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Stackable NWay Ethernet Switch User’s Guide
32 Switch Management Concepts
STA Operation Levels
STA operates on two levels: the bridge level and the port level. On the bridge level, STA calculates the Bridge
Identifier for each Switch, then sets the Root Bridge and the Designated Bridges. On the port level, STA sets
the Root Port and Designated Ports. Details are as follows:
On the Bridge Level
♦
Root Bridge
The switch with the lowest Bridge Identifier is the Root Bridge. Naturally, you will want
the Root Bridge to be the best switch among the switches in the loop to ensure the highest network
performance and reliability.
♦
Bridge Identifier
This is the combination of the Bridge Priority (a parameter that you can set) and
the MAC address of the switch. Example: 4 00 80 C8 00 01 00, where 4 is the Bridge Priority. A lower
Bridge Identifier results in a higher priority for the switch, and thus increases it probably of being
selected as the Root Bridge.
♦
Designated Bridge
From each LAN segment, the attached Bridge that has the lowest Root Path Cost
to the Root Bridge is the Designated Bridge. It forwards data packets for that LAN segment. In cases
where all Switches have the same Root Path Cost, the switch with the lowest Bridge Identifier becomes
the Designated Bridge.
♦
Root Path Cost
The Root Path Cost of a switch is the sum of the Path Cost of the Root Port and the
Root Path Costs of all the switches that the packet goes through. The Root Path Cost of the Root Bridge
is zero.
♦
Bridge Priority
This is a parameter that users can set. The smaller the number you set, the higher
the Bridge Priority is. The higher the Bridge Priority, the better the chance the Switch will be selected
as the Root Bridge.
On the Port Level
♦
Root Port
Each switch has a Root Port. This is the port that has the lowest Path Cost to the Root
Bridge. In case there are several such ports, then the one with the lowest Port Identifier is the Root
Port.
♦
Designated Port
This is the port on each Designated Bridge that is attached to the LAN segment for
which the switch is the Designated Bridge.
♦
Port Priority
The smaller this number, the higher the Port Priority is. With higher Port Priority, the
higher the probability that the port will be selected as the Root Port.
♦
Path Cost
This is a changeable parameter and may be modified according to STA specifications. Each
10Mbps and 100Mbps segment has an assigned Path Cost of 19.
User-Changeable STA Parameters
The factory default setting should cover the majority of installations. However, it is advisable to keep the
default settings as set at the factory, unless it is absolutely necessary. The user changeable parameters in the
Switch are as follows:
♦
Bridge Priority
A Bridge Priority can be from 0 to 65535. 0 is equal to the highest Bridge Priority.
♦
Bridge Hello Time
The Hello Time can be from 1 to 10 seconds. This is the interval between two
transmissions of BPDU packets sent by the Root Bridge to tell all other Switches that it is indeed the