RackSwitch G8000 Application Guide
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Chapter 5: Spanning Tree BMD00041, November 2008
Overview
Spanning Tree Protocol detects and eliminates logical loops in a bridged or switched network.
When multiple paths exist, Spanning Tree configures the network so that a switch uses only the
most efficient path. If that path fails, Spanning Tree automatically sets up another active path
on the network to sustain network operations.
The G8000 supports the following Spanning Tree Protocols:
IEEE 802.1D (2004) Rapid Spanning Tree Protocol (RSTP). RSTP enhances the Spanning
Tree Protocol to provide rapid convergence on Spanning Tree Group 1.
IEEE 802.1Q (2003) Multiple Spanning Tree Protocol, which extends RSTP to multiple
Spanning Tree Groups. MSTP provides both rapid convergence and load balancing in a
VLAN environment, using multiple VLANs in each Spanning-Tree Group (STG).
Per VLAN Rapid Spanning Tree Plus Protocol (PVRST+), which enhances the RSTP
protocol by adding the ability to have multiple spanning tree groups. PVRST+ is based on
IEEE 802.1w Rapid Spanning Tree Protocol.
The relationship between port, trunk groups, VLANs, and Spanning Trees is shown in
Table 5-1.
NOTE – Due to Spanning Tree’s sequence of discarding, learning, and forwarding, lengthy
delays may occur.
You can use a port’s spanning-tree edge command to permit a port that participates
in Spanning Tree to bypass the Discarding and Learning states, and enter directly into the
Forwarding state.
Table 5-1 Ports, Trunk Groups, and VLANs
Switch Element Belongs to
Port Trunk group
or
One or more VLANs
Trunk group One or more VLANs
VLAN (non-default) RSTP: One VLAN per Spanning Tree group
PVRST+: One VLAN per Spanning Tree Group
MSTP: Multiple VLANs per Spanning Tree group
