Lenovo Flex System Fabric CN4093 Application Manual page 177

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To prevent a network loop among the switches, STP must block one of the links
between them. In this case, it is desired that STP block the link between the blade
switches, and not one of the CN4093 uplinks or the Enterprise switch LAG.
During operation, if one CN4093 experiences an uplink failure, STP will activate
the switch‐to‐switch link so that server traffic on the affected CN4093 may pass
through to the active uplink on the other CN4093, as shown in Figure
Figure 12. Spanning Tree Restoring the Switch‐to‐Switch Link
Enterprise
Routing
Switches
Switch 1
Server
In this example, port 10 on each switch is used for the switch‐to‐switch link. To
ensure that the CN4093 switch‐to‐switch link is blocked during normal operation,
the port path cost is set to a higher value than other paths in the network. To
configure the port path cost on the switch‐to‐switch links in this example, use the
following commands on each switch.
CN 4093(config)# interface port 10
CN 4093(config-if)# spanning-tree stp 1 path-cost 60000
CN 4093(config-if)# exit
STP
Restores Link
Server Server
Chapter 10: Spanning Tree Protocols
12.
Uplink
Failure
Switch 2
Server
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