusting the type of protocol
messages the RSTP node transmits, as described below:
- STP Mode – If the switch receives an 802.1D BPDU (i.e., STP BPDU) after a
port’s migration delay timer expires, the switch assumes it is connected to an
802.1D bridge and starts using only 802.1D BPDUs.
- RSTP Mode – If RSTP is using 802.1D BPDUs on a port and receives an RSTP
BPDU after the migration delay expires, RSTP restarts the migration delay timer
and begins using RSTP BPDUs on that port.
• Multiple Spanning Tree Protocol
MSTP generates a unique spanning tree for each instance. This provides multiple
pathways across the network, thereby balancing the traffic load, preventing
wide-scale disruption when a bridge node in a single instance fails, and allowing
for faster convergence of a new topology for the failed instance.
- To allow multiple spanning trees to operate over the network, you must configure
a related set of bridges with the same MSTP configuration, allowing them to
participate in a specific set of spanning tree instances.
- A spanning tree instance can exist only on bridges that have compatible VLAN
instance assignments.
- Be careful when switching between spanning tree modes. Changing modes
stops all spanning-tree instances for the previous mode and restarts the system
in the new mode, temporarily disrupting user traffic.
Command Attributes
Basic Configuration of Global Settings
• Spanning Tree State – Enables/disables STA on this switch. (Default: Enabled)
• Spanning Tree Type – Specifies the type of spanning tree used on this switch:
- STP : Spanning Tree Protocol (IEEE 802.1D); i.e., when this option is selected,
the switch will use RSTP set to STP forced compatibility mode).
- RSTP : Rapid Spanning Tree (IEEE 802.1w); RSTP is the default.
- MSTP : Multiple Spanning Tree (IEEE 802.1s)
9. STP and RSTP BPDUs are transmitted as untagged frames, and will cross any VLAN boundaries.