Spanning Tree Considerations For Multilink Trunks; Figure 1-47. Path Cost Arbitration Example - Nortel BayStack 410 24T Using Manual

Using the BayStack 410-24T 10BASE-T Switch

Spanning Tree Considerations for MultiLink Trunks

The spanning tree Path Cost parameter is recalculated based on the aggregate
bandwidth of the trunk. For example,
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.
100 Mb/s
Path
100 Mb/s
Cost
T1 = 4
10 Mb/s
10 Mb/s
Aggregate Bandwidth
220 Mb/s
Key
10 Mb/s
100 Mb/s
Figure 1-47. Path Cost Arbitration Example
The switch can also detect trunk member ports that are physically misconfigured.
For example, in
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.
1-76
S1
T1
S2
Figure 1-48, trunk member ports 2, 4, and 6 of switch S1 are
Figure 1-47 shows a four-port trunk (T1)
T2
100 Mb/s
Path
100 Mb/s
Cost
T2 = 4
10 Mb/s
Aggregate Bandwidth
210 Mb/s
BS41062A
309985-B Rev 00