Инструкция для ZYXEL GS3700-48

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Chapter 11 Spanning Tree Protocol

GS3700/XGS3700 Series User’s Guide

107

On each bridge, the bridge communicates with the root through the root port. The root port 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.

11.1.2 How STP Works

After a bridge determines the lowest cost-spanning tree with STP, it enables the root port and the
ports that are the designated ports for connected LANs, and disables all other ports that participate
in STP. Network packets are therefore only forwarded between enabled ports, eliminating any
possible network loops.

STP-aware switches exchange Bridge Protocol Data Units (BPDUs) periodically. When the bridged
LAN topology changes, a new spanning tree is constructed.

Once a stable network topology has been established, all bridges listen for Hello BPDUs (Bridge
Protocol Data Units) transmitted from the root bridge. If a bridge does not get a Hello BPDU after a
predefined interval (Max Age), the bridge assumes that the link to the root bridge is down. This
bridge then initiates negotiations with other bridges to reconfigure the network to re-establish a
valid network topology.

11.1.3 STP Port States

STP assigns five port states to eliminate packet looping. A bridge port is not allowed to go directly
from blocking state to forwarding state so as to eliminate transient loops.

11.1.4 Multiple RSTP

MRSTP (Multiple RSTP) is ZyXEL’s proprietary feature that is compatible with RSTP and STP. With
MRSTP, you can have more than one spanning tree on your Switch and assign port(s) to each tree.
Each spanning tree operates independently with its own bridge information.

Path Cost

1Gbps

3 to 10

1 to 65535

Path Cost

10Gbps

1 to 5

1 to 65535

Table 41

STP Path Costs

LINK SPEED

RECOMMENDED
VALUE