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MSAP2000 AAMS User's Guide
This chapter introduces the Rapid Spanning Tree Protocol (RSTP).
13.1 RSTP (Rapid Spanning Tree Protocol) and STP
(Spanning Tree Protocol)
RSTP adds rapid reconfiguration capability to STP. The switch supports RSTP
and the earlier STP. RSTP and STP detect and break network loops and provide
backup links between switches, bridges or routers. They allow a device to
interact with other RSTP or STP-aware devices in your network to ensure that
only one path exists between any two stations on the network. The switch uses
RSTP by default but can still interoperate with STP switches
(although without RSTP's benefits).
The root bridge is the base of the spanning tree; it is the bridge with the lowest
identifier value
(MAC address). Path cost is the cost of transmitting a frame onto a LAN through
that port. It is assigned according to the speed of the link to which a port is
attached. The slower the media, the higher the cost - see the following table.
Table 33
Path Cost
Path Cost
Path Cost
Path Cost
Path Cost
Path Cost
On each bridge, the root port is the port through which this bridge communicates
with the root. It is the port on this switch with the lowest path cost to the root (the
root path cost). If there is no root port, then this switch has been accepted as the
root bridge of the spanning tree network.
For each LAN segment, a designated bridge is selected. This bridge has the
lowest cost to the root among the bridges connected to the LAN.
STP Path Costs
LINK SPEED
RECOMMENDED VALUE RECOMMENDED RANGE
RANGE
4Mbps
250
10Mbps
100
16Mbps
62
100Mbps
19
1Gbps
4
10Gbps
2
C
H A P T E R
Spanning Tree
100 to 1000
50 to 600
40 to 400
10 to 60
3 to 10
1 to 5
100
1 3
Protocol
ALLOWED
1 to 65535
1 to 65535
1 to 65535
1 to 65535
1 to 65535
1 to 65535
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