Nortel Networks WEB OS 212777 - Manual (Page 52)

Web OS 10.0 Application Guide
52 n Chapter 2: VLANs
212777-A, February 2002
Example of a Four-Switch Topology with a Single Spanning Tree
In the four-switch topology example shown in Figure 2-4 on page 52 , and assuming Web
switch A has a higher priority, you can have at least three loops on the network:
n
Data flowing from Web switches A to B to C and back to Web switch A.
n
Data flowing from Web switches A to C to D and back to Web switch A
n
Data flowing from Web switches A to B to C to D and back to Web switch A.
With a single Spanning Tree environment, as shown in Figure 2-4 , you will have two links
blocked to prevent loops on the network. It is possible that the blocks may be between Web
switches C and D and between Web switches B and C, depending on the bridge priority, port
priority, and port cost. The two blocks would prevent looping on the network, but the blocked
link between Web switches B and C will inadvertently isolate VLAN 3 altogether.
N OTE – For more information on bridge priority, port priority, and port cost see the Web OS
10.0 Command Reference.
Figure 2-4 VLAN 3 Isolated in a Single Spanning Tree Group
STG 1
VLAN 1
VLAN 1
VLAN 2
VLAN 3
Web Switch B
Web Switch C
Web Switch D
Web Switch A
VLAN 1
Blocked Port