ZyXEL Communications SAM1316-22, User Manual

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SAM1316-22 User’s Guide
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H A P T E R
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Spanning Tree Protocol
This chapter introduces the Spanning Tree Protocol (STP) and Rapid Spanning Tree
Protocol (RSTP).
23.1 RSTP and STP
RSTP adds rapid reconfiguration capability to STP. The SAM1316-22 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 Integrated Ethernet
Switch uses RSTP by default but can still operate 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, as illustrated in the
following table.
On each bridge, the root port is the port through which this bridge communicates
with the root. It is the port on this Integrated Ethernet Switch with the lowest path
cost to the root (the root path cost). If there is no root port, then this Integrated
Ethernet Switch has been accepted as the root bridge of the spanning tree
network.
Table 49 Path Cost
LINK SPEED
RECOMMENDED
VALUE RECOMMENDED
RANGE ALLOWED
RANGE
Path Cost 4Mbps 250 100 to 1000 1 to 65535
Path Cost 10Mbps 100 50 to 600 1 to 65535
Path Cost 16Mbps 62 40 to 400 1 to 65535
Path Cost 100Mbps 19 10 to 60 1 to 65535
Path Cost 1Gbps 4 3 to 10 1 to 65535
Path Cost 10Gbps 2 1 to 5 1 to 65535