The Switch-Centric Model - Lenovo RackSwitch G8264 Application Manual

The Switch-Centric Model

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PVRST is switch‐centric: STGs are enforced only on the switch where they are
configured. PVRST allows only one VLAN per STG, except for the default STG 1 to
which multiple VLANs can be assigned. The STG ID is not transmitted in the
Spanning Tree BPDU. Each Spanning Tree decision is based entirely on the
configuration of the particular switch.
For example, in Figure
of its own ports, VLANs, and STGs. Switch A identifies its own port 17 as part of
VLAN 2 on STG 2, and the Switch B identifies its own port 8 as part of VLAN 2 on
STG 2.
Figure 14. Implementing PVRST
Chassis
Switch A
STG 2
17
VLAN 2
18
STG 3
VLAN 3
VLAN 1
8 2
1
Application
Switch C
The VLAN participation for each Spanning Tree Group in Figure 14 on page
as follows:
VLAN 1 Participation

Assuming Switch B to be the root bridge, Switch B transmits the BPDU for STG
1 on ports 1 and 2. Switch C receives the BPDU on port 2, and Switch D receives
the BPDU on port 1. Because there is a network loop between the switches in
VLAN 1, either Switch D will block port 8 or Switch C will block port 1,
depending on the information provided in the BPDU.
 VLAN 2 Participation
Switch B, the root bridge, generates a BPDU for STG 2 from port 8. Switch A
receives this BPDU on port 17, which is assigned to VLAN 2, STG 2. Because
switch B has no additional ports participating in STG 2, this BPDU is not
forwarded to any additional ports and Switch B remains the designated root.
 VLAN 3 Participation
For VLAN 3, Switch A or Switch C may be the root bridge. If Switch A is the root
bridge for VLAN 3, STG 3, then Switch A transmits the BPDU from port 18.
Switch C receives this BPDU on port 8 and is identified as participating in
VLAN 3, STG 3. Since Switch C has no additional ports participating in STG 3,
this BPDU is not forwarded to any additional ports and Switch A remains the
designated root.
14, each switch is responsible for the proper configuration
Application
Switch B
8
2 1
STG 1
1
8
Application
Switch D
Chapter 11: Spanning Tree Protocols
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