Extreme Networks ExtremeWare 7.7, Command Reference Manual

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ExtremeWare 7.7 Command Reference Guide 1577
18
STP Commands
This chapter describes commands related to:
• Creating, configuring, enabling, and disabling Spanning Tree Protocol (STP) on the switch
• Enabling and disabling Rapid Spanning Tree Protocol (RSTP) on the switch
• Displaying and resetting STP settings on the switch
The Spanning Tree Protocol (STP) is a bridge-based mechanism for providing fault tolerance on
networks. STP is a part of the 802.1d bridge specification defined by the IEEE Computer Society. To
explain STP in terms used by the 802.1d specification, the switch will be referred to as a bridge.
STP allows you to implement parallel paths for network traffic, and ensure that:
• Redundant paths are disabled when the main paths are operational.
• A redundant path is enabled if the main path fails.
The Rapid Spanning Tree Protocol (RSTP; 802.1w) provides an enhanced spanning tree algorithm that
improves the convergence speed of bridged networks. RSTP takes advantage of point-to-point links in
the network and actively confirms that a port can safely transition to the forwarding state without
relying on any timer configurations. If a network topology change or failure occurs, RSTP rapidly
recovers network connectivity by confirming the change locally before propagating that change to other
devices across the network. For broadcast links, there is no difference in convergence time between STP
and RSTP.
RSTP supersedes legacy STP protocols, supports the existing STP parameters and configurations, and
allows for seamless interoperability with legacy STP.
The Multiple Spanning Tree Protocol (MSTP), based on IEEE 802.1Q-2003 (formerly known as IEEE
802.1s), allows the bundling of multiple VLANs into one spanning tree topology. MSTP logically
divides a Layer 2 network into regions. Each region has a unique identifier and contains multiple
spanning tree instances (MSTIs). All MSTIs are bound together using a common instance spanning tree
(CIST). The CIST is responsible for creating a loop-free topology across regions while MSTIs control the
topology inside the regions.
MSTP uses RSTP as its converging algorithm and is interoperable with the legacy STP protocols: STP
(802.1D) and RSTP (802.1w).