D-Link DES 6000 Product Manual - Page 28
STA Operation Levels, On the Bridge Level, On the Port Level
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Modular Ethernet Switch User's Guide complicated and complex subject and must be fully researched and understood. Please read the following before making any changes. ♦ Network loop detection and prevention With STA, there will be only one path between any two LANs. If there is more than one path, forwarded packets will loop indefinitely. STA detects any looped path and selects the path with the lowest path cost as the active path, while blocking the other path and using it as the backup path. ♦ Automatic topology re-configuration When the path for which there is a backup path fails, the backup path will be automatically activated, and STA will automatically re-configure the network topology. 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 the STA specification. The 1000Mbps segment has an assigned Path Cost of 4, the 100Mbps segment has an assigned Path Cost of 19, and each 10Mbps segment has an assigned Path Cost of 100, based on the STA specifications. Switch Management Concepts 23