Chapter 11 Spanning Tree Protocol; Overview; Stp Terminology; Table 20 Stp Path Costs - ZyXEL Communications ES-2108 User Manual

This chapter introduces the Spanning Tree Protocol (STP).

11.1 Overview

STP detects and breaks network loops and provides backup links between switches, bridges or
routers. It allows a switch to interact with other STP-compliant switches in your network to
ensure that only one route exists between any two stations on the network.

11.1.1 STP Terminology

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.

Table 20 STP Path Costs

LINK SPEED RECOMMENDED VALUE
Path Cost 4Mbps
Path Cost 10Mbps
Path Cost 16Mbps
Path Cost 100Mbps
Path Cost 1Gbps
Path Cost 10Gbps
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.

Chapter 11 Spanning Tree Protocol

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Spanning Tree Protocol
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ES-2108 Series User's Guide
H A P T E R
RECOMMENDED
RANGE
100 to 1000
50 to 600
40 to 400
10 to 60
3 to 10
1 to 5
11
ALLOWED RANGE
1 to 65535
1 to 65535
1 to 65535
1 to 65535
1 to 65535
1 to 65535
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