Lenovo ThinkSystem NE2552E Application Manual page 179

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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 NE2552E uplinks or the Enterprise switch LAG.
During operation, if one NE2552E experiences an uplink failure, STP will activate
the switch‐to‐switch link so that server traffic on the affected NE2552E may pass
through to the active uplink on the other NE2552E, as shown in Figure
Figure 12. Spanning Tree Restoring the Switch‐to‐Switch Link
Enterprise
Routing
Switches
Switch 1
Server
In this example, port EXT1 on each switch is used for the switch‐to‐switch link. To
ensure that the NE2552E 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.
NE2552E(config)# interface port EXT1
NE2552E(config-if)# spanning-tree stp 1 path-cost 60000
NE2552E(config-if)# exit
STP
Restores Link
Server Server
Chapter 10: Spanning Tree Protocols
12.
Uplink
Failure
Switch 2
Server
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