Lenovo Flex System Fabric CN4093, Application Manual

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CN4093 Application Guide for N/OS 8.4
Spanning Tree Protocol Modes
Enterprise NOS 8.4 supports the following STP modes:
 Rapid Spanning Tree Protocol (RSTP)
IEEE 802.1D (2004) RSTP allows devices to detect and eliminate logical loops in
a bridged or switched network. When multiple paths exist, STP configures the
network so that only the most efficient path is used. If that path fails, STP
automatically configures the best alternative active path on the network in order
to sustain network operations. RSTP is an enhanced version of IEEE 802.1D
(1998) STP, providing more rapid convergence of the Spanning Tree network
path states on STG 1.
See “Rapid Spanning Tree Protocol” on page 185 for details.
 Per ‐ VLAN Rapid Spanning Tree (PVRST+)
PVRST mode is based on RSTP to provide rapid Spanning Tree convergence, but
supports instances of Spanning Tree, allowing one STG per VLAN. PVRST
mode is compatible with Cisco R ‐ PVST/R ‐ PVST+ mode.
PVRST is the default Spanning Tree mode on the CN4093. See “PVRST Mode”
on page 173 for details.
 Multiple Spanning Tree Protocol (MSTP)
IEEE 802.1Q (2003) MSTP provides both rapid convergence and load balancing
in a VLAN environment. MSTP allows multiple STGs, with multiple VLANs in
each.
See “Multiple Spanning Tree Protocol” on page 187 for details.
Global STP Control
By default, the Spanning Tree feature is globally enabled on the switch, and is set
for PVRST mode. Spanning Tree (and thus any currently configured STP mode)
can be globally disabled or re ‐ enabled using the following commands:
Spanning Tree can be re ‐ enabled by specifying the STP mode:
CN 4093(config)# spanning-tree mode disable
(Globally disable Spanning Tree)
CN 4093(config)# spanning-tree mode {pvrst|rstp|mst}