Technical data

BLADE OS 5.1 Application Guide
BMD00136, November 2009 Chapter 5: Spanning Tree Group
 77
Rules for VLAN Tagged Ports
 Tagged ports can belong to more than one STG, but untagged ports can belong to only one STG.
 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.
 An untagged port cannot span multiple STGs.
Adding and Removing Ports from STGs
 When you add a port to a VLAN that belongs to an STG, the port is also added to the STG.
However, if the port you are adding is an untagged port and is already a member of an STG, that
port will not be added to an additional STG because an untagged port cannot belong to more
that one STG.
For example, assume that VLAN 1 belongs to STG 1. You add an untagged port, port 1, that
does not belong to any STG to VLAN 1, and port 1 will become part of STG 1.
If you add untagged port 5 (which is a member to STG 2) to STG 1, the switch will prompt you
to change the PVID from 2 to 1:
 When you remove a port from VLAN that belongs to an STG, that port will also be removed
from the STG. However, if that port belongs to another VLAN in the same STG, the port
remains in the STG.
As an example, assume that port 1 belongs to VLAN 1, and VLAN 1 belongs to STG 1. When
you remove port 1 from VLAN 1, port 1 is also removed from STG 1.
However, if port 1 belongs to both VLAN 1 and VLAN 2 and both VLANs belong to STG 1,
removing port 1 from VLAN 1 does not remove port 1 from STG 1 because VLAN 2 is still a
member of STG 1.
 An STG cannot be deleted, only disabled. If you disable the STG while it still contains VLAN
members, Spanning Tree will be off on all ports belonging to that VLAN.
The relationship between port, trunk groups, VLANs, and Spanning Trees is shown in Table 9.
"Port 5 is an UNTAGGED port and its current PVID is 2.
Confirm changing PVID from 2 to 1 [y/n]:" y