Spanning-Tree Configuration
Конфигурирование root-коммутатора
- Выбрать корневой коммутатор, наиболее подходящий в качестве исходной точки построения дерева;
- Выбрать резервный коммутатор, также подходящий в качестве исходной точки построения дерева в случае отказа основного.
Extended System IDs
Normally, a switch’s Bridge ID is a 64-bit value th at consists of a 16-bit Bridge Priority value, and a 48-bit MAC address. However, it is possible to include a VLAN ID, called an extended System ID, into a Bridge ID. Instead of adding bits to the existing Bridge ID, 12 bits of the Bridge Priority value are used for this System ID, which identifies the VLAN this STP process represents. Because 12 bits have been stolen from the Bridge Priority field, the range of priorities has been reduced. Normally, the Bridge Priority can range from 0 (or off) to 65,535, with a default value of 32,768. With extended System ID enabled, the Priority range would be 0 – 61,440, and only in multiples of 4,096. To enable the extended System ID:
Switch(config)#spanning-tree extend system-id
Enabling extended System ID accomplishes two things:
- Increases the amount of supported VLANs on the switch from 1005 to 4094.
- Includes the VLAN ID as part of the Bridge ID.
Thus, when this command is enabled, the 64-bit Bridge ID will consist of the following:
- 4-bit Priority Value
- 12-bit System ID value (VLAN ID)
- 48-bit MAC address
