IBM RackSwitch G8000, Application Manual

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RackSwitch G8000: Application Guide
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 using the following command:
Spanning Tree can be re-enabled by specifying the STP mode:
where the command options represent the following modes:
•
rstp
: RSTP mode
•
pvrst
: PVRST mode
•
mst
: MSTP mode
PVRST Mode
Note: Per-VLAN Rapid Spanning Tree (PVRST) is enabled by default on the
G8000.
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.
N/OS 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 128 availble 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, trunk groups, VLANs, and Spanning Trees is shown
in Table 13 .
RS G8000(config)#
spanning-tree mode disable
RS G8000(config)#
spanning-tree mode
{
pvrst
|
rstp
|
mst
}
Table 13. Ports, Trunk Groups, and VLANs
Switch Element Belongs To
Port Trunk group or one or more VLANs
Trunk group One or more VLANs
VLAN (non-default) • PVRST: One VLAN per STG
• RSTP: All VLANs are in STG 1
• MSTP: Multiple VLANs per STG