Spanning Tree
UM RedundConfig RSPL
Release 2.0 02/2013
3.1 Basics
33
3.1.4 Root Path Cost
Each path that connects 2 bridges is assigned a cost for the transmission
(path cost). The Switch determines this value based on the transmission
speed
(see table 3)
. It assigns a higher path cost to paths with lower
transmission speeds.
Alternatively, the Administrator can set the path cost. Like the Switch, the
Administrator assigns a higher path cost to paths with lower transmission
speeds. However, since the Administrator can choose this value freely, he
has a tool with which he can give a certain path an advantage among
redundant paths.
The root path cost is the sum of all individual costs of those paths that a data
packet has to traverse from a connected bridge‘s port to the root bridge.
Figure 17: Path costs
Data rate
Recommended value
Recommended range
Possible range
≤
100 Kbit/s
200,000,000
a
20,000,000-200,000,000 1-200,000,000
1 Mbit/s
20,000,000
a
2,000,000-200,000,000
1-200,000,000
10 Mbit/s
2,000,000
a
200,000-20,000,000
1-200,000,000
100 Mbit/s
200,000
a
20,000-2,000,000
1-200,000,000
1 Gbit/s
20,000
2,000-200,000
1-200,000,000
10 Gbit/s
2,000
200-20,000
1-200,000,000
100 Gbit/s
200
20-2,000
1-200,000,000
1 TBit/s
20
2-200
1-200,000,000
10 TBit/s
2
1-20
1-200,000,000
Table 3:
Recommended path costs for RSTP based on the data rate.
PC = 200 000 000
PC = 200 000
PC = 200 000
1
2
3
Ethernet (100 Mbit/s)
Ethernet (10 Mbit/s)
PC
Path costs