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Using the BayStack 410-24T 10BASE-T Switch
1-72
309985-A Rev 00
Spanning Tree Considerations for MultiLink Trunks
The spanning tree Path Cost parameter is recalculated based on the aggregate
bandwidth of the trunk. For example, Figure 1-46
shows a four-port trunk (T1)
with two port members operating at 100 Mb/s and two at 10 Mb/s. Trunk T1
provides an aggregate bandwidth of 220 Mb/s. The Path Cost for T1 is 4 (Path
Cost = 1000/LAN speed, in Mb/s). Another three-port trunk (T2) is configured
with an aggregate bandwidth of 210 Mb/s and a comparable Path Cost of 4. When
the Path Cost calculations for both trunks are equal, the software chooses the trunk
with the larger aggregate bandwidth (T1) to determine the most efficient path.
Figure 1-46. Path Cost Arbitration Example
The switch can also detect trunk member ports that are physically misconfigured.
For example, in Figure 1-47
, trunk member ports 2, 4, and 6 of switch S1 are
configured correctly to trunk member ports 7, 9, and 11 of switch S2. The
Spanning Tree Port Configuration screen for each switch shows the port state field
for each port in the Forwarding state.
BS41062A
T2
100 Mb/s
100 Mb/s
10 Mb/s
100 Mb/s
100 Mb/s
10 Mb/s
10 Mb/s
Path
Cost
T1 = 4
Path
Cost
T2 = 4
S1
Aggregate Bandwidth
210 Mb/s
T1
S2
Aggregate Bandwidth
220 Mb/s
Key
10 Mb/s
100 Mb/s