HP GbE2c HP GbE2c Ethernet Blade Switch for c-Class BladeSystem Application Gu - Page 62
RSTP and MSTP, Introduction, Rapid Spanning Tree Protocol, Port state changes, Port type and link type
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RSTP and MSTP Introduction Rapid Spanning Tree Protocol (IEEE 802.1w) enhances the Spanning Tree Protocol (IEEE 802.1d) to provide rapid convergence on Spanning Tree Group 1. Multiple Spanning Tree Protocol (IEEE 802.1s) extends the Rapid Spanning Tree Protocol to provide both rapid convergence and load balancing in a VLAN environment. The following topics are discussed in this chapter: • Rapid Spanning Tree Protocol (RSTP) • Multiple Spanning Tree Protocol (MSTP) Rapid Spanning Tree Protocol Rapid Spanning Tree Protocol (RSTP) provides rapid convergence of the spanning tree and provides for fast reconfiguration 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. For more information about Spanning Tree Protocol, see the "Spanning Tree Protocol" chapter in this guide. RSTP parameters are configured in Spanning Tree Group 1. STP Groups 2-128 do not apply to RSTP, and must be cleared. 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 Spanning Tree Protocol. If the switch detects 802.1d BPDUs, it responds with 802.1d-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 13 RSTP vs. STP port states Port operational status Enabled Enabled Enabled Enabled Disabled STP port state Blocking Listening Learning Forwarding Disabled RSTP port state Discarding Discarding Learning Forwarding Discarding Port type and link type Spanning Tree Configuration includes the following parameters to support RSTP and MSTP: • Edge port • Link type Although these parameters are configured for Spanning Tree Groups 1-128 (/cfg/l2/stp x/port x), they only take effect when RSTP/MSTP is turned on. Edge port A port that connects to a server or stub network is called an edge port. Therefore, ports 1-16 should have edge enabled. Edge ports can start forwarding as soon as the link is up. Edge ports do not take part in Spanning Tree, and should not receive BPDUs. If a port with edge enabled does receive a BPDU, it begins STP processing until it is re-enabled. RSTP and MSTP 62