Blade ICE G8000 manual Rapid Spanning Tree Protocol, Port state changes

RackSwitch G8000 Application Guide

Rapid Spanning Tree Protocol

Rapid Spanning Tree Protocol (RSTP) provides rapid convergence of the spanning tree and provides for fast re-configuration critical for networks carrying delay-sensitive traffic such as voice and video. RSTP significantly reduces the time to reconfigure the active topology of the network when changes occur to the physical topology or its configuration parameters. RSTP reduces the bridged-LAN topology to a single Spanning Tree.

RSTP parameters are configured in Spanning Tree Group 1. STP Groups 2-128 do not apply to RSTP. There are new STP parameters to support RSTP, and some values to existing parameters are different.

RSTP is compatible with devices that run 802.1D (1998) Spanning Tree Protocol. If the switch detects 802.1D (1998) BPDUs, it responds with 802.1D (1998)-compatible data units. RSTP is not compatible with Per VLAN Spanning Tree (PVST+) protocol.

Port state changes

The port state controls the forwarding and learning processes of Spanning Tree. In RSTP, the port state has been consolidated to the following: discarding, learning, and forwarding. Table 3 compares the port states between 802.1D (1998) Spanning Tree and 802.1D (2004) Rapid Spanning Tree.

Table 3 RSTP vs. STP Port states

Operational status	STP Port State	RSTP Port State
Enabled	Blocking	Discarding
Enabled	Listening	Discarding
Enabled	Learning	Learning
Enabled	Forwarding	Forwarding
Disabled	Disabled	Discarding

80 „ Chapter 5: Spanning Tree BMD00041, November 2008