Lenovo Flex System Fabric CN4093, Инструкция по применению

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© Copyright Lenovo 2017 Chapter 10: Spanning Tree Protocols
173
PVRST Mode
Note:
Per ‐ VLAN Rapid Spanning Tree (PVRST) is enabled by default on the
CN4093.
Using STP, network devices detect and eliminate 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.
Enterprise NOS PVRST mode is based on IEEE 802.1w RSTP. Like RSTP, PVRST
mode provides rapid Spanning Tree convergence. However, PVRST mode is
enhanced for multiple instances of Spanning Tree. In PVRST mode, each VLAN
may be automatically or manually assigned to one of 127 available STGs, with each
STG acting as an independent, simultaneous instance of STP. PVRST uses IEEE
802.1Q tagging to differentiate STP BPDUs and is compatible with Cisco
R ‐ PVST/R ‐ PVST+ modes.
The relationship between ports, LAGs, VLANs and Spanning Trees is shown in
Table 17 .
Port States
The port state controls the forwarding and learning processes of Spanning Tree. In
PVRST, the port state has been consolidated to the following:
discarding
,
learning
or
forwarding
.
Due to the sequence involved in these STP states, considerable delays may occur
while paths are being resolved. To mitigate delays, ports defined as edge ports
( “Port Type and Link Type” on page 191 ) may bypass the
discarding
and
learning
states, and enter directly into the
forwarding
state.
Table 17.
Ports, LAGs and VLANs
Switch Element Belongs To
Port LAG or one or more VLANs
LAG One or more VLANs
VLAN (non ‐ default)  PVRST: One VLAN per STG
 RSTP: All VLANs are in STG 1
 MSTP: Multiple VLANs per STG