Vlan And Stg Assignment - Lenovo CN4093 Application Manual

VLAN and STG Assignment

© Copyright Lenovo 2015
In PVRST mode, up to 128 STGs are supported. Ports cannot be added directly to
an STG. Instead, ports must be added as members of a VLAN, and the VLAN must
then be assigned to the STG.
STG 1 is the default STG. Although VLANs can be added to or deleted from
default STG 1, the STG itself cannot be deleted from the system. By default, STG 1
is enabled and includes VLAN 1, which by default includes all switch ports (except
for management VLANs and management ports).
STG 128 is reserved for switch management. By default, STG 128 is disabled, but
includes management VLAN 4095 and the management ports.
By default, all other STGs (STG 2 through 127) are enabled, though they initially
include no member VLANs. VLANs must be assigned to STGs. By default, this is
done automatically using VLAN Automatic STG Assignment (VASA), though it
can also be done manually (see
When VASA is enabled (as by default), each time a new VLAN is configured, the
switch will automatically assign that new VLAN to its own STG. Conversely, when
a VLAN is deleted, if its STG is not associated with any other VLAN, the STG is
returned to the available pool.
The specific STG number to which the VLAN is assigned is based on the VLAN
number itself. For low VLAN numbers (1 through 127), the switch will attempt to
assign the VLAN to its matching STG number. For higher numbered VLANs, the
STG assignment is based on a simple modulus calculation; the attempted STG
number will "wrap around," starting back at the top of STG list each time the end
of the list is reached. However, if the attempted STG is already in use, the switch
will select the next available STG. If an empty STG is not available when creating a
new VLAN, the VLAN is automatically assigned to default STG 1.
If ports are tagged, each tagged port sends out a special BPDU containing the
tagged information. Also, when a tagged port belongs to more than one STG, the
egress BPDUs are tagged to distinguish the BPDUs of one STG from those of
another STG.
VASA is enabled by default, but can be disabled or re-enabled using the following
command:
CN 4093(config)# [no] spanning-tree stg-auto
If VASA is disabled, when you create a new VLAN, that VLAN automatically
belongs to default STG 1. To place the VLAN in a different STG, assign it manually.
VASA applies only to PVRST mode and is ignored in RSTP and MSTP modes.
"Manually Assigning STGs" on page
Chapter 10: Spanning Tree Protocols
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