Switch-Centric Configuration - Lenovo CN4093 Application Manual

Switch-Centric Configuration

162
CN4093 Application Guide for N/OS 8.3
PVRST is switch-centric: STGs are enforced only on the switch where they are
configured. 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
each switch is responsible for the proper configuration 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 Multiple Spanning Tree Groups
The VLAN participation for each Spanning Tree Group in
as follows:
 VLAN 1 Participation
Assuming Switch B to be the root bridge, Switch B transmits the BPDU for
VLAN 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, though VLAN 2 is shared by the Switch A and Switch B,
Chassis
Switch A
STG 2
17
VLAN 2
18
STG 3
VLAN 3
STG 1
VLAN 1
2
8
1
Application
Switch C
Application
Switch B
8
2 1
1
8
Application
Switch D
Figure 14 on page 162 is