Zyxel-communications 802.11b/g Wireless Access Point NWA-1100 Instrukcja Użytkownika Pobierz pdf (Strona 72)

Chapter 6 Wireless Settings Screen

ZyXEL NWA-1100 User’s Guide

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.

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 bridge 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.

6.5.2.3 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 bridges 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.

6.5.2.4 STP Port States

STP assigns five port states (see next table) 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.

Table 12 STP Path Costs

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

Table 13 STP Port States

PORT STATES DESCRIPTIONS

Disabled STP is disabled (default).

Blocking Only configuration and management BPDUs are received and processed.

Listening All BPDUs are received and processed.

Learning All BPDUs are received and processed. Information frames are submitted to the

learning process but not forwarded.

Forwarding All BPDUs are received and processed. All information frames are received and

forwarded.

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